ScalarEvolution.cpp revision 251662
1//===- ScalarEvolution.cpp - Scalar Evolution Analysis ----------*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file contains the implementation of the scalar evolution analysis 11// engine, which is used primarily to analyze expressions involving induction 12// variables in loops. 13// 14// There are several aspects to this library. First is the representation of 15// scalar expressions, which are represented as subclasses of the SCEV class. 16// These classes are used to represent certain types of subexpressions that we 17// can handle. We only create one SCEV of a particular shape, so 18// pointer-comparisons for equality are legal. 19// 20// One important aspect of the SCEV objects is that they are never cyclic, even 21// if there is a cycle in the dataflow for an expression (ie, a PHI node). If 22// the PHI node is one of the idioms that we can represent (e.g., a polynomial 23// recurrence) then we represent it directly as a recurrence node, otherwise we 24// represent it as a SCEVUnknown node. 25// 26// In addition to being able to represent expressions of various types, we also 27// have folders that are used to build the *canonical* representation for a 28// particular expression. These folders are capable of using a variety of 29// rewrite rules to simplify the expressions. 30// 31// Once the folders are defined, we can implement the more interesting 32// higher-level code, such as the code that recognizes PHI nodes of various 33// types, computes the execution count of a loop, etc. 34// 35// TODO: We should use these routines and value representations to implement 36// dependence analysis! 37// 38//===----------------------------------------------------------------------===// 39// 40// There are several good references for the techniques used in this analysis. 41// 42// Chains of recurrences -- a method to expedite the evaluation 43// of closed-form functions 44// Olaf Bachmann, Paul S. Wang, Eugene V. Zima 45// 46// On computational properties of chains of recurrences 47// Eugene V. Zima 48// 49// Symbolic Evaluation of Chains of Recurrences for Loop Optimization 50// Robert A. van Engelen 51// 52// Efficient Symbolic Analysis for Optimizing Compilers 53// Robert A. van Engelen 54// 55// Using the chains of recurrences algebra for data dependence testing and 56// induction variable substitution 57// MS Thesis, Johnie Birch 58// 59//===----------------------------------------------------------------------===// 60 61#define DEBUG_TYPE "scalar-evolution" 62#include "llvm/Analysis/ScalarEvolution.h" 63#include "llvm/ADT/STLExtras.h" 64#include "llvm/ADT/SmallPtrSet.h" 65#include "llvm/ADT/Statistic.h" 66#include "llvm/Analysis/ConstantFolding.h" 67#include "llvm/Analysis/Dominators.h" 68#include "llvm/Analysis/InstructionSimplify.h" 69#include "llvm/Analysis/LoopInfo.h" 70#include "llvm/Analysis/ScalarEvolutionExpressions.h" 71#include "llvm/Analysis/ValueTracking.h" 72#include "llvm/Assembly/Writer.h" 73#include "llvm/IR/Constants.h" 74#include "llvm/IR/DataLayout.h" 75#include "llvm/IR/DerivedTypes.h" 76#include "llvm/IR/GlobalAlias.h" 77#include "llvm/IR/GlobalVariable.h" 78#include "llvm/IR/Instructions.h" 79#include "llvm/IR/LLVMContext.h" 80#include "llvm/IR/Operator.h" 81#include "llvm/Support/CommandLine.h" 82#include "llvm/Support/ConstantRange.h" 83#include "llvm/Support/Debug.h" 84#include "llvm/Support/ErrorHandling.h" 85#include "llvm/Support/GetElementPtrTypeIterator.h" 86#include "llvm/Support/InstIterator.h" 87#include "llvm/Support/MathExtras.h" 88#include "llvm/Support/raw_ostream.h" 89#include "llvm/Target/TargetLibraryInfo.h" 90#include <algorithm> 91using namespace llvm; 92 93STATISTIC(NumArrayLenItCounts, 94 "Number of trip counts computed with array length"); 95STATISTIC(NumTripCountsComputed, 96 "Number of loops with predictable loop counts"); 97STATISTIC(NumTripCountsNotComputed, 98 "Number of loops without predictable loop counts"); 99STATISTIC(NumBruteForceTripCountsComputed, 100 "Number of loops with trip counts computed by force"); 101 102static cl::opt<unsigned> 103MaxBruteForceIterations("scalar-evolution-max-iterations", cl::ReallyHidden, 104 cl::desc("Maximum number of iterations SCEV will " 105 "symbolically execute a constant " 106 "derived loop"), 107 cl::init(100)); 108 109// FIXME: Enable this with XDEBUG when the test suite is clean. 110static cl::opt<bool> 111VerifySCEV("verify-scev", 112 cl::desc("Verify ScalarEvolution's backedge taken counts (slow)")); 113 114INITIALIZE_PASS_BEGIN(ScalarEvolution, "scalar-evolution", 115 "Scalar Evolution Analysis", false, true) 116INITIALIZE_PASS_DEPENDENCY(LoopInfo) 117INITIALIZE_PASS_DEPENDENCY(DominatorTree) 118INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) 119INITIALIZE_PASS_END(ScalarEvolution, "scalar-evolution", 120 "Scalar Evolution Analysis", false, true) 121char ScalarEvolution::ID = 0; 122 123//===----------------------------------------------------------------------===// 124// SCEV class definitions 125//===----------------------------------------------------------------------===// 126 127//===----------------------------------------------------------------------===// 128// Implementation of the SCEV class. 129// 130 131#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 132void SCEV::dump() const { 133 print(dbgs()); 134 dbgs() << '\n'; 135} 136#endif 137 138void SCEV::print(raw_ostream &OS) const { 139 switch (getSCEVType()) { 140 case scConstant: 141 WriteAsOperand(OS, cast<SCEVConstant>(this)->getValue(), false); 142 return; 143 case scTruncate: { 144 const SCEVTruncateExpr *Trunc = cast<SCEVTruncateExpr>(this); 145 const SCEV *Op = Trunc->getOperand(); 146 OS << "(trunc " << *Op->getType() << " " << *Op << " to " 147 << *Trunc->getType() << ")"; 148 return; 149 } 150 case scZeroExtend: { 151 const SCEVZeroExtendExpr *ZExt = cast<SCEVZeroExtendExpr>(this); 152 const SCEV *Op = ZExt->getOperand(); 153 OS << "(zext " << *Op->getType() << " " << *Op << " to " 154 << *ZExt->getType() << ")"; 155 return; 156 } 157 case scSignExtend: { 158 const SCEVSignExtendExpr *SExt = cast<SCEVSignExtendExpr>(this); 159 const SCEV *Op = SExt->getOperand(); 160 OS << "(sext " << *Op->getType() << " " << *Op << " to " 161 << *SExt->getType() << ")"; 162 return; 163 } 164 case scAddRecExpr: { 165 const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(this); 166 OS << "{" << *AR->getOperand(0); 167 for (unsigned i = 1, e = AR->getNumOperands(); i != e; ++i) 168 OS << ",+," << *AR->getOperand(i); 169 OS << "}<"; 170 if (AR->getNoWrapFlags(FlagNUW)) 171 OS << "nuw><"; 172 if (AR->getNoWrapFlags(FlagNSW)) 173 OS << "nsw><"; 174 if (AR->getNoWrapFlags(FlagNW) && 175 !AR->getNoWrapFlags((NoWrapFlags)(FlagNUW | FlagNSW))) 176 OS << "nw><"; 177 WriteAsOperand(OS, AR->getLoop()->getHeader(), /*PrintType=*/false); 178 OS << ">"; 179 return; 180 } 181 case scAddExpr: 182 case scMulExpr: 183 case scUMaxExpr: 184 case scSMaxExpr: { 185 const SCEVNAryExpr *NAry = cast<SCEVNAryExpr>(this); 186 const char *OpStr = 0; 187 switch (NAry->getSCEVType()) { 188 case scAddExpr: OpStr = " + "; break; 189 case scMulExpr: OpStr = " * "; break; 190 case scUMaxExpr: OpStr = " umax "; break; 191 case scSMaxExpr: OpStr = " smax "; break; 192 } 193 OS << "("; 194 for (SCEVNAryExpr::op_iterator I = NAry->op_begin(), E = NAry->op_end(); 195 I != E; ++I) { 196 OS << **I; 197 if (llvm::next(I) != E) 198 OS << OpStr; 199 } 200 OS << ")"; 201 switch (NAry->getSCEVType()) { 202 case scAddExpr: 203 case scMulExpr: 204 if (NAry->getNoWrapFlags(FlagNUW)) 205 OS << "<nuw>"; 206 if (NAry->getNoWrapFlags(FlagNSW)) 207 OS << "<nsw>"; 208 } 209 return; 210 } 211 case scUDivExpr: { 212 const SCEVUDivExpr *UDiv = cast<SCEVUDivExpr>(this); 213 OS << "(" << *UDiv->getLHS() << " /u " << *UDiv->getRHS() << ")"; 214 return; 215 } 216 case scUnknown: { 217 const SCEVUnknown *U = cast<SCEVUnknown>(this); 218 Type *AllocTy; 219 if (U->isSizeOf(AllocTy)) { 220 OS << "sizeof(" << *AllocTy << ")"; 221 return; 222 } 223 if (U->isAlignOf(AllocTy)) { 224 OS << "alignof(" << *AllocTy << ")"; 225 return; 226 } 227 228 Type *CTy; 229 Constant *FieldNo; 230 if (U->isOffsetOf(CTy, FieldNo)) { 231 OS << "offsetof(" << *CTy << ", "; 232 WriteAsOperand(OS, FieldNo, false); 233 OS << ")"; 234 return; 235 } 236 237 // Otherwise just print it normally. 238 WriteAsOperand(OS, U->getValue(), false); 239 return; 240 } 241 case scCouldNotCompute: 242 OS << "***COULDNOTCOMPUTE***"; 243 return; 244 default: break; 245 } 246 llvm_unreachable("Unknown SCEV kind!"); 247} 248 249Type *SCEV::getType() const { 250 switch (getSCEVType()) { 251 case scConstant: 252 return cast<SCEVConstant>(this)->getType(); 253 case scTruncate: 254 case scZeroExtend: 255 case scSignExtend: 256 return cast<SCEVCastExpr>(this)->getType(); 257 case scAddRecExpr: 258 case scMulExpr: 259 case scUMaxExpr: 260 case scSMaxExpr: 261 return cast<SCEVNAryExpr>(this)->getType(); 262 case scAddExpr: 263 return cast<SCEVAddExpr>(this)->getType(); 264 case scUDivExpr: 265 return cast<SCEVUDivExpr>(this)->getType(); 266 case scUnknown: 267 return cast<SCEVUnknown>(this)->getType(); 268 case scCouldNotCompute: 269 llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!"); 270 default: 271 llvm_unreachable("Unknown SCEV kind!"); 272 } 273} 274 275bool SCEV::isZero() const { 276 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(this)) 277 return SC->getValue()->isZero(); 278 return false; 279} 280 281bool SCEV::isOne() const { 282 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(this)) 283 return SC->getValue()->isOne(); 284 return false; 285} 286 287bool SCEV::isAllOnesValue() const { 288 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(this)) 289 return SC->getValue()->isAllOnesValue(); 290 return false; 291} 292 293/// isNonConstantNegative - Return true if the specified scev is negated, but 294/// not a constant. 295bool SCEV::isNonConstantNegative() const { 296 const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(this); 297 if (!Mul) return false; 298 299 // If there is a constant factor, it will be first. 300 const SCEVConstant *SC = dyn_cast<SCEVConstant>(Mul->getOperand(0)); 301 if (!SC) return false; 302 303 // Return true if the value is negative, this matches things like (-42 * V). 304 return SC->getValue()->getValue().isNegative(); 305} 306 307SCEVCouldNotCompute::SCEVCouldNotCompute() : 308 SCEV(FoldingSetNodeIDRef(), scCouldNotCompute) {} 309 310bool SCEVCouldNotCompute::classof(const SCEV *S) { 311 return S->getSCEVType() == scCouldNotCompute; 312} 313 314const SCEV *ScalarEvolution::getConstant(ConstantInt *V) { 315 FoldingSetNodeID ID; 316 ID.AddInteger(scConstant); 317 ID.AddPointer(V); 318 void *IP = 0; 319 if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S; 320 SCEV *S = new (SCEVAllocator) SCEVConstant(ID.Intern(SCEVAllocator), V); 321 UniqueSCEVs.InsertNode(S, IP); 322 return S; 323} 324 325const SCEV *ScalarEvolution::getConstant(const APInt& Val) { 326 return getConstant(ConstantInt::get(getContext(), Val)); 327} 328 329const SCEV * 330ScalarEvolution::getConstant(Type *Ty, uint64_t V, bool isSigned) { 331 IntegerType *ITy = cast<IntegerType>(getEffectiveSCEVType(Ty)); 332 return getConstant(ConstantInt::get(ITy, V, isSigned)); 333} 334 335SCEVCastExpr::SCEVCastExpr(const FoldingSetNodeIDRef ID, 336 unsigned SCEVTy, const SCEV *op, Type *ty) 337 : SCEV(ID, SCEVTy), Op(op), Ty(ty) {} 338 339SCEVTruncateExpr::SCEVTruncateExpr(const FoldingSetNodeIDRef ID, 340 const SCEV *op, Type *ty) 341 : SCEVCastExpr(ID, scTruncate, op, ty) { 342 assert((Op->getType()->isIntegerTy() || Op->getType()->isPointerTy()) && 343 (Ty->isIntegerTy() || Ty->isPointerTy()) && 344 "Cannot truncate non-integer value!"); 345} 346 347SCEVZeroExtendExpr::SCEVZeroExtendExpr(const FoldingSetNodeIDRef ID, 348 const SCEV *op, Type *ty) 349 : SCEVCastExpr(ID, scZeroExtend, op, ty) { 350 assert((Op->getType()->isIntegerTy() || Op->getType()->isPointerTy()) && 351 (Ty->isIntegerTy() || Ty->isPointerTy()) && 352 "Cannot zero extend non-integer value!"); 353} 354 355SCEVSignExtendExpr::SCEVSignExtendExpr(const FoldingSetNodeIDRef ID, 356 const SCEV *op, Type *ty) 357 : SCEVCastExpr(ID, scSignExtend, op, ty) { 358 assert((Op->getType()->isIntegerTy() || Op->getType()->isPointerTy()) && 359 (Ty->isIntegerTy() || Ty->isPointerTy()) && 360 "Cannot sign extend non-integer value!"); 361} 362 363void SCEVUnknown::deleted() { 364 // Clear this SCEVUnknown from various maps. 365 SE->forgetMemoizedResults(this); 366 367 // Remove this SCEVUnknown from the uniquing map. 368 SE->UniqueSCEVs.RemoveNode(this); 369 370 // Release the value. 371 setValPtr(0); 372} 373 374void SCEVUnknown::allUsesReplacedWith(Value *New) { 375 // Clear this SCEVUnknown from various maps. 376 SE->forgetMemoizedResults(this); 377 378 // Remove this SCEVUnknown from the uniquing map. 379 SE->UniqueSCEVs.RemoveNode(this); 380 381 // Update this SCEVUnknown to point to the new value. This is needed 382 // because there may still be outstanding SCEVs which still point to 383 // this SCEVUnknown. 384 setValPtr(New); 385} 386 387bool SCEVUnknown::isSizeOf(Type *&AllocTy) const { 388 if (ConstantExpr *VCE = dyn_cast<ConstantExpr>(getValue())) 389 if (VCE->getOpcode() == Instruction::PtrToInt) 390 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(VCE->getOperand(0))) 391 if (CE->getOpcode() == Instruction::GetElementPtr && 392 CE->getOperand(0)->isNullValue() && 393 CE->getNumOperands() == 2) 394 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(1))) 395 if (CI->isOne()) { 396 AllocTy = cast<PointerType>(CE->getOperand(0)->getType()) 397 ->getElementType(); 398 return true; 399 } 400 401 return false; 402} 403 404bool SCEVUnknown::isAlignOf(Type *&AllocTy) const { 405 if (ConstantExpr *VCE = dyn_cast<ConstantExpr>(getValue())) 406 if (VCE->getOpcode() == Instruction::PtrToInt) 407 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(VCE->getOperand(0))) 408 if (CE->getOpcode() == Instruction::GetElementPtr && 409 CE->getOperand(0)->isNullValue()) { 410 Type *Ty = 411 cast<PointerType>(CE->getOperand(0)->getType())->getElementType(); 412 if (StructType *STy = dyn_cast<StructType>(Ty)) 413 if (!STy->isPacked() && 414 CE->getNumOperands() == 3 && 415 CE->getOperand(1)->isNullValue()) { 416 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(2))) 417 if (CI->isOne() && 418 STy->getNumElements() == 2 && 419 STy->getElementType(0)->isIntegerTy(1)) { 420 AllocTy = STy->getElementType(1); 421 return true; 422 } 423 } 424 } 425 426 return false; 427} 428 429bool SCEVUnknown::isOffsetOf(Type *&CTy, Constant *&FieldNo) const { 430 if (ConstantExpr *VCE = dyn_cast<ConstantExpr>(getValue())) 431 if (VCE->getOpcode() == Instruction::PtrToInt) 432 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(VCE->getOperand(0))) 433 if (CE->getOpcode() == Instruction::GetElementPtr && 434 CE->getNumOperands() == 3 && 435 CE->getOperand(0)->isNullValue() && 436 CE->getOperand(1)->isNullValue()) { 437 Type *Ty = 438 cast<PointerType>(CE->getOperand(0)->getType())->getElementType(); 439 // Ignore vector types here so that ScalarEvolutionExpander doesn't 440 // emit getelementptrs that index into vectors. 441 if (Ty->isStructTy() || Ty->isArrayTy()) { 442 CTy = Ty; 443 FieldNo = CE->getOperand(2); 444 return true; 445 } 446 } 447 448 return false; 449} 450 451//===----------------------------------------------------------------------===// 452// SCEV Utilities 453//===----------------------------------------------------------------------===// 454 455namespace { 456 /// SCEVComplexityCompare - Return true if the complexity of the LHS is less 457 /// than the complexity of the RHS. This comparator is used to canonicalize 458 /// expressions. 459 class SCEVComplexityCompare { 460 const LoopInfo *const LI; 461 public: 462 explicit SCEVComplexityCompare(const LoopInfo *li) : LI(li) {} 463 464 // Return true or false if LHS is less than, or at least RHS, respectively. 465 bool operator()(const SCEV *LHS, const SCEV *RHS) const { 466 return compare(LHS, RHS) < 0; 467 } 468 469 // Return negative, zero, or positive, if LHS is less than, equal to, or 470 // greater than RHS, respectively. A three-way result allows recursive 471 // comparisons to be more efficient. 472 int compare(const SCEV *LHS, const SCEV *RHS) const { 473 // Fast-path: SCEVs are uniqued so we can do a quick equality check. 474 if (LHS == RHS) 475 return 0; 476 477 // Primarily, sort the SCEVs by their getSCEVType(). 478 unsigned LType = LHS->getSCEVType(), RType = RHS->getSCEVType(); 479 if (LType != RType) 480 return (int)LType - (int)RType; 481 482 // Aside from the getSCEVType() ordering, the particular ordering 483 // isn't very important except that it's beneficial to be consistent, 484 // so that (a + b) and (b + a) don't end up as different expressions. 485 switch (LType) { 486 case scUnknown: { 487 const SCEVUnknown *LU = cast<SCEVUnknown>(LHS); 488 const SCEVUnknown *RU = cast<SCEVUnknown>(RHS); 489 490 // Sort SCEVUnknown values with some loose heuristics. TODO: This is 491 // not as complete as it could be. 492 const Value *LV = LU->getValue(), *RV = RU->getValue(); 493 494 // Order pointer values after integer values. This helps SCEVExpander 495 // form GEPs. 496 bool LIsPointer = LV->getType()->isPointerTy(), 497 RIsPointer = RV->getType()->isPointerTy(); 498 if (LIsPointer != RIsPointer) 499 return (int)LIsPointer - (int)RIsPointer; 500 501 // Compare getValueID values. 502 unsigned LID = LV->getValueID(), 503 RID = RV->getValueID(); 504 if (LID != RID) 505 return (int)LID - (int)RID; 506 507 // Sort arguments by their position. 508 if (const Argument *LA = dyn_cast<Argument>(LV)) { 509 const Argument *RA = cast<Argument>(RV); 510 unsigned LArgNo = LA->getArgNo(), RArgNo = RA->getArgNo(); 511 return (int)LArgNo - (int)RArgNo; 512 } 513 514 // For instructions, compare their loop depth, and their operand 515 // count. This is pretty loose. 516 if (const Instruction *LInst = dyn_cast<Instruction>(LV)) { 517 const Instruction *RInst = cast<Instruction>(RV); 518 519 // Compare loop depths. 520 const BasicBlock *LParent = LInst->getParent(), 521 *RParent = RInst->getParent(); 522 if (LParent != RParent) { 523 unsigned LDepth = LI->getLoopDepth(LParent), 524 RDepth = LI->getLoopDepth(RParent); 525 if (LDepth != RDepth) 526 return (int)LDepth - (int)RDepth; 527 } 528 529 // Compare the number of operands. 530 unsigned LNumOps = LInst->getNumOperands(), 531 RNumOps = RInst->getNumOperands(); 532 return (int)LNumOps - (int)RNumOps; 533 } 534 535 return 0; 536 } 537 538 case scConstant: { 539 const SCEVConstant *LC = cast<SCEVConstant>(LHS); 540 const SCEVConstant *RC = cast<SCEVConstant>(RHS); 541 542 // Compare constant values. 543 const APInt &LA = LC->getValue()->getValue(); 544 const APInt &RA = RC->getValue()->getValue(); 545 unsigned LBitWidth = LA.getBitWidth(), RBitWidth = RA.getBitWidth(); 546 if (LBitWidth != RBitWidth) 547 return (int)LBitWidth - (int)RBitWidth; 548 return LA.ult(RA) ? -1 : 1; 549 } 550 551 case scAddRecExpr: { 552 const SCEVAddRecExpr *LA = cast<SCEVAddRecExpr>(LHS); 553 const SCEVAddRecExpr *RA = cast<SCEVAddRecExpr>(RHS); 554 555 // Compare addrec loop depths. 556 const Loop *LLoop = LA->getLoop(), *RLoop = RA->getLoop(); 557 if (LLoop != RLoop) { 558 unsigned LDepth = LLoop->getLoopDepth(), 559 RDepth = RLoop->getLoopDepth(); 560 if (LDepth != RDepth) 561 return (int)LDepth - (int)RDepth; 562 } 563 564 // Addrec complexity grows with operand count. 565 unsigned LNumOps = LA->getNumOperands(), RNumOps = RA->getNumOperands(); 566 if (LNumOps != RNumOps) 567 return (int)LNumOps - (int)RNumOps; 568 569 // Lexicographically compare. 570 for (unsigned i = 0; i != LNumOps; ++i) { 571 long X = compare(LA->getOperand(i), RA->getOperand(i)); 572 if (X != 0) 573 return X; 574 } 575 576 return 0; 577 } 578 579 case scAddExpr: 580 case scMulExpr: 581 case scSMaxExpr: 582 case scUMaxExpr: { 583 const SCEVNAryExpr *LC = cast<SCEVNAryExpr>(LHS); 584 const SCEVNAryExpr *RC = cast<SCEVNAryExpr>(RHS); 585 586 // Lexicographically compare n-ary expressions. 587 unsigned LNumOps = LC->getNumOperands(), RNumOps = RC->getNumOperands(); 588 for (unsigned i = 0; i != LNumOps; ++i) { 589 if (i >= RNumOps) 590 return 1; 591 long X = compare(LC->getOperand(i), RC->getOperand(i)); 592 if (X != 0) 593 return X; 594 } 595 return (int)LNumOps - (int)RNumOps; 596 } 597 598 case scUDivExpr: { 599 const SCEVUDivExpr *LC = cast<SCEVUDivExpr>(LHS); 600 const SCEVUDivExpr *RC = cast<SCEVUDivExpr>(RHS); 601 602 // Lexicographically compare udiv expressions. 603 long X = compare(LC->getLHS(), RC->getLHS()); 604 if (X != 0) 605 return X; 606 return compare(LC->getRHS(), RC->getRHS()); 607 } 608 609 case scTruncate: 610 case scZeroExtend: 611 case scSignExtend: { 612 const SCEVCastExpr *LC = cast<SCEVCastExpr>(LHS); 613 const SCEVCastExpr *RC = cast<SCEVCastExpr>(RHS); 614 615 // Compare cast expressions by operand. 616 return compare(LC->getOperand(), RC->getOperand()); 617 } 618 619 default: 620 llvm_unreachable("Unknown SCEV kind!"); 621 } 622 } 623 }; 624} 625 626/// GroupByComplexity - Given a list of SCEV objects, order them by their 627/// complexity, and group objects of the same complexity together by value. 628/// When this routine is finished, we know that any duplicates in the vector are 629/// consecutive and that complexity is monotonically increasing. 630/// 631/// Note that we go take special precautions to ensure that we get deterministic 632/// results from this routine. In other words, we don't want the results of 633/// this to depend on where the addresses of various SCEV objects happened to 634/// land in memory. 635/// 636static void GroupByComplexity(SmallVectorImpl<const SCEV *> &Ops, 637 LoopInfo *LI) { 638 if (Ops.size() < 2) return; // Noop 639 if (Ops.size() == 2) { 640 // This is the common case, which also happens to be trivially simple. 641 // Special case it. 642 const SCEV *&LHS = Ops[0], *&RHS = Ops[1]; 643 if (SCEVComplexityCompare(LI)(RHS, LHS)) 644 std::swap(LHS, RHS); 645 return; 646 } 647 648 // Do the rough sort by complexity. 649 std::stable_sort(Ops.begin(), Ops.end(), SCEVComplexityCompare(LI)); 650 651 // Now that we are sorted by complexity, group elements of the same 652 // complexity. Note that this is, at worst, N^2, but the vector is likely to 653 // be extremely short in practice. Note that we take this approach because we 654 // do not want to depend on the addresses of the objects we are grouping. 655 for (unsigned i = 0, e = Ops.size(); i != e-2; ++i) { 656 const SCEV *S = Ops[i]; 657 unsigned Complexity = S->getSCEVType(); 658 659 // If there are any objects of the same complexity and same value as this 660 // one, group them. 661 for (unsigned j = i+1; j != e && Ops[j]->getSCEVType() == Complexity; ++j) { 662 if (Ops[j] == S) { // Found a duplicate. 663 // Move it to immediately after i'th element. 664 std::swap(Ops[i+1], Ops[j]); 665 ++i; // no need to rescan it. 666 if (i == e-2) return; // Done! 667 } 668 } 669 } 670} 671 672 673 674//===----------------------------------------------------------------------===// 675// Simple SCEV method implementations 676//===----------------------------------------------------------------------===// 677 678/// BinomialCoefficient - Compute BC(It, K). The result has width W. 679/// Assume, K > 0. 680static const SCEV *BinomialCoefficient(const SCEV *It, unsigned K, 681 ScalarEvolution &SE, 682 Type *ResultTy) { 683 // Handle the simplest case efficiently. 684 if (K == 1) 685 return SE.getTruncateOrZeroExtend(It, ResultTy); 686 687 // We are using the following formula for BC(It, K): 688 // 689 // BC(It, K) = (It * (It - 1) * ... * (It - K + 1)) / K! 690 // 691 // Suppose, W is the bitwidth of the return value. We must be prepared for 692 // overflow. Hence, we must assure that the result of our computation is 693 // equal to the accurate one modulo 2^W. Unfortunately, division isn't 694 // safe in modular arithmetic. 695 // 696 // However, this code doesn't use exactly that formula; the formula it uses 697 // is something like the following, where T is the number of factors of 2 in 698 // K! (i.e. trailing zeros in the binary representation of K!), and ^ is 699 // exponentiation: 700 // 701 // BC(It, K) = (It * (It - 1) * ... * (It - K + 1)) / 2^T / (K! / 2^T) 702 // 703 // This formula is trivially equivalent to the previous formula. However, 704 // this formula can be implemented much more efficiently. The trick is that 705 // K! / 2^T is odd, and exact division by an odd number *is* safe in modular 706 // arithmetic. To do exact division in modular arithmetic, all we have 707 // to do is multiply by the inverse. Therefore, this step can be done at 708 // width W. 709 // 710 // The next issue is how to safely do the division by 2^T. The way this 711 // is done is by doing the multiplication step at a width of at least W + T 712 // bits. This way, the bottom W+T bits of the product are accurate. Then, 713 // when we perform the division by 2^T (which is equivalent to a right shift 714 // by T), the bottom W bits are accurate. Extra bits are okay; they'll get 715 // truncated out after the division by 2^T. 716 // 717 // In comparison to just directly using the first formula, this technique 718 // is much more efficient; using the first formula requires W * K bits, 719 // but this formula less than W + K bits. Also, the first formula requires 720 // a division step, whereas this formula only requires multiplies and shifts. 721 // 722 // It doesn't matter whether the subtraction step is done in the calculation 723 // width or the input iteration count's width; if the subtraction overflows, 724 // the result must be zero anyway. We prefer here to do it in the width of 725 // the induction variable because it helps a lot for certain cases; CodeGen 726 // isn't smart enough to ignore the overflow, which leads to much less 727 // efficient code if the width of the subtraction is wider than the native 728 // register width. 729 // 730 // (It's possible to not widen at all by pulling out factors of 2 before 731 // the multiplication; for example, K=2 can be calculated as 732 // It/2*(It+(It*INT_MIN/INT_MIN)+-1). However, it requires 733 // extra arithmetic, so it's not an obvious win, and it gets 734 // much more complicated for K > 3.) 735 736 // Protection from insane SCEVs; this bound is conservative, 737 // but it probably doesn't matter. 738 if (K > 1000) 739 return SE.getCouldNotCompute(); 740 741 unsigned W = SE.getTypeSizeInBits(ResultTy); 742 743 // Calculate K! / 2^T and T; we divide out the factors of two before 744 // multiplying for calculating K! / 2^T to avoid overflow. 745 // Other overflow doesn't matter because we only care about the bottom 746 // W bits of the result. 747 APInt OddFactorial(W, 1); 748 unsigned T = 1; 749 for (unsigned i = 3; i <= K; ++i) { 750 APInt Mult(W, i); 751 unsigned TwoFactors = Mult.countTrailingZeros(); 752 T += TwoFactors; 753 Mult = Mult.lshr(TwoFactors); 754 OddFactorial *= Mult; 755 } 756 757 // We need at least W + T bits for the multiplication step 758 unsigned CalculationBits = W + T; 759 760 // Calculate 2^T, at width T+W. 761 APInt DivFactor = APInt(CalculationBits, 1).shl(T); 762 763 // Calculate the multiplicative inverse of K! / 2^T; 764 // this multiplication factor will perform the exact division by 765 // K! / 2^T. 766 APInt Mod = APInt::getSignedMinValue(W+1); 767 APInt MultiplyFactor = OddFactorial.zext(W+1); 768 MultiplyFactor = MultiplyFactor.multiplicativeInverse(Mod); 769 MultiplyFactor = MultiplyFactor.trunc(W); 770 771 // Calculate the product, at width T+W 772 IntegerType *CalculationTy = IntegerType::get(SE.getContext(), 773 CalculationBits); 774 const SCEV *Dividend = SE.getTruncateOrZeroExtend(It, CalculationTy); 775 for (unsigned i = 1; i != K; ++i) { 776 const SCEV *S = SE.getMinusSCEV(It, SE.getConstant(It->getType(), i)); 777 Dividend = SE.getMulExpr(Dividend, 778 SE.getTruncateOrZeroExtend(S, CalculationTy)); 779 } 780 781 // Divide by 2^T 782 const SCEV *DivResult = SE.getUDivExpr(Dividend, SE.getConstant(DivFactor)); 783 784 // Truncate the result, and divide by K! / 2^T. 785 786 return SE.getMulExpr(SE.getConstant(MultiplyFactor), 787 SE.getTruncateOrZeroExtend(DivResult, ResultTy)); 788} 789 790/// evaluateAtIteration - Return the value of this chain of recurrences at 791/// the specified iteration number. We can evaluate this recurrence by 792/// multiplying each element in the chain by the binomial coefficient 793/// corresponding to it. In other words, we can evaluate {A,+,B,+,C,+,D} as: 794/// 795/// A*BC(It, 0) + B*BC(It, 1) + C*BC(It, 2) + D*BC(It, 3) 796/// 797/// where BC(It, k) stands for binomial coefficient. 798/// 799const SCEV *SCEVAddRecExpr::evaluateAtIteration(const SCEV *It, 800 ScalarEvolution &SE) const { 801 const SCEV *Result = getStart(); 802 for (unsigned i = 1, e = getNumOperands(); i != e; ++i) { 803 // The computation is correct in the face of overflow provided that the 804 // multiplication is performed _after_ the evaluation of the binomial 805 // coefficient. 806 const SCEV *Coeff = BinomialCoefficient(It, i, SE, getType()); 807 if (isa<SCEVCouldNotCompute>(Coeff)) 808 return Coeff; 809 810 Result = SE.getAddExpr(Result, SE.getMulExpr(getOperand(i), Coeff)); 811 } 812 return Result; 813} 814 815//===----------------------------------------------------------------------===// 816// SCEV Expression folder implementations 817//===----------------------------------------------------------------------===// 818 819const SCEV *ScalarEvolution::getTruncateExpr(const SCEV *Op, 820 Type *Ty) { 821 assert(getTypeSizeInBits(Op->getType()) > getTypeSizeInBits(Ty) && 822 "This is not a truncating conversion!"); 823 assert(isSCEVable(Ty) && 824 "This is not a conversion to a SCEVable type!"); 825 Ty = getEffectiveSCEVType(Ty); 826 827 FoldingSetNodeID ID; 828 ID.AddInteger(scTruncate); 829 ID.AddPointer(Op); 830 ID.AddPointer(Ty); 831 void *IP = 0; 832 if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S; 833 834 // Fold if the operand is constant. 835 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op)) 836 return getConstant( 837 cast<ConstantInt>(ConstantExpr::getTrunc(SC->getValue(), Ty))); 838 839 // trunc(trunc(x)) --> trunc(x) 840 if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) 841 return getTruncateExpr(ST->getOperand(), Ty); 842 843 // trunc(sext(x)) --> sext(x) if widening or trunc(x) if narrowing 844 if (const SCEVSignExtendExpr *SS = dyn_cast<SCEVSignExtendExpr>(Op)) 845 return getTruncateOrSignExtend(SS->getOperand(), Ty); 846 847 // trunc(zext(x)) --> zext(x) if widening or trunc(x) if narrowing 848 if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op)) 849 return getTruncateOrZeroExtend(SZ->getOperand(), Ty); 850 851 // trunc(x1+x2+...+xN) --> trunc(x1)+trunc(x2)+...+trunc(xN) if we can 852 // eliminate all the truncates. 853 if (const SCEVAddExpr *SA = dyn_cast<SCEVAddExpr>(Op)) { 854 SmallVector<const SCEV *, 4> Operands; 855 bool hasTrunc = false; 856 for (unsigned i = 0, e = SA->getNumOperands(); i != e && !hasTrunc; ++i) { 857 const SCEV *S = getTruncateExpr(SA->getOperand(i), Ty); 858 hasTrunc = isa<SCEVTruncateExpr>(S); 859 Operands.push_back(S); 860 } 861 if (!hasTrunc) 862 return getAddExpr(Operands); 863 UniqueSCEVs.FindNodeOrInsertPos(ID, IP); // Mutates IP, returns NULL. 864 } 865 866 // trunc(x1*x2*...*xN) --> trunc(x1)*trunc(x2)*...*trunc(xN) if we can 867 // eliminate all the truncates. 868 if (const SCEVMulExpr *SM = dyn_cast<SCEVMulExpr>(Op)) { 869 SmallVector<const SCEV *, 4> Operands; 870 bool hasTrunc = false; 871 for (unsigned i = 0, e = SM->getNumOperands(); i != e && !hasTrunc; ++i) { 872 const SCEV *S = getTruncateExpr(SM->getOperand(i), Ty); 873 hasTrunc = isa<SCEVTruncateExpr>(S); 874 Operands.push_back(S); 875 } 876 if (!hasTrunc) 877 return getMulExpr(Operands); 878 UniqueSCEVs.FindNodeOrInsertPos(ID, IP); // Mutates IP, returns NULL. 879 } 880 881 // If the input value is a chrec scev, truncate the chrec's operands. 882 if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(Op)) { 883 SmallVector<const SCEV *, 4> Operands; 884 for (unsigned i = 0, e = AddRec->getNumOperands(); i != e; ++i) 885 Operands.push_back(getTruncateExpr(AddRec->getOperand(i), Ty)); 886 return getAddRecExpr(Operands, AddRec->getLoop(), SCEV::FlagAnyWrap); 887 } 888 889 // The cast wasn't folded; create an explicit cast node. We can reuse 890 // the existing insert position since if we get here, we won't have 891 // made any changes which would invalidate it. 892 SCEV *S = new (SCEVAllocator) SCEVTruncateExpr(ID.Intern(SCEVAllocator), 893 Op, Ty); 894 UniqueSCEVs.InsertNode(S, IP); 895 return S; 896} 897 898const SCEV *ScalarEvolution::getZeroExtendExpr(const SCEV *Op, 899 Type *Ty) { 900 assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) && 901 "This is not an extending conversion!"); 902 assert(isSCEVable(Ty) && 903 "This is not a conversion to a SCEVable type!"); 904 Ty = getEffectiveSCEVType(Ty); 905 906 // Fold if the operand is constant. 907 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op)) 908 return getConstant( 909 cast<ConstantInt>(ConstantExpr::getZExt(SC->getValue(), Ty))); 910 911 // zext(zext(x)) --> zext(x) 912 if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op)) 913 return getZeroExtendExpr(SZ->getOperand(), Ty); 914 915 // Before doing any expensive analysis, check to see if we've already 916 // computed a SCEV for this Op and Ty. 917 FoldingSetNodeID ID; 918 ID.AddInteger(scZeroExtend); 919 ID.AddPointer(Op); 920 ID.AddPointer(Ty); 921 void *IP = 0; 922 if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S; 923 924 // zext(trunc(x)) --> zext(x) or x or trunc(x) 925 if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) { 926 // It's possible the bits taken off by the truncate were all zero bits. If 927 // so, we should be able to simplify this further. 928 const SCEV *X = ST->getOperand(); 929 ConstantRange CR = getUnsignedRange(X); 930 unsigned TruncBits = getTypeSizeInBits(ST->getType()); 931 unsigned NewBits = getTypeSizeInBits(Ty); 932 if (CR.truncate(TruncBits).zeroExtend(NewBits).contains( 933 CR.zextOrTrunc(NewBits))) 934 return getTruncateOrZeroExtend(X, Ty); 935 } 936 937 // If the input value is a chrec scev, and we can prove that the value 938 // did not overflow the old, smaller, value, we can zero extend all of the 939 // operands (often constants). This allows analysis of something like 940 // this: for (unsigned char X = 0; X < 100; ++X) { int Y = X; } 941 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Op)) 942 if (AR->isAffine()) { 943 const SCEV *Start = AR->getStart(); 944 const SCEV *Step = AR->getStepRecurrence(*this); 945 unsigned BitWidth = getTypeSizeInBits(AR->getType()); 946 const Loop *L = AR->getLoop(); 947 948 // If we have special knowledge that this addrec won't overflow, 949 // we don't need to do any further analysis. 