LoopStrengthReduce.cpp revision 201360
1//===- LoopStrengthReduce.cpp - Strength Reduce IVs in Loops --------------===// 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 transformation analyzes and transforms the induction variables (and 11// computations derived from them) into forms suitable for efficient execution 12// on the target. 13// 14// This pass performs a strength reduction on array references inside loops that 15// have as one or more of their components the loop induction variable, it 16// rewrites expressions to take advantage of scaled-index addressing modes 17// available on the target, and it performs a variety of other optimizations 18// related to loop induction variables. 19// 20//===----------------------------------------------------------------------===// 21 22#define DEBUG_TYPE "loop-reduce" 23#include "llvm/Transforms/Scalar.h" 24#include "llvm/Constants.h" 25#include "llvm/Instructions.h" 26#include "llvm/IntrinsicInst.h" 27#include "llvm/DerivedTypes.h" 28#include "llvm/Analysis/IVUsers.h" 29#include "llvm/Analysis/LoopPass.h" 30#include "llvm/Analysis/ScalarEvolutionExpander.h" 31#include "llvm/Transforms/Utils/AddrModeMatcher.h" 32#include "llvm/Transforms/Utils/BasicBlockUtils.h" 33#include "llvm/Transforms/Utils/Local.h" 34#include "llvm/ADT/Statistic.h" 35#include "llvm/Support/Debug.h" 36#include "llvm/Support/CommandLine.h" 37#include "llvm/Support/ValueHandle.h" 38#include "llvm/Support/raw_ostream.h" 39#include "llvm/Target/TargetLowering.h" 40#include <algorithm> 41using namespace llvm; 42 43STATISTIC(NumReduced , "Number of IV uses strength reduced"); 44STATISTIC(NumInserted, "Number of PHIs inserted"); 45STATISTIC(NumVariable, "Number of PHIs with variable strides"); 46STATISTIC(NumEliminated, "Number of strides eliminated"); 47STATISTIC(NumShadow, "Number of Shadow IVs optimized"); 48STATISTIC(NumImmSunk, "Number of common expr immediates sunk into uses"); 49STATISTIC(NumLoopCond, "Number of loop terminating conds optimized"); 50STATISTIC(NumCountZero, "Number of count iv optimized to count toward zero"); 51 52static cl::opt<bool> EnableFullLSRMode("enable-full-lsr", 53 cl::init(false), 54 cl::Hidden); 55 56namespace { 57 58 struct BasedUser; 59 60 /// IVInfo - This structure keeps track of one IV expression inserted during 61 /// StrengthReduceStridedIVUsers. It contains the stride, the common base, as 62 /// well as the PHI node and increment value created for rewrite. 63 struct IVExpr { 64 const SCEV *Stride; 65 const SCEV *Base; 66 PHINode *PHI; 67 68 IVExpr(const SCEV *const stride, const SCEV *const base, PHINode *phi) 69 : Stride(stride), Base(base), PHI(phi) {} 70 }; 71 72 /// IVsOfOneStride - This structure keeps track of all IV expression inserted 73 /// during StrengthReduceStridedIVUsers for a particular stride of the IV. 74 struct IVsOfOneStride { 75 std::vector<IVExpr> IVs; 76 77 void addIV(const SCEV *const Stride, const SCEV *const Base, PHINode *PHI) { 78 IVs.push_back(IVExpr(Stride, Base, PHI)); 79 } 80 }; 81 82 class LoopStrengthReduce : public LoopPass { 83 IVUsers *IU; 84 ScalarEvolution *SE; 85 bool Changed; 86 87 /// IVsByStride - Keep track of all IVs that have been inserted for a 88 /// particular stride. 89 std::map<const SCEV *, IVsOfOneStride> IVsByStride; 90 91 /// DeadInsts - Keep track of instructions we may have made dead, so that 92 /// we can remove them after we are done working. 93 SmallVector<WeakVH, 16> DeadInsts; 94 95 /// TLI - Keep a pointer of a TargetLowering to consult for determining 96 /// transformation profitability. 97 const TargetLowering *TLI; 98 99 public: 100 static char ID; // Pass ID, replacement for typeid 101 explicit LoopStrengthReduce(const TargetLowering *tli = NULL) : 102 LoopPass(&ID), TLI(tli) {} 103 104 bool runOnLoop(Loop *L, LPPassManager &LPM); 105 106 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 107 // We split critical edges, so we change the CFG. However, we do update 108 // many analyses if they are around. 109 AU.addPreservedID(LoopSimplifyID); 110 AU.addPreserved("loops"); 111 AU.addPreserved("domfrontier"); 112 AU.addPreserved("domtree"); 113 114 AU.addRequiredID(LoopSimplifyID); 115 AU.addRequired<ScalarEvolution>(); 116 AU.addPreserved<ScalarEvolution>(); 117 AU.addRequired<IVUsers>(); 118 AU.addPreserved<IVUsers>(); 119 } 120 121 private: 122 void OptimizeIndvars(Loop *L); 123 124 /// OptimizeLoopTermCond - Change loop terminating condition to use the 125 /// postinc iv when possible. 126 void OptimizeLoopTermCond(Loop *L); 127 128 /// OptimizeShadowIV - If IV is used in a int-to-float cast 129 /// inside the loop then try to eliminate the cast opeation. 130 void OptimizeShadowIV(Loop *L); 131 132 /// OptimizeMax - Rewrite the loop's terminating condition 133 /// if it uses a max computation. 134 ICmpInst *OptimizeMax(Loop *L, ICmpInst *Cond, 135 IVStrideUse* &CondUse); 136 137 /// OptimizeLoopCountIV - If, after all sharing of IVs, the IV used for 138 /// deciding when to exit the loop is used only for that purpose, try to 139 /// rearrange things so it counts down to a test against zero. 140 bool OptimizeLoopCountIV(Loop *L); 141 bool OptimizeLoopCountIVOfStride(const SCEV* &Stride, 142 IVStrideUse* &CondUse, Loop *L); 143 144 /// StrengthReduceIVUsersOfStride - Strength reduce all of the users of a 145 /// single stride of IV. All of the users may have different starting 146 /// values, and this may not be the only stride. 147 void StrengthReduceIVUsersOfStride(const SCEV *Stride, 148 IVUsersOfOneStride &Uses, 149 Loop *L); 150 void StrengthReduceIVUsers(Loop *L); 151 152 ICmpInst *ChangeCompareStride(Loop *L, ICmpInst *Cond, 153 IVStrideUse* &CondUse, 154 const SCEV* &CondStride, 155 bool PostPass = false); 156 157 bool FindIVUserForCond(ICmpInst *Cond, IVStrideUse *&CondUse, 158 const SCEV* &CondStride); 159 bool RequiresTypeConversion(const Type *Ty, const Type *NewTy); 160 const SCEV *CheckForIVReuse(bool, bool, bool, const SCEV *, 161 IVExpr&, const Type*, 162 const std::vector<BasedUser>& UsersToProcess); 163 bool ValidScale(bool, int64_t, 164 const std::vector<BasedUser>& UsersToProcess); 165 bool ValidOffset(bool, int64_t, int64_t, 166 const std::vector<BasedUser>& UsersToProcess); 167 const SCEV *CollectIVUsers(const SCEV *Stride, 168 IVUsersOfOneStride &Uses, 169 Loop *L, 170 bool &AllUsesAreAddresses, 171 bool &AllUsesAreOutsideLoop, 172 std::vector<BasedUser> &UsersToProcess); 173 bool StrideMightBeShared(const SCEV *Stride, Loop *L, bool CheckPreInc); 174 bool ShouldUseFullStrengthReductionMode( 175 const std::vector<BasedUser> &UsersToProcess, 176 const Loop *L, 177 bool AllUsesAreAddresses, 178 const SCEV *Stride); 179 void PrepareToStrengthReduceFully( 180 