950 if (AR->getNoWrapFlags(SCEV::FlagNUW)) 951 return getAddRecExpr(getZeroExtendExpr(Start, Ty), 952 getZeroExtendExpr(Step, Ty), 953 L, AR->getNoWrapFlags()); 954 955 // Check whether the backedge-taken count is SCEVCouldNotCompute. 956 // Note that this serves two purposes: It filters out loops that are 957 // simply not analyzable, and it covers the case where this code is 958 // being called from within backedge-taken count analysis, such that 959 // attempting to ask for the backedge-taken count would likely result 960 // in infinite recursion. In the later case, the analysis code will 961 // cope with a conservative value, and it will take care to purge 962 // that value once it has finished. 963 const SCEV *MaxBECount = getMaxBackedgeTakenCount(L); 964 if (!isa<SCEVCouldNotCompute>(MaxBECount)) { 965 // Manually compute the final value for AR, checking for 966 // overflow. 967 968 // Check whether the backedge-taken count can be losslessly casted to 969 // the addrec's type. The count is always unsigned. 970 const SCEV *CastedMaxBECount = 971 getTruncateOrZeroExtend(MaxBECount, Start->getType()); 972 const SCEV *RecastedMaxBECount = 973 getTruncateOrZeroExtend(CastedMaxBECount, MaxBECount->getType()); 974 if (MaxBECount == RecastedMaxBECount) { 975 Type *WideTy = IntegerType::get(getContext(), BitWidth * 2); 976 // Check whether Start+Step*MaxBECount has no unsigned overflow. 977 const SCEV *ZMul = getMulExpr(CastedMaxBECount, Step); 978 const SCEV *ZAdd = getZeroExtendExpr(getAddExpr(Start, ZMul), WideTy); 979 const SCEV *WideStart = getZeroExtendExpr(Start, WideTy); 980 const SCEV *WideMaxBECount = 981 getZeroExtendExpr(CastedMaxBECount, WideTy); 982 const SCEV *OperandExtendedAdd = 983 getAddExpr(WideStart, 984 getMulExpr(WideMaxBECount, 985 getZeroExtendExpr(Step, WideTy))); 986 if (ZAdd == OperandExtendedAdd) { 987 // Cache knowledge of AR NUW, which is propagated to this AddRec. 988 const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNUW); 989 // Return the expression with the addrec on the outside. 990 return getAddRecExpr(getZeroExtendExpr(Start, Ty), 991 getZeroExtendExpr(Step, Ty), 992 L, AR->getNoWrapFlags()); 993 } 994 // Similar to above, only this time treat the step value as signed. 995 // This covers loops that count down. 996 OperandExtendedAdd = 997 getAddExpr(WideStart, 998 getMulExpr(WideMaxBECount, 999 getSignExtendExpr(Step, WideTy))); 1000 if (ZAdd == OperandExtendedAdd) { 1001 // Cache knowledge of AR NW, which is propagated to this AddRec. 1002 // Negative step causes unsigned wrap, but it still can't self-wrap. 1003 const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNW); 1004 // Return the expression with the addrec on the outside. 1005 return getAddRecExpr(getZeroExtendExpr(Start, Ty), 1006 getSignExtendExpr(Step, Ty), 1007 L, AR->getNoWrapFlags()); 1008 } 1009 } 1010 1011 // If the backedge is guarded by a comparison with the pre-inc value 1012 // the addrec is safe. Also, if the entry is guarded by a comparison 1013 // with the start value and the backedge is guarded by a comparison 1014 // with the post-inc value, the addrec is safe. 1015 if (isKnownPositive(Step)) { 1016 const SCEV *N = getConstant(APInt::getMinValue(BitWidth) - 1017 getUnsignedRange(Step).getUnsignedMax()); 1018 if (isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_ULT, AR, N) || 1019 (isLoopEntryGuardedByCond(L, ICmpInst::ICMP_ULT, Start, N) && 1020 isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_ULT, 1021 AR->getPostIncExpr(*this), N))) { 1022 // Cache knowledge of AR NUW, which is propagated to this AddRec. 1023 const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNUW); 1024 // Return the expression with the addrec on the outside. 1025 return getAddRecExpr(getZeroExtendExpr(Start, Ty), 1026 getZeroExtendExpr(Step, Ty), 1027 L, AR->getNoWrapFlags()); 1028 } 1029 } else if (isKnownNegative(Step)) { 1030 const SCEV *N = getConstant(APInt::getMaxValue(BitWidth) - 1031 getSignedRange(Step).getSignedMin()); 1032 if (isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_UGT, AR, N) || 1033 (isLoopEntryGuardedByCond(L, ICmpInst::ICMP_UGT, Start, N) && 1034 isLoopBackedgeGuardedByCond(L, ICmpInst::ICMP_UGT, 1035 AR->getPostIncExpr(*this), N))) { 1036 // Cache knowledge of AR NW, which is propagated to this AddRec. 1037 // Negative step causes unsigned wrap, but it still can't self-wrap. 1038 const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNW); 1039 // Return the expression with the addrec on the outside. 1040 return getAddRecExpr(getZeroExtendExpr(Start, Ty), 1041 getSignExtendExpr(Step, Ty), 1042 L, AR->getNoWrapFlags()); 1043 } 1044 } 1045 } 1046 } 1047 1048 // The cast wasn't folded; create an explicit cast node. 1049 // Recompute the insert position, as it may have been invalidated. 1050 if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S; 1051 SCEV *S = new (SCEVAllocator) SCEVZeroExtendExpr(ID.Intern(SCEVAllocator), 1052 Op, Ty); 1053 UniqueSCEVs.InsertNode(S, IP); 1054 return S; 1055} 1056 1057// Get the limit of a recurrence such that incrementing by Step cannot cause 1058// signed overflow as long as the value of the recurrence within the loop does 1059// not exceed this limit before incrementing. 1060static const SCEV *getOverflowLimitForStep(const SCEV *Step, 1061 ICmpInst::Predicate *Pred, 1062 ScalarEvolution *SE) { 1063 unsigned BitWidth = SE->getTypeSizeInBits(Step->getType()); 1064 if (SE->isKnownPositive(Step)) { 1065 *Pred = ICmpInst::ICMP_SLT; 1066 return SE->getConstant(APInt::getSignedMinValue(BitWidth) - 1067 SE->getSignedRange(Step).getSignedMax()); 1068 } 1069 if (SE->isKnownNegative(Step)) { 1070 *Pred = ICmpInst::ICMP_SGT; 1071 return SE->getConstant(APInt::getSignedMaxValue(BitWidth) - 1072 SE->getSignedRange(Step).getSignedMin()); 1073 } 1074 return 0; 1075} 1076 1077// The recurrence AR has been shown to have no signed wrap. Typically, if we can 1078// prove NSW for AR, then we can just as easily prove NSW for its preincrement 1079// or postincrement sibling. This allows normalizing a sign extended AddRec as 1080// such: {sext(Step + Start),+,Step} => {(Step + sext(Start),+,Step} As a 1081// result, the expression "Step + sext(PreIncAR)" is congruent with 1082// "sext(PostIncAR)" 1083static const SCEV *getPreStartForSignExtend(const SCEVAddRecExpr *AR, 1084 Type *Ty, 1085 ScalarEvolution *SE) { 1086 const Loop *L = AR->getLoop(); 1087 const SCEV *Start = AR->getStart(); 1088 const SCEV *Step = AR->getStepRecurrence(*SE); 1089 1090 // Check for a simple looking step prior to loop entry. 1091 const SCEVAddExpr *SA = dyn_cast<SCEVAddExpr>(Start); 1092 if (!SA) 1093 return 0; 1094 1095 // Create an AddExpr for "PreStart" after subtracting Step. Full SCEV 1096 // subtraction is expensive. For this purpose, perform a quick and dirty 1097 // difference, by checking for Step in the operand list. 1098 SmallVector<const SCEV *, 4> DiffOps; 1099 for (SCEVAddExpr::op_iterator I = SA->op_begin(), E = SA->op_end(); 1100 I != E; ++I) { 1101 if (*I != Step) 1102 DiffOps.push_back(*I); 1103 } 1104 if (DiffOps.size() == SA->getNumOperands()) 1105 return 0; 1106 1107 // This is a postinc AR. Check for overflow on the preinc recurrence using the 1108 // same three conditions that getSignExtendedExpr checks. 1109 1110 // 1. NSW flags on the step increment. 1111 const SCEV *PreStart = SE->getAddExpr(DiffOps, SA->getNoWrapFlags()); 1112 const SCEVAddRecExpr *PreAR = dyn_cast<SCEVAddRecExpr>( 1113 SE->getAddRecExpr(PreStart, Step, L, SCEV::FlagAnyWrap)); 1114 1115 if (PreAR && PreAR->getNoWrapFlags(SCEV::FlagNSW)) 1116 return PreStart; 1117 1118 // 2. Direct overflow check on the step operation's expression. 1119 unsigned BitWidth = SE->getTypeSizeInBits(AR->getType()); 1120 Type *WideTy = IntegerType::get(SE->getContext(), BitWidth * 2); 1121 const SCEV *OperandExtendedStart = 1122 SE->getAddExpr(SE->getSignExtendExpr(PreStart, WideTy), 1123 SE->getSignExtendExpr(Step, WideTy)); 1124 if (SE->getSignExtendExpr(Start, WideTy) == OperandExtendedStart) { 1125 // Cache knowledge of PreAR NSW. 1126 if (PreAR) 1127 const_cast<SCEVAddRecExpr *>(PreAR)->setNoWrapFlags(SCEV::FlagNSW); 1128 // FIXME: this optimization needs a unit test 1129 DEBUG(dbgs() << "SCEV: untested prestart overflow check\n"); 1130 return PreStart; 1131 } 1132 1133 // 3. Loop precondition. 1134 ICmpInst::Predicate Pred; 1135 const SCEV *OverflowLimit = getOverflowLimitForStep(Step, &Pred, SE); 1136 1137 if (OverflowLimit && 1138 SE->isLoopEntryGuardedByCond(L, Pred, PreStart, OverflowLimit)) { 1139 return PreStart; 1140 } 1141 return 0; 1142} 1143 1144// Get the normalized sign-extended expression for this AddRec's Start. 1145static const SCEV *getSignExtendAddRecStart(const SCEVAddRecExpr *AR, 1146 Type *Ty, 1147 ScalarEvolution *SE) { 1148 const SCEV *PreStart = getPreStartForSignExtend(AR, Ty, SE); 1149 if (!PreStart) 1150 return SE->getSignExtendExpr(AR->getStart(), Ty); 1151 1152 return SE->getAddExpr(SE->getSignExtendExpr(AR->getStepRecurrence(*SE), Ty), 1153 SE->getSignExtendExpr(PreStart, Ty)); 1154} 1155 1156const SCEV *ScalarEvolution::getSignExtendExpr(const SCEV *Op, 1157 Type *Ty) { 1158 assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) && 1159 "This is not an extending conversion!"); 1160 assert(isSCEVable(Ty) && 1161 "This is not a conversion to a SCEVable type!"); 1162 Ty = getEffectiveSCEVType(Ty); 1163 1164 // Fold if the operand is constant. 1165 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op)) 1166 return getConstant( 1167 cast<ConstantInt>(ConstantExpr::getSExt(SC->getValue(), Ty))); 1168 1169 // sext(sext(x)) --> sext(x) 1170 if (const SCEVSignExtendExpr *SS = dyn_cast<SCEVSignExtendExpr>(Op)) 1171 return getSignExtendExpr(SS->getOperand(), Ty); 1172 1173 // sext(zext(x)) --> zext(x) 1174 if (const SCEVZeroExtendExpr *SZ = dyn_cast<SCEVZeroExtendExpr>(Op)) 1175 return getZeroExtendExpr(SZ->getOperand(), Ty); 1176 1177 // Before doing any expensive analysis, check to see if we've already 1178 // computed a SCEV for this Op and Ty. 1179 FoldingSetNodeID ID; 1180 ID.AddInteger(scSignExtend); 1181 ID.AddPointer(Op); 1182 ID.AddPointer(Ty); 1183 void *IP = 0; 1184 if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S; 1185 1186 // If the input value is provably positive, build a zext instead. 1187 if (isKnownNonNegative(Op)) 1188 return getZeroExtendExpr(Op, Ty); 1189 1190 // sext(trunc(x)) --> sext(x) or x or trunc(x) 1191 if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) { 1192 // It's possible the bits taken off by the truncate were all sign bits. If 1193 // so, we should be able to simplify this further. 1194 const SCEV *X = ST->getOperand(); 1195 ConstantRange CR = getSignedRange(X); 1196 unsigned TruncBits = getTypeSizeInBits(ST->getType()); 1197 unsigned NewBits = getTypeSizeInBits(Ty); 1198 if (CR.truncate(TruncBits).signExtend(NewBits).contains( 1199 CR.sextOrTrunc(NewBits))) 1200 return getTruncateOrSignExtend(X, Ty); 1201 } 1202 1203 // If the input value is a chrec scev, and we can prove that the value 1204 // did not overflow the old, smaller, value, we can sign extend all of the 1205 // operands (often constants). This allows analysis of something like 1206 // this: for (signed char X = 0; X < 100; ++X) { int Y = X; } 1207 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Op)) 1208 if (AR->isAffine()) { 1209 const SCEV *Start = AR->getStart(); 1210 const SCEV *Step = AR->getStepRecurrence(*this); 1211 unsigned BitWidth = getTypeSizeInBits(AR->getType()); 1212 const Loop *L = AR->getLoop(); 1213 1214 // If we have special knowledge that this addrec won't overflow, 1215 // we don't need to do any further analysis. 1216 if (AR->getNoWrapFlags(SCEV::FlagNSW)) 1217 return getAddRecExpr(getSignExtendAddRecStart(AR, Ty, this), 1218 getSignExtendExpr(Step, Ty), 1219 L, SCEV::FlagNSW); 1220 1221 // Check whether the backedge-taken count is SCEVCouldNotCompute. 1222 // Note that this serves two purposes: It filters out loops that are 1223 // simply not analyzable, and it covers the case where this code is 1224 // being called from within backedge-taken count analysis, such that 1225 // attempting to ask for the backedge-taken count would likely result 1226 // in infinite recursion. In the later case, the analysis code will 1227 // cope with a conservative value, and it will take care to purge 1228 // that value once it has finished. 1229 const SCEV *MaxBECount = getMaxBackedgeTakenCount(L); 1230 if (!isa<SCEVCouldNotCompute>(MaxBECount)) { 1231 // Manually compute the final value for AR, checking for 1232 // overflow. 1233 1234 // Check whether the backedge-taken count can be losslessly casted to 1235 // the addrec's type. The count is always unsigned. 1236 const SCEV *CastedMaxBECount = 1237 getTruncateOrZeroExtend(MaxBECount, Start->getType()); 1238 const SCEV *RecastedMaxBECount = 1239 getTruncateOrZeroExtend(CastedMaxBECount, MaxBECount->getType()); 1240 if (MaxBECount == RecastedMaxBECount) { 1241 Type *WideTy = IntegerType::get(getContext(), BitWidth * 2); 1242 // Check whether Start+Step*MaxBECount has no signed overflow. 1243 const SCEV *SMul = getMulExpr(CastedMaxBECount, Step); 1244 const SCEV *SAdd = getSignExtendExpr(getAddExpr(Start, SMul), WideTy); 1245 const SCEV *WideStart = getSignExtendExpr(Start, WideTy); 1246 const SCEV *WideMaxBECount = 1247 getZeroExtendExpr(CastedMaxBECount, WideTy); 1248 const SCEV *OperandExtendedAdd = 1249 getAddExpr(WideStart, 1250 getMulExpr(WideMaxBECount, 1251 getSignExtendExpr(Step, WideTy))); 1252 if (SAdd == OperandExtendedAdd) { 1253 // Cache knowledge of AR NSW, which is propagated to this AddRec. 1254 const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNSW); 1255 // Return the expression with the addrec on the outside. 1256 return getAddRecExpr(getSignExtendAddRecStart(AR, Ty, this), 1257 getSignExtendExpr(Step, Ty), 1258 L, AR->getNoWrapFlags()); 1259 } 1260 // Similar to above, only this time treat the step value as unsigned. 1261 // This covers loops that count up with an unsigned step. 1262 OperandExtendedAdd = 1263 getAddExpr(WideStart, 1264 getMulExpr(WideMaxBECount, 1265 getZeroExtendExpr(Step, WideTy))); 1266 if (SAdd == OperandExtendedAdd) { 1267 // Cache knowledge of AR NSW, which is propagated to this AddRec. 1268 const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNSW); 1269 // Return the expression with the addrec on the outside. 1270 return getAddRecExpr(getSignExtendAddRecStart(AR, Ty, this), 1271 getZeroExtendExpr(Step, Ty), 1272 L, AR->getNoWrapFlags()); 1273 } 1274 } 1275 1276 // If the backedge is guarded by a comparison with the pre-inc value 1277 // the addrec is safe. Also, if the entry is guarded by a comparison 1278 // with the start value and the backedge is guarded by a comparison 1279 // with the post-inc value, the addrec is safe. 1280 ICmpInst::Predicate Pred; 1281 const SCEV *OverflowLimit = getOverflowLimitForStep(Step, &Pred, this); 1282 if (OverflowLimit && 1283 (isLoopBackedgeGuardedByCond(L, Pred, AR, OverflowLimit) || 1284 (isLoopEntryGuardedByCond(L, Pred, Start, OverflowLimit) && 1285 isLoopBackedgeGuardedByCond(L, Pred, AR->getPostIncExpr(*this), 1286 OverflowLimit)))) { 1287 // Cache knowledge of AR NSW, then propagate NSW to the wide AddRec. 1288 const_cast<SCEVAddRecExpr *>(AR)->setNoWrapFlags(SCEV::FlagNSW); 1289 return getAddRecExpr(getSignExtendAddRecStart(AR, Ty, this), 1290 getSignExtendExpr(Step, Ty), 1291 L, AR->getNoWrapFlags()); 1292 } 1293 } 1294 } 1295 1296 // The cast wasn't folded; create an explicit cast node. 1297 // Recompute the insert position, as it may have been invalidated. 1298 if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S; 1299 SCEV *S = new (SCEVAllocator) SCEVSignExtendExpr(ID.Intern(SCEVAllocator), 1300 Op, Ty); 1301 UniqueSCEVs.InsertNode(S, IP); 1302 return S; 1303} 1304 1305/// getAnyExtendExpr - Return a SCEV for the given operand extended with 1306/// unspecified bits out to the given type. 1307/// 1308const SCEV *ScalarEvolution::getAnyExtendExpr(const SCEV *Op, 1309 Type *Ty) { 1310 assert(getTypeSizeInBits(Op->getType()) < getTypeSizeInBits(Ty) && 1311 "This is not an extending conversion!"); 1312 assert(isSCEVable(Ty) && 1313 "This is not a conversion to a SCEVable type!"); 1314 Ty = getEffectiveSCEVType(Ty); 1315 1316 // Sign-extend negative constants. 1317 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Op)) 1318 if (SC->getValue()->getValue().isNegative()) 1319 return getSignExtendExpr(Op, Ty); 1320 1321 // Peel off a truncate cast. 1322 if (const SCEVTruncateExpr *T = dyn_cast<SCEVTruncateExpr>(Op)) { 1323 const SCEV *NewOp = T->getOperand(); 1324 if (getTypeSizeInBits(NewOp->getType()) < getTypeSizeInBits(Ty)) 1325 return getAnyExtendExpr(NewOp, Ty); 1326 return getTruncateOrNoop(NewOp, Ty); 1327 } 1328 1329 // Next try a zext cast. If the cast is folded, use it. 1330 const SCEV *ZExt = getZeroExtendExpr(Op, Ty); 1331 if (!isa<SCEVZeroExtendExpr>(ZExt)) 1332 return ZExt; 1333 1334 // Next try a sext cast. If the cast is folded, use it. 1335 const SCEV *SExt = getSignExtendExpr(Op, Ty); 1336 if (!isa<SCEVSignExtendExpr>(SExt)) 1337 return SExt; 1338 1339 // Force the cast to be folded into the operands of an addrec. 1340 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Op)) { 1341 SmallVector<const SCEV *, 4> Ops; 1342 for (SCEVAddRecExpr::op_iterator I = AR->op_begin(), E = AR->op_end(); 1343 I != E; ++I) 1344 Ops.push_back(getAnyExtendExpr(*I, Ty)); 1345 return getAddRecExpr(Ops, AR->getLoop(), SCEV::FlagNW); 1346 } 1347 1348 // If the expression is obviously signed, use the sext cast value. 1349 if (isa<SCEVSMaxExpr>(Op)) 1350 return SExt; 1351 1352 // Absent any other information, use the zext cast value. 1353 return ZExt; 1354} 1355 1356/// CollectAddOperandsWithScales - Process the given Ops list, which is 1357/// a list of operands to be added under the given scale, update the given 1358/// map. This is a helper function for getAddRecExpr. As an example of 1359/// what it does, given a sequence of operands that would form an add 1360/// expression like this: 1361/// 1362/// m + n + 13 + (A * (o + p + (B * q + m + 29))) + r + (-1 * r) 1363/// 1364/// where A and B are constants, update the map with these values: 1365/// 1366/// (m, 1+A*B), (n, 1), (o, A), (p, A), (q, A*B), (r, 0) 1367/// 1368/// and add 13 + A*B*29 to AccumulatedConstant. 1369/// This will allow getAddRecExpr to produce this: 1370/// 1371/// 13+A*B*29 + n + (m * (1+A*B)) + ((o + p) * A) + (q * A*B) 1372/// 1373/// This form often exposes folding opportunities that are hidden in 1374/// the original operand list. 1375/// 1376/// Return true iff it appears that any interesting folding opportunities 1377/// may be exposed. This helps getAddRecExpr short-circuit extra work in 1378/// the common case where no interesting opportunities are present, and 1379/// is also used as a check to avoid infinite recursion. 1380/// 1381static bool 1382CollectAddOperandsWithScales(DenseMap<const SCEV *, APInt> &M, 1383 SmallVector<const SCEV *, 8> &NewOps, 1384 APInt &AccumulatedConstant, 1385 const SCEV *const *Ops, size_t NumOperands, 1386 const APInt &Scale, 1387 ScalarEvolution &SE) { 1388 bool Interesting = false; 1389 1390 // Iterate over the add operands. They are sorted, with constants first. 1391 unsigned i = 0; 1392 while (const SCEVConstant *C = dyn_cast<SCEVConstant>(Ops[i])) { 1393 ++i; 1394 // Pull a buried constant out to the outside. 1395 if (Scale != 1 || AccumulatedConstant != 0 || C->getValue()->isZero()) 1396 Interesting = true; 1397 AccumulatedConstant += Scale * C->getValue()->getValue(); 1398 } 1399 1400 // Next comes everything else. We're especially interested in multiplies 1401 // here, but they're in the middle, so just visit the rest with one loop. 1402 for (; i != NumOperands; ++i) { 1403 const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Ops[i]); 1404 if (Mul && isa<SCEVConstant>(Mul->getOperand(0))) { 1405 APInt NewScale = 1406 Scale * cast<SCEVConstant>(Mul->getOperand(0))->getValue()->getValue(); 1407 if (Mul->getNumOperands() == 2 && isa<SCEVAddExpr>(Mul->getOperand(1))) { 1408 // A multiplication of a constant with another add; recurse. 1409 const SCEVAddExpr *Add = cast<SCEVAddExpr>(Mul->getOperand(1)); 1410 Interesting |= 1411 CollectAddOperandsWithScales(M, NewOps, AccumulatedConstant, 1412 Add->op_begin(), Add->getNumOperands(), 1413 NewScale, SE); 1414 } else { 1415 // A multiplication of a constant with some other value. Update 1416 // the map. 1417 SmallVector<const SCEV *, 4> MulOps(Mul->op_begin()+1, Mul->op_end()); 1418 const SCEV *Key = SE.getMulExpr(MulOps); 1419 std::pair<DenseMap<const SCEV *, APInt>::iterator, bool> Pair = 1420 M.insert(std::make_pair(Key, NewScale)); 1421 if (Pair.second) { 1422 NewOps.push_back(Pair.first->first); 1423 } else { 1424 Pair.first->second += NewScale; 1425 // The map already had an entry for this value, which may indicate 1426 // a folding opportunity. 1427 Interesting = true; 1428 } 1429 } 1430 } else { 1431 // An ordinary operand. Update the map. 1432 std::pair<DenseMap<const SCEV *, APInt>::iterator, bool> Pair = 1433 M.insert(std::make_pair(Ops[i], Scale)); 1434 if (Pair.second) { 1435 NewOps.push_back(Pair.first->first); 1436 } else { 1437 Pair.first->second += Scale; 1438 // The map already had an entry for this value, which may indicate 1439 // a folding opportunity. 1440 Interesting = true; 1441 } 1442 } 1443 } 1444 1445 return Interesting; 1446} 1447 1448namespace { 1449 struct APIntCompare { 1450 bool operator()(const APInt &LHS, const APInt &RHS) const { 1451 return LHS.ult(RHS); 1452 } 1453 }; 1454} 1455 1456/// getAddExpr - Get a canonical add expression, or something simpler if 1457/// possible. 1458const SCEV *ScalarEvolution::getAddExpr(SmallVectorImpl<const SCEV *> &Ops, 1459 SCEV::NoWrapFlags Flags) { 1460 assert(!(Flags & ~(SCEV::FlagNUW | SCEV::FlagNSW)) && 1461 "only nuw or nsw allowed"); 1462 assert(!Ops.empty() && "Cannot get empty add!"); 1463 if (Ops.size() == 1) return Ops[0]; 1464#ifndef NDEBUG 1465 Type *ETy = getEffectiveSCEVType(Ops[0]->getType()); 1466 for (unsigned i = 1, e = Ops.size(); i != e; ++i) 1467 assert(getEffectiveSCEVType(Ops[i]->getType()) == ETy && 1468 "SCEVAddExpr operand types don't match!"); 1469#endif 1470 1471 // If FlagNSW is true and all the operands are non-negative, infer FlagNUW. 1472 // And vice-versa. 1473 int SignOrUnsignMask = SCEV::FlagNUW | SCEV::FlagNSW; 1474 SCEV::NoWrapFlags SignOrUnsignWrap = maskFlags(Flags, SignOrUnsignMask); 1475 if (SignOrUnsignWrap && (SignOrUnsignWrap != SignOrUnsignMask)) { 1476 bool All = true; 1477 for (SmallVectorImpl<const SCEV *>::const_iterator I = Ops.begin(), 1478 E = Ops.end(); I != E; ++I) 1479 if (!isKnownNonNegative(*I)) { 1480 All = false; 1481 break; 1482 } 1483 if (All) Flags = setFlags(Flags, (SCEV::NoWrapFlags)SignOrUnsignMask); 1484 } 1485 1486 // Sort by complexity, this groups all similar expression types together. 1487 GroupByComplexity(Ops, LI); 1488 1489 // If there are any constants, fold them together. 1490 unsigned Idx = 0; 1491 if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(Ops[0])) { 1492 ++Idx; 1493 assert(Idx < Ops.size()); 1494 while (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) { 1495 // We found two constants, fold them together! 1496 Ops[0] = getConstant(LHSC->getValue()->getValue() + 1497 RHSC->getValue()->getValue()); 1498 if (Ops.size() == 2) return Ops[0]; 1499 Ops.erase(Ops.begin()+1); // Erase the folded element 1500 LHSC = cast<SCEVConstant>(Ops[0]); 1501 } 1502 1503 // If we are left with a constant zero being added, strip it off. 1504 if (LHSC->getValue()->isZero()) { 1505 Ops.erase(Ops.begin()); 1506 --Idx; 1507 } 1508 1509 if (Ops.size() == 1) return Ops[0]; 1510 } 1511 1512 // Okay, check to see if the same value occurs in the operand list more than 1513 // once. If so, merge them together into an multiply expression. Since we 1514 // sorted the list, these values are required to be adjacent. 1515 Type *Ty = Ops[0]->getType(); 1516 bool FoundMatch = false; 1517 for (unsigned i = 0, e = Ops.size(); i != e-1; ++i) 1518 if (Ops[i] == Ops[i+1]) { // X + Y + Y --> X + Y*2 1519 // Scan ahead to count how many equal operands there are. 1520 unsigned Count = 2; 1521 while (i+Count != e && Ops[i+Count] == Ops[i]) 1522 ++Count; 1523 // Merge the values into a multiply. 1524 const SCEV *Scale = getConstant(Ty, Count); 1525 const SCEV *Mul = getMulExpr(Scale, Ops[i]); 1526 if (Ops.size() == Count) 1527 return Mul; 1528 Ops[i] = Mul; 1529 Ops.erase(Ops.begin()+i+1, Ops.begin()+i+Count); 1530 --i; e -= Count - 1; 1531 FoundMatch = true; 1532 } 1533 if (FoundMatch) 1534 return getAddExpr(Ops, Flags); 1535 1536 // Check for truncates. If all the operands are truncated from the same 1537 // type, see if factoring out the truncate would permit the result to be 1538 // folded. eg., trunc(x) + m*trunc(n) --> trunc(x + trunc(m)*n) 1539 // if the contents of the resulting outer trunc fold to something simple. 1540 for (; Idx < Ops.size() && isa<SCEVTruncateExpr>(Ops[Idx]); ++Idx) { 1541 const SCEVTruncateExpr *Trunc = cast<SCEVTruncateExpr>(Ops[Idx]); 1542 Type *DstType = Trunc->getType(); 1543 Type *SrcType = Trunc->getOperand()->getType(); 1544 SmallVector<const SCEV *, 8> LargeOps; 1545 bool Ok = true; 1546 // Check all the operands to see if they can be represented in the 1547 // source type of the truncate. 1548 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 1549 if (const SCEVTruncateExpr *T = dyn_cast<SCEVTruncateExpr>(Ops[i])) { 1550 if (T->getOperand()->getType() != SrcType) { 1551 Ok = false; 1552 break; 1553 } 1554 LargeOps.push_back(T->getOperand()); 1555 } else if (const SCEVConstant *C = dyn_cast<SCEVConstant>(Ops[i])) { 1556 LargeOps.push_back(getAnyExtendExpr(C, SrcType)); 1557 } else if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(Ops[i])) { 1558 SmallVector<const SCEV *, 8> LargeMulOps; 1559 for (unsigned j = 0, f = M->getNumOperands(); j != f && Ok; ++j) { 1560 if (const SCEVTruncateExpr *T = 1561 dyn_cast<SCEVTruncateExpr>(M->getOperand(j))) { 1562 if (T->getOperand()->getType() != SrcType) { 1563 Ok = false; 1564 break; 1565 } 1566 LargeMulOps.push_back(T->getOperand()); 1567 } else if (const SCEVConstant *C = 1568 dyn_cast<SCEVConstant>(M->getOperand(j))) { 1569 LargeMulOps.push_back(getAnyExtendExpr(C, SrcType)); 1570 } else { 1571 Ok = false; 1572 break; 1573 } 1574 } 1575 if (Ok) 1576 LargeOps.push_back(getMulExpr(LargeMulOps)); 1577 } else { 1578 Ok = false; 1579 break; 1580 } 1581 } 1582 if (Ok) { 1583 // Evaluate the expression in the larger type. 1584 const SCEV *Fold = getAddExpr(LargeOps, Flags); 1585 // If it folds to something simple, use it. Otherwise, don't. 1586 if (isa<SCEVConstant>(Fold) || isa<SCEVUnknown>(Fold)) 1587 return getTruncateExpr(Fold, DstType); 1588 } 1589 } 1590 1591 // Skip past any other cast SCEVs. 1592 while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scAddExpr) 1593 ++Idx; 1594 1595 // If there are add operands they would be next. 1596 if (Idx < Ops.size()) { 1597 bool DeletedAdd = false; 1598 while (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[Idx])) { 1599 // If we have an add, expand the add operands onto the end of the operands 1600 // list. 1601 Ops.erase(Ops.begin()+Idx); 1602 Ops.append(Add->op_begin(), Add->op_end()); 1603 DeletedAdd = true; 1604 } 1605 1606 // If we deleted at least one add, we added operands to the end of the list, 1607 // and they are not necessarily sorted. Recurse to resort and resimplify 1608 // any operands we just acquired. 1609 if (DeletedAdd) 1610 return getAddExpr(Ops); 1611 } 1612 1613 // Skip over the add expression until we get to a multiply. 1614 while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scMulExpr) 1615 ++Idx; 1616 1617 // Check to see if there are any folding opportunities present with 1618 // operands multiplied by constant values. 1619 if (Idx < Ops.size() && isa<SCEVMulExpr>(Ops[Idx])) { 1620 uint64_t BitWidth = getTypeSizeInBits(Ty); 1621 DenseMap<const SCEV *, APInt> M; 1622 SmallVector<const SCEV *, 8> NewOps; 1623 APInt AccumulatedConstant(BitWidth, 0); 1624 if (CollectAddOperandsWithScales(M, NewOps, AccumulatedConstant, 1625 Ops.data(), Ops.size(), 1626 APInt(BitWidth, 1), *this)) { 1627 // Some interesting folding opportunity is present, so its worthwhile to 1628 // re-generate the operands list. Group the operands by constant scale, 1629 // to avoid multiplying by the same constant scale multiple times. 1630 std::map<APInt, SmallVector<const SCEV *, 4>, APIntCompare> MulOpLists; 1631 for (SmallVector<const SCEV *, 8>::const_iterator I = NewOps.begin(), 1632 E = NewOps.end(); I != E; ++I) 1633 MulOpLists[M.find(*I)->second].push_back(*I); 1634 // Re-generate the operands list. 1635 Ops.clear(); 1636 if (AccumulatedConstant != 0) 1637 Ops.push_back(getConstant(AccumulatedConstant)); 1638 for (std::map<APInt, SmallVector<const SCEV *, 4>, APIntCompare>::iterator 1639 I = MulOpLists.begin(), E = MulOpLists.end(); I != E; ++I) 1640 if (I->first != 0) 1641 Ops.push_back(getMulExpr(getConstant(I->first), 1642 getAddExpr(I->second))); 1643 if (Ops.empty()) 1644 return getConstant(Ty, 0); 1645 if (Ops.size() == 1) 1646 return Ops[0]; 1647 return getAddExpr(Ops); 1648 } 1649 } 1650 1651 // If we are adding something to a multiply expression, make sure the 1652 // something is not already an operand of the multiply. If so, merge it into 1653 // the multiply. 1654 for (; Idx < Ops.size() && isa<SCEVMulExpr>(Ops[Idx]); ++Idx) { 1655 const SCEVMulExpr *Mul = cast<SCEVMulExpr>(Ops[Idx]); 1656 for (unsigned MulOp = 0, e = Mul->getNumOperands(); MulOp != e; ++MulOp) { 1657 const SCEV *MulOpSCEV = Mul->getOperand(MulOp); 1658 if (isa<SCEVConstant>(MulOpSCEV)) 1659 continue; 1660 for (unsigned AddOp = 0, e = Ops.size(); AddOp != e; ++AddOp) 1661 if (MulOpSCEV == Ops[AddOp]) { 1662 // Fold W + X + (X * Y * Z) --> W + (X * ((Y*Z)+1)) 1663 const SCEV *InnerMul = Mul->getOperand(MulOp == 0); 1664 if (Mul->getNumOperands() != 2) { 1665 // If the multiply has more than two operands, we must get the 1666 // Y*Z term. 1667 SmallVector<const SCEV *, 4> MulOps(Mul->op_begin(), 1668 Mul->op_begin()+MulOp); 1669 MulOps.append(Mul->op_begin()+MulOp+1, Mul->op_end()); 1670 InnerMul = getMulExpr(MulOps); 1671 } 1672 const SCEV *One = getConstant(Ty, 1); 1673 const SCEV *AddOne = getAddExpr(One, InnerMul); 1674 const SCEV *OuterMul = getMulExpr(AddOne, MulOpSCEV); 1675 if (Ops.size() == 2) return OuterMul; 1676 if (AddOp < Idx) { 1677 Ops.erase(Ops.begin()+AddOp); 1678 Ops.erase(Ops.begin()+Idx-1); 1679 } else { 1680 Ops.erase(Ops.begin()+Idx); 1681 Ops.erase(Ops.begin()+AddOp-1); 1682 } 1683 Ops.push_back(OuterMul); 1684 return getAddExpr(Ops); 1685 } 1686 1687 // Check this multiply against other multiplies being added together. 1688 for (unsigned OtherMulIdx = Idx+1; 1689 OtherMulIdx < Ops.size() && isa<SCEVMulExpr>(Ops[OtherMulIdx]); 1690 ++OtherMulIdx) { 1691 const SCEVMulExpr *OtherMul = cast<SCEVMulExpr>(Ops[OtherMulIdx]); 1692 // If MulOp occurs in OtherMul, we can fold the two multiplies 1693 // together. 1694 for (unsigned OMulOp = 0, e = OtherMul->getNumOperands(); 1695 OMulOp != e; ++OMulOp) 1696 if (OtherMul->getOperand(OMulOp) == MulOpSCEV) { 1697 // Fold X + (A*B*C) + (A*D*E) --> X + (A*(B*C+D*E)) 1698 const SCEV *InnerMul1 = Mul->getOperand(MulOp == 0); 1699 if (Mul->getNumOperands() != 2) { 1700 SmallVector<const SCEV *, 4> MulOps(Mul->op_begin(), 1701 Mul->op_begin()+MulOp); 1702 MulOps.append(Mul->op_begin()+MulOp+1, Mul->op_end()); 1703 InnerMul1 = getMulExpr(MulOps); 1704 } 1705 const SCEV *InnerMul2 = OtherMul->getOperand(OMulOp == 0); 1706 if (OtherMul->getNumOperands() != 2) { 1707 SmallVector<const SCEV *, 4> MulOps(OtherMul->op_begin(), 1708 OtherMul->op_begin()+OMulOp); 1709 MulOps.append(OtherMul->op_begin()+OMulOp+1, OtherMul->op_end()); 1710 InnerMul2 = getMulExpr(MulOps); 1711 } 1712 const SCEV *InnerMulSum = getAddExpr(InnerMul1,InnerMul2); 1713 const SCEV *OuterMul = getMulExpr(MulOpSCEV, InnerMulSum); 1714 if (Ops.size() == 2) return OuterMul; 1715 Ops.erase(Ops.begin()+Idx); 1716 Ops.erase(Ops.begin()+OtherMulIdx-1); 1717 Ops.push_back(OuterMul); 1718 return getAddExpr(Ops); 1719 } 1720 } 1721 } 1722 } 1723 1724 // If there are any add recurrences in the operands list, see if any other 1725 // added values are loop invariant. If so, we can fold them into the 1726 // recurrence. 1727 while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scAddRecExpr) 1728 ++Idx; 1729 1730 // Scan over all recurrences, trying to fold loop invariants into them. 1731 for (; Idx < Ops.size() && isa<SCEVAddRecExpr>(Ops[Idx]); ++Idx) { 1732 // Scan all of the other operands to this add and add them to the vector if 1733 // they are loop invariant w.r.t. the recurrence. 1734 SmallVector<const SCEV *, 8> LIOps; 1735 const SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(Ops[Idx]); 1736 const Loop *AddRecLoop = AddRec->getLoop(); 1737 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 1738 if (isLoopInvariant(Ops[i], AddRecLoop)) { 1739 LIOps.push_back(Ops[i]); 1740 Ops.erase(Ops.begin()+i); 1741 --i; --e; 1742 } 1743 1744 // If we found some loop invariants, fold them into the recurrence. 1745 if (!LIOps.empty()) { 1746 // NLI + LI + {Start,+,Step} --> NLI + {LI+Start,+,Step} 1747 LIOps.push_back(AddRec->getStart()); 1748 1749 SmallVector<const SCEV *, 4> AddRecOps(AddRec->op_begin(), 1750 AddRec->op_end()); 1751 AddRecOps[0] = getAddExpr(LIOps); 1752 1753 // Build the new addrec. Propagate the NUW and NSW flags if both the 1754 // outer add and the inner addrec are guaranteed to have no overflow. 1755 // Always propagate NW. 1756 Flags = AddRec->getNoWrapFlags(setFlags(Flags, SCEV::FlagNW)); 1757 const SCEV *NewRec = getAddRecExpr(AddRecOps, AddRecLoop, Flags); 1758 1759 // If all of the other operands were loop invariant, we are done. 1760 if (Ops.size() == 1) return NewRec; 1761 1762 // Otherwise, add the folded AddRec by the non-invariant parts. 1763 for (unsigned i = 0;; ++i) 1764 if (Ops[i] == AddRec) { 1765 Ops[i] = NewRec; 1766 break; 1767 } 1768 return getAddExpr(Ops); 1769 } 1770 1771 // Okay, if there weren't any loop invariants to be folded, check to see if 1772 // there are multiple AddRec's with the same loop induction variable being 1773 // added together. If so, we can fold them. 1774 for (unsigned OtherIdx = Idx+1; 1775 OtherIdx < Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]); 1776 ++OtherIdx) 1777 if (AddRecLoop == cast<SCEVAddRecExpr>(Ops[OtherIdx])->getLoop()) { 1778 // Other + {A,+,B}<L> + {C,+,D}<L> --> Other + {A+C,+,B+D}<L> 1779 SmallVector<const SCEV *, 4> AddRecOps(AddRec->op_begin(), 1780 AddRec->op_end()); 1781 for (; OtherIdx != Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]); 1782 ++OtherIdx) 1783 if (const SCEVAddRecExpr *OtherAddRec = 1784 dyn_cast<SCEVAddRecExpr>(Ops[OtherIdx])) 1785 if (OtherAddRec->getLoop() == AddRecLoop) { 1786 for (unsigned i = 0, e = OtherAddRec->getNumOperands(); 1787 i != e; ++i) { 1788 if (i >= AddRecOps.size()) { 1789 AddRecOps.append(OtherAddRec->op_begin()+i, 1790 OtherAddRec->op_end()); 1791 break; 1792 } 1793 AddRecOps[i] = getAddExpr(AddRecOps[i], 1794 OtherAddRec->getOperand(i)); 1795 } 1796 Ops.erase(Ops.begin() + OtherIdx); --OtherIdx; 1797 } 1798 // Step size has changed, so we cannot guarantee no self-wraparound. 1799 Ops[Idx] = getAddRecExpr(AddRecOps, AddRecLoop, SCEV::FlagAnyWrap); 1800 return getAddExpr(Ops); 1801 } 1802 1803 // Otherwise couldn't fold anything into this recurrence. Move onto the 1804 // next one. 1805 } 1806 1807 // Okay, it looks like we really DO need an add expr. Check to see if we 1808 // already have one, otherwise create a new one. 1809 FoldingSetNodeID ID; 1810 ID.AddInteger(scAddExpr); 1811 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 1812 ID.AddPointer(Ops[i]); 1813 void *IP = 0; 1814 SCEVAddExpr *S = 1815 static_cast<SCEVAddExpr *>(UniqueSCEVs.FindNodeOrInsertPos(ID, IP)); 1816 if (!S) { 1817 const SCEV **O = SCEVAllocator.Allocate<const SCEV *>(Ops.size()); 1818 std::uninitialized_copy(Ops.begin(), Ops.end(), O); 1819 S = new (SCEVAllocator) SCEVAddExpr(ID.Intern(SCEVAllocator), 1820 O, Ops.size()); 1821 UniqueSCEVs.InsertNode(S, IP); 1822 } 1823 S->setNoWrapFlags(Flags); 1824 return S; 1825} 1826 1827static uint64_t umul_ov(uint64_t i, uint64_t j, bool &Overflow) { 1828 uint64_t k = i*j; 1829 if (j > 1 && k / j != i) Overflow = true; 1830 return k; 1831} 1832 1833/// Compute the result of "n choose k", the binomial coefficient. If an 1834/// intermediate computation overflows, Overflow will be set and the return will 1835/// be garbage. Overflow is not cleared on absence of overflow. 1836static uint64_t Choose(uint64_t n, uint64_t k, bool &Overflow) { 1837 // We use the multiplicative formula: 1838 // n(n-1)(n-2)...(n-(k-1)) / k(k-1)(k-2)...1 . 1839 // At each iteration, we take the n-th term of the numeral and divide by the 1840 // (k-n)th term of the denominator. This division will always produce an 1841 // integral result, and helps reduce the chance of overflow in the 1842 // intermediate computations. However, we can still overflow even when the 1843 // final result would fit. 1844 1845 if (n == 0 || n == k) return 1; 1846 if (k > n) return 0; 1847 1848 if (k > n/2) 1849 k = n-k; 1850 1851 uint64_t r = 1; 1852 for (uint64_t i = 1; i <= k; ++i) { 1853 r = umul_ov(r, n-(i-1), Overflow); 1854 r /= i; 1855 } 1856 return r; 1857} 1858 1859/// getMulExpr - Get a canonical multiply expression, or something simpler if 1860/// possible. 1861const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops, 1862 SCEV::NoWrapFlags Flags) { 1863 assert(Flags == maskFlags(Flags, SCEV::FlagNUW | SCEV::FlagNSW) && 1864 "only nuw or nsw allowed"); 1865 assert(!Ops.empty() && "Cannot get empty mul!"); 1866 if (Ops.size() == 1) return Ops[0]; 1867#ifndef NDEBUG 1868 Type *ETy = getEffectiveSCEVType(Ops[0]->getType()); 1869 for (unsigned i = 1, e = Ops.size(); i != e; ++i) 1870 assert(getEffectiveSCEVType(Ops[i]->getType()) == ETy && 1871 "SCEVMulExpr operand types don't match!"); 1872#endif 1873 1874 // If FlagNSW is true and all the operands are non-negative, infer FlagNUW. 1875 // And vice-versa. 1876 int SignOrUnsignMask = SCEV::FlagNUW | SCEV::FlagNSW; 1877 SCEV::NoWrapFlags SignOrUnsignWrap = maskFlags(Flags, SignOrUnsignMask); 1878 if (SignOrUnsignWrap && (SignOrUnsignWrap != SignOrUnsignMask)) { 1879 bool All = true; 1880 for (SmallVectorImpl<const SCEV *>::const_iterator I = Ops.begin(), 1881 E = Ops.end(); I != E; ++I) 1882 if (!isKnownNonNegative(*I)) { 1883 All = false; 1884 break; 1885 } 1886 if (All) Flags = setFlags(Flags, (SCEV::NoWrapFlags)SignOrUnsignMask); 1887 } 1888 1889 // Sort by complexity, this groups all similar expression types together. 1890 GroupByComplexity(Ops, LI); 1891 1892 // If there are any constants, fold them together. 1893 unsigned Idx = 0; 1894 if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(Ops[0])) { 1895 1896 // C1*(C2+V) -> C1*C2 + C1*V 1897 if (Ops.size() == 2) 1898 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[1])) 1899 if (Add->getNumOperands() == 2 && 1900 isa<SCEVConstant>(Add->getOperand(0))) 1901 return getAddExpr(getMulExpr(LHSC, Add->getOperand(0)), 1902 getMulExpr(LHSC, Add->getOperand(1))); 1903 1904 ++Idx; 1905 while (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) { 1906 // We found two constants, fold them together! 1907 ConstantInt *Fold = ConstantInt::get(getContext(), 1908 LHSC->getValue()->getValue() * 1909 RHSC->getValue()->getValue()); 1910 Ops[0] = getConstant(Fold); 1911 Ops.erase(Ops.begin()+1); // Erase the folded element 1912 if (Ops.size() == 1) return Ops[0]; 1913 LHSC = cast<SCEVConstant>(Ops[0]); 1914 } 1915 1916 // If we are left with a constant one being multiplied, strip it off. 1917 if (cast<SCEVConstant>(Ops[0])->getValue()->equalsInt(1)) { 1918 Ops.erase(Ops.begin()); 1919 --Idx; 1920 } else if (cast<SCEVConstant>(Ops[0])->getValue()->isZero()) { 1921 // If we have a multiply of zero, it will always be zero. 1922 return Ops[0]; 1923 } else if (Ops[0]->isAllOnesValue()) { 1924 // If we have a mul by -1 of an add, try distributing the -1 among the 1925 // add operands. 1926 if (Ops.size() == 2) { 1927 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[1])) { 1928 SmallVector<const SCEV *, 4> NewOps; 1929 bool AnyFolded = false; 1930 for (SCEVAddRecExpr::op_iterator I = Add->op_begin(), 1931 E = Add->op_end(); I != E; ++I) { 1932 const SCEV *Mul = getMulExpr(Ops[0], *I); 1933 if (!isa<SCEVMulExpr>(Mul)) AnyFolded = true; 1934 NewOps.push_back(Mul); 1935 } 1936 if (AnyFolded) 1937 return getAddExpr(NewOps); 1938 } 1939 else if (const SCEVAddRecExpr * 1940 AddRec = dyn_cast<SCEVAddRecExpr>(Ops[1])) { 1941 // Negation preserves a recurrence's no self-wrap property. 1942 SmallVector<const SCEV *, 4> Operands; 1943 for (SCEVAddRecExpr::op_iterator I = AddRec->op_begin(), 1944 E = AddRec->op_end(); I != E; ++I) { 1945 Operands.push_back(getMulExpr(Ops[0], *I)); 1946 } 1947 return getAddRecExpr(Operands, AddRec->getLoop(), 1948 AddRec->getNoWrapFlags(SCEV::FlagNW)); 1949 } 1950 } 1951 } 1952 1953 if (Ops.size() == 1) 1954 return Ops[0]; 1955 } 1956 1957 // Skip over the add expression until we get to a multiply. 1958 while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scMulExpr) 1959 ++Idx; 1960 1961 // If there are mul operands inline them all into this expression. 1962 if (Idx < Ops.size()) { 1963 bool DeletedMul = false; 1964 while (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Ops[Idx])) { 1965 // If we have an mul, expand the mul operands onto the end of the operands 1966 // list. 1967 Ops.erase(Ops.begin()+Idx); 1968 Ops.append(Mul->op_begin(), Mul->op_end()); 1969 DeletedMul = true; 1970 } 1971 1972 // If we deleted at least one mul, we added operands to the end of the list, 1973 // and they are not necessarily sorted. Recurse to resort and resimplify 1974 // any operands we just acquired. 1975 if (DeletedMul) 1976 return getMulExpr(Ops); 1977 } 1978 1979 // If there are any add recurrences in the operands list, see if any other 1980 // added values are loop invariant. If so, we can fold them into the 1981 // recurrence. 1982 while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scAddRecExpr) 1983 ++Idx; 1984 1985 // Scan over all recurrences, trying to fold loop invariants into them. 1986 for (; Idx < Ops.size() && isa<SCEVAddRecExpr>(Ops[Idx]); ++Idx) { 1987 // Scan all of the other operands to this mul and add them to the vector if 1988 // they are loop invariant w.r.t. the recurrence. 1989 SmallVector<const SCEV *, 8> LIOps; 1990 const SCEVAddRecExpr *AddRec = cast<SCEVAddRecExpr>(Ops[Idx]); 1991 const Loop *AddRecLoop = AddRec->getLoop(); 1992 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 1993 if (isLoopInvariant(Ops[i], AddRecLoop)) { 1994 LIOps.push_back(Ops[i]); 1995 Ops.erase(Ops.begin()+i); 1996 --i; --e; 1997 } 1998 1999 // If we found some loop invariants, fold them into the recurrence. 2000 if (!LIOps.empty()) { 2001 // NLI * LI * {Start,+,Step} --> NLI * {LI*Start,+,LI*Step} 2002 SmallVector<const SCEV *, 4> NewOps; 2003 NewOps.reserve(AddRec->getNumOperands()); 2004 const SCEV *Scale = getMulExpr(LIOps); 2005 for (unsigned i = 0, e = AddRec->getNumOperands(); i != e; ++i) 2006 NewOps.push_back(getMulExpr(Scale, AddRec->getOperand(i))); 2007 2008 // Build the new addrec. Propagate the NUW and NSW flags if both the 2009 // outer mul and the inner addrec are guaranteed to have no overflow. 2010 // 2011 // No self-wrap cannot be guaranteed after changing the step size, but 2012 // will be inferred if either NUW or NSW is true. 2013 Flags = AddRec->getNoWrapFlags(clearFlags(Flags, SCEV::FlagNW)); 2014 const SCEV *NewRec = getAddRecExpr(NewOps, AddRecLoop, Flags); 2015 2016 // If all of the other operands were loop invariant, we are done. 2017 if (Ops.size() == 1) return NewRec; 2018 2019 // Otherwise, multiply the folded AddRec by the non-invariant parts. 2020 for (unsigned i = 0;; ++i) 2021 if (Ops[i] == AddRec) { 2022 Ops[i] = NewRec; 2023 break; 2024 } 2025 return getMulExpr(Ops); 2026 } 2027 2028 // Okay, if there weren't any loop invariants to be folded, check to see if 2029 // there are multiple AddRec's with the same loop induction variable being 2030 // multiplied together. If so, we can fold them. 2031 for (unsigned OtherIdx = Idx+1; 2032 OtherIdx < Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]); 2033 ++OtherIdx) { 2034 if (AddRecLoop != cast<SCEVAddRecExpr>(Ops[OtherIdx])->getLoop()) 2035 continue; 2036 2037 // {A1,+,A2,+,...,+,An}<L> * {B1,+,B2,+,...,+,Bn}<L> 2038 // = {x=1 in [ sum y=x..2x [ sum z=max(y-x, y-n)..min(x,n) [ 2039 // choose(x, 2x)*choose(2x-y, x-z)*A_{y-z}*B_z 2040 // ]]],+,...up to x=2n}. 2041 // Note that the arguments to choose() are always integers with values 2042 // known at compile time, never SCEV objects. 2043 // 2044 // The implementation avoids pointless extra computations when the two 2045 // addrec's are of different length (mathematically, it's equivalent to 2046 // an infinite stream of zeros on the right). 2047 bool OpsModified = false; 2048 for (; OtherIdx != Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]); 2049 ++OtherIdx) { 2050 const SCEVAddRecExpr *OtherAddRec = 2051 dyn_cast<SCEVAddRecExpr>(Ops[OtherIdx]); 2052 if (!OtherAddRec || OtherAddRec->getLoop() != AddRecLoop) 2053 continue; 2054 2055 bool Overflow = false; 2056 Type *Ty = AddRec->getType(); 2057 bool LargerThan64Bits = getTypeSizeInBits(Ty) > 64; 2058 SmallVector<const SCEV*, 7> AddRecOps; 2059 for (int x = 0, xe = AddRec->getNumOperands() + 2060 OtherAddRec->getNumOperands() - 1; x != xe && !Overflow; ++x) { 2061 const SCEV *Term = getConstant(Ty, 0); 2062 for (int y = x, ye = 2*x+1; y != ye && !Overflow; ++y) { 2063 uint64_t Coeff1 = Choose(x, 2*x - y, Overflow); 2064 for (int z = std::max(y-x, y-(int)AddRec->getNumOperands()+1), 2065 ze = std::min(x+1, (int)OtherAddRec->getNumOperands()); 2066 z < ze && !Overflow; ++z) { 2067 uint64_t Coeff2 = Choose(2*x - y, x-z, Overflow); 2068 uint64_t Coeff; 2069 if (LargerThan64Bits) 2070 Coeff = umul_ov(Coeff1, Coeff2, Overflow); 2071 else 2072 Coeff = Coeff1*Coeff2; 2073 const SCEV *CoeffTerm = getConstant(Ty, Coeff); 2074 const SCEV *Term1 = AddRec->getOperand(y-z); 2075 const SCEV *Term2 = OtherAddRec->getOperand(z); 2076 Term = getAddExpr(Term, getMulExpr(CoeffTerm, Term1,Term2)); 2077 } 2078 } 2079 AddRecOps.push_back(Term); 2080 } 2081 if (!Overflow) { 2082 const SCEV *NewAddRec = getAddRecExpr(AddRecOps, AddRec->getLoop(), 2083 SCEV::FlagAnyWrap); 2084 if (Ops.size() == 2) return NewAddRec; 2085 Ops[Idx] = NewAddRec; 2086 Ops.erase(Ops.begin() + OtherIdx); --OtherIdx; 2087 OpsModified = true; 2088 AddRec = dyn_cast<SCEVAddRecExpr>(NewAddRec); 2089 if (!AddRec) 2090 break; 2091 } 2092 } 2093 if (OpsModified) 2094 return getMulExpr(Ops); 2095 } 2096 2097 // Otherwise couldn't fold anything into this recurrence. Move onto the 2098 // next one. 2099 } 2100 2101 // Okay, it looks like we really DO need an mul expr. Check to see if we 2102 // already have one, otherwise create a new one. 2103 FoldingSetNodeID ID; 2104 ID.AddInteger(scMulExpr); 2105 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 2106 ID.AddPointer(Ops[i]); 2107 void *IP = 0; 2108 SCEVMulExpr *S = 2109 static_cast<SCEVMulExpr *>(UniqueSCEVs.FindNodeOrInsertPos(ID, IP)); 2110 if (!S) { 2111 const SCEV **O = SCEVAllocator.Allocate<const SCEV *>(Ops.size()); 2112 std::uninitialized_copy(Ops.begin(), Ops.end(), O); 2113 S = new (SCEVAllocator) SCEVMulExpr(ID.Intern(SCEVAllocator), 2114 O, Ops.size()); 2115 UniqueSCEVs.InsertNode(S, IP); 2116 } 2117 S->setNoWrapFlags(Flags); 2118 return S; 2119} 2120 2121/// getUDivExpr - Get a canonical unsigned division expression, or something 2122/// simpler if possible. 2123const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS, 2124 const SCEV *RHS) { 2125 assert(getEffectiveSCEVType(LHS->getType()) == 2126 getEffectiveSCEVType(RHS->getType()) && 2127 "SCEVUDivExpr operand types don't match!"); 2128 2129 if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) { 2130 if (RHSC->getValue()->equalsInt(1)) 2131 return LHS; // X udiv 1 --> x 2132 // If the denominator is zero, the result of the udiv is undefined. Don't 2133 // try to analyze it, because the resolution chosen here may differ from 2134 // the resolution chosen in other parts of the compiler. 2135 if (!RHSC->getValue()->isZero()) { 2136 // Determine if the division can be folded into the operands of 2137 // its operands. 2138 // TODO: Generalize this to non-constants by using known-bits information. 2139 Type *Ty = LHS->getType(); 2140 unsigned LZ = RHSC->getValue()->getValue().countLeadingZeros(); 2141 unsigned MaxShiftAmt = getTypeSizeInBits(Ty) - LZ - 1; 2142 // For non-power-of-two values, effectively round the value up to the 2143 // nearest power of two. 2144 if (!RHSC->getValue()->getValue().isPowerOf2()) 2145 ++MaxShiftAmt; 2146 IntegerType *ExtTy = 2147 IntegerType::get(getContext(), getTypeSizeInBits(Ty) + MaxShiftAmt); 2148 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS)) 2149 if (const SCEVConstant *Step = 2150 dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this))) { 2151 // {X,+,N}/C --> {X/C,+,N/C} if safe and N/C can be folded. 2152 const APInt &StepInt = Step->getValue()->getValue(); 2153 const APInt &DivInt = RHSC->getValue()->getValue(); 2154 if (!StepInt.urem(DivInt) && 2155 getZeroExtendExpr(AR, ExtTy) == 2156 getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy), 2157 getZeroExtendExpr(Step, ExtTy), 2158 AR->getLoop(), SCEV::FlagAnyWrap)) { 2159 SmallVector<const SCEV *, 4> Operands; 2160 for (unsigned i = 0, e = AR->getNumOperands(); i != e; ++i) 2161 Operands.push_back(getUDivExpr(AR->getOperand(i), RHS)); 2162 return getAddRecExpr(Operands, AR->getLoop(), 2163 SCEV::FlagNW); 2164 } 2165 /// Get a canonical UDivExpr for a recurrence. 2166 /// {X,+,N}/C => {Y,+,N}/C where Y=X-(X%N). Safe when C%N=0. 2167 // We can currently only fold X%N if X is constant. 2168 const SCEVConstant *StartC = dyn_cast<SCEVConstant>(AR->getStart()); 2169 if (StartC && !DivInt.urem(StepInt) && 2170 getZeroExtendExpr(AR, ExtTy) == 2171 getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy), 2172 getZeroExtendExpr(Step, ExtTy), 2173 AR->getLoop(), SCEV::FlagAnyWrap)) { 2174 const APInt &StartInt = StartC->getValue()->getValue(); 2175 const APInt &StartRem = StartInt.urem(StepInt); 2176 if (StartRem != 0) 2177 LHS = getAddRecExpr(getConstant(StartInt - StartRem), Step, 2178 AR->getLoop(), SCEV::FlagNW); 2179 } 2180 } 2181 // (A*B)/C --> A*(B/C) if safe and B/C can be folded. 2182 if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(LHS)) { 2183 SmallVector<const SCEV *, 4> Operands; 2184 for (unsigned i = 0, e = M->getNumOperands(); i != e; ++i) 2185 Operands.push_back(getZeroExtendExpr(M->getOperand(i), ExtTy)); 2186 if (getZeroExtendExpr(M, ExtTy) == getMulExpr(Operands)) 2187 // Find an operand that's safely divisible. 2188 for (unsigned i = 0, e = M->getNumOperands(); i != e; ++i) { 2189 const SCEV *Op = M->getOperand(i); 2190 const SCEV *Div = getUDivExpr(Op, RHSC); 2191 if (!isa<SCEVUDivExpr>(Div) && getMulExpr(Div, RHSC) == Op) { 2192 Operands = SmallVector<const SCEV *, 4>(M->op_begin(), 2193 M->op_end()); 2194 Operands[i] = Div; 2195 return getMulExpr(Operands); 2196 } 2197 } 2198 } 2199 // (A+B)/C --> (A/C + B/C) if safe and A/C and B/C can be folded. 2200 if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(LHS)) { 2201 SmallVector<const SCEV *, 4> Operands; 2202 for (unsigned i = 0, e = A->getNumOperands(); i != e; ++i) 2203 Operands.push_back(getZeroExtendExpr(A->getOperand(i), ExtTy)); 2204 if (getZeroExtendExpr(A, ExtTy) == getAddExpr(Operands)) { 2205 Operands.clear(); 2206 for (unsigned i = 0, e = A->getNumOperands(); i != e; ++i) { 2207 const SCEV *Op = getUDivExpr(A->getOperand(i), RHS); 2208 if (isa<SCEVUDivExpr>(Op) || 2209 getMulExpr(Op, RHS) != A->getOperand(i)) 2210 break; 2211 Operands.push_back(Op); 2212 } 2213 if (Operands.size() == A->getNumOperands()) 2214 return getAddExpr(Operands); 2215 } 2216 } 2217 2218 // Fold if both operands are constant. 2219 if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) { 2220 Constant *LHSCV = LHSC->getValue(); 2221 Constant *RHSCV = RHSC->getValue(); 2222 return getConstant(cast<ConstantInt>(ConstantExpr::getUDiv(LHSCV, 2223 RHSCV))); 2224 } 2225 } 2226 } 2227 2228 FoldingSetNodeID ID; 2229 ID.AddInteger(scUDivExpr); 2230 ID.AddPointer(LHS); 2231 ID.AddPointer(RHS); 2232 void *IP = 0; 2233 if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S; 2234 SCEV *S = new (SCEVAllocator) SCEVUDivExpr(ID.Intern(SCEVAllocator), 2235 LHS, RHS); 2236 UniqueSCEVs.InsertNode(S, IP); 2237 return S; 2238} 2239 2240 2241/// getAddRecExpr - Get an add recurrence expression for the specified loop. 2242/// Simplify the expression as much as possible. 2243const SCEV *ScalarEvolution::getAddRecExpr(const SCEV *Start, const SCEV *Step, 2244 const Loop *L, 2245 SCEV::NoWrapFlags Flags) { 2246 SmallVector<const SCEV *, 4> Operands; 2247 Operands.push_back(Start); 2248 if (const SCEVAddRecExpr *StepChrec = dyn_cast<SCEVAddRecExpr>(Step)) 2249 if (StepChrec->getLoop() == L) { 2250 Operands.append(StepChrec->op_begin(), StepChrec->op_end()); 2251 return getAddRecExpr(Operands, L, maskFlags(Flags, SCEV::FlagNW)); 2252 } 2253 2254 Operands.push_back(Step); 2255 return getAddRecExpr(Operands, L, Flags); 2256} 2257 2258/// getAddRecExpr - Get an add recurrence expression for the specified loop. 2259/// Simplify the expression as much as possible. 2260const SCEV * 2261ScalarEvolution::getAddRecExpr(SmallVectorImpl<const SCEV *> &Operands, 2262 const Loop *L, SCEV::NoWrapFlags Flags) { 2263 if (Operands.size() == 1) return Operands[0]; 2264#ifndef NDEBUG 2265 Type *ETy = getEffectiveSCEVType(Operands[0]->getType()); 2266 for (unsigned i = 1, e = Operands.size(); i != e; ++i) 2267 assert(getEffectiveSCEVType(Operands[i]->getType()) == ETy && 2268 "SCEVAddRecExpr operand types don't match!"); 2269 for (unsigned i = 0, e = Operands.size(); i != e; ++i) 2270 assert(isLoopInvariant(Operands[i], L) && 2271 "SCEVAddRecExpr operand is not loop-invariant!"); 2272#endif 2273 2274 if (Operands.back()->isZero()) { 2275 Operands.pop_back(); 2276 return getAddRecExpr(Operands, L, SCEV::FlagAnyWrap); // {X,+,0} --> X 2277 } 2278 2279 // It's tempting to want to call getMaxBackedgeTakenCount count here and 2280 // use that information to infer NUW and NSW flags. However, computing a 2281 // BE count requires calling getAddRecExpr, so we may not yet have a 2282 // meaningful BE count at this point (and if we don't, we'd be stuck 2283 // with a SCEVCouldNotCompute as the cached BE count). 2284 2285 // If FlagNSW is true and all the operands are non-negative, infer FlagNUW. 2286 // And vice-versa. 2287 int SignOrUnsignMask = SCEV::FlagNUW | SCEV::FlagNSW; 2288 SCEV::NoWrapFlags SignOrUnsignWrap = maskFlags(Flags, SignOrUnsignMask); 2289 if (SignOrUnsignWrap && (SignOrUnsignWrap != SignOrUnsignMask)) { 2290 bool All = true; 2291 for (SmallVectorImpl<const SCEV *>::const_iterator I = Operands.begin(), 2292 E = Operands.end(); I != E; ++I) 2293 if (!isKnownNonNegative(*I)) { 2294 All = false; 2295 break; 2296 } 2297 if (All) Flags = setFlags(Flags, (SCEV::NoWrapFlags)SignOrUnsignMask); 2298 } 2299 2300 // Canonicalize nested AddRecs in by nesting them in order of loop depth. 2301 if (const SCEVAddRecExpr *NestedAR = dyn_cast<SCEVAddRecExpr>(Operands[0])) { 2302 const Loop *NestedLoop = NestedAR->getLoop(); 2303 if (L->contains(NestedLoop) ? 2304 (L->getLoopDepth() < NestedLoop->getLoopDepth()) : 2305 (!NestedLoop->contains(L) && 2306 DT->dominates(L->getHeader(), NestedLoop->getHeader()))) { 2307 SmallVector<const SCEV *, 4> NestedOperands(NestedAR->op_begin(), 2308 NestedAR->op_end()); 2309 Operands[0] = NestedAR->getStart(); 2310 // AddRecs require their operands be loop-invariant with respect to their 2311 // loops. Don't perform this transformation if it would break this 2312 // requirement. 2313 bool AllInvariant = true; 2314 for (unsigned i = 0, e = Operands.size(); i != e; ++i) 2315 if (!isLoopInvariant(Operands[i], L)) { 2316 AllInvariant = false; 2317 break; 2318 } 2319 if (AllInvariant) { 2320 // Create a recurrence for the outer loop with the same step size. 2321 // 2322 // The outer recurrence keeps its NW flag but only keeps NUW/NSW if the 2323 // inner recurrence has the same property. 2324 SCEV::NoWrapFlags OuterFlags = 2325 maskFlags(Flags, SCEV::FlagNW | NestedAR->getNoWrapFlags()); 2326 2327 NestedOperands[0] = getAddRecExpr(Operands, L, OuterFlags); 2328 AllInvariant = true; 2329 for (unsigned i = 0, e = NestedOperands.size(); i != e; ++i) 2330 if (!isLoopInvariant(NestedOperands[i], NestedLoop)) { 2331 AllInvariant = false; 2332 break; 2333 } 2334 if (AllInvariant) { 2335 // Ok, both add recurrences are valid after the transformation. 2336 // 2337 // The inner recurrence keeps its NW flag but only keeps NUW/NSW if 2338 // the outer recurrence has the same property. 2339 SCEV::NoWrapFlags InnerFlags = 2340 maskFlags(NestedAR->getNoWrapFlags(), SCEV::FlagNW | Flags); 2341 return getAddRecExpr(NestedOperands, NestedLoop, InnerFlags); 2342 } 2343 } 2344 // Reset Operands to its original state. 2345 Operands[0] = NestedAR; 2346 } 2347 } 2348 2349 // Okay, it looks like we really DO need an addrec expr. Check to see if we 2350 // already have one, otherwise create a new one. 2351 FoldingSetNodeID ID; 2352 ID.AddInteger(scAddRecExpr); 2353 for (unsigned i = 0, e = Operands.size(); i != e; ++i) 2354 ID.AddPointer(Operands[i]); 2355 ID.AddPointer(L); 2356 void *IP = 0; 2357 SCEVAddRecExpr *S = 2358 static_cast<SCEVAddRecExpr *>(UniqueSCEVs.FindNodeOrInsertPos(ID, IP)); 2359 if (!S) { 2360 const SCEV **O = SCEVAllocator.Allocate<const SCEV *>(Operands.size()); 2361 std::uninitialized_copy(Operands.begin(), Operands.end(), O); 2362 S = new (SCEVAllocator) SCEVAddRecExpr(ID.Intern(SCEVAllocator), 2363 O, Operands.size(), L); 2364 UniqueSCEVs.InsertNode(S, IP); 2365 } 2366 S->setNoWrapFlags(Flags); 2367 return S; 2368} 2369 2370const SCEV *ScalarEvolution::getSMaxExpr(const SCEV *LHS, 2371 const SCEV *RHS) { 2372 SmallVector<const SCEV *, 2> Ops; 2373 Ops.push_back(LHS); 2374 Ops.push_back(RHS); 2375 return getSMaxExpr(Ops); 2376} 2377 2378const SCEV * 2379ScalarEvolution::getSMaxExpr(SmallVectorImpl<const SCEV *> &Ops) { 2380 assert(!Ops.empty() && "Cannot get empty smax!"); 2381 if (Ops.size() == 1) return Ops[0]; 2382#ifndef NDEBUG 2383 Type *ETy = getEffectiveSCEVType(Ops[0]->getType()); 2384 for (unsigned i = 1, e = Ops.size(); i != e; ++i) 2385 assert(getEffectiveSCEVType(Ops[i]->getType()) == ETy && 2386 "SCEVSMaxExpr operand types don't match!"); 2387#endif 2388 2389 // Sort by complexity, this groups all similar expression types together. 2390 GroupByComplexity(Ops, LI); 2391 2392 // If there are any constants, fold them together. 2393 unsigned Idx = 0; 2394 if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(Ops[0])) { 2395 ++Idx; 2396 assert(Idx < Ops.size()); 2397 while (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) { 2398 // We found two constants, fold them together! 2399 ConstantInt *Fold = ConstantInt::get(getContext(), 2400 APIntOps::smax(LHSC->getValue()->getValue(), 2401 RHSC->getValue()->getValue())); 2402 Ops[0] = getConstant(Fold); 2403 Ops.erase(Ops.begin()+1); // Erase the folded element 2404 if (Ops.size() == 1) return Ops[0]; 2405 LHSC = cast<SCEVConstant>(Ops[0]); 2406 } 2407 2408 // If we are left with a constant minimum-int, strip it off. 2409 if (cast<SCEVConstant>(Ops[0])->getValue()->isMinValue(true)) { 2410 Ops.erase(Ops.begin()); 2411 --Idx; 2412 } else if (cast<SCEVConstant>(Ops[0])->getValue()->isMaxValue(true)) { 2413 // If we have an smax with a constant maximum-int, it will always be 2414 // maximum-int. 2415 return Ops[0]; 2416 } 2417 2418 if (Ops.size() == 1) return Ops[0]; 2419 } 2420 2421 // Find the first SMax 2422 while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scSMaxExpr) 2423 ++Idx; 2424 2425 // Check to see if one of the operands is an SMax. If so, expand its operands 2426 // onto our operand list, and recurse to simplify. 2427 if (Idx < Ops.size()) { 2428 bool DeletedSMax = false; 2429 while (const SCEVSMaxExpr *SMax = dyn_cast<SCEVSMaxExpr>(Ops[Idx])) { 2430 Ops.erase(Ops.begin()+Idx); 2431 Ops.append(SMax->op_begin(), SMax->op_end()); 2432 DeletedSMax = true; 2433 } 2434 2435 if (DeletedSMax) 2436 return getSMaxExpr(Ops); 2437 } 2438 2439 // Okay, check to see if the same value occurs in the operand list twice. If 2440 // so, delete one. Since we sorted the list, these values are required to 2441 // be adjacent. 2442 for (unsigned i = 0, e = Ops.size()-1; i != e; ++i) 2443 // X smax Y smax Y --> X smax Y 2444 // X smax Y --> X, if X is always greater than Y 2445 if (Ops[i] == Ops[i+1] || 2446 isKnownPredicate(ICmpInst::ICMP_SGE, Ops[i], Ops[i+1])) { 2447 Ops.erase(Ops.begin()+i+1, Ops.begin()+i+2); 2448 --i; --e; 2449 } else if (isKnownPredicate(ICmpInst::ICMP_SLE, Ops[i], Ops[i+1])) { 2450 Ops.erase(Ops.begin()+i, Ops.begin()+i+1); 2451 --i; --e; 2452 } 2453 2454 if (Ops.size() == 1) return Ops[0]; 2455 2456 assert(!Ops.empty() && "Reduced smax down to nothing!"); 2457 2458 // Okay, it looks like we really DO need an smax expr. Check to see if we 2459 // already have one, otherwise create a new one. 2460 FoldingSetNodeID ID; 2461 ID.AddInteger(scSMaxExpr); 2462 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 2463 ID.AddPointer(Ops[i]); 2464 void *IP = 0; 2465 if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S; 2466 const SCEV **O = SCEVAllocator.Allocate<const SCEV *>(Ops.size()); 2467 std::uninitialized_copy(Ops.begin(), Ops.end(), O); 2468 SCEV *S = new (SCEVAllocator) SCEVSMaxExpr(ID.Intern(SCEVAllocator), 2469 O, Ops.size()); 2470 UniqueSCEVs.InsertNode(S, IP); 2471 return S; 2472} 2473 2474const SCEV *ScalarEvolution::getUMaxExpr(const SCEV *LHS, 2475 const SCEV *RHS) { 2476 SmallVector<const SCEV *, 2> Ops; 2477 Ops.push_back(LHS); 2478 Ops.push_back(RHS); 2479 return getUMaxExpr(Ops); 2480} 2481 2482const SCEV * 2483ScalarEvolution::getUMaxExpr(SmallVectorImpl<const SCEV *> &Ops) { 2484 assert(!Ops.empty() && "Cannot get empty umax!"); 2485 if (Ops.size() == 1) return Ops[0]; 2486#ifndef NDEBUG 2487 Type *ETy = getEffectiveSCEVType(Ops[0]->getType()); 2488 for (unsigned i = 1, e = Ops.size(); i != e; ++i) 2489 assert(getEffectiveSCEVType(Ops[i]->getType()) == ETy && 2490 "SCEVUMaxExpr operand types don't match!"); 2491#endif 2492 2493 // Sort by complexity, this groups all similar expression types together. 2494 GroupByComplexity(Ops, LI); 2495 2496 // If there are any constants, fold them together. 2497 unsigned Idx = 0; 2498 if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(Ops[0])) { 2499 ++Idx; 2500 assert(Idx < Ops.size()); 2501 while (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) { 2502 // We found two constants, fold them together! 2503 ConstantInt *Fold = ConstantInt::get(getContext(), 2504 APIntOps::umax(LHSC->getValue()->getValue(), 2505 RHSC->getValue()->getValue())); 2506 Ops[0] = getConstant(Fold); 2507 Ops.erase(Ops.begin()+1); // Erase the folded element 2508 if (Ops.size() == 1) return Ops[0]; 2509 LHSC = cast<SCEVConstant>(Ops[0]); 2510 } 2511 2512 // If we are left with a constant minimum-int, strip it off. 2513 if (cast<SCEVConstant>(Ops[0])->getValue()->isMinValue(false)) { 2514 Ops.erase(Ops.begin()); 2515 --Idx; 2516 } else if (cast<SCEVConstant>(Ops[0])->getValue()->isMaxValue(false)) { 2517 // If we have an umax with a constant maximum-int, it will always be 2518 // maximum-int. 2519 return Ops[0]; 2520 } 2521 2522 if (Ops.size() == 1) return Ops[0]; 2523 } 2524 2525 // Find the first UMax 2526 while (Idx < Ops.size() && Ops[Idx]->getSCEVType() < scUMaxExpr) 2527 ++Idx; 2528 2529 // Check to see if one of the operands is a UMax. If so, expand its operands 2530 // onto our operand list, and recurse to simplify. 2531 if (Idx < Ops.size()) { 2532 bool DeletedUMax = false; 2533 while (const SCEVUMaxExpr *UMax = dyn_cast<SCEVUMaxExpr>(Ops[Idx])) { 2534 Ops.erase(Ops.begin()+Idx); 2535 Ops.append(UMax->op_begin(), UMax->op_end()); 2536 DeletedUMax = true; 2537 } 2538 2539 if (DeletedUMax) 2540 return getUMaxExpr(Ops); 2541 } 2542 2543 // Okay, check to see if the same value occurs in the operand list twice. If 2544 // so, delete one. Since we sorted the list, these values are required to 2545 // be adjacent. 2546 for (unsigned i = 0, e = Ops.size()-1; i != e; ++i) 2547 // X umax Y umax Y --> X umax Y 2548 // X umax Y --> X, if X is always greater than Y 2549 if (Ops[i] == Ops[i+1] || 2550 isKnownPredicate(ICmpInst::ICMP_UGE, Ops[i], Ops[i+1])) { 2551 Ops.erase(Ops.begin()+i+1, Ops.begin()+i+2); 2552 --i; --e; 2553 } else if (isKnownPredicate(ICmpInst::ICMP_ULE, Ops[i], Ops[i+1])) { 2554 Ops.erase(Ops.begin()+i, Ops.begin()+i+1); 2555 --i; --e; 2556 } 2557 2558 if (Ops.size() == 1) return Ops[0]; 2559 2560 assert(!Ops.empty() && "Reduced umax down to nothing!"); 2561 2562 // Okay, it looks like we really DO need a umax expr. Check to see if we 2563 // already have one, otherwise create a new one. 2564 FoldingSetNodeID ID; 2565 ID.AddInteger(scUMaxExpr); 2566 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 2567 ID.AddPointer(Ops[i]); 2568 void *IP = 0; 2569 if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S; 2570 const SCEV **O = SCEVAllocator.Allocate<const SCEV *>(Ops.size()); 2571 std::uninitialized_copy(Ops.begin(), Ops.end(), O); 2572 SCEV *S = new (SCEVAllocator) SCEVUMaxExpr(ID.Intern(SCEVAllocator), 2573 O, Ops.size()); 2574 UniqueSCEVs.InsertNode(S, IP); 2575 return S; 2576} 2577 2578const SCEV *ScalarEvolution::getSMinExpr(const SCEV *LHS, 2579 const SCEV *RHS) { 2580 // ~smax(~x, ~y) == smin(x, y). 2581 return getNotSCEV(getSMaxExpr(getNotSCEV(LHS), getNotSCEV(RHS))); 2582} 2583 2584const SCEV *ScalarEvolution::getUMinExpr(const SCEV *LHS, 2585 const SCEV *RHS) { 2586 // ~umax(~x, ~y) == umin(x, y) 2587 return getNotSCEV(getUMaxExpr(getNotSCEV(LHS), getNotSCEV(RHS))); 2588} 2589 2590const SCEV *ScalarEvolution::getSizeOfExpr(Type *AllocTy) { 2591 // If we have DataLayout, we can bypass creating a target-independent 2592 // constant expression and then folding it back into a ConstantInt. 2593 // This is just a compile-time optimization. 2594 if (TD) 2595 return getConstant(TD->getIntPtrType(getContext()), 2596 TD->getTypeAllocSize(AllocTy)); 2597 2598 Constant *C = ConstantExpr::getSizeOf(AllocTy); 2599 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 2600 if (Constant *Folded = ConstantFoldConstantExpression(CE, TD, TLI)) 2601 C = Folded; 2602 Type *Ty = getEffectiveSCEVType(PointerType::getUnqual(AllocTy)); 2603 return getTruncateOrZeroExtend(getSCEV(C), Ty); 2604} 2605 2606const SCEV *ScalarEvolution::getAlignOfExpr(Type *AllocTy) { 2607 Constant *C = ConstantExpr::getAlignOf(AllocTy); 2608 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 2609 if (Constant *Folded = ConstantFoldConstantExpression(CE, TD, TLI)) 2610 C = Folded; 2611 Type *Ty = getEffectiveSCEVType(PointerType::getUnqual(AllocTy)); 2612 return getTruncateOrZeroExtend(getSCEV(C), Ty); 2613} 2614 2615const SCEV *ScalarEvolution::getOffsetOfExpr(StructType *STy, 2616 unsigned FieldNo) { 2617 // If we have DataLayout, we can bypass creating a target-independent 2618 // constant expression and then folding it back into a ConstantInt. 2619 // This is just a compile-time optimization. 2620 if (TD) 2621 return getConstant(TD->getIntPtrType(getContext()), 2622 TD->getStructLayout(STy)->getElementOffset(FieldNo)); 2623 2624 Constant *C = ConstantExpr::getOffsetOf(STy, FieldNo); 2625 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 2626 if (Constant *Folded = ConstantFoldConstantExpression(CE, TD, TLI)) 2627 C = Folded; 2628 Type *Ty = getEffectiveSCEVType(PointerType::getUnqual(STy)); 2629 return getTruncateOrZeroExtend(getSCEV(C), Ty); 2630} 2631 2632const SCEV *ScalarEvolution::getOffsetOfExpr(Type *CTy, 2633 Constant *FieldNo) { 2634 Constant *C = ConstantExpr::getOffsetOf(CTy, FieldNo); 2635 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) 2636 if (Constant *Folded = ConstantFoldConstantExpression(CE, TD, TLI)) 2637 C = Folded; 2638 Type *Ty = getEffectiveSCEVType(PointerType::getUnqual(CTy)); 2639 return getTruncateOrZeroExtend(getSCEV(C), Ty); 2640} 2641 2642const SCEV *ScalarEvolution::getUnknown(Value *V) { 2643 // Don't attempt to do anything other than create a SCEVUnknown object 2644 // here. createSCEV only calls getUnknown after checking for all other 2645 // interesting possibilities, and any other code that calls getUnknown 2646 // is doing so in order to hide a value from SCEV canonicalization. 2647 2648 FoldingSetNodeID ID; 2649 ID.AddInteger(scUnknown); 2650 ID.AddPointer(V); 2651 void *IP = 0; 2652 if (SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) { 2653 assert(cast<SCEVUnknown>(S)->getValue() == V && 2654 "Stale SCEVUnknown in uniquing map!"); 2655 return S; 2656 } 2657 SCEV *S = new (SCEVAllocator) SCEVUnknown(ID.Intern(SCEVAllocator), V, this, 2658 FirstUnknown); 2659 FirstUnknown = cast<SCEVUnknown>(S); 2660 UniqueSCEVs.InsertNode(S, IP); 2661 return S; 2662} 2663 2664//===----------------------------------------------------------------------===// 2665// Basic SCEV Analysis and PHI Idiom Recognition Code 2666// 2667 2668/// isSCEVable - Test if values of the given type are analyzable within 2669/// the SCEV framework. This primarily includes integer types, and it 2670/// can optionally include pointer types if the ScalarEvolution class 2671/// has access to target-specific information. 2672bool ScalarEvolution::isSCEVable(Type *Ty) const { 2673 // Integers and pointers are always SCEVable. 2674 return Ty->isIntegerTy() || Ty->isPointerTy(); 2675} 2676 2677/// getTypeSizeInBits - Return the size in bits of the specified type, 2678/// for which isSCEVable must return true. 2679uint64_t ScalarEvolution::getTypeSizeInBits(Type *Ty) const { 2680 assert(isSCEVable(Ty) && "Type is not SCEVable!"); 2681 2682 // If we have a DataLayout, use it! 2683 if (TD) 2684 return TD->getTypeSizeInBits(Ty); 2685 2686 // Integer types have fixed sizes. 2687 if (Ty->isIntegerTy()) 2688 return Ty->getPrimitiveSizeInBits(); 2689 2690 // The only other support type is pointer. Without DataLayout, conservatively 2691 // assume pointers are 64-bit. 2692 assert(Ty->isPointerTy() && "isSCEVable permitted a non-SCEVable type!"); 2693 return 64; 2694} 2695 2696/// getEffectiveSCEVType - Return a type with the same bitwidth as 2697/// the given type and which represents how SCEV will treat the given 2698/// type, for which isSCEVable must return true. For pointer types, 2699/// this is the pointer-sized integer type. 2700Type *ScalarEvolution::getEffectiveSCEVType(Type *Ty) const { 2701 assert(isSCEVable(Ty) && "Type is not SCEVable!"); 2702 2703 if (Ty->isIntegerTy()) 2704 return Ty; 2705 2706 // The only other support type is pointer. 2707 assert(Ty->isPointerTy() && "Unexpected non-pointer non-integer type!"); 2708 if (TD) return TD->getIntPtrType(getContext()); 2709 2710 // Without DataLayout, conservatively assume pointers are 64-bit. 2711 return Type::getInt64Ty(getContext()); 2712} 2713 2714const SCEV *ScalarEvolution::getCouldNotCompute() { 2715 return &CouldNotCompute; 2716} 2717 2718/// getSCEV - Return an existing SCEV if it exists, otherwise analyze the 2719/// expression and create a new one. 2720const SCEV *ScalarEvolution::getSCEV(Value *V) { 2721 assert(isSCEVable(V->getType()) && "Value is not SCEVable!"); 2722 2723 ValueExprMapType::const_iterator I = ValueExprMap.find_as(V); 2724 if (I != ValueExprMap.end()) return I->second; 2725 const SCEV *S = createSCEV(V); 2726 2727 // The process of creating a SCEV for V may have caused other SCEVs 2728 // to have been created, so it's necessary to insert the new entry 2729 // from scratch, rather than trying to remember the insert position 2730 // above. 2731 ValueExprMap.insert(std::make_pair(SCEVCallbackVH(V, this), S)); 2732 return S; 2733} 2734 2735/// getNegativeSCEV - Return a SCEV corresponding to -V = -1*V 2736/// 2737const SCEV *ScalarEvolution::getNegativeSCEV(const SCEV *V) { 2738 if (const SCEVConstant *VC = dyn_cast<SCEVConstant>(V)) 2739 return getConstant( 2740 cast<ConstantInt>(ConstantExpr::getNeg(VC->getValue()))); 2741 2742 Type *Ty = V->getType(); 2743 Ty = getEffectiveSCEVType(Ty); 2744 return getMulExpr(V, 2745 getConstant(cast<ConstantInt>(Constant::getAllOnesValue(Ty)))); 2746} 2747 2748/// getNotSCEV - Return a SCEV corresponding to ~V = -1-V 2749const SCEV *ScalarEvolution::getNotSCEV(const SCEV *V) { 2750 if (const SCEVConstant *VC = dyn_cast<SCEVConstant>(V)) 2751 return getConstant( 2752 cast<ConstantInt>(ConstantExpr::getNot(VC->getValue()))); 2753 2754 Type *Ty = V->getType(); 2755 Ty = getEffectiveSCEVType(Ty); 2756 const SCEV *AllOnes = 2757 getConstant(cast<ConstantInt>(Constant::getAllOnesValue(Ty))); 2758 return getMinusSCEV(AllOnes, V); 2759} 2760 2761/// getMinusSCEV - Return LHS-RHS. Minus is represented in SCEV as A+B*-1. 2762const SCEV *ScalarEvolution::getMinusSCEV(const SCEV *LHS, const SCEV *RHS, 2763 SCEV::NoWrapFlags Flags) { 2764 assert(!maskFlags(Flags, SCEV::FlagNUW) && "subtraction does not have NUW"); 2765 2766 // Fast path: X - X --> 0. 2767 if (LHS == RHS) 2768 return getConstant(LHS->getType(), 0); 2769 2770 // X - Y --> X + -Y 2771 return getAddExpr(LHS, getNegativeSCEV(RHS), Flags); 2772} 2773 2774/// getTruncateOrZeroExtend - Return a SCEV corresponding to a conversion of the 2775/// input value to the specified type. If the type must be extended, it is zero 2776/// extended. 2777const SCEV * 2778ScalarEvolution::getTruncateOrZeroExtend(const SCEV *V, Type *Ty) { 2779 Type *SrcTy = V->getType(); 2780 assert((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) && 2781 (Ty->isIntegerTy() || Ty->isPointerTy()) && 2782 "Cannot truncate or zero extend with non-integer arguments!"); 2783 if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty)) 2784 return V; // No conversion 2785 if (getTypeSizeInBits(SrcTy) > getTypeSizeInBits(Ty)) 2786 return getTruncateExpr(V, Ty); 2787 return getZeroExtendExpr(V, Ty); 2788} 2789 2790/// getTruncateOrSignExtend - Return a SCEV corresponding to a conversion of the 2791/// input value to the specified type. If the type must be extended, it is sign 2792/// extended. 2793const SCEV * 2794ScalarEvolution::getTruncateOrSignExtend(const SCEV *V, 2795 Type *Ty) { 2796 Type *SrcTy = V->getType(); 2797 assert((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) && 2798 (Ty->isIntegerTy() || Ty->isPointerTy()) && 2799 "Cannot truncate or zero extend with non-integer arguments!"); 2800 if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty)) 2801 return V; // No conversion 2802 if (getTypeSizeInBits(SrcTy) > getTypeSizeInBits(Ty)) 2803 return getTruncateExpr(V, Ty); 2804 return getSignExtendExpr(V, Ty); 2805} 2806 2807/// getNoopOrZeroExtend - Return a SCEV corresponding to a conversion of the 2808/// input value to the specified type. If the type must be extended, it is zero 2809/// extended. The conversion must not be narrowing. 2810const SCEV * 2811ScalarEvolution::getNoopOrZeroExtend(const SCEV *V, Type *Ty) { 2812 Type *SrcTy = V->getType(); 2813 assert((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) && 2814 (Ty->isIntegerTy() || Ty->isPointerTy()) && 2815 "Cannot noop or zero extend with non-integer arguments!"); 2816 assert(getTypeSizeInBits(SrcTy) <= getTypeSizeInBits(Ty) && 2817 "getNoopOrZeroExtend cannot truncate!"); 2818 if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty)) 2819 return V; // No conversion 2820 return getZeroExtendExpr(V, Ty); 2821} 2822 2823/// getNoopOrSignExtend - Return a SCEV corresponding to a conversion of the 2824/// input value to the specified type. If the type must be extended, it is sign 2825/// extended. The conversion must not be narrowing. 2826const SCEV * 2827ScalarEvolution::getNoopOrSignExtend(const SCEV *V, Type *Ty) { 2828 Type *SrcTy = V->getType(); 2829 assert((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) && 2830 (Ty->isIntegerTy() || Ty->isPointerTy()) && 2831 "Cannot noop or sign extend with non-integer arguments!"); 2832 assert(getTypeSizeInBits(SrcTy) <= getTypeSizeInBits(Ty) && 2833 "getNoopOrSignExtend cannot truncate!"); 2834 if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty)) 2835 return V; // No conversion 2836 return getSignExtendExpr(V, Ty); 2837} 2838 2839/// getNoopOrAnyExtend - Return a SCEV corresponding to a conversion of 2840/// the input value to the specified type. If the type must be extended, 2841/// it is extended with unspecified bits. The conversion must not be 2842/// narrowing. 2843const SCEV * 2844ScalarEvolution::getNoopOrAnyExtend(const SCEV *V, Type *Ty) { 2845 Type *SrcTy = V->getType(); 2846 assert((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) && 2847 (Ty->isIntegerTy() || Ty->isPointerTy()) && 2848 "Cannot noop or any extend with non-integer arguments!"); 2849 assert(getTypeSizeInBits(SrcTy) <= getTypeSizeInBits(Ty) && 2850 "getNoopOrAnyExtend cannot truncate!"); 2851 if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty)) 2852 return V; // No conversion 2853 return getAnyExtendExpr(V, Ty); 2854} 2855 2856/// getTruncateOrNoop - Return a SCEV corresponding to a conversion of the 2857/// input value to the specified type. The conversion must not be widening. 2858const SCEV * 2859ScalarEvolution::getTruncateOrNoop(const SCEV *V, Type *Ty) { 2860 Type *SrcTy = V->getType(); 2861 assert((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) && 2862 (Ty->isIntegerTy() || Ty->isPointerTy()) && 2863 "Cannot truncate or noop with non-integer arguments!"); 2864 assert(getTypeSizeInBits(SrcTy) >= getTypeSizeInBits(Ty) && 2865 "getTruncateOrNoop cannot extend!"); 2866 if (getTypeSizeInBits(SrcTy) == getTypeSizeInBits(Ty)) 2867 return V; // No conversion 2868 return getTruncateExpr(V, Ty); 2869} 2870 2871/// getUMaxFromMismatchedTypes - Promote the operands to the wider of 2872/// the types using zero-extension, and then perform a umax operation 2873/// with them. 2874const SCEV *ScalarEvolution::getUMaxFromMismatchedTypes(const SCEV *LHS, 2875 const SCEV *RHS) { 2876 const SCEV *PromotedLHS = LHS; 2877 const SCEV *PromotedRHS = RHS; 2878 2879 if (getTypeSizeInBits(LHS->getType()) > getTypeSizeInBits(RHS->getType())) 2880 PromotedRHS = getZeroExtendExpr(RHS, LHS->getType()); 2881 else 2882 PromotedLHS = getNoopOrZeroExtend(LHS, RHS->getType()); 2883 2884 return getUMaxExpr(PromotedLHS, PromotedRHS); 2885} 2886 2887/// getUMinFromMismatchedTypes - Promote the operands to the wider of 2888/// the types using zero-extension, and then perform a umin operation 2889/// with them. 2890const SCEV *ScalarEvolution::getUMinFromMismatchedTypes(const SCEV *LHS, 2891 const SCEV *RHS) { 2892 const SCEV *PromotedLHS = LHS; 2893 const SCEV *PromotedRHS = RHS; 2894 2895 if (getTypeSizeInBits(LHS->getType()) > getTypeSizeInBits(RHS->getType())) 2896 PromotedRHS = getZeroExtendExpr(RHS, LHS->getType()); 2897 else 2898 PromotedLHS = getNoopOrZeroExtend(LHS, RHS->getType()); 2899 2900 return getUMinExpr(PromotedLHS, PromotedRHS); 2901} 2902 2903/// getPointerBase - Transitively follow the chain of pointer-type operands 2904/// until reaching a SCEV that does not have a single pointer operand. This 2905/// returns a SCEVUnknown pointer for well-formed pointer-type expressions, 2906/// but corner cases do exist. 2907const SCEV *ScalarEvolution::getPointerBase(const SCEV *V) { 2908 // A pointer operand may evaluate to a nonpointer expression, such as null. 2909 if (!V->getType()->isPointerTy()) 2910 return V; 2911 2912 if (const SCEVCastExpr *Cast = dyn_cast<SCEVCastExpr>(V)) { 2913 return getPointerBase(Cast->getOperand()); 2914 } 2915 else if (const SCEVNAryExpr *NAry = dyn_cast<SCEVNAryExpr>(V)) { 2916 const SCEV *PtrOp = 0; 2917 for (SCEVNAryExpr::op_iterator I = NAry->op_begin(), E = NAry->op_end(); 2918 I != E; ++I) { 2919 if ((*I)->getType()->isPointerTy()) { 2920 // Cannot find the base of an expression with multiple pointer operands. 2921 if (PtrOp) 2922 return V; 2923 PtrOp = *I; 2924 } 2925 } 2926 if (!PtrOp) 2927 return V; 2928 return getPointerBase(PtrOp); 2929 } 2930 return V; 2931} 2932 2933/// PushDefUseChildren - Push users of the given Instruction 2934/// onto the given Worklist. 2935static void 2936PushDefUseChildren(Instruction *I, 2937 SmallVectorImpl<Instruction *> &Worklist) { 2938 // Push the def-use children onto the Worklist stack. 2939 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); 2940 UI != UE; ++UI) 2941 Worklist.push_back(cast<Instruction>(*UI)); 2942} 2943 2944/// ForgetSymbolicValue - This looks up computed SCEV values for all 2945/// instructions that depend on the given instruction and removes them from 2946/// the ValueExprMapType map if they reference SymName. This is used during PHI 2947/// resolution. 2948void 2949ScalarEvolution::ForgetSymbolicName(Instruction *PN, const SCEV *SymName) { 2950 SmallVector<Instruction *, 16> Worklist; 2951 PushDefUseChildren(PN, Worklist); 2952 2953 SmallPtrSet<Instruction *, 8> Visited; 2954 Visited.insert(PN); 2955 while (!Worklist.empty()) { 2956 Instruction *I = Worklist.pop_back_val(); 2957 if (!Visited.insert(I)) continue; 2958 2959 ValueExprMapType::iterator It = 2960 ValueExprMap.find_as(static_cast<Value *>(I)); 2961 if (It != ValueExprMap.end()) { 2962 const SCEV *Old = It->second; 2963 2964 // Short-circuit the def-use traversal if the symbolic name 2965 // ceases to appear in expressions. 2966 if (Old != SymName && !hasOperand(Old, SymName)) 2967 continue; 2968 2969 // SCEVUnknown for a PHI either means that it has an unrecognized 2970 // structure, it's a PHI that's in the progress of being computed 2971 // by createNodeForPHI, or it's a single-value PHI. In the first case, 2972 // additional loop trip count information isn't going to change anything. 2973 // In the second case, createNodeForPHI will perform the necessary 2974 // updates on its own when it gets to that point. In the third, we do 2975 // want to forget the SCEVUnknown. 2976 if (!isa<PHINode>(I) || 2977 !isa<SCEVUnknown>(Old) || 2978 (I != PN && Old == SymName)) { 2979 forgetMemoizedResults(Old); 2980 ValueExprMap.erase(It); 2981 } 2982 } 2983 2984 PushDefUseChildren(I, Worklist); 2985 } 2986} 2987 2988/// createNodeForPHI - PHI nodes have two cases. Either the PHI node exists in 2989/// a loop header, making it a potential recurrence, or it doesn't. 2990/// 2991const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) { 2992 if (const Loop *L = LI->getLoopFor(PN->getParent())) 2993 if (L->getHeader() == PN->getParent()) { 2994 // The loop may have multiple entrances or multiple exits; we can analyze 2995 // this phi as an addrec if it has a unique entry value and a unique 2996 // backedge value. 2997 Value *BEValueV = 0, *StartValueV = 0; 2998 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 2999 Value *V = PN->getIncomingValue(i); 3000 if (L->contains(PN->getIncomingBlock(i))) { 3001 if (!BEValueV) { 3002 BEValueV = V; 3003 } else if (BEValueV != V) { 3004 BEValueV = 0; 3005 break; 3006 } 3007 } else if (!StartValueV) { 3008 StartValueV = V; 3009 } else if (StartValueV != V) { 3010 StartValueV = 0; 3011 break; 3012 } 3013 } 3014 if (BEValueV && StartValueV) { 3015 // While we are analyzing this PHI node, handle its value symbolically. 3016 const SCEV *SymbolicName = getUnknown(PN); 3017 assert(ValueExprMap.find_as(PN) == ValueExprMap.end() && 3018 "PHI node already processed?"); 3019 ValueExprMap.insert(std::make_pair(SCEVCallbackVH(PN, this), SymbolicName)); 3020 3021 // Using this symbolic name for the PHI, analyze the value coming around 3022 // the back-edge. 3023 const SCEV *BEValue = getSCEV(BEValueV); 3024 3025 // NOTE: If BEValue is loop invariant, we know that the PHI node just 3026 // has a special value for the first iteration of the loop. 3027 3028 // If the value coming around the backedge is an add with the symbolic 3029 // value we just inserted, then we found a simple induction variable! 3030 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(BEValue)) { 3031 // If there is a single occurrence of the symbolic value, replace it 3032 // with a recurrence. 3033 unsigned FoundIndex = Add->getNumOperands(); 3034 for (unsigned i = 0, e = Add->getNumOperands(); i != e; ++i) 3035 if (Add->getOperand(i) == SymbolicName) 3036 if (FoundIndex == e) { 3037 FoundIndex = i; 3038 break; 3039 } 3040 3041 if (FoundIndex != Add->getNumOperands()) { 3042 // Create an add with everything but the specified operand. 3043 SmallVector<const SCEV *, 8> Ops; 3044 for (unsigned i = 0, e = Add->getNumOperands(); i != e; ++i) 3045 if (i != FoundIndex) 3046 Ops.push_back(Add->getOperand(i)); 3047 const SCEV *Accum = getAddExpr(Ops); 3048 3049 // This is not a valid addrec if the step amount is varying each 3050 // loop iteration, but is not itself an addrec in this loop. 3051 if (isLoopInvariant(Accum, L) || 3052 (isa<SCEVAddRecExpr>(Accum) && 3053 cast<SCEVAddRecExpr>(Accum)->getLoop() == L)) { 3054 SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap; 3055 3056 // If the increment doesn't overflow, then neither the addrec nor 3057 // the post-increment will overflow. 3058 if (const AddOperator *OBO = dyn_cast<AddOperator>(BEValueV)) { 3059 if (OBO->hasNoUnsignedWrap()) 3060 Flags = setFlags(Flags, SCEV::FlagNUW); 3061 if (OBO->hasNoSignedWrap()) 3062 Flags = setFlags(Flags, SCEV::FlagNSW); 3063 } else if (const GEPOperator *GEP = 3064 dyn_cast<GEPOperator>(BEValueV)) { 3065 // If the increment is an inbounds GEP, then we know the address 3066 // space cannot be wrapped around. We cannot make any guarantee 3067 // about signed or unsigned overflow because pointers are 3068 // unsigned but we may have a negative index from the base 3069 // pointer. 3070 if (GEP->isInBounds()) 3071 Flags = setFlags(Flags, SCEV::FlagNW); 3072 } 3073 3074 const SCEV *StartVal = getSCEV(StartValueV); 3075 const SCEV *PHISCEV = getAddRecExpr(StartVal, Accum, L, Flags); 3076 3077 // Since the no-wrap flags are on the increment, they apply to the 3078 // post-incremented value as well. 3079 if (isLoopInvariant(Accum, L)) 3080 (void)getAddRecExpr(getAddExpr(StartVal, Accum), 3081 Accum, L, Flags); 3082 3083 // Okay, for the entire analysis of this edge we assumed the PHI 3084 // to be symbolic. We now need to go back and purge all of the 3085 // entries for the scalars that use the symbolic expression. 3086 ForgetSymbolicName(PN, SymbolicName); 3087 ValueExprMap[SCEVCallbackVH(PN, this)] = PHISCEV; 3088 return PHISCEV; 3089 } 3090 } 3091 } else if (const SCEVAddRecExpr *AddRec = 3092 dyn_cast<SCEVAddRecExpr>(BEValue)) { 3093 // Otherwise, this could be a loop like this: 3094 // i = 0; for (j = 1; ..; ++j) { .... i = j; } 3095 // In this case, j = {1,+,1} and BEValue is j. 3096 // Because the other in-value of i (0) fits the evolution of BEValue 3097 // i really is an addrec evolution. 3098 if (AddRec->getLoop() == L && AddRec->isAffine()) { 3099 const SCEV *StartVal = getSCEV(StartValueV); 3100 3101 // If StartVal = j.start - j.stride, we can use StartVal as the 3102 // initial step of the addrec evolution. 3103 if (StartVal == getMinusSCEV(AddRec->getOperand(0), 3104 AddRec->getOperand(1))) { 3105 // FIXME: For constant StartVal, we should be able to infer 3106 // no-wrap flags. 3107 const SCEV *PHISCEV = 3108 getAddRecExpr(StartVal, AddRec->getOperand(1), L, 3109 SCEV::FlagAnyWrap); 3110 3111 // Okay, for the entire analysis of this edge we assumed the PHI 3112 // to be symbolic. We now need to go back and purge all of the 3113 // entries for the scalars that use the symbolic expression. 3114 ForgetSymbolicName(PN, SymbolicName); 3115 ValueExprMap[SCEVCallbackVH(PN, this)] = PHISCEV; 3116 return PHISCEV; 3117 } 3118 } 3119 } 3120 } 3121 } 3122 3123 // If the PHI has a single incoming value, follow that value, unless the 3124 // PHI's incoming blocks are in a different loop, in which case doing so 3125 // risks breaking LCSSA form. Instcombine would normally zap these, but 3126 // it doesn't have DominatorTree information, so it may miss cases. 3127 if (Value *V = SimplifyInstruction(PN, TD, TLI, DT)) 3128 if (LI->replacementPreservesLCSSAForm(PN, V)) 3129 return getSCEV(V); 3130 3131 // If it's not a loop phi, we can't handle it yet. 3132 return getUnknown(PN); 3133} 3134 3135/// createNodeForGEP - Expand GEP instructions into add and multiply 3136/// operations. This allows them to be analyzed by regular SCEV code. 3137/// 3138const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) { 3139 3140 // Don't blindly transfer the inbounds flag from the GEP instruction to the 3141 // Add expression, because the Instruction may be guarded by control flow 3142 // and the no-overflow bits may not be valid for the expression in any 3143 // context. 3144 bool isInBounds = GEP->isInBounds(); 3145 3146 Type *IntPtrTy = getEffectiveSCEVType(GEP->getType()); 3147 Value *Base = GEP->getOperand(0); 3148 // Don't attempt to analyze GEPs over unsized objects. 3149 if (!cast<PointerType>(Base->getType())->getElementType()->isSized()) 3150 return getUnknown(GEP); 3151 const SCEV *TotalOffset = getConstant(IntPtrTy, 0); 3152 gep_type_iterator GTI = gep_type_begin(GEP); 3153 for (GetElementPtrInst::op_iterator I = llvm::next(GEP->op_begin()), 3154 E = GEP->op_end(); 3155 I != E; ++I) { 3156 Value *Index = *I; 3157 // Compute the (potentially symbolic) offset in bytes for this index. 3158 if (StructType *STy = dyn_cast<StructType>(*GTI++)) { 3159 // For a struct, add the member offset. 3160 unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue(); 3161 const SCEV *FieldOffset = getOffsetOfExpr(STy, FieldNo); 3162 3163 // Add the field offset to the running total offset. 3164 TotalOffset = getAddExpr(TotalOffset, FieldOffset); 3165 } else { 3166 // For an array, add the element offset, explicitly scaled. 3167 const SCEV *ElementSize = getSizeOfExpr(*GTI); 3168 const SCEV *IndexS = getSCEV(Index); 3169 // Getelementptr indices are signed. 3170 IndexS = getTruncateOrSignExtend(IndexS, IntPtrTy); 3171 3172 // Multiply the index by the element size to compute the element offset. 3173 const SCEV *LocalOffset = getMulExpr(IndexS, ElementSize, 3174 isInBounds ? SCEV::FlagNSW : 3175 SCEV::FlagAnyWrap); 3176 3177 // Add the element offset to the running total offset. 3178 TotalOffset = getAddExpr(TotalOffset, LocalOffset); 3179 } 3180 } 3181 3182 // Get the SCEV for the GEP base. 3183 const SCEV *BaseS = getSCEV(Base); 3184 3185 // Add the total offset from all the GEP indices to the base. 3186 return getAddExpr(BaseS, TotalOffset, 3187 isInBounds ? SCEV::FlagNSW : SCEV::FlagAnyWrap); 3188} 3189 3190/// GetMinTrailingZeros - Determine the minimum number of zero bits that S is 3191/// guaranteed to end in (at every loop iteration). It is, at the same time, 3192/// the minimum number of times S is divisible by 2. For example, given {4,+,8} 3193/// it returns 2. If S is guaranteed to be 0, it returns the bitwidth of S. 3194uint32_t 3195ScalarEvolution::GetMinTrailingZeros(const SCEV *S) { 3196 if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S)) 3197 return C->getValue()->getValue().countTrailingZeros(); 3198 3199 if (const SCEVTruncateExpr *T = dyn_cast<SCEVTruncateExpr>(S)) 3200 return std::min(GetMinTrailingZeros(T->getOperand()), 3201 (uint32_t)getTypeSizeInBits(T->getType())); 3202 3203 if (const SCEVZeroExtendExpr *E = dyn_cast<SCEVZeroExtendExpr>(S)) { 3204 uint32_t OpRes = GetMinTrailingZeros(E->getOperand()); 3205 return OpRes == getTypeSizeInBits(E->getOperand()->getType()) ? 3206 getTypeSizeInBits(E->getType()) : OpRes; 3207 } 3208 3209 if (const SCEVSignExtendExpr *E = dyn_cast<SCEVSignExtendExpr>(S)) { 3210 uint32_t OpRes = GetMinTrailingZeros(E->getOperand()); 3211 return OpRes == getTypeSizeInBits(E->getOperand()->getType()) ? 3212 getTypeSizeInBits(E->getType()) : OpRes; 3213 } 3214 3215 if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(S)) { 3216 // The result is the min of all operands results. 3217 uint32_t MinOpRes = GetMinTrailingZeros(A->getOperand(0)); 3218 for (unsigned i = 1, e = A->getNumOperands(); MinOpRes && i != e; ++i) 3219 MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(A->getOperand(i))); 3220 return MinOpRes; 3221 } 3222 3223 if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(S)) { 3224 // The result is the sum of all operands results. 3225 uint32_t SumOpRes = GetMinTrailingZeros(M->getOperand(0)); 3226 uint32_t BitWidth = getTypeSizeInBits(M->getType()); 3227 for (unsigned i = 1, e = M->getNumOperands(); 3228 SumOpRes != BitWidth && i != e; ++i) 3229 SumOpRes = std::min(SumOpRes + GetMinTrailingZeros(M->getOperand(i)), 3230 BitWidth); 3231 return SumOpRes; 3232 } 3233 3234 if (const SCEVAddRecExpr *A = dyn_cast<SCEVAddRecExpr>(S)) { 3235 // The result is the min of all operands results. 3236 uint32_t MinOpRes = GetMinTrailingZeros(A->getOperand(0)); 3237 for (unsigned i = 1, e = A->getNumOperands(); MinOpRes && i != e; ++i) 3238 MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(A->getOperand(i))); 3239 return MinOpRes; 3240 } 3241 3242 if (const SCEVSMaxExpr *M = dyn_cast<SCEVSMaxExpr>(S)) { 3243 // The result is the min of all operands results. 3244 uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0)); 3245 for (unsigned i = 1, e = M->getNumOperands(); MinOpRes && i != e; ++i) 3246 MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i))); 3247 return MinOpRes; 3248 } 3249 3250 if (const SCEVUMaxExpr *M = dyn_cast<SCEVUMaxExpr>(S)) { 3251 // The result is the min of all operands results. 3252 uint32_t MinOpRes = GetMinTrailingZeros(M->getOperand(0)); 3253 for (unsigned i = 1, e = M->getNumOperands(); MinOpRes && i != e; ++i) 3254 MinOpRes = std::min(MinOpRes, GetMinTrailingZeros(M->getOperand(i))); 3255 return MinOpRes; 3256 } 3257 3258 if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) { 3259 // For a SCEVUnknown, ask ValueTracking. 3260 unsigned BitWidth = getTypeSizeInBits(U->getType()); 3261 APInt Zeros(BitWidth, 0), Ones(BitWidth, 0); 3262 ComputeMaskedBits(U->getValue(), Zeros, Ones); 3263 return Zeros.countTrailingOnes(); 3264 } 3265 3266 // SCEVUDivExpr 3267 return 0; 3268} 3269 3270/// getUnsignedRange - Determine the unsigned range for a particular SCEV. 3271/// 3272ConstantRange 3273ScalarEvolution::getUnsignedRange(const SCEV *S) { 3274 // See if we've computed this range already. 3275 DenseMap<const SCEV *, ConstantRange>::iterator I = UnsignedRanges.find(S); 3276 if (I != UnsignedRanges.end()) 3277 return I->second; 3278 3279 if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S)) 3280 return setUnsignedRange(C, ConstantRange(C->getValue()->getValue())); 3281 3282 unsigned BitWidth = getTypeSizeInBits(S->getType()); 3283 ConstantRange ConservativeResult(BitWidth, /*isFullSet=*/true); 3284 3285 // If the value has known zeros, the maximum unsigned value will have those 3286 // known zeros as well. 3287 uint32_t TZ = GetMinTrailingZeros(S); 3288 if (TZ != 0) 3289 ConservativeResult = 3290 ConstantRange(APInt::getMinValue(BitWidth), 3291 APInt::getMaxValue(BitWidth).lshr(TZ).shl(TZ) + 1); 3292 3293 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { 3294 ConstantRange X = getUnsignedRange(Add->getOperand(0)); 3295 for (unsigned i = 1, e = Add->getNumOperands(); i != e; ++i) 3296 X = X.add(getUnsignedRange(Add->getOperand(i))); 3297 return setUnsignedRange(Add, ConservativeResult.intersectWith(X)); 3298 } 3299 3300 if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) { 3301 ConstantRange X = getUnsignedRange(Mul->getOperand(0)); 3302 for (unsigned i = 1, e = Mul->getNumOperands(); i != e; ++i) 3303 X = X.multiply(getUnsignedRange(Mul->getOperand(i))); 3304 return setUnsignedRange(Mul, ConservativeResult.intersectWith(X)); 3305 } 3306 3307 if (const SCEVSMaxExpr *SMax = dyn_cast<SCEVSMaxExpr>(S)) { 3308 ConstantRange X = getUnsignedRange(SMax->getOperand(0)); 3309 for (unsigned i = 1, e = SMax->getNumOperands(); i != e; ++i) 3310 X = X.smax(getUnsignedRange(SMax->getOperand(i))); 3311 return setUnsignedRange(SMax, ConservativeResult.intersectWith(X)); 3312 } 3313 3314 if (const SCEVUMaxExpr *UMax = dyn_cast<SCEVUMaxExpr>(S)) { 3315 ConstantRange X = getUnsignedRange(UMax->getOperand(0)); 3316 for (unsigned i = 1, e = UMax->getNumOperands(); i != e; ++i) 3317 X = X.umax(getUnsignedRange(UMax->getOperand(i))); 3318 return setUnsignedRange(UMax, ConservativeResult.intersectWith(X)); 3319 } 3320 3321 if (const SCEVUDivExpr *UDiv = dyn_cast<SCEVUDivExpr>(S)) { 3322 ConstantRange X = getUnsignedRange(UDiv->getLHS()); 3323 ConstantRange Y = getUnsignedRange(UDiv->getRHS()); 3324 return setUnsignedRange(UDiv, ConservativeResult.intersectWith(X.udiv(Y))); 3325 } 3326 3327 if (const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(S)) { 3328 ConstantRange X = getUnsignedRange(ZExt->getOperand()); 3329 return setUnsignedRange(ZExt, 3330 ConservativeResult.intersectWith(X.zeroExtend(BitWidth))); 3331 } 3332 3333 if (const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(S)) { 3334 ConstantRange X = getUnsignedRange(SExt->getOperand()); 3335 return setUnsignedRange(SExt, 3336 ConservativeResult.intersectWith(X.signExtend(BitWidth))); 3337 } 3338 3339 if (const SCEVTruncateExpr *Trunc = dyn_cast<SCEVTruncateExpr>(S)) { 3340 ConstantRange X = getUnsignedRange(Trunc->getOperand()); 3341 return setUnsignedRange(Trunc, 3342 ConservativeResult.intersectWith(X.truncate(BitWidth))); 3343 } 3344 3345 if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(S)) { 3346 // If there's no unsigned wrap, the value will never be less than its 3347 // initial value. 3348 if (AddRec->getNoWrapFlags(SCEV::FlagNUW)) 3349 if (const SCEVConstant *C = dyn_cast<SCEVConstant>(AddRec->getStart())) 3350 if (!C->getValue()->isZero()) 3351 ConservativeResult = 3352 ConservativeResult.intersectWith( 3353 ConstantRange(C->getValue()->getValue(), APInt(BitWidth, 0))); 3354 3355 // TODO: non-affine addrec 3356 if (AddRec->isAffine()) { 3357 Type *Ty = AddRec->getType(); 3358 const SCEV *MaxBECount = getMaxBackedgeTakenCount(AddRec->getLoop()); 3359 if (!isa<SCEVCouldNotCompute>(MaxBECount) && 3360 getTypeSizeInBits(MaxBECount->getType()) <= BitWidth) { 3361 MaxBECount = getNoopOrZeroExtend(MaxBECount, Ty); 3362 3363 const SCEV *Start = AddRec->getStart(); 3364 const SCEV *Step = AddRec->getStepRecurrence(*this); 3365 3366 ConstantRange StartRange = getUnsignedRange(Start); 3367 ConstantRange StepRange = getSignedRange(Step); 3368 ConstantRange MaxBECountRange = getUnsignedRange(MaxBECount); 3369 ConstantRange EndRange = 3370 StartRange.add(MaxBECountRange.multiply(StepRange)); 3371 3372 // Check for overflow. This must be done with ConstantRange arithmetic 3373 // because we could be called from within the ScalarEvolution overflow 3374 // checking code. 3375 ConstantRange ExtStartRange = StartRange.zextOrTrunc(BitWidth*2+1); 3376 ConstantRange ExtStepRange = StepRange.sextOrTrunc(BitWidth*2+1); 3377 ConstantRange ExtMaxBECountRange = 3378 MaxBECountRange.zextOrTrunc(BitWidth*2+1); 3379 ConstantRange ExtEndRange = EndRange.zextOrTrunc(BitWidth*2+1); 3380 if (ExtStartRange.add(ExtMaxBECountRange.multiply(ExtStepRange)) != 3381 ExtEndRange) 3382 return setUnsignedRange(AddRec, ConservativeResult); 3383 3384 APInt Min = APIntOps::umin(StartRange.getUnsignedMin(), 3385 EndRange.getUnsignedMin()); 3386 APInt Max = APIntOps::umax(StartRange.getUnsignedMax(), 3387 EndRange.getUnsignedMax()); 3388 if (Min.isMinValue() && Max.isMaxValue()) 3389 return setUnsignedRange(AddRec, ConservativeResult); 3390 return setUnsignedRange(AddRec, 3391 ConservativeResult.intersectWith(ConstantRange(Min, Max+1))); 3392 } 3393 } 3394 3395 return setUnsignedRange(AddRec, ConservativeResult); 3396 } 3397 3398 if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) { 3399 // For a SCEVUnknown, ask ValueTracking. 3400 APInt Zeros(BitWidth, 0), Ones(BitWidth, 0); 3401 ComputeMaskedBits(U->getValue(), Zeros, Ones, TD); 3402 if (Ones == ~Zeros + 1) 3403 return setUnsignedRange(U, ConservativeResult); 3404 return setUnsignedRange(U, 3405 ConservativeResult.intersectWith(ConstantRange(Ones, ~Zeros + 1))); 3406 } 3407 3408 return setUnsignedRange(S, ConservativeResult); 3409} 3410 3411/// getSignedRange - Determine the signed range for a particular SCEV. 3412/// 3413ConstantRange 3414ScalarEvolution::getSignedRange(const SCEV *S) { 3415 // See if we've computed this range already. 3416 DenseMap<const SCEV *, ConstantRange>::iterator I = SignedRanges.find(S); 3417 if (I != SignedRanges.end()) 3418 return I->second; 3419 3420 if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S)) 3421 return setSignedRange(C, ConstantRange(C->getValue()->getValue())); 3422 3423 unsigned BitWidth = getTypeSizeInBits(S->getType()); 3424 ConstantRange ConservativeResult(BitWidth, /*isFullSet=*/true); 3425 3426 // If the value has known zeros, the maximum signed value will have those 3427 // known zeros as well. 3428 uint32_t TZ = GetMinTrailingZeros(S); 3429 if (TZ != 0) 3430 ConservativeResult = 3431 ConstantRange(APInt::getSignedMinValue(BitWidth), 3432 APInt::getSignedMaxValue(BitWidth).ashr(TZ).shl(TZ) + 1); 3433 3434 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) { 3435 ConstantRange X = getSignedRange(Add->getOperand(0)); 3436 for (unsigned i = 1, e = Add->getNumOperands(); i != e; ++i) 3437 X = X.add(getSignedRange(Add->getOperand(i))); 3438 return setSignedRange(Add, ConservativeResult.intersectWith(X)); 3439 } 3440 3441 if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) { 3442 ConstantRange X = getSignedRange(Mul->getOperand(0)); 3443 for (unsigned i = 1, e = Mul->getNumOperands(); i != e; ++i) 3444 X = X.multiply(getSignedRange(Mul->getOperand(i))); 3445 return setSignedRange(Mul, ConservativeResult.intersectWith(X)); 3446 } 3447 3448 if (const SCEVSMaxExpr *SMax = dyn_cast<SCEVSMaxExpr>(S)) { 3449 ConstantRange X = getSignedRange(SMax->getOperand(0)); 3450 for (unsigned i = 1, e = SMax->getNumOperands(); i != e; ++i) 3451 X = X.smax(getSignedRange(SMax->getOperand(i))); 3452 return setSignedRange(SMax, ConservativeResult.intersectWith(X)); 3453 } 3454 3455 if (const SCEVUMaxExpr *UMax = dyn_cast<SCEVUMaxExpr>(S)) { 3456 ConstantRange X = getSignedRange(UMax->getOperand(0)); 3457 for (unsigned i = 1, e = UMax->getNumOperands(); i != e; ++i) 3458 X = X.umax(getSignedRange(UMax->getOperand(i))); 3459 return setSignedRange(UMax, ConservativeResult.intersectWith(X)); 3460 } 3461 3462 if (const SCEVUDivExpr *UDiv = dyn_cast<SCEVUDivExpr>(S)) { 3463 ConstantRange X = getSignedRange(UDiv->getLHS()); 3464 ConstantRange Y = getSignedRange(UDiv->getRHS()); 3465 return setSignedRange(UDiv, ConservativeResult.intersectWith(X.udiv(Y))); 3466 } 3467 3468 if (const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(S)) { 3469 ConstantRange X = getSignedRange(ZExt->getOperand()); 3470 return setSignedRange(ZExt, 3471 ConservativeResult.intersectWith(X.zeroExtend(BitWidth))); 3472 } 3473 3474 if (const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(S)) { 3475 ConstantRange X = getSignedRange(SExt->getOperand()); 3476 return setSignedRange(SExt, 3477 ConservativeResult.intersectWith(X.signExtend(BitWidth))); 3478 } 3479 3480 if (const SCEVTruncateExpr *Trunc = dyn_cast<SCEVTruncateExpr>(S)) { 3481 ConstantRange X = getSignedRange(Trunc->getOperand()); 3482 return setSignedRange(Trunc, 3483 ConservativeResult.intersectWith(X.truncate(BitWidth))); 3484 } 3485 3486 if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(S)) { 3487 // If there's no signed wrap, and all the operands have the same sign or 3488 // zero, the value won't ever change sign. 3489 if (AddRec->getNoWrapFlags(SCEV::FlagNSW)) { 3490 bool AllNonNeg = true; 3491 bool AllNonPos = true; 3492 for (unsigned i = 0, e = AddRec->getNumOperands(); i != e; ++i) { 3493 if (!isKnownNonNegative(AddRec->getOperand(i))) AllNonNeg = false; 3494 if (!isKnownNonPositive(AddRec->getOperand(i))) AllNonPos = false; 3495 } 3496 if (AllNonNeg) 3497 ConservativeResult = ConservativeResult.intersectWith( 3498 ConstantRange(APInt(BitWidth, 0), 3499 APInt::getSignedMinValue(BitWidth))); 3500 else if (AllNonPos) 3501 ConservativeResult = ConservativeResult.intersectWith( 3502 ConstantRange(APInt::getSignedMinValue(BitWidth), 3503 APInt(BitWidth, 1))); 3504 } 3505 3506 // TODO: non-affine addrec 3507 if (AddRec->isAffine()) { 3508 Type *Ty = AddRec->getType(); 3509 const SCEV *MaxBECount = getMaxBackedgeTakenCount(AddRec->getLoop()); 3510 if (!isa<SCEVCouldNotCompute>(MaxBECount) && 3511 getTypeSizeInBits(MaxBECount->getType()) <= BitWidth) { 3512 MaxBECount = getNoopOrZeroExtend(MaxBECount, Ty); 3513 3514 const SCEV *Start = AddRec->getStart(); 3515 const SCEV *Step = AddRec->getStepRecurrence(*this); 3516 3517 ConstantRange StartRange = getSignedRange(Start); 3518 ConstantRange StepRange = getSignedRange(Step); 3519 ConstantRange MaxBECountRange = getUnsignedRange(MaxBECount); 3520 ConstantRange EndRange = 3521 StartRange.add(MaxBECountRange.multiply(StepRange)); 3522 3523 // Check for overflow. This must be done with ConstantRange arithmetic 3524 // because we could be called from within the ScalarEvolution overflow 3525 // checking code. 3526 ConstantRange ExtStartRange = StartRange.sextOrTrunc(BitWidth*2+1); 3527 ConstantRange ExtStepRange = StepRange.sextOrTrunc(BitWidth*2+1); 3528 ConstantRange ExtMaxBECountRange = 3529 MaxBECountRange.zextOrTrunc(BitWidth*2+1); 3530 ConstantRange ExtEndRange = EndRange.sextOrTrunc(BitWidth*2+1); 3531 if (ExtStartRange.add(ExtMaxBECountRange.multiply(ExtStepRange)) != 3532 ExtEndRange) 3533 return setSignedRange(AddRec, ConservativeResult); 3534 3535 APInt Min = APIntOps::smin(StartRange.getSignedMin(), 3536 EndRange.getSignedMin()); 3537 APInt Max = APIntOps::smax(StartRange.getSignedMax(), 3538 EndRange.getSignedMax()); 3539 if (Min.isMinSignedValue() && Max.isMaxSignedValue()) 3540 return setSignedRange(AddRec, ConservativeResult); 3541 return setSignedRange(AddRec, 3542 ConservativeResult.intersectWith(ConstantRange(Min, Max+1))); 3543 } 3544 } 3545 3546 return setSignedRange(AddRec, ConservativeResult); 3547 } 3548 3549 if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) { 3550 // For a SCEVUnknown, ask ValueTracking. 