std::vector<BasedUser> &UsersToProcess, 181 const SCEV *Stride, 182 const SCEV *CommonExprs, 183 const Loop *L, 184 SCEVExpander &PreheaderRewriter); 185 void PrepareToStrengthReduceFromSmallerStride( 186 std::vector<BasedUser> &UsersToProcess, 187 Value *CommonBaseV, 188 const IVExpr &ReuseIV, 189 Instruction *PreInsertPt); 190 void PrepareToStrengthReduceWithNewPhi( 191 std::vector<BasedUser> &UsersToProcess, 192 const SCEV *Stride, 193 const SCEV *CommonExprs, 194 Value *CommonBaseV, 195 Instruction *IVIncInsertPt, 196 const Loop *L, 197 SCEVExpander &PreheaderRewriter); 198 199 void DeleteTriviallyDeadInstructions(); 200 }; 201} 202 203char LoopStrengthReduce::ID = 0; 204static RegisterPass<LoopStrengthReduce> 205X("loop-reduce", "Loop Strength Reduction"); 206 207Pass *llvm::createLoopStrengthReducePass(const TargetLowering *TLI) { 208 return new LoopStrengthReduce(TLI); 209} 210 211/// DeleteTriviallyDeadInstructions - If any of the instructions is the 212/// specified set are trivially dead, delete them and see if this makes any of 213/// their operands subsequently dead. 214void LoopStrengthReduce::DeleteTriviallyDeadInstructions() { 215 while (!DeadInsts.empty()) { 216 Instruction *I = dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()); 217 218 if (I == 0 || !isInstructionTriviallyDead(I)) 219 continue; 220 221 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI) 222 if (Instruction *U = dyn_cast<Instruction>(*OI)) { 223 *OI = 0; 224 if (U->use_empty()) 225 DeadInsts.push_back(U); 226 } 227 228 I->eraseFromParent(); 229 Changed = true; 230 } 231} 232 233/// isAddressUse - Returns true if the specified instruction is using the 234/// specified value as an address. 235static bool isAddressUse(Instruction *Inst, Value *OperandVal) { 236 bool isAddress = isa<LoadInst>(Inst); 237 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 238 if (SI->getOperand(1) == OperandVal) 239 isAddress = true; 240 } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) { 241 // Addressing modes can also be folded into prefetches and a variety 242 // of intrinsics. 243 switch (II->getIntrinsicID()) { 244 default: break; 245 case Intrinsic::prefetch: 246 case Intrinsic::x86_sse2_loadu_dq: 247 case Intrinsic::x86_sse2_loadu_pd: 248 case Intrinsic::x86_sse_loadu_ps: 249 case Intrinsic::x86_sse_storeu_ps: 250 case Intrinsic::x86_sse2_storeu_pd: 251 case Intrinsic::x86_sse2_storeu_dq: 252 case Intrinsic::x86_sse2_storel_dq: 253 if (II->getOperand(1) == OperandVal) 254 isAddress = true; 255 break; 256 } 257 } 258 return isAddress; 259} 260 261/// getAccessType - Return the type of the memory being accessed. 262static const Type *getAccessType(const Instruction *Inst) { 263 const Type *AccessTy = Inst->getType(); 264 if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) 265 AccessTy = SI->getOperand(0)->getType(); 266 else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) { 267 // Addressing modes can also be folded into prefetches and a variety 268 // of intrinsics. 269 switch (II->getIntrinsicID()) { 270 default: break; 271 case Intrinsic::x86_sse_storeu_ps: 272 case Intrinsic::x86_sse2_storeu_pd: 273 case Intrinsic::x86_sse2_storeu_dq: 274 case Intrinsic::x86_sse2_storel_dq: 275 AccessTy = II->getOperand(1)->getType(); 276 break; 277 } 278 } 279 return AccessTy; 280} 281 282namespace { 283 /// BasedUser - For a particular base value, keep information about how we've 284 /// partitioned the expression so far. 285 struct BasedUser { 286 /// Base - The Base value for the PHI node that needs to be inserted for 287 /// this use. As the use is processed, information gets moved from this 288 /// field to the Imm field (below). BasedUser values are sorted by this 289 /// field. 290 const SCEV *Base; 291 292 /// Inst - The instruction using the induction variable. 293 Instruction *Inst; 294 295 /// OperandValToReplace - The operand value of Inst to replace with the 296 /// EmittedBase. 297 Value *OperandValToReplace; 298 299 /// Imm - The immediate value that should be added to the base immediately 300 /// before Inst, because it will be folded into the imm field of the 301 /// instruction. This is also sometimes used for loop-variant values that 302 /// must be added inside the loop. 303 const SCEV *Imm; 304 305 /// Phi - The induction variable that performs the striding that 306 /// should be used for this user. 307 PHINode *Phi; 308 309 // isUseOfPostIncrementedValue - True if this should use the 310 // post-incremented version of this IV, not the preincremented version. 311 // This can only be set in special cases, such as the terminating setcc 312 // instruction for a loop and uses outside the loop that are dominated by 313 // the loop. 314 bool isUseOfPostIncrementedValue; 315 316 BasedUser(IVStrideUse &IVSU, ScalarEvolution *se) 317 : Base(IVSU.getOffset()), Inst(IVSU.getUser()), 318 OperandValToReplace(IVSU.getOperandValToReplace()), 319 Imm(se->getIntegerSCEV(0, Base->getType())), 320 isUseOfPostIncrementedValue(IVSU.isUseOfPostIncrementedValue()) {} 321 322 // Once we rewrite the code to insert the new IVs we want, update the 323 // operands of Inst to use the new expression 'NewBase', with 'Imm' added 324 // to it. 325 void RewriteInstructionToUseNewBase(const SCEV *NewBase, 326 Instruction *InsertPt, 327 SCEVExpander &Rewriter, Loop *L, Pass *P, 328 SmallVectorImpl<WeakVH> &DeadInsts, 329 ScalarEvolution *SE); 330 331 Value *InsertCodeForBaseAtPosition(const SCEV *NewBase, 332 const Type *Ty, 333 SCEVExpander &Rewriter, 334 Instruction *IP, 335 ScalarEvolution *SE); 336 void dump() const; 337 }; 338} 339 340void BasedUser::dump() const { 341 dbgs() << " Base=" << *Base; 342 dbgs() << " Imm=" << *Imm; 343 dbgs() << " Inst: " << *Inst; 344} 345 346Value *BasedUser::InsertCodeForBaseAtPosition(const SCEV *NewBase, 347 const Type *Ty, 348 SCEVExpander &Rewriter, 349 Instruction *IP, 350 ScalarEvolution *SE) { 351 Value *Base = Rewriter.expandCodeFor(NewBase, 0, IP); 352 353 // Wrap the base in a SCEVUnknown so that ScalarEvolution doesn't try to 354 // re-analyze it. 355 const SCEV *NewValSCEV = SE->getUnknown(Base); 356 357 // Always emit the immediate into the same block as the user. 358 NewValSCEV = SE->getAddExpr(NewValSCEV, Imm); 359 360 return Rewriter.expandCodeFor(NewValSCEV, Ty, IP); 361} 362 363 364// Once we rewrite the code to insert the new IVs we want, update the 365// operands of Inst to use the new expression 'NewBase', with 'Imm' added 366// to it. NewBasePt is the last instruction which contributes to the 367// value of NewBase in the case that it's a diffferent instruction from 368// the PHI that NewBase is computed from, or null otherwise. 369// 370void BasedUser::RewriteInstructionToUseNewBase(const SCEV *NewBase, 371 Instruction *NewBasePt, 372 SCEVExpander &Rewriter, Loop *L, Pass *P, 373 SmallVectorImpl<WeakVH> &DeadInsts, 374 ScalarEvolution *SE) { 375 if (!isa<PHINode>(Inst)) { 376 // By default, insert code at the user instruction. 377 BasicBlock::iterator InsertPt = Inst; 378 379 // However, if the Operand is itself an instruction, the (potentially 380 // complex) inserted code may be shared by many users. Because of this, we 381 // want to emit code for the computation of the operand right before its old 382 // computation. This is usually safe, because we obviously used to use the 383 // computation when it was computed in its current block. However, in some 384 // cases (e.g. use of a post-incremented induction variable) the NewBase 385 // value will be pinned to live somewhere after the original computation. 386 // In this case, we have to back off. 387 // 388 // If this is a use outside the loop (which means after, since it is based 389 // on a loop indvar) we use the post-incremented value, so that we don't 390 // artificially make the preinc value live out the bottom of the loop. 391 if (!isUseOfPostIncrementedValue && L->contains(Inst)) { 392 if (NewBasePt && isa<PHINode>(OperandValToReplace)) { 393 InsertPt = NewBasePt; 394 ++InsertPt; 395 } else if (Instruction *OpInst 396 = dyn_cast<Instruction>(OperandValToReplace)) { 397 InsertPt = OpInst; 398 while (isa<PHINode>(InsertPt)) ++InsertPt; 399 } 400 } 401 Value *NewVal = InsertCodeForBaseAtPosition(NewBase, 402 OperandValToReplace->getType(), 403 Rewriter, InsertPt, SE); 404 // Replace the use of the operand Value with the new Phi we just created. 405 Inst->replaceUsesOfWith(OperandValToReplace, NewVal); 406 407 DEBUG(dbgs() << " Replacing with "); 408 DEBUG(WriteAsOperand(dbgs(), NewVal, /*PrintType=*/false)); 409 DEBUG(dbgs() << ", which has value " << *NewBase << " plus IMM " 410 << *Imm << "\n"); 411 return; 412 } 413 414 // PHI nodes are more complex. We have to insert one copy of the NewBase+Imm 415 // expression into each operand block that uses it. Note that PHI nodes can 416 // have multiple entries for the same predecessor. We use a map to make sure 417 // that a PHI node only has a single Value* for each predecessor (which also 418 // prevents us from inserting duplicate code in some blocks). 419 DenseMap<BasicBlock*, Value*> InsertedCode; 420 PHINode *PN = cast<PHINode>(Inst); 421 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { 422 if (PN->getIncomingValue(i) == OperandValToReplace) { 423 // If the original expression is outside the loop, put the replacement 424 // code in the same place as the original expression, 425 // which need not be an immediate predecessor of this PHI. This way we 426 // need only one copy of it even if it is referenced multiple times in 427 // the PHI. We don't do this when the original expression is inside the 428 // loop because multiple copies sometimes do useful sinking of code in 429 // that case(?). 430 Instruction *OldLoc = dyn_cast<Instruction>(OperandValToReplace); 431 BasicBlock *PHIPred = PN->getIncomingBlock(i); 432 if (L->contains(OldLoc)) { 433 // If this is a critical edge, split the edge so that we do not insert 434 // the code on all predecessor/successor paths. We do this unless this 435 // is the canonical backedge for this loop, as this can make some 436 // inserted code be in an illegal position. 437 if (e != 1 && PHIPred->getTerminator()->getNumSuccessors() > 1 && 438 !isa<IndirectBrInst>(PHIPred->getTerminator()) && 439 (PN->getParent() != L->getHeader() || !L->contains(PHIPred))) { 440 441 // First step, split the critical edge. 442 BasicBlock *NewBB = SplitCriticalEdge(PHIPred, PN->getParent(), 443 P, false); 444 445 // Next step: move the basic block. In particular, if the PHI node 446 // is outside of the loop, and PredTI is in the loop, we want to 447 // move the block to be immediately before the PHI block, not 448 // immediately after PredTI. 449 if (L->contains(PHIPred) && !L->contains(PN)) 450 NewBB->moveBefore(PN->getParent()); 451 452 // Splitting the edge can reduce the number of PHI entries we have. 453 e = PN->getNumIncomingValues(); 454 PHIPred = NewBB; 455 i = PN->getBasicBlockIndex(PHIPred); 456 } 457 } 458 Value *&Code = InsertedCode[PHIPred]; 459 if (!Code) { 460 // Insert the code into the end of the predecessor block. 461 Instruction *InsertPt = (L->contains(OldLoc)) ? 462 PHIPred->getTerminator() : 463 OldLoc->getParent()->getTerminator(); 464 Code = InsertCodeForBaseAtPosition(NewBase, PN->getType(), 465 Rewriter, InsertPt, SE); 466 467 DEBUG(dbgs() << " Changing PHI use to "); 468 DEBUG(WriteAsOperand(dbgs(), Code, /*PrintType=*/false)); 469 DEBUG(dbgs() << ", which has value " << *NewBase << " plus IMM " 470 << *Imm << "\n"); 471 } 472 473 // Replace the use of the operand Value with the new Phi we just created. 474 PN->setIncomingValue(i, Code); 475 Rewriter.clear(); 476 } 477 } 478 479 // PHI node might have become a constant value after SplitCriticalEdge. 480 DeadInsts.push_back(Inst); 481} 482 483 484/// fitsInAddressMode - Return true if V can be subsumed within an addressing 485/// mode, and does not need to be put in a register first. 486static bool fitsInAddressMode(const SCEV *V, const Type *AccessTy, 487 const TargetLowering *TLI, bool HasBaseReg) { 488 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(V)) { 489 int64_t VC = SC->getValue()->getSExtValue(); 490 if (TLI) { 491 TargetLowering::AddrMode AM; 492 AM.BaseOffs = VC; 493 AM.HasBaseReg = HasBaseReg; 494 return TLI->isLegalAddressingMode(AM, AccessTy); 495 } else { 496 // Defaults to PPC. PPC allows a sign-extended 16-bit immediate field. 497 return (VC > -(1 << 16) && VC < (1 << 16)-1); 498 } 499 } 500 501 if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(V)) 502 if (GlobalValue *GV = dyn_cast<GlobalValue>(SU->getValue())) { 503 if (TLI) { 504 TargetLowering::AddrMode AM; 505 AM.BaseGV = GV; 506 AM.HasBaseReg = HasBaseReg; 507 return TLI->isLegalAddressingMode(AM, AccessTy); 508 } else { 509 // Default: assume global addresses are not legal. 510 } 511 } 512 513 return false; 514} 515 516/// MoveLoopVariantsToImmediateField - Move any subexpressions from Val that are 517/// loop varying to the Imm operand. 518static void MoveLoopVariantsToImmediateField(const SCEV *&Val, const SCEV *&Imm, 519 Loop *L, ScalarEvolution *SE) { 520 if (Val->isLoopInvariant(L)) return; // Nothing to do. 521 522 if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) { 523 SmallVector<const SCEV *, 4> NewOps; 524 NewOps.reserve(SAE->getNumOperands()); 525 526 for (unsigned i = 0; i != SAE->getNumOperands(); ++i) 527 if (!SAE->getOperand(i)->isLoopInvariant(L)) { 528 // If this is a loop-variant expression, it must stay in the immediate 529 // field of the expression. 