3551 if (!U->getValue()->getType()->isIntegerTy() && !TD) 3552 return setSignedRange(U, ConservativeResult); 3553 unsigned NS = ComputeNumSignBits(U->getValue(), TD); 3554 if (NS == 1) 3555 return setSignedRange(U, ConservativeResult); 3556 return setSignedRange(U, ConservativeResult.intersectWith( 3557 ConstantRange(APInt::getSignedMinValue(BitWidth).ashr(NS - 1), 3558 APInt::getSignedMaxValue(BitWidth).ashr(NS - 1)+1))); 3559 } 3560 3561 return setSignedRange(S, ConservativeResult); 3562} 3563 3564/// createSCEV - We know that there is no SCEV for the specified value. 3565/// Analyze the expression. 3566/// 3567const SCEV *ScalarEvolution::createSCEV(Value *V) { 3568 if (!isSCEVable(V->getType())) 3569 return getUnknown(V); 3570 3571 unsigned Opcode = Instruction::UserOp1; 3572 if (Instruction *I = dyn_cast<Instruction>(V)) { 3573 Opcode = I->getOpcode(); 3574 3575 // Don't attempt to analyze instructions in blocks that aren't 3576 // reachable. Such instructions don't matter, and they aren't required 3577 // to obey basic rules for definitions dominating uses which this 3578 // analysis depends on. 3579 if (!DT->isReachableFromEntry(I->getParent())) 3580 return getUnknown(V); 3581 } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 3582 Opcode = CE->getOpcode(); 3583 else if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) 3584 return getConstant(CI); 3585 else if (isa<ConstantPointerNull>(V)) 3586 return getConstant(V->getType(), 0); 3587 else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) 3588 return GA->mayBeOverridden() ? getUnknown(V) : getSCEV(GA->getAliasee()); 3589 else 3590 return getUnknown(V); 3591 3592 Operator *U = cast<Operator>(V); 3593 switch (Opcode) { 3594 case Instruction::Add: { 3595 // The simple thing to do would be to just call getSCEV on both operands 3596 // and call getAddExpr with the result. However if we're looking at a 3597 // bunch of things all added together, this can be quite inefficient, 3598 // because it leads to N-1 getAddExpr calls for N ultimate operands. 3599 // Instead, gather up all the operands and make a single getAddExpr call. 3600 // LLVM IR canonical form means we need only traverse the left operands. 3601 // 3602 // Don't apply this instruction's NSW or NUW flags to the new 3603 // expression. The instruction may be guarded by control flow that the 3604 // no-wrap behavior depends on. Non-control-equivalent instructions can be 3605 // mapped to the same SCEV expression, and it would be incorrect to transfer 3606 // NSW/NUW semantics to those operations. 3607 SmallVector<const SCEV *, 4> AddOps; 3608 AddOps.push_back(getSCEV(U->getOperand(1))); 3609 for (Value *Op = U->getOperand(0); ; Op = U->getOperand(0)) { 3610 unsigned Opcode = Op->getValueID() - Value::InstructionVal; 3611 if (Opcode != Instruction::Add && Opcode != Instruction::Sub) 3612 break; 3613 U = cast<Operator>(Op); 3614 const SCEV *Op1 = getSCEV(U->getOperand(1)); 3615 if (Opcode == Instruction::Sub) 3616 AddOps.push_back(getNegativeSCEV(Op1)); 3617 else 3618 AddOps.push_back(Op1); 3619 } 3620 AddOps.push_back(getSCEV(U->getOperand(0))); 3621 return getAddExpr(AddOps); 3622 } 3623 case Instruction::Mul: { 3624 // Don't transfer NSW/NUW for the same reason as AddExpr. 3625 SmallVector<const SCEV *, 4> MulOps; 3626 MulOps.push_back(getSCEV(U->getOperand(1))); 3627 for (Value *Op = U->getOperand(0); 3628 Op->getValueID() == Instruction::Mul + Value::InstructionVal; 3629 Op = U->getOperand(0)) { 3630 U = cast<Operator>(Op); 3631 MulOps.push_back(getSCEV(U->getOperand(1))); 3632 } 3633 MulOps.push_back(getSCEV(U->getOperand(0))); 3634 return getMulExpr(MulOps); 3635 } 3636 case Instruction::UDiv: 3637 return getUDivExpr(getSCEV(U->getOperand(0)), 3638 getSCEV(U->getOperand(1))); 3639 case Instruction::Sub: 3640 return getMinusSCEV(getSCEV(U->getOperand(0)), 3641 getSCEV(U->getOperand(1))); 3642 case Instruction::And: 3643 // For an expression like x&255 that merely masks off the high bits, 3644 // use zext(trunc(x)) as the SCEV expression. 3645 if (ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1))) { 3646 if (CI->isNullValue()) 3647 return getSCEV(U->getOperand(1)); 3648 if (CI->isAllOnesValue()) 3649 return getSCEV(U->getOperand(0)); 3650 const APInt &A = CI->getValue(); 3651 3652 // Instcombine's ShrinkDemandedConstant may strip bits out of 3653 // constants, obscuring what would otherwise be a low-bits mask. 3654 // Use ComputeMaskedBits to compute what ShrinkDemandedConstant 3655 // knew about to reconstruct a low-bits mask value. 3656 unsigned LZ = A.countLeadingZeros(); 3657 unsigned BitWidth = A.getBitWidth(); 3658 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); 3659 ComputeMaskedBits(U->getOperand(0), KnownZero, KnownOne, TD); 3660 3661 APInt EffectiveMask = APInt::getLowBitsSet(BitWidth, BitWidth - LZ); 3662 3663 if (LZ != 0 && !((~A & ~KnownZero) & EffectiveMask)) 3664 return 3665 getZeroExtendExpr(getTruncateExpr(getSCEV(U->getOperand(0)), 3666 IntegerType::get(getContext(), BitWidth - LZ)), 3667 U->getType()); 3668 } 3669 break; 3670 3671 case Instruction::Or: 3672 // If the RHS of the Or is a constant, we may have something like: 3673 // X*4+1 which got turned into X*4|1. Handle this as an Add so loop 3674 // optimizations will transparently handle this case. 3675 // 3676 // In order for this transformation to be safe, the LHS must be of the 3677 // form X*(2^n) and the Or constant must be less than 2^n. 3678 if (ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1))) { 3679 const SCEV *LHS = getSCEV(U->getOperand(0)); 3680 const APInt &CIVal = CI->getValue(); 3681 if (GetMinTrailingZeros(LHS) >= 3682 (CIVal.getBitWidth() - CIVal.countLeadingZeros())) { 3683 // Build a plain add SCEV. 3684 const SCEV *S = getAddExpr(LHS, getSCEV(CI)); 3685 // If the LHS of the add was an addrec and it has no-wrap flags, 3686 // transfer the no-wrap flags, since an or won't introduce a wrap. 3687 if (const SCEVAddRecExpr *NewAR = dyn_cast<SCEVAddRecExpr>(S)) { 3688 const SCEVAddRecExpr *OldAR = cast<SCEVAddRecExpr>(LHS); 3689 const_cast<SCEVAddRecExpr *>(NewAR)->setNoWrapFlags( 3690 OldAR->getNoWrapFlags()); 3691 } 3692 return S; 3693 } 3694 } 3695 break; 3696 case Instruction::Xor: 3697 if (ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1))) { 3698 // If the RHS of the xor is a signbit, then this is just an add. 3699 // Instcombine turns add of signbit into xor as a strength reduction step. 3700 if (CI->getValue().isSignBit()) 3701 return getAddExpr(getSCEV(U->getOperand(0)), 3702 getSCEV(U->getOperand(1))); 3703 3704 // If the RHS of xor is -1, then this is a not operation. 3705 if (CI->isAllOnesValue()) 3706 return getNotSCEV(getSCEV(U->getOperand(0))); 3707 3708 // Model xor(and(x, C), C) as and(~x, C), if C is a low-bits mask. 3709 // This is a variant of the check for xor with -1, and it handles 3710 // the case where instcombine has trimmed non-demanded bits out 3711 // of an xor with -1. 3712 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getOperand(0))) 3713 if (ConstantInt *LCI = dyn_cast<ConstantInt>(BO->getOperand(1))) 3714 if (BO->getOpcode() == Instruction::And && 3715 LCI->getValue() == CI->getValue()) 3716 if (const SCEVZeroExtendExpr *Z = 3717 dyn_cast<SCEVZeroExtendExpr>(getSCEV(U->getOperand(0)))) { 3718 Type *UTy = U->getType(); 3719 const SCEV *Z0 = Z->getOperand(); 3720 Type *Z0Ty = Z0->getType(); 3721 unsigned Z0TySize = getTypeSizeInBits(Z0Ty); 3722 3723 // If C is a low-bits mask, the zero extend is serving to 3724 // mask off the high bits. Complement the operand and 3725 // re-apply the zext. 3726 if (APIntOps::isMask(Z0TySize, CI->getValue())) 3727 return getZeroExtendExpr(getNotSCEV(Z0), UTy); 3728 3729 // If C is a single bit, it may be in the sign-bit position 3730 // before the zero-extend. In this case, represent the xor 3731 // using an add, which is equivalent, and re-apply the zext. 3732 APInt Trunc = CI->getValue().trunc(Z0TySize); 3733 if (Trunc.zext(getTypeSizeInBits(UTy)) == CI->getValue() && 3734 Trunc.isSignBit()) 3735 return getZeroExtendExpr(getAddExpr(Z0, getConstant(Trunc)), 3736 UTy); 3737 } 3738 } 3739 break; 3740 3741 case Instruction::Shl: 3742 // Turn shift left of a constant amount into a multiply. 3743 if (ConstantInt *SA = dyn_cast<ConstantInt>(U->getOperand(1))) { 3744 uint32_t BitWidth = cast<IntegerType>(U->getType())->getBitWidth(); 3745 3746 // If the shift count is not less than the bitwidth, the result of 3747 // the shift is undefined. Don't try to analyze it, because the 3748 // resolution chosen here may differ from the resolution chosen in 3749 // other parts of the compiler. 3750 if (SA->getValue().uge(BitWidth)) 3751 break; 3752 3753 Constant *X = ConstantInt::get(getContext(), 3754 APInt(BitWidth, 1).shl(SA->getZExtValue())); 3755 return getMulExpr(getSCEV(U->getOperand(0)), getSCEV(X)); 3756 } 3757 break; 3758 3759 case Instruction::LShr: 3760 // Turn logical shift right of a constant into a unsigned divide. 3761 if (ConstantInt *SA = dyn_cast<ConstantInt>(U->getOperand(1))) { 3762 uint32_t BitWidth = cast<IntegerType>(U->getType())->getBitWidth(); 3763 3764 // If the shift count is not less than the bitwidth, the result of 3765 // the shift is undefined. Don't try to analyze it, because the 3766 // resolution chosen here may differ from the resolution chosen in 3767 // other parts of the compiler. 3768 if (SA->getValue().uge(BitWidth)) 3769 break; 3770 3771 Constant *X = ConstantInt::get(getContext(), 3772 APInt(BitWidth, 1).shl(SA->getZExtValue())); 3773 return getUDivExpr(getSCEV(U->getOperand(0)), getSCEV(X)); 3774 } 3775 break; 3776 3777 case Instruction::AShr: 3778 // For a two-shift sext-inreg, use sext(trunc(x)) as the SCEV expression. 3779 if (ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1))) 3780 if (Operator *L = dyn_cast<Operator>(U->getOperand(0))) 3781 if (L->getOpcode() == Instruction::Shl && 3782 L->getOperand(1) == U->getOperand(1)) { 3783 uint64_t BitWidth = getTypeSizeInBits(U->getType()); 3784 3785 // If the shift count is not less than the bitwidth, the result of 3786 // the shift is undefined. Don't try to analyze it, because the 3787 // resolution chosen here may differ from the resolution chosen in 3788 // other parts of the compiler. 3789 if (CI->getValue().uge(BitWidth)) 3790 break; 3791 3792 uint64_t Amt = BitWidth - CI->getZExtValue(); 3793 if (Amt == BitWidth) 3794 return getSCEV(L->getOperand(0)); // shift by zero --> noop 3795 return 3796 getSignExtendExpr(getTruncateExpr(getSCEV(L->getOperand(0)), 3797 IntegerType::get(getContext(), 3798 Amt)), 3799 U->getType()); 3800 } 3801 break; 3802 3803 case Instruction::Trunc: 3804 return getTruncateExpr(getSCEV(U->getOperand(0)), U->getType()); 3805 3806 case Instruction::ZExt: 3807 return getZeroExtendExpr(getSCEV(U->getOperand(0)), U->getType()); 3808 3809 case Instruction::SExt: 3810 return getSignExtendExpr(getSCEV(U->getOperand(0)), U->getType()); 3811 3812 case Instruction::BitCast: 3813 // BitCasts are no-op casts so we just eliminate the cast. 3814 if (isSCEVable(U->getType()) && isSCEVable(U->getOperand(0)->getType())) 3815 return getSCEV(U->getOperand(0)); 3816 break; 3817 3818 // It's tempting to handle inttoptr and ptrtoint as no-ops, however this can 3819 // lead to pointer expressions which cannot safely be expanded to GEPs, 3820 // because ScalarEvolution doesn't respect the GEP aliasing rules when 3821 // simplifying integer expressions. 3822 3823 case Instruction::GetElementPtr: 3824 return createNodeForGEP(cast<GEPOperator>(U)); 3825 3826 case Instruction::PHI: 3827 return createNodeForPHI(cast<PHINode>(U)); 3828 3829 case Instruction::Select: 3830 // This could be a smax or umax that was lowered earlier. 3831 // Try to recover it. 3832 if (ICmpInst *ICI = dyn_cast<ICmpInst>(U->getOperand(0))) { 3833 Value *LHS = ICI->getOperand(0); 3834 Value *RHS = ICI->getOperand(1); 3835 switch (ICI->getPredicate()) { 3836 case ICmpInst::ICMP_SLT: 3837 case ICmpInst::ICMP_SLE: 3838 std::swap(LHS, RHS); 3839 // fall through 3840 case ICmpInst::ICMP_SGT: 3841 case ICmpInst::ICMP_SGE: 3842 // a >s b ? a+x : b+x -> smax(a, b)+x 3843 // a >s b ? b+x : a+x -> smin(a, b)+x 3844 if (LHS->getType() == U->getType()) { 3845 const SCEV *LS = getSCEV(LHS); 3846 const SCEV *RS = getSCEV(RHS); 3847 const SCEV *LA = getSCEV(U->getOperand(1)); 3848 const SCEV *RA = getSCEV(U->getOperand(2)); 3849 const SCEV *LDiff = getMinusSCEV(LA, LS); 3850 const SCEV *RDiff = getMinusSCEV(RA, RS); 3851 if (LDiff == RDiff) 3852 return getAddExpr(getSMaxExpr(LS, RS), LDiff); 3853 LDiff = getMinusSCEV(LA, RS); 3854 RDiff = getMinusSCEV(RA, LS); 3855 if (LDiff == RDiff) 3856 return getAddExpr(getSMinExpr(LS, RS), LDiff); 3857 } 3858 break; 3859 case ICmpInst::ICMP_ULT: 3860 case ICmpInst::ICMP_ULE: 3861 std::swap(LHS, RHS); 3862 // fall through 3863 case ICmpInst::ICMP_UGT: 3864 case ICmpInst::ICMP_UGE: 3865 // a >u b ? a+x : b+x -> umax(a, b)+x 3866 // a >u b ? b+x : a+x -> umin(a, b)+x 3867 if (LHS->getType() == U->getType()) { 3868 const SCEV *LS = getSCEV(LHS); 3869 const SCEV *RS = getSCEV(RHS); 3870 const SCEV *LA = getSCEV(U->getOperand(1)); 3871 const SCEV *RA = getSCEV(U->getOperand(2)); 3872 const SCEV *LDiff = getMinusSCEV(LA, LS); 3873 const SCEV *RDiff = getMinusSCEV(RA, RS); 3874 if (LDiff == RDiff) 3875 return getAddExpr(getUMaxExpr(LS, RS), LDiff); 3876 LDiff = getMinusSCEV(LA, RS); 3877 RDiff = getMinusSCEV(RA, LS); 3878 if (LDiff == RDiff) 3879 return getAddExpr(getUMinExpr(LS, RS), LDiff); 3880 } 3881 break; 3882 case ICmpInst::ICMP_NE: 3883 // n != 0 ? n+x : 1+x -> umax(n, 1)+x 3884 if (LHS->getType() == U->getType() && 3885 isa<ConstantInt>(RHS) && 3886 cast<ConstantInt>(RHS)->isZero()) { 3887 const SCEV *One = getConstant(LHS->getType(), 1); 3888 const SCEV *LS = getSCEV(LHS); 3889 const SCEV *LA = getSCEV(U->getOperand(1)); 3890 const SCEV *RA = getSCEV(U->getOperand(2)); 3891 const SCEV *LDiff = getMinusSCEV(LA, LS); 3892 const SCEV *RDiff = getMinusSCEV(RA, One); 3893 if (LDiff == RDiff) 3894 return getAddExpr(getUMaxExpr(One, LS), LDiff); 3895 } 3896 break; 3897 case ICmpInst::ICMP_EQ: 3898 // n == 0 ? 1+x : n+x -> umax(n, 1)+x 3899 if (LHS->getType() == U->getType() && 3900 isa<ConstantInt>(RHS) && 3901 cast<ConstantInt>(RHS)->isZero()) { 3902 const SCEV *One = getConstant(LHS->getType(), 1); 3903 const SCEV *LS = getSCEV(LHS); 3904 const SCEV *LA = getSCEV(U->getOperand(1)); 3905 const SCEV *RA = getSCEV(U->getOperand(2)); 3906 const SCEV *LDiff = getMinusSCEV(LA, One); 3907 const SCEV *RDiff = getMinusSCEV(RA, LS); 3908 if (LDiff == RDiff) 3909 return getAddExpr(getUMaxExpr(One, LS), LDiff); 3910 } 3911 break; 3912 default: 3913 break; 3914 } 3915 } 3916 3917 default: // We cannot analyze this expression. 3918 break; 3919 } 3920 3921 return getUnknown(V); 3922} 3923 3924 3925 3926//===----------------------------------------------------------------------===// 3927// Iteration Count Computation Code 3928// 3929 3930/// getSmallConstantTripCount - Returns the maximum trip count of this loop as a 3931/// normal unsigned value. Returns 0 if the trip count is unknown or not 3932/// constant. Will also return 0 if the maximum trip count is very large (>= 3933/// 2^32). 3934/// 3935/// This "trip count" assumes that control exits via ExitingBlock. More 3936/// precisely, it is the number of times that control may reach ExitingBlock 3937/// before taking the branch. For loops with multiple exits, it may not be the 3938/// number times that the loop header executes because the loop may exit 3939/// prematurely via another branch. 3940/// 3941/// FIXME: We conservatively call getBackedgeTakenCount(L) instead of 3942/// getExitCount(L, ExitingBlock) to compute a safe trip count considering all 3943/// loop exits. getExitCount() may return an exact count for this branch 3944/// assuming no-signed-wrap. The number of well-defined iterations may actually 3945/// be higher than this trip count if this exit test is skipped and the loop 3946/// exits via a different branch. Ideally, getExitCount() would know whether it 3947/// depends on a NSW assumption, and we would only fall back to a conservative 3948/// trip count in that case. 3949unsigned ScalarEvolution:: 3950getSmallConstantTripCount(Loop *L, BasicBlock */*ExitingBlock*/) { 3951 const SCEVConstant *ExitCount = 3952 dyn_cast<SCEVConstant>(getBackedgeTakenCount(L)); 3953 if (!ExitCount) 3954 return 0; 3955 3956 ConstantInt *ExitConst = ExitCount->getValue(); 3957 3958 // Guard against huge trip counts. 3959 if (ExitConst->getValue().getActiveBits() > 32) 3960 return 0; 3961 3962 // In case of integer overflow, this returns 0, which is correct. 3963 return ((unsigned)ExitConst->getZExtValue()) + 1; 3964} 3965 3966/// getSmallConstantTripMultiple - Returns the largest constant divisor of the 3967/// trip count of this loop as a normal unsigned value, if possible. This 3968/// means that the actual trip count is always a multiple of the returned 3969/// value (don't forget the trip count could very well be zero as well!). 3970/// 3971/// Returns 1 if the trip count is unknown or not guaranteed to be the 3972/// multiple of a constant (which is also the case if the trip count is simply 3973/// constant, use getSmallConstantTripCount for that case), Will also return 1 3974/// if the trip count is very large (>= 2^32). 3975/// 3976/// As explained in the comments for getSmallConstantTripCount, this assumes 3977/// that control exits the loop via ExitingBlock. 3978unsigned ScalarEvolution:: 3979getSmallConstantTripMultiple(Loop *L, BasicBlock */*ExitingBlock*/) { 3980 const SCEV *ExitCount = getBackedgeTakenCount(L); 3981 if (ExitCount == getCouldNotCompute()) 3982 return 1; 3983 3984 // Get the trip count from the BE count by adding 1. 3985 const SCEV *TCMul = getAddExpr(ExitCount, 3986 getConstant(ExitCount->getType(), 1)); 3987 // FIXME: SCEV distributes multiplication as V1*C1 + V2*C1. We could attempt 3988 // to factor simple cases. 3989 if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(TCMul)) 3990 TCMul = Mul->getOperand(0); 3991 3992 const SCEVConstant *MulC = dyn_cast<SCEVConstant>(TCMul); 3993 if (!MulC) 3994 return 1; 3995 3996 ConstantInt *Result = MulC->getValue(); 3997 3998 // Guard against huge trip counts (this requires checking 3999 // for zero to handle the case where the trip count == -1 and the 4000 // addition wraps). 4001 if (!Result || Result->getValue().getActiveBits() > 32 || 4002 Result->getValue().getActiveBits() == 0) 4003 return 1; 4004 4005 return (unsigned)Result->getZExtValue(); 4006} 4007 4008// getExitCount - Get the expression for the number of loop iterations for which 4009// this loop is guaranteed not to exit via ExitingBlock. Otherwise return 4010// SCEVCouldNotCompute. 4011const SCEV *ScalarEvolution::getExitCount(Loop *L, BasicBlock *ExitingBlock) { 4012 return getBackedgeTakenInfo(L).getExact(ExitingBlock, this); 4013} 4014 4015/// getBackedgeTakenCount - If the specified loop has a predictable 4016/// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute 4017/// object. The backedge-taken count is the number of times the loop header 4018/// will be branched to from within the loop. This is one less than the 4019/// trip count of the loop, since it doesn't count the first iteration, 4020/// when the header is branched to from outside the loop. 4021/// 4022/// Note that it is not valid to call this method on a loop without a 4023/// loop-invariant backedge-taken count (see 4024/// hasLoopInvariantBackedgeTakenCount). 4025/// 4026const SCEV *ScalarEvolution::getBackedgeTakenCount(const Loop *L) { 4027 return getBackedgeTakenInfo(L).getExact(this); 4028} 4029 4030/// getMaxBackedgeTakenCount - Similar to getBackedgeTakenCount, except 4031/// return the least SCEV value that is known never to be less than the 4032/// actual backedge taken count. 4033const SCEV *ScalarEvolution::getMaxBackedgeTakenCount(const Loop *L) { 4034 return getBackedgeTakenInfo(L).getMax(this); 4035} 4036 4037/// PushLoopPHIs - Push PHI nodes in the header of the given loop 4038/// onto the given Worklist. 4039static void 4040PushLoopPHIs(const Loop *L, SmallVectorImpl<Instruction *> &Worklist) { 4041 BasicBlock *Header = L->getHeader(); 4042 4043 // Push all Loop-header PHIs onto the Worklist stack. 4044 for (BasicBlock::iterator I = Header->begin(); 4045 PHINode *PN = dyn_cast<PHINode>(I); ++I) 4046 Worklist.push_back(PN); 4047} 4048 4049const ScalarEvolution::BackedgeTakenInfo & 4050ScalarEvolution::getBackedgeTakenInfo(const Loop *L) { 4051 // Initially insert an invalid entry for this loop. If the insertion 4052 // succeeds, proceed to actually compute a backedge-taken count and 4053 // update the value. The temporary CouldNotCompute value tells SCEV 4054 // code elsewhere that it shouldn't attempt to request a new 4055 // backedge-taken count, which could result in infinite recursion. 4056 std::pair<DenseMap<const Loop *, BackedgeTakenInfo>::iterator, bool> Pair = 4057 BackedgeTakenCounts.insert(std::make_pair(L, BackedgeTakenInfo())); 4058 if (!Pair.second) 4059 return Pair.first->second; 4060 4061 // ComputeBackedgeTakenCount may allocate memory for its result. Inserting it 4062 // into the BackedgeTakenCounts map transfers ownership. Otherwise, the result 4063 // must be cleared in this scope. 4064 BackedgeTakenInfo Result = ComputeBackedgeTakenCount(L); 4065 4066 if (Result.getExact(this) != getCouldNotCompute()) { 4067 assert(isLoopInvariant(Result.getExact(this), L) && 4068 isLoopInvariant(Result.getMax(this), L) && 4069 "Computed backedge-taken count isn't loop invariant for loop!"); 4070 ++NumTripCountsComputed; 4071 } 4072 else if (Result.getMax(this) == getCouldNotCompute() && 4073 isa<PHINode>(L->getHeader()->begin())) { 4074 // Only count loops that have phi nodes as not being computable. 4075 ++NumTripCountsNotComputed; 4076 } 4077 4078 // Now that we know more about the trip count for this loop, forget any 4079 // existing SCEV values for PHI nodes in this loop since they are only 4080 // conservative estimates made without the benefit of trip count 4081 // information. This is similar to the code in forgetLoop, except that 4082 // it handles SCEVUnknown PHI nodes specially. 4083 if (Result.hasAnyInfo()) { 4084 SmallVector<Instruction *, 16> Worklist; 4085 PushLoopPHIs(L, Worklist); 4086 4087 SmallPtrSet<Instruction *, 8> Visited; 4088 while (!Worklist.empty()) { 4089 Instruction *I = Worklist.pop_back_val(); 4090 if (!Visited.insert(I)) continue; 4091 4092 ValueExprMapType::iterator It = 4093 ValueExprMap.find_as(static_cast<Value *>(I)); 4094 if (It != ValueExprMap.end()) { 4095 const SCEV *Old = It->second; 4096 4097 // SCEVUnknown for a PHI either means that it has an unrecognized 4098 // structure, or it's a PHI that's in the progress of being computed 4099 // by createNodeForPHI. In the former case, additional loop trip 4100 // count information isn't going to change anything. In the later 4101 // case, createNodeForPHI will perform the necessary updates on its 4102 // own when it gets to that point. 4103 if (!isa<PHINode>(I) || !isa<SCEVUnknown>(Old)) { 4104 forgetMemoizedResults(Old); 4105 ValueExprMap.erase(It); 4106 } 4107 if (PHINode *PN = dyn_cast<PHINode>(I)) 4108 ConstantEvolutionLoopExitValue.erase(PN); 4109 } 4110 4111 PushDefUseChildren(I, Worklist); 4112 } 4113 } 4114 4115 // Re-lookup the insert position, since the call to 4116 // ComputeBackedgeTakenCount above could result in a 4117 // recusive call to getBackedgeTakenInfo (on a different 4118 // loop), which would invalidate the iterator computed 4119 // earlier. 4120 return BackedgeTakenCounts.find(L)->second = Result; 4121} 4122 4123/// forgetLoop - This method should be called by the client when it has 4124/// changed a loop in a way that may effect ScalarEvolution's ability to 4125/// compute a trip count, or if the loop is deleted. 4126void ScalarEvolution::forgetLoop(const Loop *L) { 4127 // Drop any stored trip count value. 4128 DenseMap<const Loop*, BackedgeTakenInfo>::iterator BTCPos = 4129 BackedgeTakenCounts.find(L); 4130 if (BTCPos != BackedgeTakenCounts.end()) { 4131 BTCPos->second.clear(); 4132 BackedgeTakenCounts.erase(BTCPos); 4133 } 4134 4135 // Drop information about expressions based on loop-header PHIs. 4136 SmallVector<Instruction *, 16> Worklist; 4137 PushLoopPHIs(L, Worklist); 4138 4139 SmallPtrSet<Instruction *, 8> Visited; 4140 while (!Worklist.empty()) { 4141 Instruction *I = Worklist.pop_back_val(); 4142 if (!Visited.insert(I)) continue; 4143 4144 ValueExprMapType::iterator It = 4145 ValueExprMap.find_as(static_cast<Value *>(I)); 4146 if (It != ValueExprMap.end()) { 4147 forgetMemoizedResults(It->second); 4148 ValueExprMap.erase(It); 4149 if (PHINode *PN = dyn_cast<PHINode>(I)) 4150 ConstantEvolutionLoopExitValue.erase(PN); 4151 } 4152 4153 PushDefUseChildren(I, Worklist); 4154 } 4155 4156 // Forget all contained loops too, to avoid dangling entries in the 4157 // ValuesAtScopes map. 4158 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) 4159 forgetLoop(*I); 4160} 4161 4162/// forgetValue - This method should be called by the client when it has 4163/// changed a value in a way that may effect its value, or which may 4164/// disconnect it from a def-use chain linking it to a loop. 4165void ScalarEvolution::forgetValue(Value *V) { 4166 Instruction *I = dyn_cast<Instruction>(V); 4167 if (!I) return; 4168 4169 // Drop information about expressions based on loop-header PHIs. 4170 SmallVector<Instruction *, 16> Worklist; 4171 Worklist.push_back(I); 4172 4173 SmallPtrSet<Instruction *, 8> Visited; 4174 while (!Worklist.empty()) { 4175 I = Worklist.pop_back_val(); 4176 if (!Visited.insert(I)) continue; 4177 4178 ValueExprMapType::iterator It = 4179 ValueExprMap.find_as(static_cast<Value *>(I)); 4180 if (It != ValueExprMap.end()) { 4181 forgetMemoizedResults(It->second); 4182 ValueExprMap.erase(It); 4183 if (PHINode *PN = dyn_cast<PHINode>(I)) 4184 ConstantEvolutionLoopExitValue.erase(PN); 4185 } 4186 4187 PushDefUseChildren(I, Worklist); 4188 } 4189} 4190 4191/// getExact - Get the exact loop backedge taken count considering all loop 4192/// exits. A computable result can only be return for loops with a single exit. 4193/// Returning the minimum taken count among all exits is incorrect because one 4194/// of the loop's exit limit's may have been skipped. HowFarToZero assumes that 4195/// the limit of each loop test is never skipped. This is a valid assumption as 4196/// long as the loop exits via that test. For precise results, it is the 4197/// caller's responsibility to specify the relevant loop exit using 4198/// getExact(ExitingBlock, SE). 4199const SCEV * 4200ScalarEvolution::BackedgeTakenInfo::getExact(ScalarEvolution *SE) const { 4201 // If any exits were not computable, the loop is not computable. 4202 if (!ExitNotTaken.isCompleteList()) return SE->getCouldNotCompute(); 4203 4204 // We need exactly one computable exit. 4205 if (!ExitNotTaken.ExitingBlock) return SE->getCouldNotCompute(); 4206 assert(ExitNotTaken.ExactNotTaken && "uninitialized not-taken info"); 4207 4208 const SCEV *BECount = 0; 4209 for (const ExitNotTakenInfo *ENT = &ExitNotTaken; 4210 ENT != 0; ENT = ENT->getNextExit()) { 4211 4212 assert(ENT->ExactNotTaken != SE->getCouldNotCompute() && "bad exit SCEV"); 4213 4214 if (!BECount) 4215 BECount = ENT->ExactNotTaken; 4216 else if (BECount != ENT->ExactNotTaken) 4217 return SE->getCouldNotCompute(); 4218 } 4219 assert(BECount && "Invalid not taken count for loop exit"); 4220 return BECount; 4221} 4222 4223/// getExact - Get the exact not taken count for this loop exit. 4224const SCEV * 4225ScalarEvolution::BackedgeTakenInfo::getExact(BasicBlock *ExitingBlock, 4226 ScalarEvolution *SE) const { 4227 for (const ExitNotTakenInfo *ENT = &ExitNotTaken; 4228 ENT != 0; ENT = ENT->getNextExit()) { 4229 4230 if (ENT->ExitingBlock == ExitingBlock) 4231 return ENT->ExactNotTaken; 4232 } 4233 return SE->getCouldNotCompute(); 4234} 4235 4236/// getMax - Get the max backedge taken count for the loop. 4237const SCEV * 4238ScalarEvolution::BackedgeTakenInfo::getMax(ScalarEvolution *SE) const { 4239 return Max ? Max : SE->getCouldNotCompute(); 4240} 4241 4242bool ScalarEvolution::BackedgeTakenInfo::hasOperand(const SCEV *S, 4243 ScalarEvolution *SE) const { 4244 if (Max && Max != SE->getCouldNotCompute() && SE->hasOperand(Max, S)) 4245 return true; 4246 4247 if (!ExitNotTaken.ExitingBlock) 4248 return false; 4249 4250 for (const ExitNotTakenInfo *ENT = &ExitNotTaken; 4251 ENT != 0; ENT = ENT->getNextExit()) { 4252 4253 if (ENT->ExactNotTaken != SE->getCouldNotCompute() 4254 && SE->hasOperand(ENT->ExactNotTaken, S)) { 4255 return true; 4256 } 4257 } 4258 return false; 4259} 4260 4261/// Allocate memory for BackedgeTakenInfo and copy the not-taken count of each 4262/// computable exit into a persistent ExitNotTakenInfo array. 4263ScalarEvolution::BackedgeTakenInfo::BackedgeTakenInfo( 4264 SmallVectorImpl< std::pair<BasicBlock *, const SCEV *> > &ExitCounts, 4265 bool Complete, const SCEV *MaxCount) : Max(MaxCount) { 4266 4267 if (!Complete) 4268 ExitNotTaken.setIncomplete(); 4269 4270 unsigned NumExits = ExitCounts.size(); 4271 if (NumExits == 0) return; 4272 4273 ExitNotTaken.ExitingBlock = ExitCounts[0].first; 4274 ExitNotTaken.ExactNotTaken = ExitCounts[0].second; 4275 if (NumExits == 1) return; 4276 4277 // Handle the rare case of multiple computable exits. 4278 ExitNotTakenInfo *ENT = new ExitNotTakenInfo[NumExits-1]; 4279 4280 ExitNotTakenInfo *PrevENT = &ExitNotTaken; 4281 for (unsigned i = 1; i < NumExits; ++i, PrevENT = ENT, ++ENT) { 4282 PrevENT->setNextExit(ENT); 4283 ENT->ExitingBlock = ExitCounts[i].first; 4284 ENT->ExactNotTaken = ExitCounts[i].second; 4285 } 4286} 4287 4288/// clear - Invalidate this result and free the ExitNotTakenInfo array. 4289void ScalarEvolution::BackedgeTakenInfo::clear() { 4290 ExitNotTaken.ExitingBlock = 0; 4291 ExitNotTaken.ExactNotTaken = 0; 4292 delete[] ExitNotTaken.getNextExit(); 4293} 4294 4295/// ComputeBackedgeTakenCount - Compute the number of times the backedge 4296/// of the specified loop will execute. 4297ScalarEvolution::BackedgeTakenInfo 4298ScalarEvolution::ComputeBackedgeTakenCount(const Loop *L) { 4299 SmallVector<BasicBlock *, 8> ExitingBlocks; 4300 L->getExitingBlocks(ExitingBlocks); 4301 4302 // Examine all exits and pick the most conservative values. 4303 const SCEV *MaxBECount = getCouldNotCompute(); 4304 bool CouldComputeBECount = true; 4305 SmallVector<std::pair<BasicBlock *, const SCEV *>, 4> ExitCounts; 4306 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) { 4307 ExitLimit EL = ComputeExitLimit(L, ExitingBlocks[i]); 4308 if (EL.Exact == getCouldNotCompute()) 4309 // We couldn't compute an exact value for this exit, so 4310 // we won't be able to compute an exact value for the loop. 4311 CouldComputeBECount = false; 4312 else 4313 ExitCounts.push_back(std::make_pair(ExitingBlocks[i], EL.Exact)); 4314 4315 if (MaxBECount == getCouldNotCompute()) 4316 MaxBECount = EL.Max; 4317 else if (EL.Max != getCouldNotCompute()) { 4318 // We cannot take the "min" MaxBECount, because non-unit stride loops may 4319 // skip some loop tests. Taking the max over the exits is sufficiently 4320 // conservative. TODO: We could do better taking into consideration 4321 // that (1) the loop has unit stride (2) the last loop test is 4322 // less-than/greater-than (3) any loop test is less-than/greater-than AND 4323 // falls-through some constant times less then the other tests. 4324 MaxBECount = getUMaxFromMismatchedTypes(MaxBECount, EL.Max); 4325 } 4326 } 4327 4328 return BackedgeTakenInfo(ExitCounts, CouldComputeBECount, MaxBECount); 4329} 4330 4331/// ComputeExitLimit - Compute the number of times the backedge of the specified 4332/// loop will execute if it exits via the specified block. 4333ScalarEvolution::ExitLimit 4334ScalarEvolution::ComputeExitLimit(const Loop *L, BasicBlock *ExitingBlock) { 4335 4336 // Okay, we've chosen an exiting block. See what condition causes us to 4337 // exit at this block. 4338 // 4339 // FIXME: we should be able to handle switch instructions (with a single exit) 4340 BranchInst *ExitBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator()); 4341 if (ExitBr == 0) return getCouldNotCompute(); 4342 assert(ExitBr->isConditional() && "If unconditional, it can't be in loop!"); 4343 4344 // At this point, we know we have a conditional branch that determines whether 4345 // the loop is exited. However, we don't know if the branch is executed each 4346 // time through the loop. If not, then the execution count of the branch will 4347 // not be equal to the trip count of the loop. 4348 // 4349 // Currently we check for this by checking to see if the Exit branch goes to 4350 // the loop header. If so, we know it will always execute the same number of 4351 // times as the loop. We also handle the case where the exit block *is* the 4352 // loop header. This is common for un-rotated loops. 4353 // 4354 // If both of those tests fail, walk up the unique predecessor chain to the 4355 // header, stopping if there is an edge that doesn't exit the loop. If the 4356 // header is reached, the execution count of the branch will be equal to the 4357 // trip count of the loop. 4358 // 4359 // More extensive analysis could be done to handle more cases here. 4360 // 4361 if (ExitBr->getSuccessor(0) != L->getHeader() && 4362 ExitBr->getSuccessor(1) != L->getHeader() && 4363 ExitBr->getParent() != L->getHeader()) { 4364 // The simple checks failed, try climbing the unique predecessor chain 4365 // up to the header. 