530 Imm = SE->getAddExpr(Imm, SAE->getOperand(i)); 531 } else { 532 NewOps.push_back(SAE->getOperand(i)); 533 } 534 535 if (NewOps.empty()) 536 Val = SE->getIntegerSCEV(0, Val->getType()); 537 else 538 Val = SE->getAddExpr(NewOps); 539 } else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) { 540 // Try to pull immediates out of the start value of nested addrec's. 541 const SCEV *Start = SARE->getStart(); 542 MoveLoopVariantsToImmediateField(Start, Imm, L, SE); 543 544 SmallVector<const SCEV *, 4> Ops(SARE->op_begin(), SARE->op_end()); 545 Ops[0] = Start; 546 Val = SE->getAddRecExpr(Ops, SARE->getLoop()); 547 } else { 548 // Otherwise, all of Val is variant, move the whole thing over. 549 Imm = SE->getAddExpr(Imm, Val); 550 Val = SE->getIntegerSCEV(0, Val->getType()); 551 } 552} 553 554 555/// MoveImmediateValues - Look at Val, and pull out any additions of constants 556/// that can fit into the immediate field of instructions in the target. 557/// Accumulate these immediate values into the Imm value. 558static void MoveImmediateValues(const TargetLowering *TLI, 559 const Type *AccessTy, 560 const SCEV *&Val, const SCEV *&Imm, 561 bool isAddress, Loop *L, 562 ScalarEvolution *SE) { 563 if (const SCEVAddExpr *SAE = dyn_cast<SCEVAddExpr>(Val)) { 564 SmallVector<const SCEV *, 4> NewOps; 565 NewOps.reserve(SAE->getNumOperands()); 566 567 for (unsigned i = 0; i != SAE->getNumOperands(); ++i) { 568 const SCEV *NewOp = SAE->getOperand(i); 569 MoveImmediateValues(TLI, AccessTy, NewOp, Imm, isAddress, L, SE); 570 571 if (!NewOp->isLoopInvariant(L)) { 572 // If this is a loop-variant expression, it must stay in the immediate 573 // field of the expression. 574 Imm = SE->getAddExpr(Imm, NewOp); 575 } else { 576 NewOps.push_back(NewOp); 577 } 578 } 579 580 if (NewOps.empty()) 581 Val = SE->getIntegerSCEV(0, Val->getType()); 582 else 583 Val = SE->getAddExpr(NewOps); 584 return; 585 } else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Val)) { 586 // Try to pull immediates out of the start value of nested addrec's. 587 const SCEV *Start = SARE->getStart(); 588 MoveImmediateValues(TLI, AccessTy, Start, Imm, isAddress, L, SE); 589 590 if (Start != SARE->getStart()) { 591 SmallVector<const SCEV *, 4> Ops(SARE->op_begin(), SARE->op_end()); 592 Ops[0] = Start; 593 Val = SE->getAddRecExpr(Ops, SARE->getLoop()); 594 } 595 return; 596 } else if (const SCEVMulExpr *SME = dyn_cast<SCEVMulExpr>(Val)) { 597 // Transform "8 * (4 + v)" -> "32 + 8*V" if "32" fits in the immed field. 598 if (isAddress && 599 fitsInAddressMode(SME->getOperand(0), AccessTy, TLI, false) && 600 SME->getNumOperands() == 2 && SME->isLoopInvariant(L)) { 601 602 const SCEV *SubImm = SE->getIntegerSCEV(0, Val->getType()); 603 const SCEV *NewOp = SME->getOperand(1); 604 MoveImmediateValues(TLI, AccessTy, NewOp, SubImm, isAddress, L, SE); 605 606 // If we extracted something out of the subexpressions, see if we can 607 // simplify this! 608 if (NewOp != SME->getOperand(1)) { 609 // Scale SubImm up by "8". If the result is a target constant, we are 610 // good. 611 SubImm = SE->getMulExpr(SubImm, SME->getOperand(0)); 612 if (fitsInAddressMode(SubImm, AccessTy, TLI, false)) { 613 // Accumulate the immediate. 614 Imm = SE->getAddExpr(Imm, SubImm); 615 616 // Update what is left of 'Val'. 617 Val = SE->getMulExpr(SME->getOperand(0), NewOp); 618 return; 619 } 620 } 621 } 622 } 623 624 // Loop-variant expressions must stay in the immediate field of the 625 // expression. 626 if ((isAddress && fitsInAddressMode(Val, AccessTy, TLI, false)) || 627 !Val->isLoopInvariant(L)) { 628 Imm = SE->getAddExpr(Imm, Val); 629 Val = SE->getIntegerSCEV(0, Val->getType()); 630 return; 631 } 632 633 // Otherwise, no immediates to move. 634} 635 636static void MoveImmediateValues(const TargetLowering *TLI, 637 Instruction *User, 638 const SCEV *&Val, const SCEV *&Imm, 639 bool isAddress, Loop *L, 640 ScalarEvolution *SE) { 641 const Type *AccessTy = getAccessType(User); 642 MoveImmediateValues(TLI, AccessTy, Val, Imm, isAddress, L, SE); 643} 644 645/// SeparateSubExprs - Decompose Expr into all of the subexpressions that are 646/// added together. This is used to reassociate common addition subexprs 647/// together for maximal sharing when rewriting bases. 648static void SeparateSubExprs(SmallVector<const SCEV *, 16> &SubExprs, 649 const SCEV *Expr, 650 ScalarEvolution *SE) { 651 if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(Expr)) { 652 for (unsigned j = 0, e = AE->getNumOperands(); j != e; ++j) 653 SeparateSubExprs(SubExprs, AE->getOperand(j), SE); 654 } else if (const SCEVAddRecExpr *SARE = dyn_cast<SCEVAddRecExpr>(Expr)) { 655 const SCEV *Zero = SE->getIntegerSCEV(0, Expr->getType()); 656 if (SARE->getOperand(0) == Zero) { 657 SubExprs.push_back(Expr); 658 } else { 659 // Compute the addrec with zero as its base. 660 SmallVector<const SCEV *, 4> Ops(SARE->op_begin(), SARE->op_end()); 661 Ops[0] = Zero; // Start with zero base. 662 SubExprs.push_back(SE->getAddRecExpr(Ops, SARE->getLoop())); 663 664 665 SeparateSubExprs(SubExprs, SARE->getOperand(0), SE); 666 } 667 } else if (!Expr->isZero()) { 668 // Do not add zero. 669 SubExprs.push_back(Expr); 670 } 671} 672 673// This is logically local to the following function, but C++ says we have 674// to make it file scope. 675struct SubExprUseData { unsigned Count; bool notAllUsesAreFree; }; 676 677/// RemoveCommonExpressionsFromUseBases - Look through all of the Bases of all 678/// the Uses, removing any common subexpressions, except that if all such 679/// subexpressions can be folded into an addressing mode for all uses inside 680/// the loop (this case is referred to as "free" in comments herein) we do 681/// not remove anything. This looks for things like (a+b+c) and 682/// (a+c+d) and computes the common (a+c) subexpression. The common expression 683/// is *removed* from the Bases and returned. 684static const SCEV * 685RemoveCommonExpressionsFromUseBases(std::vector<BasedUser> &Uses, 686 ScalarEvolution *SE, Loop *L, 687 const TargetLowering *TLI) { 688 unsigned NumUses = Uses.size(); 689 690 // Only one use? This is a very common case, so we handle it specially and 691 // cheaply. 692 const SCEV *Zero = SE->getIntegerSCEV(0, Uses[0].Base->getType()); 693 const SCEV *Result = Zero; 694 const SCEV *FreeResult = Zero; 695 if (NumUses == 1) { 696 // If the use is inside the loop, use its base, regardless of what it is: 697 // it is clearly shared across all the IV's. If the use is outside the loop 698 // (which means after it) we don't want to factor anything *into* the loop, 699 // so just use 0 as the base. 700 if (L->contains(Uses[0].Inst)) 701 std::swap(Result, Uses[0].Base); 702 return Result; 703 } 704 705 // To find common subexpressions, count how many of Uses use each expression. 706 // If any subexpressions are used Uses.size() times, they are common. 707 // Also track whether all uses of each expression can be moved into an 708 // an addressing mode "for free"; such expressions are left within the loop. 709 // struct SubExprUseData { unsigned Count; bool notAllUsesAreFree; }; 710 std::map<const SCEV *, SubExprUseData> SubExpressionUseData; 711 712 // UniqueSubExprs - Keep track of all of the subexpressions we see in the 713 // order we see them. 714 SmallVector<const SCEV *, 16> UniqueSubExprs; 715 716 SmallVector<const SCEV *, 16> SubExprs; 717 unsigned NumUsesInsideLoop = 0; 718 for (unsigned i = 0; i != NumUses; ++i) { 719 // If the user is outside the loop, just ignore it for base computation. 720 // Since the user is outside the loop, it must be *after* the loop (if it 721 // were before, it could not be based on the loop IV). We don't want users 722 // after the loop to affect base computation of values *inside* the loop, 723 // because we can always add their offsets to the result IV after the loop 724 // is done, ensuring we get good code inside the loop. 725 if (!L->contains(Uses[i].Inst)) 726 continue; 727 NumUsesInsideLoop++; 728 729 // If the base is zero (which is common), return zero now, there are no 730 // CSEs we can find. 731 if (Uses[i].Base == Zero) return Zero; 732 733 // If this use is as an address we may be able to put CSEs in the addressing 734 // mode rather than hoisting them. 735 bool isAddrUse = isAddressUse(Uses[i].Inst, Uses[i].OperandValToReplace); 736 // We may need the AccessTy below, but only when isAddrUse, so compute it 737 // only in that case. 738 const Type *AccessTy = 0; 739 if (isAddrUse) 740 AccessTy = getAccessType(Uses[i].Inst); 741 742 // Split the expression into subexprs. 743 SeparateSubExprs(SubExprs, Uses[i].Base, SE); 744 // Add one to SubExpressionUseData.Count for each subexpr present, and 745 // if the subexpr is not a valid immediate within an addressing mode use, 746 // set SubExpressionUseData.notAllUsesAreFree. We definitely want to 747 // hoist these out of the loop (if they are common to all uses). 748 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) { 749 if (++SubExpressionUseData[SubExprs[j]].Count == 1) 750 UniqueSubExprs.push_back(SubExprs[j]); 751 if (!isAddrUse || !fitsInAddressMode(SubExprs[j], AccessTy, TLI, false)) 752 SubExpressionUseData[SubExprs[j]].notAllUsesAreFree = true; 753 } 754 SubExprs.clear(); 755 } 756 757 // Now that we know how many times each is used, build Result. Iterate over 758 // UniqueSubexprs so that we have a stable ordering. 759 for (unsigned i = 0, e = UniqueSubExprs.size(); i != e; ++i) { 760 std::map<const SCEV *, SubExprUseData>::iterator I = 761 SubExpressionUseData.find(UniqueSubExprs[i]); 762 assert(I != SubExpressionUseData.end() && "Entry not found?"); 763 if (I->second.Count == NumUsesInsideLoop) { // Found CSE! 764 if (I->second.notAllUsesAreFree) 765 Result = SE->getAddExpr(Result, I->first); 766 else 767 FreeResult = SE->getAddExpr(FreeResult, I->first); 768 } else 769 // Remove non-cse's from SubExpressionUseData. 770 SubExpressionUseData.erase(I); 771 } 772 773 if (FreeResult != Zero) { 774 // We have some subexpressions that can be subsumed into addressing 775 // modes in every use inside the loop. However, it's possible that 776 // there are so many of them that the combined FreeResult cannot 777 // be subsumed, or that the target cannot handle both a FreeResult 778 // and a Result in the same instruction (for example because it would 779 // require too many registers). Check this. 780 for (unsigned i=0; i<NumUses; ++i) { 781 if (!L->contains(Uses[i].Inst)) 782 continue; 783 // We know this is an addressing mode use; if there are any uses that 784 // are not, FreeResult would be Zero. 785 const Type *AccessTy = getAccessType(Uses[i].Inst); 786 if (!fitsInAddressMode(FreeResult, AccessTy, TLI, Result!=Zero)) { 787 // FIXME: could split up FreeResult into pieces here, some hoisted 788 // and some not. There is no obvious advantage to this. 789 Result = SE->getAddExpr(Result, FreeResult); 790 FreeResult = Zero; 791 break; 792 } 793 } 794 } 795 796 // If we found no CSE's, return now. 797 if (Result == Zero) return Result; 798 799 // If we still have a FreeResult, remove its subexpressions from 800 // SubExpressionUseData. This means they will remain in the use Bases. 801 if (FreeResult != Zero) { 802 SeparateSubExprs(SubExprs, FreeResult, SE); 803 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) { 804 std::map<const SCEV *, SubExprUseData>::iterator I = 805 SubExpressionUseData.find(SubExprs[j]); 806 SubExpressionUseData.erase(I); 807 } 808 SubExprs.clear(); 809 } 810 811 // Otherwise, remove all of the CSE's we found from each of the base values. 812 for (unsigned i = 0; i != NumUses; ++i) { 813 // Uses outside the loop don't necessarily include the common base, but 814 // the final IV value coming into those uses does. Instead of trying to 815 // remove the pieces of the common base, which might not be there, 816 // subtract off the base to compensate for this. 817 if (!L->contains(Uses[i].Inst)) { 818 Uses[i].Base = SE->getMinusSCEV(Uses[i].Base, Result); 819 continue; 820 } 821 822 // Split the expression into subexprs. 823 SeparateSubExprs(SubExprs, Uses[i].Base, SE); 824 825 // Remove any common subexpressions. 826 for (unsigned j = 0, e = SubExprs.size(); j != e; ++j) 827 if (SubExpressionUseData.count(SubExprs[j])) { 828 SubExprs.erase(SubExprs.begin()+j); 829 --j; --e; 830 } 831 832 // Finally, add the non-shared expressions together. 833 if (SubExprs.empty()) 834 Uses[i].Base = Zero; 835 else 836 Uses[i].Base = SE->getAddExpr(SubExprs); 837 SubExprs.clear(); 838 } 839 840 return Result; 841} 842 843/// ValidScale - Check whether the given Scale is valid for all loads and 844/// stores in UsersToProcess. 845/// 846bool LoopStrengthReduce::ValidScale(bool HasBaseReg, int64_t Scale, 847 const std::vector<BasedUser>& UsersToProcess) { 848 if (!TLI) 849 return true; 850 851 for (unsigned i = 0, e = UsersToProcess.size(); i!=e; ++i) { 852 // If this is a load or other access, pass the type of the access in. 853 const Type *AccessTy = 854 Type::getVoidTy(UsersToProcess[i].Inst->getContext()); 855 if (isAddressUse(UsersToProcess[i].Inst, 856 UsersToProcess[i].OperandValToReplace)) 857 AccessTy = getAccessType(UsersToProcess[i].Inst); 858 else if (isa<PHINode>(UsersToProcess[i].Inst)) 859 continue; 860 861 TargetLowering::AddrMode AM; 862 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm)) 863 AM.BaseOffs = SC->getValue()->getSExtValue(); 864 AM.HasBaseReg = HasBaseReg || !UsersToProcess[i].Base->isZero(); 865 AM.Scale = Scale; 866 867 // If load[imm+r*scale] is illegal, bail out. 868 if (!TLI->isLegalAddressingMode(AM, AccessTy)) 869 return false; 870 } 871 return true; 872} 873 874/// ValidOffset - Check whether the given Offset is valid for all loads and 875/// stores in UsersToProcess. 