4366 bool Ok = false; 4367 for (BasicBlock *BB = ExitBr->getParent(); BB; ) { 4368 BasicBlock *Pred = BB->getUniquePredecessor(); 4369 if (!Pred) 4370 return getCouldNotCompute(); 4371 TerminatorInst *PredTerm = Pred->getTerminator(); 4372 for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i) { 4373 BasicBlock *PredSucc = PredTerm->getSuccessor(i); 4374 if (PredSucc == BB) 4375 continue; 4376 // If the predecessor has a successor that isn't BB and isn't 4377 // outside the loop, assume the worst. 4378 if (L->contains(PredSucc)) 4379 return getCouldNotCompute(); 4380 } 4381 if (Pred == L->getHeader()) { 4382 Ok = true; 4383 break; 4384 } 4385 BB = Pred; 4386 } 4387 if (!Ok) 4388 return getCouldNotCompute(); 4389 } 4390 4391 // Proceed to the next level to examine the exit condition expression. 4392 return ComputeExitLimitFromCond(L, ExitBr->getCondition(), 4393 ExitBr->getSuccessor(0), 4394 ExitBr->getSuccessor(1), 4395 /*IsSubExpr=*/false); 4396} 4397 4398/// ComputeExitLimitFromCond - Compute the number of times the 4399/// backedge of the specified loop will execute if its exit condition 4400/// were a conditional branch of ExitCond, TBB, and FBB. 4401/// 4402/// @param IsSubExpr is true if ExitCond does not directly control the exit 4403/// branch. In this case, we cannot assume that the loop only exits when the 4404/// condition is true and cannot infer that failing to meet the condition prior 4405/// to integer wraparound results in undefined behavior. 4406ScalarEvolution::ExitLimit 4407ScalarEvolution::ComputeExitLimitFromCond(const Loop *L, 4408 Value *ExitCond, 4409 BasicBlock *TBB, 4410 BasicBlock *FBB, 4411 bool IsSubExpr) { 4412 // Check if the controlling expression for this loop is an And or Or. 4413 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(ExitCond)) { 4414 if (BO->getOpcode() == Instruction::And) { 4415 // Recurse on the operands of the and. 4416 bool EitherMayExit = L->contains(TBB); 4417 ExitLimit EL0 = ComputeExitLimitFromCond(L, BO->getOperand(0), TBB, FBB, 4418 IsSubExpr || EitherMayExit); 4419 ExitLimit EL1 = ComputeExitLimitFromCond(L, BO->getOperand(1), TBB, FBB, 4420 IsSubExpr || EitherMayExit); 4421 const SCEV *BECount = getCouldNotCompute(); 4422 const SCEV *MaxBECount = getCouldNotCompute(); 4423 if (EitherMayExit) { 4424 // Both conditions must be true for the loop to continue executing. 4425 // Choose the less conservative count. 4426 if (EL0.Exact == getCouldNotCompute() || 4427 EL1.Exact == getCouldNotCompute()) 4428 BECount = getCouldNotCompute(); 4429 else 4430 BECount = getUMinFromMismatchedTypes(EL0.Exact, EL1.Exact); 4431 if (EL0.Max == getCouldNotCompute()) 4432 MaxBECount = EL1.Max; 4433 else if (EL1.Max == getCouldNotCompute()) 4434 MaxBECount = EL0.Max; 4435 else 4436 MaxBECount = getUMinFromMismatchedTypes(EL0.Max, EL1.Max); 4437 } else { 4438 // Both conditions must be true at the same time for the loop to exit. 4439 // For now, be conservative. 4440 assert(L->contains(FBB) && "Loop block has no successor in loop!"); 4441 if (EL0.Max == EL1.Max) 4442 MaxBECount = EL0.Max; 4443 if (EL0.Exact == EL1.Exact) 4444 BECount = EL0.Exact; 4445 } 4446 4447 return ExitLimit(BECount, MaxBECount); 4448 } 4449 if (BO->getOpcode() == Instruction::Or) { 4450 // Recurse on the operands of the or. 4451 bool EitherMayExit = L->contains(FBB); 4452 ExitLimit EL0 = ComputeExitLimitFromCond(L, BO->getOperand(0), TBB, FBB, 4453 IsSubExpr || EitherMayExit); 4454 ExitLimit EL1 = ComputeExitLimitFromCond(L, BO->getOperand(1), TBB, FBB, 4455 IsSubExpr || EitherMayExit); 4456 const SCEV *BECount = getCouldNotCompute(); 4457 const SCEV *MaxBECount = getCouldNotCompute(); 4458 if (EitherMayExit) { 4459 // Both conditions must be false for the loop to continue executing. 4460 // Choose the less conservative count. 4461 if (EL0.Exact == getCouldNotCompute() || 4462 EL1.Exact == getCouldNotCompute()) 4463 BECount = getCouldNotCompute(); 4464 else 4465 BECount = getUMinFromMismatchedTypes(EL0.Exact, EL1.Exact); 4466 if (EL0.Max == getCouldNotCompute()) 4467 MaxBECount = EL1.Max; 4468 else if (EL1.Max == getCouldNotCompute()) 4469 MaxBECount = EL0.Max; 4470 else 4471 MaxBECount = getUMinFromMismatchedTypes(EL0.Max, EL1.Max); 4472 } else { 4473 // Both conditions must be false at the same time for the loop to exit. 4474 // For now, be conservative. 4475 assert(L->contains(TBB) && "Loop block has no successor in loop!"); 4476 if (EL0.Max == EL1.Max) 4477 MaxBECount = EL0.Max; 4478 if (EL0.Exact == EL1.Exact) 4479 BECount = EL0.Exact; 4480 } 4481 4482 return ExitLimit(BECount, MaxBECount); 4483 } 4484 } 4485 4486 // With an icmp, it may be feasible to compute an exact backedge-taken count. 4487 // Proceed to the next level to examine the icmp. 4488 if (ICmpInst *ExitCondICmp = dyn_cast<ICmpInst>(ExitCond)) 4489 return ComputeExitLimitFromICmp(L, ExitCondICmp, TBB, FBB, IsSubExpr); 4490 4491 // Check for a constant condition. These are normally stripped out by 4492 // SimplifyCFG, but ScalarEvolution may be used by a pass which wishes to 4493 // preserve the CFG and is temporarily leaving constant conditions 4494 // in place. 4495 if (ConstantInt *CI = dyn_cast<ConstantInt>(ExitCond)) { 4496 if (L->contains(FBB) == !CI->getZExtValue()) 4497 // The backedge is always taken. 4498 return getCouldNotCompute(); 4499 else 4500 // The backedge is never taken. 4501 return getConstant(CI->getType(), 0); 4502 } 4503 4504 // If it's not an integer or pointer comparison then compute it the hard way. 4505 return ComputeExitCountExhaustively(L, ExitCond, !L->contains(TBB)); 4506} 4507 4508/// ComputeExitLimitFromICmp - Compute the number of times the 4509/// backedge of the specified loop will execute if its exit condition 4510/// were a conditional branch of the ICmpInst ExitCond, TBB, and FBB. 4511ScalarEvolution::ExitLimit 4512ScalarEvolution::ComputeExitLimitFromICmp(const Loop *L, 4513 ICmpInst *ExitCond, 4514 BasicBlock *TBB, 4515 BasicBlock *FBB, 4516 bool IsSubExpr) { 4517 4518 // If the condition was exit on true, convert the condition to exit on false 4519 ICmpInst::Predicate Cond; 4520 if (!L->contains(FBB)) 4521 Cond = ExitCond->getPredicate(); 4522 else 4523 Cond = ExitCond->getInversePredicate(); 4524 4525 // Handle common loops like: for (X = "string"; *X; ++X) 4526 if (LoadInst *LI = dyn_cast<LoadInst>(ExitCond->getOperand(0))) 4527 if (Constant *RHS = dyn_cast<Constant>(ExitCond->getOperand(1))) { 4528 ExitLimit ItCnt = 4529 ComputeLoadConstantCompareExitLimit(LI, RHS, L, Cond); 4530 if (ItCnt.hasAnyInfo()) 4531 return ItCnt; 4532 } 4533 4534 const SCEV *LHS = getSCEV(ExitCond->getOperand(0)); 4535 const SCEV *RHS = getSCEV(ExitCond->getOperand(1)); 4536 4537 // Try to evaluate any dependencies out of the loop. 4538 LHS = getSCEVAtScope(LHS, L); 4539 RHS = getSCEVAtScope(RHS, L); 4540 4541 // At this point, we would like to compute how many iterations of the 4542 // loop the predicate will return true for these inputs. 4543 if (isLoopInvariant(LHS, L) && !isLoopInvariant(RHS, L)) { 4544 // If there is a loop-invariant, force it into the RHS. 4545 std::swap(LHS, RHS); 4546 Cond = ICmpInst::getSwappedPredicate(Cond); 4547 } 4548 4549 // Simplify the operands before analyzing them. 4550 (void)SimplifyICmpOperands(Cond, LHS, RHS); 4551 4552 // If we have a comparison of a chrec against a constant, try to use value 4553 // ranges to answer this query. 4554 if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) 4555 if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(LHS)) 4556 if (AddRec->getLoop() == L) { 4557 // Form the constant range. 4558 ConstantRange CompRange( 4559 ICmpInst::makeConstantRange(Cond, RHSC->getValue()->getValue())); 4560 4561 const SCEV *Ret = AddRec->getNumIterationsInRange(CompRange, *this); 4562 if (!isa<SCEVCouldNotCompute>(Ret)) return Ret; 4563 } 4564 4565 switch (Cond) { 4566 case ICmpInst::ICMP_NE: { // while (X != Y) 4567 // Convert to: while (X-Y != 0) 4568 ExitLimit EL = HowFarToZero(getMinusSCEV(LHS, RHS), L, IsSubExpr); 4569 if (EL.hasAnyInfo()) return EL; 4570 break; 4571 } 4572 case ICmpInst::ICMP_EQ: { // while (X == Y) 4573 // Convert to: while (X-Y == 0) 4574 ExitLimit EL = HowFarToNonZero(getMinusSCEV(LHS, RHS), L); 4575 if (EL.hasAnyInfo()) return EL; 4576 break; 4577 } 4578 case ICmpInst::ICMP_SLT: { 4579 ExitLimit EL = HowManyLessThans(LHS, RHS, L, true, IsSubExpr); 4580 if (EL.hasAnyInfo()) return EL; 4581 break; 4582 } 4583 case ICmpInst::ICMP_SGT: { 4584 ExitLimit EL = HowManyLessThans(getNotSCEV(LHS), 4585 getNotSCEV(RHS), L, true, IsSubExpr); 4586 if (EL.hasAnyInfo()) return EL; 4587 break; 4588 } 4589 case ICmpInst::ICMP_ULT: { 4590 ExitLimit EL = HowManyLessThans(LHS, RHS, L, false, IsSubExpr); 4591 if (EL.hasAnyInfo()) return EL; 4592 break; 4593 } 4594 case ICmpInst::ICMP_UGT: { 4595 ExitLimit EL = HowManyLessThans(getNotSCEV(LHS), 4596 getNotSCEV(RHS), L, false, IsSubExpr); 4597 if (EL.hasAnyInfo()) return EL; 4598 break; 4599 } 4600 default: 4601#if 0 4602 dbgs() << "ComputeBackedgeTakenCount "; 4603 if (ExitCond->getOperand(0)->getType()->isUnsigned()) 4604 dbgs() << "[unsigned] "; 4605 dbgs() << *LHS << " " 4606 << Instruction::getOpcodeName(Instruction::ICmp) 4607 << " " << *RHS << "\n"; 4608#endif 4609 break; 4610 } 4611 return ComputeExitCountExhaustively(L, ExitCond, !L->contains(TBB)); 4612} 4613 4614static ConstantInt * 4615EvaluateConstantChrecAtConstant(const SCEVAddRecExpr *AddRec, ConstantInt *C, 4616 ScalarEvolution &SE) { 4617 const SCEV *InVal = SE.getConstant(C); 4618 const SCEV *Val = AddRec->evaluateAtIteration(InVal, SE); 4619 assert(isa<SCEVConstant>(Val) && 4620 "Evaluation of SCEV at constant didn't fold correctly?"); 4621 return cast<SCEVConstant>(Val)->getValue(); 4622} 4623 4624/// ComputeLoadConstantCompareExitLimit - Given an exit condition of 4625/// 'icmp op load X, cst', try to see if we can compute the backedge 4626/// execution count. 4627ScalarEvolution::ExitLimit 4628ScalarEvolution::ComputeLoadConstantCompareExitLimit( 4629 LoadInst *LI, 4630 Constant *RHS, 4631 const Loop *L, 4632 ICmpInst::Predicate predicate) { 4633 4634 if (LI->isVolatile()) return getCouldNotCompute(); 4635 4636 // Check to see if the loaded pointer is a getelementptr of a global. 4637 // TODO: Use SCEV instead of manually grubbing with GEPs. 4638 GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0)); 4639 if (!GEP) return getCouldNotCompute(); 4640 4641 // Make sure that it is really a constant global we are gepping, with an 4642 // initializer, and make sure the first IDX is really 0. 4643 GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)); 4644 if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer() || 4645 GEP->getNumOperands() < 3 || !isa<Constant>(GEP->getOperand(1)) || 4646 !cast<Constant>(GEP->getOperand(1))->isNullValue()) 4647 return getCouldNotCompute(); 4648 4649 // Okay, we allow one non-constant index into the GEP instruction. 4650 Value *VarIdx = 0; 4651 std::vector<Constant*> Indexes; 4652 unsigned VarIdxNum = 0; 4653 for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) 4654 if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(i))) { 4655 Indexes.push_back(CI); 4656 } else if (!isa<ConstantInt>(GEP->getOperand(i))) { 4657 if (VarIdx) return getCouldNotCompute(); // Multiple non-constant idx's. 4658 VarIdx = GEP->getOperand(i); 4659 VarIdxNum = i-2; 4660 Indexes.push_back(0); 4661 } 4662 4663 // Loop-invariant loads may be a byproduct of loop optimization. Skip them. 4664 if (!VarIdx) 4665 return getCouldNotCompute(); 4666 4667 // Okay, we know we have a (load (gep GV, 0, X)) comparison with a constant. 4668 // Check to see if X is a loop variant variable value now. 4669 const SCEV *Idx = getSCEV(VarIdx); 4670 Idx = getSCEVAtScope(Idx, L); 4671 4672 // We can only recognize very limited forms of loop index expressions, in 4673 // particular, only affine AddRec's like {C1,+,C2}. 4674 const SCEVAddRecExpr *IdxExpr = dyn_cast<SCEVAddRecExpr>(Idx); 4675 if (!IdxExpr || !IdxExpr->isAffine() || isLoopInvariant(IdxExpr, L) || 4676 !isa<SCEVConstant>(IdxExpr->getOperand(0)) || 4677 !isa<SCEVConstant>(IdxExpr->getOperand(1))) 4678 return getCouldNotCompute(); 4679 4680 unsigned MaxSteps = MaxBruteForceIterations; 4681 for (unsigned IterationNum = 0; IterationNum != MaxSteps; ++IterationNum) { 4682 ConstantInt *ItCst = ConstantInt::get( 4683 cast<IntegerType>(IdxExpr->getType()), IterationNum); 4684 ConstantInt *Val = EvaluateConstantChrecAtConstant(IdxExpr, ItCst, *this); 4685 4686 // Form the GEP offset. 4687 Indexes[VarIdxNum] = Val; 4688 4689 Constant *Result = ConstantFoldLoadThroughGEPIndices(GV->getInitializer(), 4690 Indexes); 4691 if (Result == 0) break; // Cannot compute! 4692 4693 // Evaluate the condition for this iteration. 4694 Result = ConstantExpr::getICmp(predicate, Result, RHS); 4695 if (!isa<ConstantInt>(Result)) break; // Couldn't decide for sure 4696 if (cast<ConstantInt>(Result)->getValue().isMinValue()) { 4697#if 0 4698 dbgs() << "\n***\n*** Computed loop count " << *ItCst 4699 << "\n*** From global " << *GV << "*** BB: " << *L->getHeader() 4700 << "***\n"; 4701#endif 4702 ++NumArrayLenItCounts; 4703 return getConstant(ItCst); // Found terminating iteration! 4704 } 4705 } 4706 return getCouldNotCompute(); 4707} 4708 4709 4710/// CanConstantFold - Return true if we can constant fold an instruction of the 4711/// specified type, assuming that all operands were constants. 4712static bool CanConstantFold(const Instruction *I) { 4713 if (isa<BinaryOperator>(I) || isa<CmpInst>(I) || 4714 isa<SelectInst>(I) || isa<CastInst>(I) || isa<GetElementPtrInst>(I) || 4715 isa<LoadInst>(I)) 4716 return true; 4717 4718 if (const CallInst *CI = dyn_cast<CallInst>(I)) 4719 if (const Function *F = CI->getCalledFunction()) 4720 return canConstantFoldCallTo(F); 4721 return false; 4722} 4723 4724/// Determine whether this instruction can constant evolve within this loop 4725/// assuming its operands can all constant evolve. 4726static bool canConstantEvolve(Instruction *I, const Loop *L) { 4727 // An instruction outside of the loop can't be derived from a loop PHI. 4728 if (!L->contains(I)) return false; 4729 4730 if (isa<PHINode>(I)) { 4731 if (L->getHeader() == I->getParent()) 4732 return true; 4733 else 4734 // We don't currently keep track of the control flow needed to evaluate 4735 // PHIs, so we cannot handle PHIs inside of loops. 4736 return false; 4737 } 4738 4739 // If we won't be able to constant fold this expression even if the operands 4740 // are constants, bail early. 4741 return CanConstantFold(I); 4742} 4743 4744/// getConstantEvolvingPHIOperands - Implement getConstantEvolvingPHI by 4745/// recursing through each instruction operand until reaching a loop header phi. 4746static PHINode * 4747getConstantEvolvingPHIOperands(Instruction *UseInst, const Loop *L, 4748 DenseMap<Instruction *, PHINode *> &PHIMap) { 4749 4750 // Otherwise, we can evaluate this instruction if all of its operands are 4751 // constant or derived from a PHI node themselves. 4752 PHINode *PHI = 0; 4753 for (Instruction::op_iterator OpI = UseInst->op_begin(), 4754 OpE = UseInst->op_end(); OpI != OpE; ++OpI) { 4755 4756 if (isa<Constant>(*OpI)) continue; 4757 4758 Instruction *OpInst = dyn_cast<Instruction>(*OpI); 4759 if (!OpInst || !canConstantEvolve(OpInst, L)) return 0; 4760 4761 PHINode *P = dyn_cast<PHINode>(OpInst); 4762 if (!P) 4763 // If this operand is already visited, reuse the prior result. 4764 // We may have P != PHI if this is the deepest point at which the 4765 // inconsistent paths meet. 4766 P = PHIMap.lookup(OpInst); 4767 if (!P) { 4768 // Recurse and memoize the results, whether a phi is found or not. 4769 // This recursive call invalidates pointers into PHIMap. 4770 P = getConstantEvolvingPHIOperands(OpInst, L, PHIMap); 4771 PHIMap[OpInst] = P; 4772 } 4773 if (P == 0) return 0; // Not evolving from PHI 4774 if (PHI && PHI != P) return 0; // Evolving from multiple different PHIs. 4775 PHI = P; 4776 } 4777 // This is a expression evolving from a constant PHI! 4778 return PHI; 4779} 4780 4781/// getConstantEvolvingPHI - Given an LLVM value and a loop, return a PHI node 4782/// in the loop that V is derived from. We allow arbitrary operations along the 4783/// way, but the operands of an operation must either be constants or a value 4784/// derived from a constant PHI. If this expression does not fit with these 4785/// constraints, return null. 4786static PHINode *getConstantEvolvingPHI(Value *V, const Loop *L) { 4787 Instruction *I = dyn_cast<Instruction>(V); 4788 if (I == 0 || !canConstantEvolve(I, L)) return 0; 4789 4790 if (PHINode *PN = dyn_cast<PHINode>(I)) { 4791 return PN; 4792 } 4793 4794 // Record non-constant instructions contained by the loop. 4795 DenseMap<Instruction *, PHINode *> PHIMap; 4796 return getConstantEvolvingPHIOperands(I, L, PHIMap); 4797} 4798 4799/// EvaluateExpression - Given an expression that passes the 4800/// getConstantEvolvingPHI predicate, evaluate its value assuming the PHI node 4801/// in the loop has the value PHIVal. If we can't fold this expression for some 4802/// reason, return null. 4803static Constant *EvaluateExpression(Value *V, const Loop *L, 4804 DenseMap<Instruction *, Constant *> &Vals, 4805 const DataLayout *TD, 4806 const TargetLibraryInfo *TLI) { 4807 // Convenient constant check, but redundant for recursive calls. 4808 if (Constant *C = dyn_cast<Constant>(V)) return C; 4809 Instruction *I = dyn_cast<Instruction>(V); 4810 if (!I) return 0; 4811 4812 if (Constant *C = Vals.lookup(I)) return C; 4813 4814 // An instruction inside the loop depends on a value outside the loop that we 4815 // weren't given a mapping for, or a value such as a call inside the loop. 4816 if (!canConstantEvolve(I, L)) return 0; 4817 4818 // An unmapped PHI can be due to a branch or another loop inside this loop, 4819 // or due to this not being the initial iteration through a loop where we 4820 // couldn't compute the evolution of this particular PHI last time. 4821 if (isa<PHINode>(I)) return 0; 4822 4823 std::vector<Constant*> Operands(I->getNumOperands()); 4824 4825 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 4826 Instruction *Operand = dyn_cast<Instruction>(I->getOperand(i)); 4827 if (!Operand) { 4828 Operands[i] = dyn_cast<Constant>(I->getOperand(i)); 4829 if (!Operands[i]) return 0; 4830 continue; 4831 } 4832 Constant *C = EvaluateExpression(Operand, L, Vals, TD, TLI); 4833 Vals[Operand] = C; 4834 if (!C) return 0; 4835 Operands[i] = C; 4836 } 4837 4838 if (CmpInst *CI = dyn_cast<CmpInst>(I)) 4839 return ConstantFoldCompareInstOperands(CI->getPredicate(), Operands[0], 4840 Operands[1], TD, TLI); 4841 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 4842 if (!LI->isVolatile()) 4843 return ConstantFoldLoadFromConstPtr(Operands[0], TD); 4844 } 4845 return ConstantFoldInstOperands(I->getOpcode(), I->getType(), Operands, TD, 4846 TLI); 4847} 4848 4849/// getConstantEvolutionLoopExitValue - If we know that the specified Phi is 4850/// in the header of its containing loop, we know the loop executes a 4851/// constant number of times, and the PHI node is just a recurrence 4852/// involving constants, fold it. 4853Constant * 4854ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN, 4855 const APInt &BEs, 4856 const Loop *L) { 4857 DenseMap<PHINode*, Constant*>::const_iterator I = 4858 ConstantEvolutionLoopExitValue.find(PN); 4859 if (I != ConstantEvolutionLoopExitValue.end()) 4860 return I->second; 4861 4862 if (BEs.ugt(MaxBruteForceIterations)) 4863 return ConstantEvolutionLoopExitValue[PN] = 0; // Not going to evaluate it. 4864 4865 Constant *&RetVal = ConstantEvolutionLoopExitValue[PN]; 4866 4867 DenseMap<Instruction *, Constant *> CurrentIterVals; 4868 BasicBlock *Header = L->getHeader(); 4869 assert(PN->getParent() == Header && "Can't evaluate PHI not in loop header!"); 4870 4871 // Since the loop is canonicalized, the PHI node must have two entries. One 4872 // entry must be a constant (coming in from outside of the loop), and the 4873 // second must be derived from the same PHI. 4874 bool SecondIsBackedge = L->contains(PN->getIncomingBlock(1)); 4875 PHINode *PHI = 0; 4876 for (BasicBlock::iterator I = Header->begin(); 4877 (PHI = dyn_cast<PHINode>(I)); ++I) { 4878 Constant *StartCST = 4879 dyn_cast<Constant>(PHI->getIncomingValue(!SecondIsBackedge)); 4880 if (StartCST == 0) continue; 4881 CurrentIterVals[PHI] = StartCST; 4882 } 4883 if (!CurrentIterVals.count(PN)) 4884 return RetVal = 0; 4885 4886 Value *BEValue = PN->getIncomingValue(SecondIsBackedge); 4887 4888 // Execute the loop symbolically to determine the exit value. 4889 if (BEs.getActiveBits() >= 32) 4890 return RetVal = 0; // More than 2^32-1 iterations?? Not doing it! 4891 4892 unsigned NumIterations = BEs.getZExtValue(); // must be in range 4893 unsigned IterationNum = 0; 4894 for (; ; ++IterationNum) { 4895 if (IterationNum == NumIterations) 4896 return RetVal = CurrentIterVals[PN]; // Got exit value! 4897 4898 // Compute the value of the PHIs for the next iteration. 4899 // EvaluateExpression adds non-phi values to the CurrentIterVals map. 4900 DenseMap<Instruction *, Constant *> NextIterVals; 4901 Constant *NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD, 4902 TLI); 4903 if (NextPHI == 0) 4904 return 0; // Couldn't evaluate! 4905 NextIterVals[PN] = NextPHI; 4906 4907 bool StoppedEvolving = NextPHI == CurrentIterVals[PN]; 4908 4909 // Also evaluate the other PHI nodes. However, we don't get to stop if we 4910 // cease to be able to evaluate one of them or if they stop evolving, 4911 // because that doesn't necessarily prevent us from computing PN. 4912 SmallVector<std::pair<PHINode *, Constant *>, 8> PHIsToCompute; 4913 for (DenseMap<Instruction *, Constant *>::const_iterator 4914 I = CurrentIterVals.begin(), E = CurrentIterVals.end(); I != E; ++I){ 4915 PHINode *PHI = dyn_cast<PHINode>(I->first); 4916 if (!PHI || PHI == PN || PHI->getParent() != Header) continue; 4917 PHIsToCompute.push_back(std::make_pair(PHI, I->second)); 4918 } 4919 // We use two distinct loops because EvaluateExpression may invalidate any 4920 // iterators into CurrentIterVals. 4921 for (SmallVectorImpl<std::pair<PHINode *, Constant*> >::const_iterator 4922 I = PHIsToCompute.begin(), E = PHIsToCompute.end(); I != E; ++I) { 4923 PHINode *PHI = I->first; 4924 Constant *&NextPHI = NextIterVals[PHI]; 4925 if (!NextPHI) { // Not already computed. 4926 Value *BEValue = PHI->getIncomingValue(SecondIsBackedge); 4927 NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD, TLI); 4928 } 4929 if (NextPHI != I->second) 4930 StoppedEvolving = false; 4931 } 4932 4933 // If all entries in CurrentIterVals == NextIterVals then we can stop 4934 // iterating, the loop can't continue to change. 4935 if (StoppedEvolving) 4936 return RetVal = CurrentIterVals[PN]; 4937 4938 CurrentIterVals.swap(NextIterVals); 4939 } 4940} 4941 4942/// ComputeExitCountExhaustively - If the loop is known to execute a 4943/// constant number of times (the condition evolves only from constants), 4944/// try to evaluate a few iterations of the loop until we get the exit 4945/// condition gets a value of ExitWhen (true or false). If we cannot 4946/// evaluate the trip count of the loop, return getCouldNotCompute(). 4947const SCEV *ScalarEvolution::ComputeExitCountExhaustively(const Loop *L, 4948 Value *Cond, 4949 bool ExitWhen) { 4950 PHINode *PN = getConstantEvolvingPHI(Cond, L); 4951 if (PN == 0) return getCouldNotCompute(); 4952 4953 // If the loop is canonicalized, the PHI will have exactly two entries. 4954 // That's the only form we support here. 4955 if (PN->getNumIncomingValues() != 2) return getCouldNotCompute(); 4956 4957 DenseMap<Instruction *, Constant *> CurrentIterVals; 4958 BasicBlock *Header = L->getHeader(); 4959 assert(PN->getParent() == Header && "Can't evaluate PHI not in loop header!"); 4960 4961 // One entry must be a constant (coming in from outside of the loop), and the 4962 // second must be derived from the same PHI. 4963 bool SecondIsBackedge = L->contains(PN->getIncomingBlock(1)); 4964 PHINode *PHI = 0; 4965 for (BasicBlock::iterator I = Header->begin(); 4966 (PHI = dyn_cast<PHINode>(I)); ++I) { 4967 Constant *StartCST = 4968 dyn_cast<Constant>(PHI->getIncomingValue(!SecondIsBackedge)); 4969 if (StartCST == 0) continue; 4970 CurrentIterVals[PHI] = StartCST; 4971 } 4972 if (!CurrentIterVals.count(PN)) 4973 return getCouldNotCompute(); 4974 4975 // Okay, we find a PHI node that defines the trip count of this loop. Execute 4976 // the loop symbolically to determine when the condition gets a value of 4977 // "ExitWhen". 4978 4979 unsigned MaxIterations = MaxBruteForceIterations; // Limit analysis. 4980 for (unsigned IterationNum = 0; IterationNum != MaxIterations;++IterationNum){ 4981 ConstantInt *CondVal = 4982 dyn_cast_or_null<ConstantInt>(EvaluateExpression(Cond, L, CurrentIterVals, 4983 TD, TLI)); 4984 4985 // Couldn't symbolically evaluate. 4986 if (!CondVal) return getCouldNotCompute(); 4987 4988 if (CondVal->getValue() == uint64_t(ExitWhen)) { 4989 ++NumBruteForceTripCountsComputed; 4990 return getConstant(Type::getInt32Ty(getContext()), IterationNum); 4991 } 4992 4993 // Update all the PHI nodes for the next iteration. 4994 DenseMap<Instruction *, Constant *> NextIterVals; 4995 4996 // Create a list of which PHIs we need to compute. We want to do this before 4997 // calling EvaluateExpression on them because that may invalidate iterators 4998 // into CurrentIterVals. 4999 SmallVector<PHINode *, 8> PHIsToCompute; 5000 for (DenseMap<Instruction *, Constant *>::const_iterator 5001 I = CurrentIterVals.begin(), E = CurrentIterVals.end(); I != E; ++I){ 5002 PHINode *PHI = dyn_cast<PHINode>(I->first); 5003 if (!PHI || PHI->getParent() != Header) continue; 5004 PHIsToCompute.push_back(PHI); 5005 } 5006 for (SmallVectorImpl<PHINode *>::const_iterator I = PHIsToCompute.begin(), 5007 E = PHIsToCompute.end(); I != E; ++I) { 5008 PHINode *PHI = *I; 5009 Constant *&NextPHI = NextIterVals[PHI]; 5010 if (NextPHI) continue; // Already computed! 5011 5012 Value *BEValue = PHI->getIncomingValue(SecondIsBackedge); 5013 NextPHI = EvaluateExpression(BEValue, L, CurrentIterVals, TD, TLI); 5014 } 5015 CurrentIterVals.swap(NextIterVals); 5016 } 5017 5018 // Too many iterations were needed to evaluate. 5019 return getCouldNotCompute(); 5020} 5021 5022/// getSCEVAtScope - Return a SCEV expression for the specified value 5023/// at the specified scope in the program. The L value specifies a loop 5024/// nest to evaluate the expression at, where null is the top-level or a 5025/// specified loop is immediately inside of the loop. 5026/// 5027/// This method can be used to compute the exit value for a variable defined 5028/// in a loop by querying what the value will hold in the parent loop. 5029/// 5030/// In the case that a relevant loop exit value cannot be computed, the 5031/// original value V is returned. 5032const SCEV *ScalarEvolution::getSCEVAtScope(const SCEV *V, const Loop *L) { 5033 // Check to see if we've folded this expression at this loop before. 5034 std::map<const Loop *, const SCEV *> &Values = ValuesAtScopes[V]; 5035 std::pair<std::map<const Loop *, const SCEV *>::iterator, bool> Pair = 5036 Values.insert(std::make_pair(L, static_cast<const SCEV *>(0))); 5037 if (!Pair.second) 5038 return Pair.first->second ? Pair.first->second : V; 5039 5040 // Otherwise compute it. 5041 const SCEV *C = computeSCEVAtScope(V, L); 5042 ValuesAtScopes[V][L] = C; 5043 return C; 5044} 5045 5046/// This builds up a Constant using the ConstantExpr interface. That way, we 5047/// will return Constants for objects which aren't represented by a 5048/// SCEVConstant, because SCEVConstant is restricted to ConstantInt. 5049/// Returns NULL if the SCEV isn't representable as a Constant. 5050static Constant *BuildConstantFromSCEV(const SCEV *V) { 5051 switch (V->getSCEVType()) { 5052 default: // TODO: smax, umax. 5053 case scCouldNotCompute: 5054 case scAddRecExpr: 5055 break; 5056 case scConstant: 5057 return cast<SCEVConstant>(V)->getValue(); 5058 case scUnknown: 5059 return dyn_cast<Constant>(cast<SCEVUnknown>(V)->getValue()); 5060 case scSignExtend: { 5061 const SCEVSignExtendExpr *SS = cast<SCEVSignExtendExpr>(V); 5062 if (Constant *CastOp = BuildConstantFromSCEV(SS->getOperand())) 5063 return ConstantExpr::getSExt(CastOp, SS->getType()); 5064 break; 5065 } 5066 case scZeroExtend: { 5067 const SCEVZeroExtendExpr *SZ = cast<SCEVZeroExtendExpr>(V); 5068 if (Constant *CastOp = BuildConstantFromSCEV(SZ->getOperand())) 5069 return ConstantExpr::getZExt(CastOp, SZ->getType()); 5070 break; 5071 } 5072 case scTruncate: { 5073 const SCEVTruncateExpr *ST = cast<SCEVTruncateExpr>(V); 5074 if (Constant *CastOp = BuildConstantFromSCEV(ST->getOperand())) 5075 return ConstantExpr::getTrunc(CastOp, ST->getType()); 5076 break; 5077 } 5078 case scAddExpr: { 5079 const SCEVAddExpr *SA = cast<SCEVAddExpr>(V); 5080 if (Constant *C = BuildConstantFromSCEV(SA->getOperand(0))) { 5081 if (C->getType()->isPointerTy()) 5082 C = ConstantExpr::getBitCast(C, Type::getInt8PtrTy(C->getContext())); 5083 for (unsigned i = 1, e = SA->getNumOperands(); i != e; ++i) { 5084 Constant *C2 = BuildConstantFromSCEV(SA->getOperand(i)); 5085 if (!C2) return 0; 5086 5087 // First pointer! 5088 if (!C->getType()->isPointerTy() && C2->getType()->isPointerTy()) { 5089 std::swap(C, C2); 5090 // The offsets have been converted to bytes. We can add bytes to an 5091 // i8* by GEP with the byte count in the first index. 5092 C = ConstantExpr::getBitCast(C,Type::getInt8PtrTy(C->getContext())); 5093 } 5094 5095 // Don't bother trying to sum two pointers. We probably can't 5096 // statically compute a load that results from it anyway. 5097 if (C2->getType()->isPointerTy()) 5098 return 0; 5099 5100 if (C->getType()->isPointerTy()) { 5101 if (cast<PointerType>(C->getType())->getElementType()->isStructTy()) 5102 C2 = ConstantExpr::getIntegerCast( 5103 C2, Type::getInt32Ty(C->getContext()), true); 5104 C = ConstantExpr::getGetElementPtr(C, C2); 5105 } else 5106 C = ConstantExpr::getAdd(C, C2); 5107 } 5108 return C; 5109 } 5110 break; 5111 } 5112 case scMulExpr: { 5113 const SCEVMulExpr *SM = cast<SCEVMulExpr>(V); 5114 if (Constant *C = BuildConstantFromSCEV(SM->getOperand(0))) { 5115 // Don't bother with pointers at all. 5116 if (C->getType()->isPointerTy()) return 0; 5117 for (unsigned i = 1, e = SM->getNumOperands(); i != e; ++i) { 5118 Constant *C2 = BuildConstantFromSCEV(SM->getOperand(i)); 5119 if (!C2 || C2->getType()->isPointerTy()) return 0; 5120 C = ConstantExpr::getMul(C, C2); 5121 } 5122 return C; 5123 } 5124 break; 5125 } 5126 case scUDivExpr: { 5127 const SCEVUDivExpr *SU = cast<SCEVUDivExpr>(V); 5128 if (Constant *LHS = BuildConstantFromSCEV(SU->getLHS())) 5129 if (Constant *RHS = BuildConstantFromSCEV(SU->getRHS())) 5130 if (LHS->getType() == RHS->getType()) 5131 return ConstantExpr::getUDiv(LHS, RHS); 5132 break; 5133 } 5134 } 5135 return 0; 5136} 5137 5138const SCEV *ScalarEvolution::computeSCEVAtScope(const SCEV *V, const Loop *L) { 5139 if (isa<SCEVConstant>(V)) return V; 5140 5141 // If this instruction is evolved from a constant-evolving PHI, compute the 5142 // exit value from the loop without using SCEVs. 5143 if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V)) { 5144 if (Instruction *I = dyn_cast<Instruction>(SU->getValue())) { 5145 const Loop *LI = (*this->LI)[I->getParent()]; 5146 if (LI && LI->getParentLoop() == L) // Looking for loop exit value. 5147 if (PHINode *PN = dyn_cast<PHINode>(I)) 5148 if (PN->getParent() == LI->getHeader()) { 5149 // Okay, there is no closed form solution for the PHI node. Check 5150 // to see if the loop that contains it has a known backedge-taken 5151 // count. If so, we may be able to force computation of the exit 5152 // value. 5153 const SCEV *BackedgeTakenCount = getBackedgeTakenCount(LI); 5154 if (const SCEVConstant *BTCC = 5155 dyn_cast<SCEVConstant>(BackedgeTakenCount)) { 5156 // Okay, we know how many times the containing loop executes. If 5157 // this is a constant evolving PHI node, get the final value at 5158 // the specified iteration number. 5159 Constant *RV = getConstantEvolutionLoopExitValue(PN, 5160 BTCC->getValue()->getValue(), 5161 LI); 5162 if (RV) return getSCEV(RV); 5163 } 5164 } 5165 5166 // Okay, this is an expression that we cannot symbolically evaluate 5167 // into a SCEV. Check to see if it's possible to symbolically evaluate 5168 // the arguments into constants, and if so, try to constant propagate the 5169 // result. This is particularly useful for computing loop exit values. 5170 if (CanConstantFold(I)) { 5171 SmallVector<Constant *, 4> Operands; 5172 bool MadeImprovement = false; 5173 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { 5174 Value *Op = I->getOperand(i); 5175 if (Constant *C = dyn_cast<Constant>(Op)) { 5176 Operands.push_back(C); 5177 continue; 5178 } 5179 5180 // If any of the operands is non-constant and if they are 5181 // non-integer and non-pointer, don't even try to analyze them 5182 // with scev techniques. 5183 if (!isSCEVable(Op->getType())) 5184 return V; 5185 5186 const SCEV *OrigV = getSCEV(Op); 5187 const SCEV *OpV = getSCEVAtScope(OrigV, L); 5188 MadeImprovement |= OrigV != OpV; 5189 5190 Constant *C = BuildConstantFromSCEV(OpV); 5191 if (!C) return V; 5192 if (C->getType() != Op->getType()) 5193 C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false, 5194 Op->getType(), 5195 false), 5196 C, Op->getType()); 5197 Operands.push_back(C); 5198 } 5199 5200 // Check to see if getSCEVAtScope actually made an improvement. 5201 if (MadeImprovement) { 5202 Constant *C = 0; 5203 if (const CmpInst *CI = dyn_cast<CmpInst>(I)) 5204 C = ConstantFoldCompareInstOperands(CI->getPredicate(), 5205 Operands[0], Operands[1], TD, 5206 TLI); 5207 else if (const LoadInst *LI = dyn_cast<LoadInst>(I)) { 5208 if (!LI->isVolatile()) 5209 C = ConstantFoldLoadFromConstPtr(Operands[0], TD); 5210 } else 5211 C = ConstantFoldInstOperands(I->getOpcode(), I->getType(), 5212 Operands, TD, TLI); 5213 if (!C) return V; 5214 return getSCEV(C); 5215 } 5216 } 5217 } 5218 5219 // This is some other type of SCEVUnknown, just return it. 5220 return V; 5221 } 5222 5223 if (const SCEVCommutativeExpr *Comm = dyn_cast<SCEVCommutativeExpr>(V)) { 5224 // Avoid performing the look-up in the common case where the specified 5225 // expression has no loop-variant portions. 5226 for (unsigned i = 0, e = Comm->getNumOperands(); i != e; ++i) { 5227 const SCEV *OpAtScope = getSCEVAtScope(Comm->getOperand(i), L); 5228 if (OpAtScope != Comm->getOperand(i)) { 5229 // Okay, at least one of these operands is loop variant but might be 5230 // foldable. Build a new instance of the folded commutative expression. 5231 SmallVector<const SCEV *, 8> NewOps(Comm->op_begin(), 5232 Comm->op_begin()+i); 5233 NewOps.push_back(OpAtScope); 5234 5235 for (++i; i != e; ++i) { 5236 OpAtScope = getSCEVAtScope(Comm->getOperand(i), L); 5237 NewOps.push_back(OpAtScope); 5238 } 5239 if (isa<SCEVAddExpr>(Comm)) 5240 return getAddExpr(NewOps); 5241 if (isa<SCEVMulExpr>(Comm)) 5242 return getMulExpr(NewOps); 5243 if (isa<SCEVSMaxExpr>(Comm)) 5244 return getSMaxExpr(NewOps); 5245 if (isa<SCEVUMaxExpr>(Comm)) 5246 return getUMaxExpr(NewOps); 5247 llvm_unreachable("Unknown commutative SCEV type!"); 5248 } 5249 } 5250 // If we got here, all operands are loop invariant. 5251 return Comm; 5252 } 5253 5254 if (const SCEVUDivExpr *Div = dyn_cast<SCEVUDivExpr>(V)) { 5255 const SCEV *LHS = getSCEVAtScope(Div->getLHS(), L); 5256 const SCEV *RHS = getSCEVAtScope(Div->getRHS(), L); 5257 if (LHS == Div->getLHS() && RHS == Div->getRHS()) 5258 return Div; // must be loop invariant 5259 return getUDivExpr(LHS, RHS); 5260 } 5261 5262 // If this is a loop recurrence for a loop that does not contain L, then we 5263 // are dealing with the final value computed by the loop. 5264 if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(V)) { 5265 // First, attempt to evaluate each operand. 5266 // Avoid performing the look-up in the common case where the specified 5267 // expression has no loop-variant portions. 5268 for (unsigned i = 0, e = AddRec->getNumOperands(); i != e; ++i) { 5269 const SCEV *OpAtScope = getSCEVAtScope(AddRec->getOperand(i), L); 5270 if (OpAtScope == AddRec->getOperand(i)) 5271 continue; 5272 5273 // Okay, at least one of these operands is loop variant but might be 5274 // foldable. Build a new instance of the folded commutative expression. 5275 SmallVector<const SCEV *, 8> NewOps(AddRec->op_begin(), 5276 AddRec->op_begin()+i); 5277 NewOps.push_back(OpAtScope); 5278 for (++i; i != e; ++i) 5279 NewOps.push_back(getSCEVAtScope(AddRec->getOperand(i), L)); 5280 5281 const SCEV *FoldedRec = 5282 getAddRecExpr(NewOps, AddRec->getLoop(), 5283 AddRec->getNoWrapFlags(SCEV::FlagNW)); 5284 AddRec = dyn_cast<SCEVAddRecExpr>(FoldedRec); 5285 // The addrec may be folded to a nonrecurrence, for example, if the 5286 // induction variable is multiplied by zero after constant folding. Go 5287 // ahead and return the folded value. 5288 if (!AddRec) 5289 return FoldedRec; 5290 break; 5291 } 5292 5293 // If the scope is outside the addrec's loop, evaluate it by using the 5294 // loop exit value of the addrec. 5295 if (!AddRec->getLoop()->contains(L)) { 5296 // To evaluate this recurrence, we need to know how many times the AddRec 5297 // loop iterates. Compute this now. 5298 const SCEV *BackedgeTakenCount = getBackedgeTakenCount(AddRec->getLoop()); 5299 if (BackedgeTakenCount == getCouldNotCompute()) return AddRec; 5300 5301 // Then, evaluate the AddRec. 5302 return AddRec->evaluateAtIteration(BackedgeTakenCount, *this); 5303 } 5304 5305 return AddRec; 5306 } 5307 5308 if (const SCEVZeroExtendExpr *Cast = dyn_cast<SCEVZeroExtendExpr>(V)) { 5309 const SCEV *Op = getSCEVAtScope(Cast->getOperand(), L); 5310 if (Op == Cast->getOperand()) 5311 return Cast; // must be loop invariant 5312 return getZeroExtendExpr(Op, Cast->getType()); 5313 } 5314 5315 if (const SCEVSignExtendExpr *Cast = dyn_cast<SCEVSignExtendExpr>(V)) { 5316 const SCEV *Op = getSCEVAtScope(Cast->getOperand(), L); 5317 if (Op == Cast->getOperand()) 5318 return Cast; // must be loop invariant 5319 return getSignExtendExpr(Op, Cast->getType()); 5320 } 5321 5322 if (const SCEVTruncateExpr *Cast = dyn_cast<SCEVTruncateExpr>(V)) { 5323 const SCEV *Op = getSCEVAtScope(Cast->getOperand(), L); 5324 if (Op == Cast->getOperand()) 5325 return Cast; // must be loop invariant 5326 return getTruncateExpr(Op, Cast->getType()); 5327 } 5328 5329 llvm_unreachable("Unknown SCEV type!"); 5330} 5331 5332/// getSCEVAtScope - This is a convenience function which does 5333/// getSCEVAtScope(getSCEV(V), L). 5334const SCEV *ScalarEvolution::getSCEVAtScope(Value *V, const Loop *L) { 5335 return getSCEVAtScope(getSCEV(V), L); 5336} 5337 5338/// SolveLinEquationWithOverflow - Finds the minimum unsigned root of the 5339/// following equation: 5340/// 5341/// A * X = B (mod N) 5342/// 5343/// where N = 2^BW and BW is the common bit width of A and B. The signedness of 5344/// A and B isn't important. 5345/// 5346/// If the equation does not have a solution, SCEVCouldNotCompute is returned. 5347static const SCEV *SolveLinEquationWithOverflow(const APInt &A, const APInt &B, 5348 ScalarEvolution &SE) { 5349 uint32_t BW = A.getBitWidth(); 5350 assert(BW == B.getBitWidth() && "Bit widths must be the same."); 5351 assert(A != 0 && "A must be non-zero."); 5352 5353 // 1. D = gcd(A, N) 5354 // 5355 // The gcd of A and N may have only one prime factor: 2. The number of 5356 // trailing zeros in A is its multiplicity 5357 uint32_t Mult2 = A.countTrailingZeros(); 5358 // D = 2^Mult2 5359 5360 // 2. Check if B is divisible by D. 5361 // 5362 // B is divisible by D if and only if the multiplicity of prime factor 2 for B 5363 // is not less than multiplicity of this prime factor for D. 5364 if (B.countTrailingZeros() < Mult2) 5365 return SE.getCouldNotCompute(); 5366 5367 // 3. Compute I: the multiplicative inverse of (A / D) in arithmetic 5368 // modulo (N / D). 5369 // 5370 // (N / D) may need BW+1 bits in its representation. Hence, we'll use this 5371 // bit width during computations. 5372 APInt AD = A.lshr(Mult2).zext(BW + 1); // AD = A / D 5373 APInt Mod(BW + 1, 0); 5374 Mod.setBit(BW - Mult2); // Mod = N / D 5375 APInt I = AD.multiplicativeInverse(Mod); 5376 5377 // 4. Compute the minimum unsigned root of the equation: 5378 // I * (B / D) mod (N / D) 5379 APInt Result = (I * B.lshr(Mult2).zext(BW + 1)).urem(Mod); 5380 5381 // The result is guaranteed to be less than 2^BW so we may truncate it to BW 5382 // bits. 5383 return SE.getConstant(Result.trunc(BW)); 5384} 5385 5386/// SolveQuadraticEquation - Find the roots of the quadratic equation for the 5387/// given quadratic chrec {L,+,M,+,N}. This returns either the two roots (which 5388/// might be the same) or two SCEVCouldNotCompute objects. 5389/// 5390static std::pair<const SCEV *,const SCEV *> 5391SolveQuadraticEquation(const SCEVAddRecExpr *AddRec, ScalarEvolution &SE) { 5392 assert(AddRec->getNumOperands() == 3 && "This is not a quadratic chrec!"); 5393 const SCEVConstant *LC = dyn_cast<SCEVConstant>(AddRec->getOperand(0)); 5394 const SCEVConstant *MC = dyn_cast<SCEVConstant>(AddRec->getOperand(1)); 5395 const SCEVConstant *NC = dyn_cast<SCEVConstant>(AddRec->getOperand(2)); 5396 5397 // We currently can only solve this if the coefficients are constants. 5398 if (!LC || !MC || !NC) { 5399 const SCEV *CNC = SE.getCouldNotCompute(); 5400 return std::make_pair(CNC, CNC); 5401 } 5402 5403 uint32_t BitWidth = LC->getValue()->getValue().getBitWidth(); 5404 const APInt &L = LC->getValue()->getValue(); 5405 const APInt &M = MC->getValue()->getValue(); 5406 const APInt &N = NC->getValue()->getValue(); 5407 APInt Two(BitWidth, 2); 5408 APInt Four(BitWidth, 4); 5409 5410 { 5411 using namespace APIntOps; 5412 const APInt& C = L; 5413 // Convert from chrec coefficients to polynomial coefficients AX^2+BX+C 5414 // The B coefficient is M-N/2 5415 APInt B(M); 5416 B -= sdiv(N,Two); 5417 5418 // The A coefficient is N/2 5419 APInt A(N.sdiv(Two)); 5420 5421 // Compute the B^2-4ac term. 5422 APInt SqrtTerm(B); 5423 SqrtTerm *= B; 5424 SqrtTerm -= Four * (A * C); 5425 5426 if (SqrtTerm.isNegative()) { 5427 // The loop is provably infinite. 5428 const SCEV *CNC = SE.getCouldNotCompute(); 5429 return std::make_pair(CNC, CNC); 5430 } 5431 5432 // Compute sqrt(B^2-4ac). This is guaranteed to be the nearest 5433 // integer value or else APInt::sqrt() will assert. 5434 APInt SqrtVal(SqrtTerm.sqrt()); 5435 5436 // Compute the two solutions for the quadratic formula. 5437 // The divisions must be performed as signed divisions. 5438 APInt NegB(-B); 5439 APInt TwoA(A << 1); 5440 if (TwoA.isMinValue()) { 5441 const SCEV *CNC = SE.getCouldNotCompute(); 5442 return std::make_pair(CNC, CNC); 5443 } 5444 5445 LLVMContext &Context = SE.getContext(); 5446 5447 ConstantInt *Solution1 = 5448 ConstantInt::get(Context, (NegB + SqrtVal).sdiv(TwoA)); 5449 ConstantInt *Solution2 = 5450 ConstantInt::get(Context, (NegB - SqrtVal).sdiv(TwoA)); 5451 5452 return std::make_pair(SE.getConstant(Solution1), 5453 SE.getConstant(Solution2)); 5454 } // end APIntOps namespace 5455} 5456 5457/// HowFarToZero - Return the number of times a backedge comparing the specified 5458/// value to zero will execute. If not computable, return CouldNotCompute. 5459/// 5460/// This is only used for loops with a "x != y" exit test. The exit condition is 5461/// now expressed as a single expression, V = x-y. So the exit test is 5462/// effectively V != 0. We know and take advantage of the fact that this 5463/// expression only being used in a comparison by zero context. 5464ScalarEvolution::ExitLimit 5465ScalarEvolution::HowFarToZero(const SCEV *V, const Loop *L, bool IsSubExpr) { 5466 // If the value is a constant 5467 if (const SCEVConstant *C = dyn_cast<SCEVConstant>(V)) { 5468 // If the value is already zero, the branch will execute zero times. 5469 if (C->getValue()->isZero()) return C; 5470 return getCouldNotCompute(); // Otherwise it will loop infinitely. 5471 } 5472 5473 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(V); 5474 if (!AddRec || AddRec->getLoop() != L) 5475 return getCouldNotCompute(); 5476 5477 // If this is a quadratic (3-term) AddRec {L,+,M,+,N}, find the roots of 5478 // the quadratic equation to solve it. 5479 if (AddRec->isQuadratic() && AddRec->getType()->isIntegerTy()) { 5480 std::pair<const SCEV *,const SCEV *> Roots = 5481 SolveQuadraticEquation(AddRec, *this); 5482 const SCEVConstant *R1 = dyn_cast<SCEVConstant>(Roots.first); 5483 const SCEVConstant *R2 = dyn_cast<SCEVConstant>(Roots.second); 5484 if (R1 && R2) { 5485#if 0 5486 dbgs() << "HFTZ: " << *V << " - sol#1: " << *R1 5487 << " sol#2: " << *R2 << "\n"; 5488#endif 5489 // Pick the smallest positive root value. 5490 if (ConstantInt *CB = 5491 dyn_cast<ConstantInt>(ConstantExpr::getICmp(CmpInst::ICMP_ULT, 5492 R1->getValue(), 5493 R2->getValue()))) { 5494 if (CB->getZExtValue() == false) 5495 std::swap(R1, R2); // R1 is the minimum root now. 5496 5497 // We can only use this value if the chrec ends up with an exact zero 5498 // value at this index. When solving for "X*X != 5", for example, we 5499 // should not accept a root of 2. 5500 const SCEV *Val = AddRec->evaluateAtIteration(R1, *this); 5501 if (Val->isZero()) 5502 return R1; // We found a quadratic root! 5503 } 5504 } 5505 return getCouldNotCompute(); 5506 } 5507 5508 // Otherwise we can only handle this if it is affine. 5509 if (!AddRec->isAffine()) 5510 return getCouldNotCompute(); 5511 5512 // If this is an affine expression, the execution count of this branch is 5513 // the minimum unsigned root of the following equation: 5514 // 5515 // Start + Step*N = 0 (mod 2^BW) 5516 // 5517 // equivalent to: 5518 // 5519 // Step*N = -Start (mod 2^BW) 5520 // 5521 // where BW is the common bit width of Start and Step. 5522 5523 // Get the initial value for the loop. 5524 const SCEV *Start = getSCEVAtScope(AddRec->getStart(), L->getParentLoop()); 5525 const SCEV *Step = getSCEVAtScope(AddRec->getOperand(1), L->getParentLoop()); 5526 5527 // For now we handle only constant steps. 5528 // 5529 // TODO: Handle a nonconstant Step given AddRec<NUW>. If the 5530 // AddRec is NUW, then (in an unsigned sense) it cannot be counting up to wrap 5531 // to 0, it must be counting down to equal 0. Consequently, N = Start / -Step. 5532 // We have not yet seen any such cases. 5533 const SCEVConstant *StepC = dyn_cast<SCEVConstant>(Step); 5534 if (StepC == 0 || StepC->getValue()->equalsInt(0)) 5535 return getCouldNotCompute(); 5536 5537 // For positive steps (counting up until unsigned overflow): 5538 // N = -Start/Step (as unsigned) 5539 // For negative steps (counting down to zero): 5540 // N = Start/-Step 5541 // First compute the unsigned distance from zero in the direction of Step. 5542 bool CountDown = StepC->getValue()->getValue().isNegative(); 5543 const SCEV *Distance = CountDown ? Start : getNegativeSCEV(Start); 5544 5545 // Handle unitary steps, which cannot wraparound. 5546 // 1*N = -Start; -1*N = Start (mod 2^BW), so: 5547 // N = Distance (as unsigned) 5548 if (StepC->getValue()->equalsInt(1) || StepC->getValue()->isAllOnesValue()) { 5549 ConstantRange CR = getUnsignedRange(Start); 5550 const SCEV *MaxBECount; 5551 if (!CountDown && CR.getUnsignedMin().isMinValue()) 5552 // When counting up, the worst starting value is 1, not 0. 5553 MaxBECount = CR.getUnsignedMax().isMinValue() 5554 ? getConstant(APInt::getMinValue(CR.getBitWidth())) 5555 : getConstant(APInt::getMaxValue(CR.getBitWidth())); 5556 else 5557 MaxBECount = getConstant(CountDown ? CR.getUnsignedMax() 5558 : -CR.getUnsignedMin()); 5559 return ExitLimit(Distance, MaxBECount); 5560 } 5561 5562 // If the recurrence is known not to wraparound, unsigned divide computes the 5563 // back edge count. (Ideally we would have an "isexact" bit for udiv). We know 5564 // that the value will either become zero (and thus the loop terminates), that 5565 // the loop will terminate through some other exit condition first, or that 5566 // the loop has undefined behavior. This means we can't "miss" the exit 5567 // value, even with nonunit stride. 5568 // 5569 // This is only valid for expressions that directly compute the loop exit. It 5570 // is invalid for subexpressions in which the loop may exit through this 5571 // branch even if this subexpression is false. In that case, the trip count 5572 // computed by this udiv could be smaller than the number of well-defined 5573 // iterations. 5574 if (!IsSubExpr && AddRec->getNoWrapFlags(SCEV::FlagNW)) 5575 return getUDivExpr(Distance, CountDown ? getNegativeSCEV(Step) : Step); 5576 5577 // Then, try to solve the above equation provided that Start is constant. 5578 if (const SCEVConstant *StartC = dyn_cast<SCEVConstant>(Start)) 5579 return SolveLinEquationWithOverflow(StepC->getValue()->getValue(), 5580 -StartC->getValue()->getValue(), 5581 *this); 5582 return getCouldNotCompute(); 5583} 5584 5585/// HowFarToNonZero - Return the number of times a backedge checking the 5586/// specified value for nonzero will execute. If not computable, return 5587/// CouldNotCompute 5588ScalarEvolution::ExitLimit 5589ScalarEvolution::HowFarToNonZero(const SCEV *V, const Loop *L) { 5590 // Loops that look like: while (X == 0) are very strange indeed. We don't 5591 // handle them yet except for the trivial case. This could be expanded in the 5592 // future as needed. 5593 5594 // If the value is a constant, check to see if it is known to be non-zero 5595 // already. If so, the backedge will execute zero times. 5596 if (const SCEVConstant *C = dyn_cast<SCEVConstant>(V)) { 5597 if (!C->getValue()->isNullValue()) 5598 return getConstant(C->getType(), 0); 5599 return getCouldNotCompute(); // Otherwise it will loop infinitely. 5600 } 5601 5602 // We could implement others, but I really doubt anyone writes loops like 5603 // this, and if they did, they would already be constant folded. 5604 return getCouldNotCompute(); 5605} 5606 5607/// getPredecessorWithUniqueSuccessorForBB - Return a predecessor of BB 5608/// (which may not be an immediate predecessor) which has exactly one 5609/// successor from which BB is reachable, or null if no such block is 5610/// found. 5611/// 5612std::pair<BasicBlock *, BasicBlock *> 5613ScalarEvolution::getPredecessorWithUniqueSuccessorForBB(BasicBlock *BB) { 5614 // If the block has a unique predecessor, then there is no path from the 5615 // predecessor to the block that does not go through the direct edge 5616 // from the predecessor to the block. 5617 if (BasicBlock *Pred = BB->getSinglePredecessor()) 5618 return std::make_pair(Pred, BB); 5619 5620 // A loop's header is defined to be a block that dominates the loop. 5621 // If the header has a unique predecessor outside the loop, it must be 5622 // a block that has exactly one successor that can reach the loop. 5623 if (Loop *L = LI->getLoopFor(BB)) 5624 return std::make_pair(L->getLoopPredecessor(), L->getHeader()); 5625 5626 return std::pair<BasicBlock *, BasicBlock *>(); 5627} 5628 5629/// HasSameValue - SCEV structural equivalence is usually sufficient for 5630/// testing whether two expressions are equal, however for the purposes of 5631/// looking for a condition guarding a loop, it can be useful to be a little 5632/// more general, since a front-end may have replicated the controlling 5633/// expression. 5634/// 5635static bool HasSameValue(const SCEV *A, const SCEV *B) { 5636 // Quick check to see if they are the same SCEV. 5637 if (A == B) return true; 5638 5639 // Otherwise, if they're both SCEVUnknown, it's possible that they hold 5640 // two different instructions with the same value. Check for this case. 5641 if (const SCEVUnknown *AU = dyn_cast<SCEVUnknown>(A)) 5642 if (const SCEVUnknown *BU = dyn_cast<SCEVUnknown>(B)) 5643 if (const Instruction *AI = dyn_cast<Instruction>(AU->getValue())) 5644 if (const Instruction *BI = dyn_cast<Instruction>(BU->getValue())) 5645 if (AI->isIdenticalTo(BI) && !AI->mayReadFromMemory()) 5646 return true; 5647 5648 // Otherwise assume they may have a different value. 5649 return false; 5650} 5651 5652/// SimplifyICmpOperands - Simplify LHS and RHS in a comparison with 5653/// predicate Pred. Return true iff any changes were made. 5654/// 5655bool ScalarEvolution::SimplifyICmpOperands(ICmpInst::Predicate &Pred, 5656 const SCEV *&LHS, const SCEV *&RHS, 5657 unsigned Depth) { 5658 bool Changed = false; 5659 5660 // If we hit the max recursion limit bail out. 5661 if (Depth >= 3) 5662 return false; 5663 5664 // Canonicalize a constant to the right side. 5665 if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) { 5666 // Check for both operands constant. 5667 if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) { 5668 if (ConstantExpr::getICmp(Pred, 5669 LHSC->getValue(), 5670 RHSC->getValue())->isNullValue()) 5671 goto trivially_false; 5672 else 5673 goto trivially_true; 5674 } 5675 // Otherwise swap the operands to put the constant on the right. 5676 std::swap(LHS, RHS); 5677 Pred = ICmpInst::getSwappedPredicate(Pred); 5678 Changed = true; 5679 } 5680 5681 // If we're comparing an addrec with a value which is loop-invariant in the 5682 // addrec's loop, put the addrec on the left. Also make a dominance check, 5683 // as both operands could be addrecs loop-invariant in each other's loop. 5684 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(RHS)) { 5685 const Loop *L = AR->getLoop(); 5686 if (isLoopInvariant(LHS, L) && properlyDominates(LHS, L->getHeader())) { 5687 std::swap(LHS, RHS); 5688 Pred = ICmpInst::getSwappedPredicate(Pred); 5689 Changed = true; 5690 } 5691 } 5692 5693 // If there's a constant operand, canonicalize comparisons with boundary 5694 // cases, and canonicalize *-or-equal comparisons to regular comparisons. 5695 if (const SCEVConstant *RC = dyn_cast<SCEVConstant>(RHS)) { 5696 const APInt &RA = RC->getValue()->getValue(); 5697 switch (Pred) { 5698 default: llvm_unreachable("Unexpected ICmpInst::Predicate value!"); 5699 case ICmpInst::ICMP_EQ: 5700 case ICmpInst::ICMP_NE: 5701 // Fold ((-1) * %a) + %b == 0 (equivalent to %b-%a == 0) into %a == %b. 5702 if (!RA) 5703 if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(LHS)) 5704 if (const SCEVMulExpr *ME = dyn_cast<SCEVMulExpr>(AE->getOperand(0))) 5705 if (AE->getNumOperands() == 2 && ME->getNumOperands() == 2 && 5706 ME->getOperand(0)->isAllOnesValue()) { 5707 RHS = AE->getOperand(1); 5708 LHS = ME->getOperand(1); 5709 Changed = true; 5710 } 5711 break; 5712 case ICmpInst::ICMP_UGE: 5713 if ((RA - 1).isMinValue()) { 5714 Pred = ICmpInst::ICMP_NE; 5715 RHS = getConstant(RA - 1); 5716 Changed = true; 5717 break; 5718 } 5719 if (RA.isMaxValue()) { 5720 Pred = ICmpInst::ICMP_EQ; 5721 Changed = true; 5722 break; 5723 } 5724 if (RA.isMinValue()) goto trivially_true; 5725 5726 Pred = ICmpInst::ICMP_UGT; 5727 RHS = getConstant(RA - 1); 5728 Changed = true; 5729 break; 5730 case ICmpInst::ICMP_ULE: 5731 if ((RA + 1).isMaxValue()) { 5732 Pred = ICmpInst::ICMP_NE; 5733 RHS = getConstant(RA + 1); 5734 Changed = true; 5735 break; 5736 } 5737 if (RA.isMinValue()) { 5738 Pred = ICmpInst::ICMP_EQ; 5739 Changed = true; 5740 break; 5741 } 5742 if (RA.isMaxValue()) goto trivially_true; 5743 5744 Pred = ICmpInst::ICMP_ULT; 5745 RHS = getConstant(RA + 1); 5746 Changed = true; 5747 break; 5748 case ICmpInst::ICMP_SGE: 5749 if ((RA - 1).isMinSignedValue()) { 5750 Pred = ICmpInst::ICMP_NE; 5751 RHS = getConstant(RA - 1); 5752 Changed = true; 5753 break; 5754 } 5755 if (RA.isMaxSignedValue()) { 5756 Pred = ICmpInst::ICMP_EQ; 5757 Changed = true; 5758 break; 5759 } 5760 if (RA.isMinSignedValue()) goto trivially_true; 5761 5762 Pred = ICmpInst::ICMP_SGT; 5763 RHS = getConstant(RA - 1); 5764 Changed = true; 5765 break; 5766 case ICmpInst::ICMP_SLE: 5767 if ((RA + 1).isMaxSignedValue()) { 5768 Pred = ICmpInst::ICMP_NE; 5769 RHS = getConstant(RA + 1); 5770 Changed = true; 5771 break; 5772 } 5773 if (RA.isMinSignedValue()) { 5774 Pred = ICmpInst::ICMP_EQ; 5775 Changed = true; 5776 break; 5777 } 5778 if (RA.isMaxSignedValue()) goto trivially_true; 5779 5780 Pred = ICmpInst::ICMP_SLT; 5781 RHS = getConstant(RA + 1); 5782 Changed = true; 5783 break; 5784 case ICmpInst::ICMP_UGT: 5785 if (RA.isMinValue()) { 5786 Pred = ICmpInst::ICMP_NE; 5787 Changed = true; 5788 break; 5789 } 5790 if ((RA + 1).isMaxValue()) { 5791 Pred = ICmpInst::ICMP_EQ; 5792 RHS = getConstant(RA + 1); 5793 Changed = true; 5794 break; 5795 } 5796 if (RA.isMaxValue()) goto trivially_false; 5797 break; 5798 case ICmpInst::ICMP_ULT: 5799 if (RA.isMaxValue()) { 5800 Pred = ICmpInst::ICMP_NE; 5801 Changed = true; 5802 break; 5803 } 5804 if ((RA - 1).isMinValue()) { 5805 Pred = ICmpInst::ICMP_EQ; 5806 RHS = getConstant(RA - 1); 5807 Changed = true; 5808 break; 5809 } 5810 if (RA.isMinValue()) goto trivially_false; 5811 break; 5812 case ICmpInst::ICMP_SGT: 5813 if (RA.isMinSignedValue()) { 5814 Pred = ICmpInst::ICMP_NE; 5815 Changed = true; 5816 break; 5817 } 5818 if ((RA + 1).isMaxSignedValue()) { 5819 Pred = ICmpInst::ICMP_EQ; 5820 RHS = getConstant(RA + 1); 5821 Changed = true; 5822 break; 5823 } 5824 if (RA.isMaxSignedValue()) goto trivially_false; 5825 break; 5826 case ICmpInst::ICMP_SLT: 5827 if (RA.isMaxSignedValue()) { 5828 Pred = ICmpInst::ICMP_NE; 5829 Changed = true; 5830 break; 5831 } 5832 if ((RA - 1).isMinSignedValue()) { 5833 Pred = ICmpInst::ICMP_EQ; 5834 RHS = getConstant(RA - 1); 5835 Changed = true; 5836 break; 5837 } 5838 if (RA.isMinSignedValue()) goto trivially_false; 5839 break; 5840 } 5841 } 5842 5843 // Check for obvious equality. 5844 if (HasSameValue(LHS, RHS)) { 5845 if (ICmpInst::isTrueWhenEqual(Pred)) 5846 goto trivially_true; 5847 if (ICmpInst::isFalseWhenEqual(Pred)) 5848 goto trivially_false; 5849 } 5850 5851 // If possible, canonicalize GE/LE comparisons to GT/LT comparisons, by 5852 // adding or subtracting 1 from one of the operands. 5853 switch (Pred) { 5854 case ICmpInst::ICMP_SLE: 5855 if (!getSignedRange(RHS).getSignedMax().isMaxSignedValue()) { 5856 RHS = getAddExpr(getConstant(RHS->getType(), 1, true), RHS, 5857 SCEV::FlagNSW); 5858 Pred = ICmpInst::ICMP_SLT; 5859 Changed = true; 5860 } else if (!getSignedRange(LHS).getSignedMin().isMinSignedValue()) { 5861 LHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), LHS, 5862 SCEV::FlagNSW); 5863 Pred = ICmpInst::ICMP_SLT; 5864 Changed = true; 5865 } 5866 break; 5867 case ICmpInst::ICMP_SGE: 5868 if (!getSignedRange(RHS).getSignedMin().isMinSignedValue()) { 5869 RHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), RHS, 5870 SCEV::FlagNSW); 5871 Pred = ICmpInst::ICMP_SGT; 5872 Changed = true; 5873 } else if (!getSignedRange(LHS).getSignedMax().isMaxSignedValue()) { 5874 LHS = getAddExpr(getConstant(RHS->getType(), 1, true), LHS, 5875 SCEV::FlagNSW); 5876 Pred = ICmpInst::ICMP_SGT; 5877 Changed = true; 5878 } 5879 break; 5880 case ICmpInst::ICMP_ULE: 5881 if (!getUnsignedRange(RHS).getUnsignedMax().isMaxValue()) { 5882 RHS = getAddExpr(getConstant(RHS->getType(), 1, true), RHS, 5883 SCEV::FlagNUW); 5884 Pred = ICmpInst::ICMP_ULT; 5885 Changed = true; 5886 } else if (!getUnsignedRange(LHS).getUnsignedMin().isMinValue()) { 5887 LHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), LHS, 5888 SCEV::FlagNUW); 5889 Pred = ICmpInst::ICMP_ULT; 5890 Changed = true; 5891 } 5892 break; 5893 case ICmpInst::ICMP_UGE: 5894 if (!getUnsignedRange(RHS).getUnsignedMin().isMinValue()) { 5895 RHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), RHS, 5896 SCEV::FlagNUW); 5897 Pred = ICmpInst::ICMP_UGT; 5898 Changed = true; 5899 } else if (!getUnsignedRange(LHS).getUnsignedMax().isMaxValue()) { 5900 LHS = getAddExpr(getConstant(RHS->getType(), 1, true), LHS, 5901 SCEV::FlagNUW); 5902 Pred = ICmpInst::ICMP_UGT; 5903 Changed = true; 5904 } 5905 break; 5906 default: 5907 break; 5908 } 5909 5910 // TODO: More simplifications are possible here. 5911 5912 // Recursively simplify until we either hit a recursion limit or nothing 5913 // changes. 5914 if (Changed) 5915 return SimplifyICmpOperands(Pred, LHS, RHS, Depth+1); 5916 5917 return Changed; 5918 5919trivially_true: 5920 // Return 0 == 0. 5921 LHS = RHS = getConstant(ConstantInt::getFalse(getContext())); 5922 Pred = ICmpInst::ICMP_EQ; 5923 return true; 5924 5925trivially_false: 5926 // Return 0 != 0. 5927 LHS = RHS = getConstant(ConstantInt::getFalse(getContext())); 5928 Pred = ICmpInst::ICMP_NE; 5929 return true; 5930} 5931 5932bool ScalarEvolution::isKnownNegative(const SCEV *S) { 5933 return getSignedRange(S).getSignedMax().isNegative(); 5934} 5935 5936bool ScalarEvolution::isKnownPositive(const SCEV *S) { 5937 return getSignedRange(S).getSignedMin().isStrictlyPositive(); 5938} 5939 5940bool ScalarEvolution::isKnownNonNegative(const SCEV *S) { 5941 return !getSignedRange(S).getSignedMin().isNegative(); 5942} 5943 5944bool ScalarEvolution::isKnownNonPositive(const SCEV *S) { 5945 return !getSignedRange(S).getSignedMax().isStrictlyPositive(); 5946} 5947 5948bool ScalarEvolution::isKnownNonZero(const SCEV *S) { 5949 return isKnownNegative(S) || isKnownPositive(S); 5950} 5951 5952bool ScalarEvolution::isKnownPredicate(ICmpInst::Predicate Pred, 5953 const SCEV *LHS, const SCEV *RHS) { 5954 // Canonicalize the inputs first. 5955 (void)SimplifyICmpOperands(Pred, LHS, RHS); 5956 5957 // If LHS or RHS is an addrec, check to see if the condition is true in 5958 // every iteration of the loop. 5959 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS)) 5960 if (isLoopEntryGuardedByCond( 5961 AR->getLoop(), Pred, AR->getStart(), RHS) && 5962 isLoopBackedgeGuardedByCond( 5963 AR->getLoop(), Pred, AR->getPostIncExpr(*this), RHS)) 5964 return true; 5965 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(RHS)) 5966 if (isLoopEntryGuardedByCond( 5967 AR->getLoop(), Pred, LHS, AR->getStart()) && 5968 isLoopBackedgeGuardedByCond( 5969 AR->getLoop(), Pred, LHS, AR->getPostIncExpr(*this))) 5970 return true; 5971 5972 // Otherwise see what can be done with known constant ranges. 5973 return isKnownPredicateWithRanges(Pred, LHS, RHS); 5974} 5975 5976bool 5977ScalarEvolution::isKnownPredicateWithRanges(ICmpInst::Predicate Pred, 5978 const SCEV *LHS, const SCEV *RHS) { 5979 if (HasSameValue(LHS, RHS)) 5980 return ICmpInst::isTrueWhenEqual(Pred); 5981 5982 // This code is split out from isKnownPredicate because it is called from 5983 // within isLoopEntryGuardedByCond. 5984 switch (Pred) { 5985 default: 5986 llvm_unreachable("Unexpected ICmpInst::Predicate value!"); 5987 case ICmpInst::ICMP_SGT: 5988 Pred = ICmpInst::ICMP_SLT; 5989 std::swap(LHS, RHS); 5990 case ICmpInst::ICMP_SLT: { 5991 ConstantRange LHSRange = getSignedRange(LHS); 5992 ConstantRange RHSRange = getSignedRange(RHS); 5993 if (LHSRange.getSignedMax().slt(RHSRange.getSignedMin())) 5994 return true; 5995 if (LHSRange.getSignedMin().sge(RHSRange.getSignedMax())) 5996 return false; 5997 break; 5998 } 5999 case ICmpInst::ICMP_SGE: 6000 Pred = ICmpInst::ICMP_SLE; 6001 std::swap(LHS, RHS); 6002 case ICmpInst::ICMP_SLE: { 6003 ConstantRange LHSRange = getSignedRange(LHS); 6004 ConstantRange RHSRange = getSignedRange(RHS); 6005 if (LHSRange.getSignedMax().sle(RHSRange.getSignedMin())) 6006 return true; 6007 if (LHSRange.getSignedMin().sgt(RHSRange.getSignedMax())) 6008 return false; 6009 break; 6010 } 6011 case ICmpInst::ICMP_UGT: 6012 Pred = ICmpInst::ICMP_ULT; 6013 std::swap(LHS, RHS); 6014 case ICmpInst::ICMP_ULT: { 6015 ConstantRange LHSRange = getUnsignedRange(LHS); 6016 ConstantRange RHSRange = getUnsignedRange(RHS); 6017 if (LHSRange.getUnsignedMax().ult(RHSRange.getUnsignedMin())) 6018 return true; 6019 if (LHSRange.getUnsignedMin().uge(RHSRange.getUnsignedMax())) 6020 return false; 6021 break; 6022 } 6023 case ICmpInst::ICMP_UGE: 6024 Pred = ICmpInst::ICMP_ULE; 6025 std::swap(LHS, RHS); 6026 case ICmpInst::ICMP_ULE: { 6027 ConstantRange LHSRange = getUnsignedRange(LHS); 6028 ConstantRange RHSRange = getUnsignedRange(RHS); 6029 if (LHSRange.getUnsignedMax().ule(RHSRange.getUnsignedMin())) 6030 return true; 6031 if (LHSRange.getUnsignedMin().ugt(RHSRange.getUnsignedMax())) 6032 return false; 6033 break; 6034 } 6035 case ICmpInst::ICMP_NE: { 6036 if (getUnsignedRange(LHS).intersectWith(getUnsignedRange(RHS)).isEmptySet()) 6037 return true; 6038 if (getSignedRange(LHS).intersectWith(getSignedRange(RHS)).isEmptySet()) 6039 return true; 6040 6041 const SCEV *Diff = getMinusSCEV(LHS, RHS); 6042 if (isKnownNonZero(Diff)) 6043 return true; 6044 break; 6045 } 6046 case ICmpInst::ICMP_EQ: 6047 // The check at the top of the function catches the case where 6048 // the values are known to be equal. 6049 break; 6050 } 6051 return false; 6052} 6053 6054/// isLoopBackedgeGuardedByCond - Test whether the backedge of the loop is 6055/// protected by a conditional between LHS and RHS. This is used to 6056/// to eliminate casts. 6057bool 6058ScalarEvolution::isLoopBackedgeGuardedByCond(const Loop *L, 6059 ICmpInst::Predicate Pred, 6060 const SCEV *LHS, const SCEV *RHS) { 6061 // Interpret a null as meaning no loop, where there is obviously no guard 6062 // (interprocedural conditions notwithstanding). 6063 if (!L) return true; 6064 6065 BasicBlock *Latch = L->getLoopLatch(); 6066 if (!Latch) 6067 return false; 6068 6069 BranchInst *LoopContinuePredicate = 6070 dyn_cast<BranchInst>(Latch->getTerminator()); 6071 if (!LoopContinuePredicate || 6072 LoopContinuePredicate->isUnconditional()) 6073 return false; 6074 6075 return isImpliedCond(Pred, LHS, RHS, 6076 LoopContinuePredicate->getCondition(), 6077 LoopContinuePredicate->getSuccessor(0) != L->getHeader()); 6078} 6079 6080/// isLoopEntryGuardedByCond - Test whether entry to the loop is protected 6081/// by a conditional between LHS and RHS. This is used to help avoid max 6082/// expressions in loop trip counts, and to eliminate casts. 6083bool 6084ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L, 6085 ICmpInst::Predicate Pred, 6086 const SCEV *LHS, const SCEV *RHS) { 6087 // Interpret a null as meaning no loop, where there is obviously no guard 6088 // (interprocedural conditions notwithstanding). 6089 if (!L) return false; 6090 6091 // Starting at the loop predecessor, climb up the predecessor chain, as long 6092 // as there are predecessors that can be found that have unique successors 6093 // leading to the original header. 6094 for (std::pair<BasicBlock *, BasicBlock *> 6095 Pair(L->getLoopPredecessor(), L->getHeader()); 6096 Pair.first; 6097 Pair = getPredecessorWithUniqueSuccessorForBB(Pair.first)) { 6098 6099 BranchInst *LoopEntryPredicate = 6100 dyn_cast<BranchInst>(Pair.first->getTerminator()); 6101 if (!LoopEntryPredicate || 6102 LoopEntryPredicate->isUnconditional()) 6103 continue; 6104 6105 if (isImpliedCond(Pred, LHS, RHS, 6106 LoopEntryPredicate->getCondition(), 6107 LoopEntryPredicate->getSuccessor(0) != Pair.second)) 6108 return true; 6109 } 6110 6111 return false; 6112} 6113 6114/// RAII wrapper to prevent recursive application of isImpliedCond. 6115/// ScalarEvolution's PendingLoopPredicates set must be empty unless we are 6116/// currently evaluating isImpliedCond. 6117struct MarkPendingLoopPredicate { 6118 Value *Cond; 6119 DenseSet<Value*> &LoopPreds; 6120 bool Pending; 6121 6122 MarkPendingLoopPredicate(Value *C, DenseSet<Value*> &LP) 6123 : Cond(C), LoopPreds(LP) { 6124 Pending = !LoopPreds.insert(Cond).second; 6125 } 6126 ~MarkPendingLoopPredicate() { 6127 if (!Pending) 6128 LoopPreds.erase(Cond); 6129 } 6130}; 6131 6132/// isImpliedCond - Test whether the condition described by Pred, LHS, 6133/// and RHS is true whenever the given Cond value evaluates to true. 6134bool ScalarEvolution::isImpliedCond(ICmpInst::Predicate Pred, 6135 const SCEV *LHS, const SCEV *RHS, 6136 Value *FoundCondValue, 6137 bool Inverse) { 6138 MarkPendingLoopPredicate Mark(FoundCondValue, PendingLoopPredicates); 6139 if (Mark.Pending) 6140 return false; 6141 6142 // Recursively handle And and Or conditions. 6143 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(FoundCondValue)) { 6144 if (BO->getOpcode() == Instruction::And) { 6145 if (!Inverse) 6146 return isImpliedCond(Pred, LHS, RHS, BO->getOperand(0), Inverse) || 6147 isImpliedCond(Pred, LHS, RHS, BO->getOperand(1), Inverse); 6148 } else if (BO->getOpcode() == Instruction::Or) { 6149 if (Inverse) 6150 return isImpliedCond(Pred, LHS, RHS, BO->getOperand(0), Inverse) || 6151 isImpliedCond(Pred, LHS, RHS, BO->getOperand(1), Inverse); 6152 } 6153 } 6154 6155 ICmpInst *ICI = dyn_cast<ICmpInst>(FoundCondValue); 6156 if (!ICI) return false; 6157 6158 // Bail if the ICmp's operands' types are wider than the needed type 6159 // before attempting to call getSCEV on them. This avoids infinite 6160 // recursion, since the analysis of widening casts can require loop 6161 // exit condition information for overflow checking, which would 6162 // lead back here. 6163 if (getTypeSizeInBits(LHS->getType()) < 6164 getTypeSizeInBits(ICI->getOperand(0)->getType())) 6165 return false; 6166 6167 // Now that we found a conditional branch that dominates the loop or controls 6168 // the loop latch. Check to see if it is the comparison we are looking for. 6169 ICmpInst::Predicate FoundPred; 6170 if (Inverse) 6171 FoundPred = ICI->getInversePredicate(); 6172 else 6173 FoundPred = ICI->getPredicate(); 6174 6175 const SCEV *FoundLHS = getSCEV(ICI->getOperand(0)); 6176 const SCEV *FoundRHS = getSCEV(ICI->getOperand(1)); 6177 6178 // Balance the types. The case where FoundLHS' type is wider than 6179 // LHS' type is checked for above. 