876/// 877bool LoopStrengthReduce::ValidOffset(bool HasBaseReg, 878 int64_t Offset, 879 int64_t Scale, 880 const std::vector<BasedUser>& UsersToProcess) { 881 if (!TLI) 882 return true; 883 884 for (unsigned i=0, e = UsersToProcess.size(); i!=e; ++i) { 885 // If this is a load or other access, pass the type of the access in. 886 const Type *AccessTy = 887 Type::getVoidTy(UsersToProcess[i].Inst->getContext()); 888 if (isAddressUse(UsersToProcess[i].Inst, 889 UsersToProcess[i].OperandValToReplace)) 890 AccessTy = getAccessType(UsersToProcess[i].Inst); 891 else if (isa<PHINode>(UsersToProcess[i].Inst)) 892 continue; 893 894 TargetLowering::AddrMode AM; 895 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(UsersToProcess[i].Imm)) 896 AM.BaseOffs = SC->getValue()->getSExtValue(); 897 AM.BaseOffs = (uint64_t)AM.BaseOffs + (uint64_t)Offset; 898 AM.HasBaseReg = HasBaseReg || !UsersToProcess[i].Base->isZero(); 899 AM.Scale = Scale; 900 901 // If load[imm+r*scale] is illegal, bail out. 902 if (!TLI->isLegalAddressingMode(AM, AccessTy)) 903 return false; 904 } 905 return true; 906} 907 908/// RequiresTypeConversion - Returns true if converting Ty1 to Ty2 is not 909/// a nop. 910bool LoopStrengthReduce::RequiresTypeConversion(const Type *Ty1, 911 const Type *Ty2) { 912 if (Ty1 == Ty2) 913 return false; 914 Ty1 = SE->getEffectiveSCEVType(Ty1); 915 Ty2 = SE->getEffectiveSCEVType(Ty2); 916 if (Ty1 == Ty2) 917 return false; 918 if (Ty1->canLosslesslyBitCastTo(Ty2)) 919 return false; 920 if (TLI && TLI->isTruncateFree(Ty1, Ty2)) 921 return false; 922 return true; 923} 924 925/// CheckForIVReuse - Returns the multiple if the stride is the multiple 926/// of a previous stride and it is a legal value for the target addressing 927/// mode scale component and optional base reg. This allows the users of 928/// this stride to be rewritten as prev iv * factor. It returns 0 if no 929/// reuse is possible. Factors can be negative on same targets, e.g. ARM. 930/// 931/// If all uses are outside the loop, we don't require that all multiplies 932/// be folded into the addressing mode, nor even that the factor be constant; 933/// a multiply (executed once) outside the loop is better than another IV 934/// within. Well, usually. 935const SCEV *LoopStrengthReduce::CheckForIVReuse(bool HasBaseReg, 936 bool AllUsesAreAddresses, 937 bool AllUsesAreOutsideLoop, 938 const SCEV *Stride, 939 IVExpr &IV, const Type *Ty, 940 const std::vector<BasedUser>& UsersToProcess) { 941 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride)) { 942 int64_t SInt = SC->getValue()->getSExtValue(); 943 for (unsigned NewStride = 0, e = IU->StrideOrder.size(); 944 NewStride != e; ++NewStride) { 945 std::map<const SCEV *, IVsOfOneStride>::iterator SI = 946 IVsByStride.find(IU->StrideOrder[NewStride]); 947 if (SI == IVsByStride.end() || !isa<SCEVConstant>(SI->first)) 948 continue; 949 // The other stride has no uses, don't reuse it. 950 std::map<const SCEV *, IVUsersOfOneStride *>::iterator UI = 951 IU->IVUsesByStride.find(IU->StrideOrder[NewStride]); 952 if (UI->second->Users.empty()) 953 continue; 954 int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue(); 955 if (SI->first != Stride && 956 (unsigned(abs64(SInt)) < SSInt || (SInt % SSInt) != 0)) 957 continue; 958 int64_t Scale = SInt / SSInt; 959 // Check that this stride is valid for all the types used for loads and 960 // stores; if it can be used for some and not others, we might as well use 961 // the original stride everywhere, since we have to create the IV for it 962 // anyway. If the scale is 1, then we don't need to worry about folding 963 // multiplications. 964 if (Scale == 1 || 965 (AllUsesAreAddresses && 966 ValidScale(HasBaseReg, Scale, UsersToProcess))) { 967 // Prefer to reuse an IV with a base of zero. 968 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(), 969 IE = SI->second.IVs.end(); II != IE; ++II) 970 // Only reuse previous IV if it would not require a type conversion 971 // and if the base difference can be folded. 972 if (II->Base->isZero() && 973 !RequiresTypeConversion(II->Base->getType(), Ty)) { 974 IV = *II; 975 return SE->getIntegerSCEV(Scale, Stride->getType()); 976 } 977 // Otherwise, settle for an IV with a foldable base. 978 if (AllUsesAreAddresses) 979 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(), 980 IE = SI->second.IVs.end(); II != IE; ++II) 981 // Only reuse previous IV if it would not require a type conversion 982 // and if the base difference can be folded. 983 if (SE->getEffectiveSCEVType(II->Base->getType()) == 984 SE->getEffectiveSCEVType(Ty) && 985 isa<SCEVConstant>(II->Base)) { 986 int64_t Base = 987 cast<SCEVConstant>(II->Base)->getValue()->getSExtValue(); 988 if (Base > INT32_MIN && Base <= INT32_MAX && 989 ValidOffset(HasBaseReg, -Base * Scale, 990 Scale, UsersToProcess)) { 991 IV = *II; 992 return SE->getIntegerSCEV(Scale, Stride->getType()); 993 } 994 } 995 } 996 } 997 } else if (AllUsesAreOutsideLoop) { 998 // Accept nonconstant strides here; it is really really right to substitute 999 // an existing IV if we can. 1000 for (unsigned NewStride = 0, e = IU->StrideOrder.size(); 1001 NewStride != e; ++NewStride) { 1002 std::map<const SCEV *, IVsOfOneStride>::iterator SI = 1003 IVsByStride.find(IU->StrideOrder[NewStride]); 1004 if (SI == IVsByStride.end() || !isa<SCEVConstant>(SI->first)) 1005 continue; 1006 int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue(); 1007 if (SI->first != Stride && SSInt != 1) 1008 continue; 1009 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(), 1010 IE = SI->second.IVs.end(); II != IE; ++II) 1011 // Accept nonzero base here. 1012 // Only reuse previous IV if it would not require a type conversion. 1013 if (!RequiresTypeConversion(II->Base->getType(), Ty)) { 1014 IV = *II; 1015 return Stride; 1016 } 1017 } 1018 // Special case, old IV is -1*x and this one is x. Can treat this one as 1019 // -1*old. 1020 for (unsigned NewStride = 0, e = IU->StrideOrder.size(); 1021 NewStride != e; ++NewStride) { 1022 std::map<const SCEV *, IVsOfOneStride>::iterator SI = 1023 IVsByStride.find(IU->StrideOrder[NewStride]); 1024 if (SI == IVsByStride.end()) 1025 continue; 1026 if (const SCEVMulExpr *ME = dyn_cast<SCEVMulExpr>(SI->first)) 1027 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(ME->getOperand(0))) 1028 if (Stride == ME->getOperand(1) && 1029 SC->getValue()->getSExtValue() == -1LL) 1030 for (std::vector<IVExpr>::iterator II = SI->second.IVs.begin(), 1031 IE = SI->second.IVs.end(); II != IE; ++II) 1032 // Accept nonzero base here. 1033 // Only reuse previous IV if it would not require type conversion. 1034 if (!RequiresTypeConversion(II->Base->getType(), Ty)) { 1035 IV = *II; 1036 return SE->getIntegerSCEV(-1LL, Stride->getType()); 1037 } 1038 } 1039 } 1040 return SE->getIntegerSCEV(0, Stride->getType()); 1041} 1042 1043/// PartitionByIsUseOfPostIncrementedValue - Simple boolean predicate that 1044/// returns true if Val's isUseOfPostIncrementedValue is true. 1045static bool PartitionByIsUseOfPostIncrementedValue(const BasedUser &Val) { 1046 return Val.isUseOfPostIncrementedValue; 1047} 1048 1049/// isNonConstantNegative - Return true if the specified scev is negated, but 1050/// not a constant. 1051static bool isNonConstantNegative(const SCEV *Expr) { 1052 const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(Expr); 1053 if (!Mul) return false; 1054 1055 // If there is a constant factor, it will be first. 1056 const SCEVConstant *SC = dyn_cast<SCEVConstant>(Mul->getOperand(0)); 1057 if (!SC) return false; 1058 1059 // Return true if the value is negative, this matches things like (-42 * V). 1060 return SC->getValue()->getValue().isNegative(); 1061} 1062 1063/// CollectIVUsers - Transform our list of users and offsets to a bit more 1064/// complex table. In this new vector, each 'BasedUser' contains 'Base', the 1065/// base of the strided accesses, as well as the old information from Uses. We 1066/// progressively move information from the Base field to the Imm field, until 1067/// we eventually have the full access expression to rewrite the use. 1068const SCEV *LoopStrengthReduce::CollectIVUsers(const SCEV *Stride, 1069 IVUsersOfOneStride &Uses, 1070 Loop *L, 1071 bool &AllUsesAreAddresses, 1072 bool &AllUsesAreOutsideLoop, 1073 std::vector<BasedUser> &UsersToProcess) { 1074 // FIXME: Generalize to non-affine IV's. 1075 if (!Stride->isLoopInvariant(L)) 1076 return SE->getIntegerSCEV(0, Stride->getType()); 1077 1078 UsersToProcess.reserve(Uses.Users.size()); 1079 for (ilist<IVStrideUse>::iterator I = Uses.Users.begin(), 1080 E = Uses.Users.end(); I != E; ++I) { 1081 UsersToProcess.push_back(BasedUser(*I, SE)); 1082 1083 // Move any loop variant operands from the offset field to the immediate 1084 // field of the use, so that we don't try to use something before it is 1085 // computed. 1086 MoveLoopVariantsToImmediateField(UsersToProcess.back().Base, 1087 UsersToProcess.back().Imm, L, SE); 1088 assert(UsersToProcess.back().Base->isLoopInvariant(L) && 1089 "Base value is not loop invariant!"); 1090 } 1091 1092 // We now have a whole bunch of uses of like-strided induction variables, but 1093 // they might all have different bases. We want to emit one PHI node for this 1094 // stride which we fold as many common expressions (between the IVs) into as 1095 // possible. Start by identifying the common expressions in the base values 1096 // for the strides (e.g. if we have "A+C+B" and "A+B+D" as our bases, find 1097 // "A+B"), emit it to the preheader, then remove the expression from the 1098 // UsersToProcess base values. 1099 const SCEV *CommonExprs = 1100 RemoveCommonExpressionsFromUseBases(UsersToProcess, SE, L, TLI); 1101 1102 // Next, figure out what we can represent in the immediate fields of 1103 // instructions. If we can represent anything there, move it to the imm 1104 // fields of the BasedUsers. We do this so that it increases the commonality 1105 // of the remaining uses. 1106 unsigned NumPHI = 0; 1107 bool HasAddress = false; 1108 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) { 1109 // If the user is not in the current loop, this means it is using the exit 1110 // value of the IV. Do not put anything in the base, make sure it's all in 1111 // the immediate field to allow as much factoring as possible. 1112 if (!L->contains(UsersToProcess[i].Inst)) { 1113 UsersToProcess[i].Imm = SE->getAddExpr(UsersToProcess[i].Imm, 1114 UsersToProcess[i].Base); 1115 UsersToProcess[i].Base = 1116 SE->getIntegerSCEV(0, UsersToProcess[i].Base->getType()); 1117 } else { 1118 // Not all uses are outside the loop. 1119 AllUsesAreOutsideLoop = false; 1120 1121 // Addressing modes can be folded into loads and stores. Be careful that 1122 // the store is through the expression, not of the expression though. 1123 bool isPHI = false; 1124 bool isAddress = isAddressUse(UsersToProcess[i].Inst, 1125 UsersToProcess[i].OperandValToReplace); 1126 if (isa<PHINode>(UsersToProcess[i].Inst)) { 1127 isPHI = true; 1128 ++NumPHI; 1129 } 1130 1131 if (isAddress) 1132 HasAddress = true; 1133 1134 // If this use isn't an address, then not all uses are addresses. 1135 if (!isAddress && !isPHI) 1136 AllUsesAreAddresses = false; 1137 1138 MoveImmediateValues(TLI, UsersToProcess[i].Inst, UsersToProcess[i].Base, 1139 UsersToProcess[i].Imm, isAddress, L, SE); 1140 } 1141 } 1142 1143 // If one of the use is a PHI node and all other uses are addresses, still 1144 // allow iv reuse. Essentially we are trading one constant multiplication 1145 // for one fewer iv. 1146 if (NumPHI > 1) 1147 AllUsesAreAddresses = false; 1148 1149 // There are no in-loop address uses. 1150 if (AllUsesAreAddresses && (!HasAddress && !AllUsesAreOutsideLoop)) 1151 AllUsesAreAddresses = false; 1152 1153 return CommonExprs; 1154} 1155 1156/// ShouldUseFullStrengthReductionMode - Test whether full strength-reduction 1157/// is valid and profitable for the given set of users of a stride. In 1158/// full strength-reduction mode, all addresses at the current stride are 1159/// strength-reduced all the way down to pointer arithmetic. 1160/// 1161bool LoopStrengthReduce::ShouldUseFullStrengthReductionMode( 1162 const std::vector<BasedUser> &UsersToProcess, 1163 const Loop *L, 1164 bool AllUsesAreAddresses, 1165 const SCEV *Stride) { 1166 if (!EnableFullLSRMode) 1167 return false; 1168 1169 // The heuristics below aim to avoid increasing register pressure, but 1170 // fully strength-reducing all the addresses increases the number of 1171 // add instructions, so don't do this when optimizing for size. 1172 // TODO: If the loop is large, the savings due to simpler addresses 1173 // may oughtweight the costs of the extra increment instructions. 1174 if (L->getHeader()->getParent()->hasFnAttr(Attribute::OptimizeForSize)) 1175 return false; 1176 1177 // TODO: For now, don't do full strength reduction if there could 1178 // potentially be greater-stride multiples of the current stride 1179 // which could reuse the current stride IV. 1180 if (IU->StrideOrder.back() != Stride) 1181 return false; 1182 1183 // Iterate through the uses to find conditions that automatically rule out 1184 // full-lsr mode. 1185 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ) { 1186 const SCEV *Base = UsersToProcess[i].Base; 1187 const SCEV *Imm = UsersToProcess[i].Imm; 1188 // If any users have a loop-variant component, they can't be fully 1189 // strength-reduced. 