6180 if (getTypeSizeInBits(LHS->getType()) > 6181 getTypeSizeInBits(FoundLHS->getType())) { 6182 if (CmpInst::isSigned(Pred)) { 6183 FoundLHS = getSignExtendExpr(FoundLHS, LHS->getType()); 6184 FoundRHS = getSignExtendExpr(FoundRHS, LHS->getType()); 6185 } else { 6186 FoundLHS = getZeroExtendExpr(FoundLHS, LHS->getType()); 6187 FoundRHS = getZeroExtendExpr(FoundRHS, LHS->getType()); 6188 } 6189 } 6190 6191 // Canonicalize the query to match the way instcombine will have 6192 // canonicalized the comparison. 6193 if (SimplifyICmpOperands(Pred, LHS, RHS)) 6194 if (LHS == RHS) 6195 return CmpInst::isTrueWhenEqual(Pred); 6196 if (SimplifyICmpOperands(FoundPred, FoundLHS, FoundRHS)) 6197 if (FoundLHS == FoundRHS) 6198 return CmpInst::isFalseWhenEqual(FoundPred); 6199 6200 // Check to see if we can make the LHS or RHS match. 6201 if (LHS == FoundRHS || RHS == FoundLHS) { 6202 if (isa<SCEVConstant>(RHS)) { 6203 std::swap(FoundLHS, FoundRHS); 6204 FoundPred = ICmpInst::getSwappedPredicate(FoundPred); 6205 } else { 6206 std::swap(LHS, RHS); 6207 Pred = ICmpInst::getSwappedPredicate(Pred); 6208 } 6209 } 6210 6211 // Check whether the found predicate is the same as the desired predicate. 6212 if (FoundPred == Pred) 6213 return isImpliedCondOperands(Pred, LHS, RHS, FoundLHS, FoundRHS); 6214 6215 // Check whether swapping the found predicate makes it the same as the 6216 // desired predicate. 6217 if (ICmpInst::getSwappedPredicate(FoundPred) == Pred) { 6218 if (isa<SCEVConstant>(RHS)) 6219 return isImpliedCondOperands(Pred, LHS, RHS, FoundRHS, FoundLHS); 6220 else 6221 return isImpliedCondOperands(ICmpInst::getSwappedPredicate(Pred), 6222 RHS, LHS, FoundLHS, FoundRHS); 6223 } 6224 6225 // Check whether the actual condition is beyond sufficient. 6226 if (FoundPred == ICmpInst::ICMP_EQ) 6227 if (ICmpInst::isTrueWhenEqual(Pred)) 6228 if (isImpliedCondOperands(Pred, LHS, RHS, FoundLHS, FoundRHS)) 6229 return true; 6230 if (Pred == ICmpInst::ICMP_NE) 6231 if (!ICmpInst::isTrueWhenEqual(FoundPred)) 6232 if (isImpliedCondOperands(FoundPred, LHS, RHS, FoundLHS, FoundRHS)) 6233 return true; 6234 6235 // Otherwise assume the worst. 6236 return false; 6237} 6238 6239/// isImpliedCondOperands - Test whether the condition described by Pred, 6240/// LHS, and RHS is true whenever the condition described by Pred, FoundLHS, 6241/// and FoundRHS is true. 6242bool ScalarEvolution::isImpliedCondOperands(ICmpInst::Predicate Pred, 6243 const SCEV *LHS, const SCEV *RHS, 6244 const SCEV *FoundLHS, 6245 const SCEV *FoundRHS) { 6246 return isImpliedCondOperandsHelper(Pred, LHS, RHS, 6247 FoundLHS, FoundRHS) || 6248 // ~x < ~y --> x > y 6249 isImpliedCondOperandsHelper(Pred, LHS, RHS, 6250 getNotSCEV(FoundRHS), 6251 getNotSCEV(FoundLHS)); 6252} 6253 6254/// isImpliedCondOperandsHelper - Test whether the condition described by 6255/// Pred, LHS, and RHS is true whenever the condition described by Pred, 6256/// FoundLHS, and FoundRHS is true. 6257bool 6258ScalarEvolution::isImpliedCondOperandsHelper(ICmpInst::Predicate Pred, 6259 const SCEV *LHS, const SCEV *RHS, 6260 const SCEV *FoundLHS, 6261 const SCEV *FoundRHS) { 6262 switch (Pred) { 6263 default: llvm_unreachable("Unexpected ICmpInst::Predicate value!"); 6264 case ICmpInst::ICMP_EQ: 6265 case ICmpInst::ICMP_NE: 6266 if (HasSameValue(LHS, FoundLHS) && HasSameValue(RHS, FoundRHS)) 6267 return true; 6268 break; 6269 case ICmpInst::ICMP_SLT: 6270 case ICmpInst::ICMP_SLE: 6271 if (isKnownPredicateWithRanges(ICmpInst::ICMP_SLE, LHS, FoundLHS) && 6272 isKnownPredicateWithRanges(ICmpInst::ICMP_SGE, RHS, FoundRHS)) 6273 return true; 6274 break; 6275 case ICmpInst::ICMP_SGT: 6276 case ICmpInst::ICMP_SGE: 6277 if (isKnownPredicateWithRanges(ICmpInst::ICMP_SGE, LHS, FoundLHS) && 6278 isKnownPredicateWithRanges(ICmpInst::ICMP_SLE, RHS, FoundRHS)) 6279 return true; 6280 break; 6281 case ICmpInst::ICMP_ULT: 6282 case ICmpInst::ICMP_ULE: 6283 if (isKnownPredicateWithRanges(ICmpInst::ICMP_ULE, LHS, FoundLHS) && 6284 isKnownPredicateWithRanges(ICmpInst::ICMP_UGE, RHS, FoundRHS)) 6285 return true; 6286 break; 6287 case ICmpInst::ICMP_UGT: 6288 case ICmpInst::ICMP_UGE: 6289 if (isKnownPredicateWithRanges(ICmpInst::ICMP_UGE, LHS, FoundLHS) && 6290 isKnownPredicateWithRanges(ICmpInst::ICMP_ULE, RHS, FoundRHS)) 6291 return true; 6292 break; 6293 } 6294 6295 return false; 6296} 6297 6298/// getBECount - Subtract the end and start values and divide by the step, 6299/// rounding up, to get the number of times the backedge is executed. Return 6300/// CouldNotCompute if an intermediate computation overflows. 6301const SCEV *ScalarEvolution::getBECount(const SCEV *Start, 6302 const SCEV *End, 6303 const SCEV *Step, 6304 bool NoWrap) { 6305 assert(!isKnownNegative(Step) && 6306 "This code doesn't handle negative strides yet!"); 6307 6308 Type *Ty = Start->getType(); 6309 6310 // When Start == End, we have an exact BECount == 0. Short-circuit this case 6311 // here because SCEV may not be able to determine that the unsigned division 6312 // after rounding is zero. 6313 if (Start == End) 6314 return getConstant(Ty, 0); 6315 6316 const SCEV *NegOne = getConstant(Ty, (uint64_t)-1); 6317 const SCEV *Diff = getMinusSCEV(End, Start); 6318 const SCEV *RoundUp = getAddExpr(Step, NegOne); 6319 6320 // Add an adjustment to the difference between End and Start so that 6321 // the division will effectively round up. 6322 const SCEV *Add = getAddExpr(Diff, RoundUp); 6323 6324 if (!NoWrap) { 6325 // Check Add for unsigned overflow. 6326 // TODO: More sophisticated things could be done here. 6327 Type *WideTy = IntegerType::get(getContext(), 6328 getTypeSizeInBits(Ty) + 1); 6329 const SCEV *EDiff = getZeroExtendExpr(Diff, WideTy); 6330 const SCEV *ERoundUp = getZeroExtendExpr(RoundUp, WideTy); 6331 const SCEV *OperandExtendedAdd = getAddExpr(EDiff, ERoundUp); 6332 if (getZeroExtendExpr(Add, WideTy) != OperandExtendedAdd) 6333 return getCouldNotCompute(); 6334 } 6335 6336 return getUDivExpr(Add, Step); 6337} 6338 6339/// HowManyLessThans - Return the number of times a backedge containing the 6340/// specified less-than comparison will execute. If not computable, return 6341/// CouldNotCompute. 6342/// 6343/// @param IsSubExpr is true when the LHS < RHS condition does not directly 6344/// control the branch. In this case, we can only compute an iteration count for 6345/// a subexpression that cannot overflow before evaluating true. 6346ScalarEvolution::ExitLimit 6347ScalarEvolution::HowManyLessThans(const SCEV *LHS, const SCEV *RHS, 6348 const Loop *L, bool isSigned, 6349 bool IsSubExpr) { 6350 // Only handle: "ADDREC < LoopInvariant". 6351 if (!isLoopInvariant(RHS, L)) return getCouldNotCompute(); 6352 6353 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(LHS); 6354 if (!AddRec || AddRec->getLoop() != L) 6355 return getCouldNotCompute(); 6356 6357 // Check to see if we have a flag which makes analysis easy. 6358 bool NoWrap = false; 6359 if (!IsSubExpr) { 6360 NoWrap = AddRec->getNoWrapFlags( 6361 (SCEV::NoWrapFlags)(((isSigned ? SCEV::FlagNSW : SCEV::FlagNUW)) 6362 | SCEV::FlagNW)); 6363 } 6364 if (AddRec->isAffine()) { 6365 unsigned BitWidth = getTypeSizeInBits(AddRec->getType()); 6366 const SCEV *Step = AddRec->getStepRecurrence(*this); 6367 6368 if (Step->isZero()) 6369 return getCouldNotCompute(); 6370 if (Step->isOne()) { 6371 // With unit stride, the iteration never steps past the limit value. 6372 } else if (isKnownPositive(Step)) { 6373 // Test whether a positive iteration can step past the limit 6374 // value and past the maximum value for its type in a single step. 6375 // Note that it's not sufficient to check NoWrap here, because even 6376 // though the value after a wrap is undefined, it's not undefined 6377 // behavior, so if wrap does occur, the loop could either terminate or 6378 // loop infinitely, but in either case, the loop is guaranteed to 6379 // iterate at least until the iteration where the wrapping occurs. 6380 const SCEV *One = getConstant(Step->getType(), 1); 6381 if (isSigned) { 6382 APInt Max = APInt::getSignedMaxValue(BitWidth); 6383 if ((Max - getSignedRange(getMinusSCEV(Step, One)).getSignedMax()) 6384 .slt(getSignedRange(RHS).getSignedMax())) 6385 return getCouldNotCompute(); 6386 } else { 6387 APInt Max = APInt::getMaxValue(BitWidth); 6388 if ((Max - getUnsignedRange(getMinusSCEV(Step, One)).getUnsignedMax()) 6389 .ult(getUnsignedRange(RHS).getUnsignedMax())) 6390 return getCouldNotCompute(); 6391 } 6392 } else 6393 // TODO: Handle negative strides here and below. 6394 return getCouldNotCompute(); 6395 6396 // We know the LHS is of the form {n,+,s} and the RHS is some loop-invariant 6397 // m. So, we count the number of iterations in which {n,+,s} < m is true. 6398 // Note that we cannot simply return max(m-n,0)/s because it's not safe to 6399 // treat m-n as signed nor unsigned due to overflow possibility. 6400 6401 // First, we get the value of the LHS in the first iteration: n 6402 const SCEV *Start = AddRec->getOperand(0); 6403 6404 // Determine the minimum constant start value. 6405 const SCEV *MinStart = getConstant(isSigned ? 6406 getSignedRange(Start).getSignedMin() : 6407 getUnsignedRange(Start).getUnsignedMin()); 6408 6409 // If we know that the condition is true in order to enter the loop, 6410 // then we know that it will run exactly (m-n)/s times. Otherwise, we 6411 // only know that it will execute (max(m,n)-n)/s times. In both cases, 6412 // the division must round up. 6413 const SCEV *End = RHS; 6414 if (!isLoopEntryGuardedByCond(L, 6415 isSigned ? ICmpInst::ICMP_SLT : 6416 ICmpInst::ICMP_ULT, 6417 getMinusSCEV(Start, Step), RHS)) 6418 End = isSigned ? getSMaxExpr(RHS, Start) 6419 : getUMaxExpr(RHS, Start); 6420 6421 // Determine the maximum constant end value. 6422 const SCEV *MaxEnd = getConstant(isSigned ? 6423 getSignedRange(End).getSignedMax() : 6424 getUnsignedRange(End).getUnsignedMax()); 6425 6426 // If MaxEnd is within a step of the maximum integer value in its type, 6427 // adjust it down to the minimum value which would produce the same effect. 6428 // This allows the subsequent ceiling division of (N+(step-1))/step to 6429 // compute the correct value. 6430 const SCEV *StepMinusOne = getMinusSCEV(Step, 6431 getConstant(Step->getType(), 1)); 6432 MaxEnd = isSigned ? 6433 getSMinExpr(MaxEnd, 6434 getMinusSCEV(getConstant(APInt::getSignedMaxValue(BitWidth)), 6435 StepMinusOne)) : 6436 getUMinExpr(MaxEnd, 6437 getMinusSCEV(getConstant(APInt::getMaxValue(BitWidth)), 6438 StepMinusOne)); 6439 6440 // Finally, we subtract these two values and divide, rounding up, to get 6441 // the number of times the backedge is executed. 6442 const SCEV *BECount = getBECount(Start, End, Step, NoWrap); 6443 6444 // The maximum backedge count is similar, except using the minimum start 6445 // value and the maximum end value. 6446 // If we already have an exact constant BECount, use it instead. 6447 const SCEV *MaxBECount = isa<SCEVConstant>(BECount) ? BECount 6448 : getBECount(MinStart, MaxEnd, Step, NoWrap); 6449 6450 // If the stride is nonconstant, and NoWrap == true, then 6451 // getBECount(MinStart, MaxEnd) may not compute. This would result in an 6452 // exact BECount and invalid MaxBECount, which should be avoided to catch 6453 // more optimization opportunities. 6454 if (isa<SCEVCouldNotCompute>(MaxBECount)) 6455 MaxBECount = BECount; 6456 6457 return ExitLimit(BECount, MaxBECount); 6458 } 6459 6460 return getCouldNotCompute(); 6461} 6462 6463/// getNumIterationsInRange - Return the number of iterations of this loop that 6464/// produce values in the specified constant range. Another way of looking at 6465/// this is that it returns the first iteration number where the value is not in 6466/// the condition, thus computing the exit count. If the iteration count can't 6467/// be computed, an instance of SCEVCouldNotCompute is returned. 6468const SCEV *SCEVAddRecExpr::getNumIterationsInRange(ConstantRange Range, 6469 ScalarEvolution &SE) const { 6470 if (Range.isFullSet()) // Infinite loop. 6471 return SE.getCouldNotCompute(); 6472 6473 // If the start is a non-zero constant, shift the range to simplify things. 6474 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(getStart())) 6475 if (!SC->getValue()->isZero()) { 6476 SmallVector<const SCEV *, 4> Operands(op_begin(), op_end()); 6477 Operands[0] = SE.getConstant(SC->getType(), 0); 6478 const SCEV *Shifted = SE.getAddRecExpr(Operands, getLoop(), 6479 getNoWrapFlags(FlagNW)); 6480 if (const SCEVAddRecExpr *ShiftedAddRec = 6481 dyn_cast<SCEVAddRecExpr>(Shifted)) 6482 return ShiftedAddRec->getNumIterationsInRange( 6483 Range.subtract(SC->getValue()->getValue()), SE); 6484 // This is strange and shouldn't happen. 6485 return SE.getCouldNotCompute(); 6486 } 6487 6488 // The only time we can solve this is when we have all constant indices. 6489 // Otherwise, we cannot determine the overflow conditions. 6490 for (unsigned i = 0, e = getNumOperands(); i != e; ++i) 6491 if (!isa<SCEVConstant>(getOperand(i))) 6492 return SE.getCouldNotCompute(); 6493 6494 6495 // Okay at this point we know that all elements of the chrec are constants and 6496 // that the start element is zero. 6497 6498 // First check to see if the range contains zero. If not, the first 6499 // iteration exits. 6500 unsigned BitWidth = SE.getTypeSizeInBits(getType()); 6501 if (!Range.contains(APInt(BitWidth, 0))) 6502 return SE.getConstant(getType(), 0); 6503 6504 if (isAffine()) { 6505 // If this is an affine expression then we have this situation: 6506 // Solve {0,+,A} in Range === Ax in Range 6507 6508 // We know that zero is in the range. If A is positive then we know that 6509 // the upper value of the range must be the first possible exit value. 6510 // If A is negative then the lower of the range is the last possible loop 6511 // value. Also note that we already checked for a full range. 6512 APInt One(BitWidth,1); 6513 APInt A = cast<SCEVConstant>(getOperand(1))->getValue()->getValue(); 6514 APInt End = A.sge(One) ? (Range.getUpper() - One) : Range.getLower(); 6515 6516 // The exit value should be (End+A)/A. 6517 APInt ExitVal = (End + A).udiv(A); 6518 ConstantInt *ExitValue = ConstantInt::get(SE.getContext(), ExitVal); 6519 6520 // Evaluate at the exit value. If we really did fall out of the valid 6521 // range, then we computed our trip count, otherwise wrap around or other 6522 // things must have happened. 6523 ConstantInt *Val = EvaluateConstantChrecAtConstant(this, ExitValue, SE); 6524 if (Range.contains(Val->getValue())) 6525 return SE.getCouldNotCompute(); // Something strange happened 6526 6527 // Ensure that the previous value is in the range. This is a sanity check. 6528 assert(Range.contains( 6529 EvaluateConstantChrecAtConstant(this, 6530 ConstantInt::get(SE.getContext(), ExitVal - One), SE)->getValue()) && 6531 "Linear scev computation is off in a bad way!"); 6532 return SE.getConstant(ExitValue); 6533 } else if (isQuadratic()) { 6534 // If this is a quadratic (3-term) AddRec {L,+,M,+,N}, find the roots of the 6535 // quadratic equation to solve it. To do this, we must frame our problem in 6536 // terms of figuring out when zero is crossed, instead of when 6537 // Range.getUpper() is crossed. 6538 SmallVector<const SCEV *, 4> NewOps(op_begin(), op_end()); 6539 NewOps[0] = SE.getNegativeSCEV(SE.getConstant(Range.getUpper())); 6540 const SCEV *NewAddRec = SE.getAddRecExpr(NewOps, getLoop(), 6541 // getNoWrapFlags(FlagNW) 6542 FlagAnyWrap); 6543 6544 // Next, solve the constructed addrec 6545 std::pair<const SCEV *,const SCEV *> Roots = 6546 SolveQuadraticEquation(cast<SCEVAddRecExpr>(NewAddRec), SE); 6547 const SCEVConstant *R1 = dyn_cast<SCEVConstant>(Roots.first); 6548 const SCEVConstant *R2 = dyn_cast<SCEVConstant>(Roots.second); 6549 if (R1) { 6550 // Pick the smallest positive root value. 6551 if (ConstantInt *CB = 6552 dyn_cast<ConstantInt>(ConstantExpr::getICmp(ICmpInst::ICMP_ULT, 6553 R1->getValue(), R2->getValue()))) { 6554 if (CB->getZExtValue() == false) 6555 std::swap(R1, R2); // R1 is the minimum root now. 6556 6557 // Make sure the root is not off by one. The returned iteration should 6558 // not be in the range, but the previous one should be. When solving 6559 // for "X*X < 5", for example, we should not return a root of 2. 6560 ConstantInt *R1Val = EvaluateConstantChrecAtConstant(this, 6561 R1->getValue(), 6562 SE); 6563 if (Range.contains(R1Val->getValue())) { 6564 // The next iteration must be out of the range... 6565 ConstantInt *NextVal = 6566 ConstantInt::get(SE.getContext(), R1->getValue()->getValue()+1); 6567 6568 R1Val = EvaluateConstantChrecAtConstant(this, NextVal, SE); 6569 if (!Range.contains(R1Val->getValue())) 6570 return SE.getConstant(NextVal); 6571 return SE.getCouldNotCompute(); // Something strange happened 6572 } 6573 6574 // If R1 was not in the range, then it is a good return value. Make 6575 // sure that R1-1 WAS in the range though, just in case. 6576 ConstantInt *NextVal = 6577 ConstantInt::get(SE.getContext(), R1->getValue()->getValue()-1); 6578 R1Val = EvaluateConstantChrecAtConstant(this, NextVal, SE); 6579 if (Range.contains(R1Val->getValue())) 6580 return R1; 6581 return SE.getCouldNotCompute(); // Something strange happened 6582 } 6583 } 6584 } 6585 6586 return SE.getCouldNotCompute(); 6587} 6588 6589 6590 6591//===----------------------------------------------------------------------===// 6592// SCEVCallbackVH Class Implementation 6593//===----------------------------------------------------------------------===// 6594 6595void ScalarEvolution::SCEVCallbackVH::deleted() { 6596 assert(SE && "SCEVCallbackVH called with a null ScalarEvolution!"); 6597 if (PHINode *PN = dyn_cast<PHINode>(getValPtr())) 6598 SE->ConstantEvolutionLoopExitValue.erase(PN); 6599 SE->ValueExprMap.erase(getValPtr()); 6600 // this now dangles! 6601} 6602 6603void ScalarEvolution::SCEVCallbackVH::allUsesReplacedWith(Value *V) { 6604 assert(SE && "SCEVCallbackVH called with a null ScalarEvolution!"); 6605 6606 // Forget all the expressions associated with users of the old value, 6607 // so that future queries will recompute the expressions using the new 6608 // value. 6609 Value *Old = getValPtr(); 6610 SmallVector<User *, 16> Worklist; 6611 SmallPtrSet<User *, 8> Visited; 6612 for (Value::use_iterator UI = Old->use_begin(), UE = Old->use_end(); 6613 UI != UE; ++UI) 6614 Worklist.push_back(*UI); 6615 while (!Worklist.empty()) { 6616 User *U = Worklist.pop_back_val(); 6617 // Deleting the Old value will cause this to dangle. Postpone 6618 // that until everything else is done. 6619 if (U == Old) 6620 continue; 6621 if (!Visited.insert(U)) 6622 continue; 6623 if (PHINode *PN = dyn_cast<PHINode>(U)) 6624 SE->ConstantEvolutionLoopExitValue.erase(PN); 6625 SE->ValueExprMap.erase(U); 6626 for (Value::use_iterator UI = U->use_begin(), UE = U->use_end(); 6627 UI != UE; ++UI) 6628 Worklist.push_back(*UI); 6629 } 6630 // Delete the Old value. 6631 if (PHINode *PN = dyn_cast<PHINode>(Old)) 6632 SE->ConstantEvolutionLoopExitValue.erase(PN); 6633 SE->ValueExprMap.erase(Old); 6634 // this now dangles! 6635} 6636 6637ScalarEvolution::SCEVCallbackVH::SCEVCallbackVH(Value *V, ScalarEvolution *se) 6638 : CallbackVH(V), SE(se) {} 6639 6640//===----------------------------------------------------------------------===// 6641// ScalarEvolution Class Implementation 6642//===----------------------------------------------------------------------===// 6643 6644ScalarEvolution::ScalarEvolution() 6645 : FunctionPass(ID), FirstUnknown(0) { 6646 initializeScalarEvolutionPass(*PassRegistry::getPassRegistry()); 6647} 6648 6649bool ScalarEvolution::runOnFunction(Function &F) { 6650 this->F = &F; 6651 LI = &getAnalysis<LoopInfo>(); 6652 TD = getAnalysisIfAvailable<DataLayout>(); 6653 TLI = &getAnalysis<TargetLibraryInfo>(); 6654 DT = &getAnalysis<DominatorTree>(); 6655 return false; 6656} 6657 6658void ScalarEvolution::releaseMemory() { 6659 // Iterate through all the SCEVUnknown instances and call their 6660 // destructors, so that they release their references to their values. 6661 for (SCEVUnknown *U = FirstUnknown; U; U = U->Next) 6662 U->~SCEVUnknown(); 6663 FirstUnknown = 0; 6664 6665 ValueExprMap.clear(); 6666 6667 // Free any extra memory created for ExitNotTakenInfo in the unlikely event 6668 // that a loop had multiple computable exits. 6669 for (DenseMap<const Loop*, BackedgeTakenInfo>::iterator I = 6670 BackedgeTakenCounts.begin(), E = BackedgeTakenCounts.end(); 6671 I != E; ++I) { 6672 I->second.clear(); 6673 } 6674 6675 assert(PendingLoopPredicates.empty() && "isImpliedCond garbage"); 6676 6677 BackedgeTakenCounts.clear(); 6678 ConstantEvolutionLoopExitValue.clear(); 6679 ValuesAtScopes.clear(); 6680 LoopDispositions.clear(); 6681 BlockDispositions.clear(); 6682 UnsignedRanges.clear(); 6683 SignedRanges.clear(); 6684 UniqueSCEVs.clear(); 6685 SCEVAllocator.Reset(); 6686} 6687 6688void ScalarEvolution::getAnalysisUsage(AnalysisUsage &AU) const { 6689 AU.setPreservesAll(); 6690 AU.addRequiredTransitive<LoopInfo>(); 6691 AU.addRequiredTransitive<DominatorTree>(); 6692 AU.addRequired<TargetLibraryInfo>(); 6693} 6694 6695bool ScalarEvolution::hasLoopInvariantBackedgeTakenCount(const Loop *L) { 6696 return !isa<SCEVCouldNotCompute>(getBackedgeTakenCount(L)); 6697} 6698 6699static void PrintLoopInfo(raw_ostream &OS, ScalarEvolution *SE, 6700 const Loop *L) { 6701 // Print all inner loops first 6702 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) 6703 PrintLoopInfo(OS, SE, *I); 6704 6705 OS << "Loop "; 6706 WriteAsOperand(OS, L->getHeader(), /*PrintType=*/false); 6707 OS << ": "; 6708 6709 SmallVector<BasicBlock *, 8> ExitBlocks; 6710 L->getExitBlocks(ExitBlocks); 6711 if (ExitBlocks.size() != 1) 6712 OS << "<multiple exits> "; 6713 6714 if (SE->hasLoopInvariantBackedgeTakenCount(L)) { 6715 OS << "backedge-taken count is " << *SE->getBackedgeTakenCount(L); 6716 } else { 6717 OS << "Unpredictable backedge-taken count. "; 6718 } 6719 6720 OS << "\n" 6721 "Loop "; 6722 WriteAsOperand(OS, L->getHeader(), /*PrintType=*/false); 6723 OS << ": "; 6724 6725 if (!isa<SCEVCouldNotCompute>(SE->getMaxBackedgeTakenCount(L))) { 6726 OS << "max backedge-taken count is " << *SE->getMaxBackedgeTakenCount(L); 6727 } else { 6728 OS << "Unpredictable max backedge-taken count. "; 6729 } 6730 6731 OS << "\n"; 6732} 6733 6734void ScalarEvolution::print(raw_ostream &OS, const Module *) const { 6735 // ScalarEvolution's implementation of the print method is to print 6736 // out SCEV values of all instructions that are interesting. Doing 6737 // this potentially causes it to create new SCEV objects though, 6738 // which technically conflicts with the const qualifier. This isn't 6739 // observable from outside the class though, so casting away the 6740 // const isn't dangerous. 6741 ScalarEvolution &SE = *const_cast<ScalarEvolution *>(this); 6742 6743 OS << "Classifying expressions for: "; 6744 WriteAsOperand(OS, F, /*PrintType=*/false); 6745 OS << "\n"; 6746 for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) 6747 if (isSCEVable(I->getType()) && !isa<CmpInst>(*I)) { 6748 OS << *I << '\n'; 6749 OS << " --> "; 6750 const SCEV *SV = SE.getSCEV(&*I); 6751 SV->print(OS); 6752 6753 const Loop *L = LI->getLoopFor((*I).getParent()); 6754 6755 const SCEV *AtUse = SE.getSCEVAtScope(SV, L); 6756 if (AtUse != SV) { 6757 OS << " --> "; 6758 AtUse->print(OS); 6759 } 6760 6761 if (L) { 6762 OS << "\t\t" "Exits: "; 6763 const SCEV *ExitValue = SE.getSCEVAtScope(SV, L->getParentLoop()); 6764 if (!SE.isLoopInvariant(ExitValue, L)) { 6765 OS << "<<Unknown>>"; 6766 } else { 6767 OS << *ExitValue; 6768 } 6769 } 6770 6771 OS << "\n"; 6772 } 6773 6774 OS << "Determining loop execution counts for: "; 6775 WriteAsOperand(OS, F, /*PrintType=*/false); 6776 OS << "\n"; 6777 for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) 6778 PrintLoopInfo(OS, &SE, *I); 6779} 6780 6781ScalarEvolution::LoopDisposition 6782ScalarEvolution::getLoopDisposition(const SCEV *S, const Loop *L) { 6783 std::map<const Loop *, LoopDisposition> &Values = LoopDispositions[S]; 6784 std::pair<std::map<const Loop *, LoopDisposition>::iterator, bool> Pair = 6785 Values.insert(std::make_pair(L, LoopVariant)); 6786 if (!Pair.second) 6787 return Pair.first->second; 6788 6789 LoopDisposition D = computeLoopDisposition(S, L); 6790 return LoopDispositions[S][L] = D; 6791} 6792 6793ScalarEvolution::LoopDisposition 6794ScalarEvolution::computeLoopDisposition(const SCEV *S, const Loop *L) { 6795 switch (S->getSCEVType()) { 6796 case scConstant: 6797 return LoopInvariant; 6798 case scTruncate: 6799 case scZeroExtend: 6800 case scSignExtend: 6801 return getLoopDisposition(cast<SCEVCastExpr>(S)->getOperand(), L); 6802 case scAddRecExpr: { 6803 const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(S); 6804 6805 // If L is the addrec's loop, it's computable. 6806 if (AR->getLoop() == L) 6807 return LoopComputable; 6808 6809 // Add recurrences are never invariant in the function-body (null loop). 6810 if (!L) 6811 return LoopVariant; 6812 6813 // This recurrence is variant w.r.t. L if L contains AR's loop. 6814 if (L->contains(AR->getLoop())) 6815 return LoopVariant; 6816 6817 // This recurrence is invariant w.r.t. L if AR's loop contains L. 6818 if (AR->getLoop()->contains(L)) 6819 return LoopInvariant; 6820 6821 // This recurrence is variant w.r.t. L if any of its operands 6822 // are variant. 6823 for (SCEVAddRecExpr::op_iterator I = AR->op_begin(), E = AR->op_end(); 6824 I != E; ++I) 6825 if (!isLoopInvariant(*I, L)) 6826 return LoopVariant; 6827 6828 // Otherwise it's loop-invariant. 6829 return LoopInvariant; 6830 } 6831 case scAddExpr: 6832 case scMulExpr: 6833 case scUMaxExpr: 6834 case scSMaxExpr: { 6835 const SCEVNAryExpr *NAry = cast<SCEVNAryExpr>(S); 6836 bool HasVarying = false; 6837 for (SCEVNAryExpr::op_iterator I = NAry->op_begin(), E = NAry->op_end(); 6838 I != E; ++I) { 6839 LoopDisposition D = getLoopDisposition(*I, L); 6840 if (D == LoopVariant) 6841 return LoopVariant; 6842 if (D == LoopComputable) 6843 HasVarying = true; 6844 } 6845 return HasVarying ? LoopComputable : LoopInvariant; 6846 } 6847 case scUDivExpr: { 6848 const SCEVUDivExpr *UDiv = cast<SCEVUDivExpr>(S); 6849 LoopDisposition LD = getLoopDisposition(UDiv->getLHS(), L); 6850 if (LD == LoopVariant) 6851 return LoopVariant; 6852 LoopDisposition RD = getLoopDisposition(UDiv->getRHS(), L); 6853 if (RD == LoopVariant) 6854 return LoopVariant; 6855 return (LD == LoopInvariant && RD == LoopInvariant) ? 6856 LoopInvariant : LoopComputable; 6857 } 6858 case scUnknown: 6859 // All non-instruction values are loop invariant. All instructions are loop 6860 // invariant if they are not contained in the specified loop. 6861 // Instructions are never considered invariant in the function body 6862 // (null loop) because they are defined within the "loop". 6863 if (Instruction *I = dyn_cast<Instruction>(cast<SCEVUnknown>(S)->getValue())) 6864 return (L && !L->contains(I)) ? LoopInvariant : LoopVariant; 6865 return LoopInvariant; 6866 case scCouldNotCompute: 6867 llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!"); 6868 default: llvm_unreachable("Unknown SCEV kind!"); 6869 } 6870} 6871 6872bool ScalarEvolution::isLoopInvariant(const SCEV *S, const Loop *L) { 6873 return getLoopDisposition(S, L) == LoopInvariant; 6874} 6875 6876bool ScalarEvolution::hasComputableLoopEvolution(const SCEV *S, const Loop *L) { 6877 return getLoopDisposition(S, L) == LoopComputable; 6878} 6879 6880ScalarEvolution::BlockDisposition 6881ScalarEvolution::getBlockDisposition(const SCEV *S, const BasicBlock *BB) { 6882 std::map<const BasicBlock *, BlockDisposition> &Values = BlockDispositions[S]; 6883 std::pair<std::map<const BasicBlock *, BlockDisposition>::iterator, bool> 6884 Pair = Values.insert(std::make_pair(BB, DoesNotDominateBlock)); 6885 if (!Pair.second) 6886 return Pair.first->second; 6887 6888 BlockDisposition D = computeBlockDisposition(S, BB); 6889 return BlockDispositions[S][BB] = D; 6890} 6891 6892ScalarEvolution::BlockDisposition 6893ScalarEvolution::computeBlockDisposition(const SCEV *S, const BasicBlock *BB) { 6894 switch (S->getSCEVType()) { 6895 case scConstant: 6896 return ProperlyDominatesBlock; 6897 case scTruncate: 6898 case scZeroExtend: 6899 case scSignExtend: 6900 return getBlockDisposition(cast<SCEVCastExpr>(S)->getOperand(), BB); 6901 case scAddRecExpr: { 6902 // This uses a "dominates" query instead of "properly dominates" query 6903 // to test for proper dominance too, because the instruction which 6904 // produces the addrec's value is a PHI, and a PHI effectively properly 6905 // dominates its entire containing block. 6906 const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(S); 6907 if (!DT->dominates(AR->getLoop()->getHeader(), BB)) 6908 return DoesNotDominateBlock; 6909 } 6910 // FALL THROUGH into SCEVNAryExpr handling. 6911 case scAddExpr: 6912 case scMulExpr: 6913 case scUMaxExpr: 6914 case scSMaxExpr: { 6915 const SCEVNAryExpr *NAry = cast<SCEVNAryExpr>(S); 6916 bool Proper = true; 6917 for (SCEVNAryExpr::op_iterator I = NAry->op_begin(), E = NAry->op_end(); 6918 I != E; ++I) { 6919 BlockDisposition D = getBlockDisposition(*I, BB); 6920 if (D == DoesNotDominateBlock) 6921 return DoesNotDominateBlock; 6922 if (D == DominatesBlock) 6923 Proper = false; 6924 } 6925 return Proper ? ProperlyDominatesBlock : DominatesBlock; 6926 } 6927 case scUDivExpr: { 6928 const SCEVUDivExpr *UDiv = cast<SCEVUDivExpr>(S); 6929 const SCEV *LHS = UDiv->getLHS(), *RHS = UDiv->getRHS(); 6930 BlockDisposition LD = getBlockDisposition(LHS, BB); 6931 if (LD == DoesNotDominateBlock) 6932 return DoesNotDominateBlock; 6933 BlockDisposition RD = getBlockDisposition(RHS, BB); 6934 if (RD == DoesNotDominateBlock) 6935 return DoesNotDominateBlock; 6936 return (LD == ProperlyDominatesBlock && RD == ProperlyDominatesBlock) ? 6937 ProperlyDominatesBlock : DominatesBlock; 6938 } 6939 case scUnknown: 6940 if (Instruction *I = 6941 dyn_cast<Instruction>(cast<SCEVUnknown>(S)->getValue())) { 6942 if (I->getParent() == BB) 6943 return DominatesBlock; 6944 if (DT->properlyDominates(I->getParent(), BB)) 6945 return ProperlyDominatesBlock; 6946 return DoesNotDominateBlock; 6947 } 6948 return ProperlyDominatesBlock; 6949 case scCouldNotCompute: 6950 llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!"); 6951 default: 6952 llvm_unreachable("Unknown SCEV kind!"); 6953 } 6954} 6955 6956bool ScalarEvolution::dominates(const SCEV *S, const BasicBlock *BB) { 6957 return getBlockDisposition(S, BB) >= DominatesBlock; 6958} 6959 6960bool ScalarEvolution::properlyDominates(const SCEV *S, const BasicBlock *BB) { 6961 return getBlockDisposition(S, BB) == ProperlyDominatesBlock; 6962} 6963 6964namespace { 6965// Search for a SCEV expression node within an expression tree. 6966// Implements SCEVTraversal::Visitor. 6967struct SCEVSearch { 6968 const SCEV *Node; 6969 bool IsFound; 6970 6971 SCEVSearch(const SCEV *N): Node(N), IsFound(false) {} 6972 6973 bool follow(const SCEV *S) { 6974 IsFound |= (S == Node); 6975 return !IsFound; 6976 } 6977 bool isDone() const { return IsFound; } 6978}; 6979} 6980 6981bool ScalarEvolution::hasOperand(const SCEV *S, const SCEV *Op) const { 6982 SCEVSearch Search(Op); 6983 visitAll(S, Search); 6984 return Search.IsFound; 6985} 6986 6987void ScalarEvolution::forgetMemoizedResults(const SCEV *S) { 6988 ValuesAtScopes.erase(S); 6989 LoopDispositions.erase(S); 6990 BlockDispositions.erase(S); 6991 UnsignedRanges.erase(S); 6992 SignedRanges.erase(S); 6993 6994 for (DenseMap<const Loop*, BackedgeTakenInfo>::iterator I = 6995 BackedgeTakenCounts.begin(), E = BackedgeTakenCounts.end(); I != E; ) { 6996 BackedgeTakenInfo &BEInfo = I->second; 6997 if (BEInfo.hasOperand(S, this)) { 6998 BEInfo.clear(); 6999 BackedgeTakenCounts.erase(I++); 7000 } 7001 else 7002 ++I; 7003 } 7004} 7005 7006typedef DenseMap<const Loop *, std::string> VerifyMap; 7007 7008/// replaceSubString - Replaces all occurences of From in Str with To. 7009static void replaceSubString(std::string &Str, StringRef From, StringRef To) { 7010 size_t Pos = 0; 7011 while ((Pos = Str.find(From, Pos)) != std::string::npos) { 7012 Str.replace(Pos, From.size(), To.data(), To.size()); 7013 Pos += To.size(); 7014 } 7015} 7016 7017/// getLoopBackedgeTakenCounts - Helper method for verifyAnalysis. 7018static void 7019getLoopBackedgeTakenCounts(Loop *L, VerifyMap &Map, ScalarEvolution &SE) { 7020 for (Loop::reverse_iterator I = L->rbegin(), E = L->rend(); I != E; ++I) { 7021 getLoopBackedgeTakenCounts(*I, Map, SE); // recurse. 7022 7023 std::string &S = Map[L]; 7024 if (S.empty()) { 7025 raw_string_ostream OS(S); 7026 SE.getBackedgeTakenCount(L)->print(OS); 7027 7028 // false and 0 are semantically equivalent. This can happen in dead loops. 7029 replaceSubString(OS.str(), "false", "0"); 7030 // Remove wrap flags, their use in SCEV is highly fragile. 7031 // FIXME: Remove this when SCEV gets smarter about them. 7032 replaceSubString(OS.str(), "<nw>", ""); 7033 replaceSubString(OS.str(), "<nsw>", ""); 7034 replaceSubString(OS.str(), "<nuw>", ""); 7035 } 7036 } 7037} 7038 7039void ScalarEvolution::verifyAnalysis() const { 7040 if (!VerifySCEV) 7041 return; 7042 7043 ScalarEvolution &SE = *const_cast<ScalarEvolution *>(this); 7044 7045 // Gather stringified backedge taken counts for all loops using SCEV's caches. 7046 // FIXME: It would be much better to store actual values instead of strings, 7047 // but SCEV pointers will change if we drop the caches. 7048 VerifyMap BackedgeDumpsOld, BackedgeDumpsNew; 7049 for (LoopInfo::reverse_iterator I = LI->rbegin(), E = LI->rend(); I != E; ++I) 7050 getLoopBackedgeTakenCounts(*I, BackedgeDumpsOld, SE); 7051 7052 // Gather stringified backedge taken counts for all loops without using 7053 // SCEV's caches. 7054 SE.releaseMemory(); 7055 for (LoopInfo::reverse_iterator I = LI->rbegin(), E = LI->rend(); I != E; ++I) 7056 getLoopBackedgeTakenCounts(*I, BackedgeDumpsNew, SE); 7057 7058 // Now compare whether they're the same with and without caches. This allows 7059 // verifying that no pass changed the cache. 7060 assert(BackedgeDumpsOld.size() == BackedgeDumpsNew.size() && 7061 "New loops suddenly appeared!"); 7062 7063 for (VerifyMap::iterator OldI = BackedgeDumpsOld.begin(), 7064 OldE = BackedgeDumpsOld.end(), 7065 NewI = BackedgeDumpsNew.begin(); 7066 OldI != OldE; ++OldI, ++NewI) { 7067 assert(OldI->first == NewI->first && "Loop order changed!"); 7068 7069 // Compare the stringified SCEVs. We don't care if undef backedgetaken count 7070 // changes. 7071 // FIXME: We currently ignore SCEV changes from/to CouldNotCompute. This 7072 // means that a pass is buggy or SCEV has to learn a new pattern but is 7073 // usually not harmful. 7074 if (OldI->second != NewI->second && 7075 OldI->second.find("undef") == std::string::npos && 7076 NewI->second.find("undef") == std::string::npos && 7077 OldI->second != "***COULDNOTCOMPUTE***" && 7078 NewI->second != "***COULDNOTCOMPUTE***") { 7079 dbgs() << "SCEVValidator: SCEV for loop '" 7080 << OldI->first->getHeader()->getName() 7081 << "' changed from '" << OldI->second 7082 << "' to '" << NewI->second << "'!\n"; 7083 std::abort(); 7084 } 7085 } 7086 7087 // TODO: Verify more things. 7088} 7089