1190 if (Imm && !Imm->isLoopInvariant(L)) 1191 return false; 1192 // If there are to users with the same base and the difference between 1193 // the two Imm values can't be folded into the address, full 1194 // strength reduction would increase register pressure. 1195 do { 1196 const SCEV *CurImm = UsersToProcess[i].Imm; 1197 if ((CurImm || Imm) && CurImm != Imm) { 1198 if (!CurImm) CurImm = SE->getIntegerSCEV(0, Stride->getType()); 1199 if (!Imm) Imm = SE->getIntegerSCEV(0, Stride->getType()); 1200 const Instruction *Inst = UsersToProcess[i].Inst; 1201 const Type *AccessTy = getAccessType(Inst); 1202 const SCEV *Diff = SE->getMinusSCEV(UsersToProcess[i].Imm, Imm); 1203 if (!Diff->isZero() && 1204 (!AllUsesAreAddresses || 1205 !fitsInAddressMode(Diff, AccessTy, TLI, /*HasBaseReg=*/true))) 1206 return false; 1207 } 1208 } while (++i != e && Base == UsersToProcess[i].Base); 1209 } 1210 1211 // If there's exactly one user in this stride, fully strength-reducing it 1212 // won't increase register pressure. If it's starting from a non-zero base, 1213 // it'll be simpler this way. 1214 if (UsersToProcess.size() == 1 && !UsersToProcess[0].Base->isZero()) 1215 return true; 1216 1217 // Otherwise, if there are any users in this stride that don't require 1218 // a register for their base, full strength-reduction will increase 1219 // register pressure. 1220 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) 1221 if (UsersToProcess[i].Base->isZero()) 1222 return false; 1223 1224 // Otherwise, go for it. 1225 return true; 1226} 1227 1228/// InsertAffinePhi Create and insert a PHI node for an induction variable 1229/// with the specified start and step values in the specified loop. 1230/// 1231/// If NegateStride is true, the stride should be negated by using a 1232/// subtract instead of an add. 1233/// 1234/// Return the created phi node. 1235/// 1236static PHINode *InsertAffinePhi(const SCEV *Start, const SCEV *Step, 1237 Instruction *IVIncInsertPt, 1238 const Loop *L, 1239 SCEVExpander &Rewriter) { 1240 assert(Start->isLoopInvariant(L) && "New PHI start is not loop invariant!"); 1241 assert(Step->isLoopInvariant(L) && "New PHI stride is not loop invariant!"); 1242 1243 BasicBlock *Header = L->getHeader(); 1244 BasicBlock *Preheader = L->getLoopPreheader(); 1245 BasicBlock *LatchBlock = L->getLoopLatch(); 1246 const Type *Ty = Start->getType(); 1247 Ty = Rewriter.SE.getEffectiveSCEVType(Ty); 1248 1249 PHINode *PN = PHINode::Create(Ty, "lsr.iv", Header->begin()); 1250 PN->addIncoming(Rewriter.expandCodeFor(Start, Ty, Preheader->getTerminator()), 1251 Preheader); 1252 1253 // If the stride is negative, insert a sub instead of an add for the 1254 // increment. 1255 bool isNegative = isNonConstantNegative(Step); 1256 const SCEV *IncAmount = Step; 1257 if (isNegative) 1258 IncAmount = Rewriter.SE.getNegativeSCEV(Step); 1259 1260 // Insert an add instruction right before the terminator corresponding 1261 // to the back-edge or just before the only use. The location is determined 1262 // by the caller and passed in as IVIncInsertPt. 1263 Value *StepV = Rewriter.expandCodeFor(IncAmount, Ty, 1264 Preheader->getTerminator()); 1265 Instruction *IncV; 1266 if (isNegative) { 1267 IncV = BinaryOperator::CreateSub(PN, StepV, "lsr.iv.next", 1268 IVIncInsertPt); 1269 } else { 1270 IncV = BinaryOperator::CreateAdd(PN, StepV, "lsr.iv.next", 1271 IVIncInsertPt); 1272 } 1273 if (!isa<ConstantInt>(StepV)) ++NumVariable; 1274 1275 PN->addIncoming(IncV, LatchBlock); 1276 1277 ++NumInserted; 1278 return PN; 1279} 1280 1281static void SortUsersToProcess(std::vector<BasedUser> &UsersToProcess) { 1282 // We want to emit code for users inside the loop first. To do this, we 1283 // rearrange BasedUser so that the entries at the end have 1284 // isUseOfPostIncrementedValue = false, because we pop off the end of the 1285 // vector (so we handle them first). 1286 std::partition(UsersToProcess.begin(), UsersToProcess.end(), 1287 PartitionByIsUseOfPostIncrementedValue); 1288 1289 // Sort this by base, so that things with the same base are handled 1290 // together. By partitioning first and stable-sorting later, we are 1291 // guaranteed that within each base we will pop off users from within the 1292 // loop before users outside of the loop with a particular base. 1293 // 1294 // We would like to use stable_sort here, but we can't. The problem is that 1295 // const SCEV *'s don't have a deterministic ordering w.r.t to each other, so 1296 // we don't have anything to do a '<' comparison on. Because we think the 1297 // number of uses is small, do a horrible bubble sort which just relies on 1298 // ==. 1299 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) { 1300 // Get a base value. 1301 const SCEV *Base = UsersToProcess[i].Base; 1302 1303 // Compact everything with this base to be consecutive with this one. 1304 for (unsigned j = i+1; j != e; ++j) { 1305 if (UsersToProcess[j].Base == Base) { 1306 std::swap(UsersToProcess[i+1], UsersToProcess[j]); 1307 ++i; 1308 } 1309 } 1310 } 1311} 1312 1313/// PrepareToStrengthReduceFully - Prepare to fully strength-reduce 1314/// UsersToProcess, meaning lowering addresses all the way down to direct 1315/// pointer arithmetic. 1316/// 1317void 1318LoopStrengthReduce::PrepareToStrengthReduceFully( 1319 std::vector<BasedUser> &UsersToProcess, 1320 const SCEV *Stride, 1321 const SCEV *CommonExprs, 1322 const Loop *L, 1323 SCEVExpander &PreheaderRewriter) { 1324 DEBUG(dbgs() << " Fully reducing all users\n"); 1325 1326 // Rewrite the UsersToProcess records, creating a separate PHI for each 1327 // unique Base value. 1328 Instruction *IVIncInsertPt = L->getLoopLatch()->getTerminator(); 1329 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ) { 1330 // TODO: The uses are grouped by base, but not sorted. We arbitrarily 1331 // pick the first Imm value here to start with, and adjust it for the 1332 // other uses. 1333 const SCEV *Imm = UsersToProcess[i].Imm; 1334 const SCEV *Base = UsersToProcess[i].Base; 1335 const SCEV *Start = SE->getAddExpr(CommonExprs, Base, Imm); 1336 PHINode *Phi = InsertAffinePhi(Start, Stride, IVIncInsertPt, L, 1337 PreheaderRewriter); 1338 // Loop over all the users with the same base. 1339 do { 1340 UsersToProcess[i].Base = SE->getIntegerSCEV(0, Stride->getType()); 1341 UsersToProcess[i].Imm = SE->getMinusSCEV(UsersToProcess[i].Imm, Imm); 1342 UsersToProcess[i].Phi = Phi; 1343 assert(UsersToProcess[i].Imm->isLoopInvariant(L) && 1344 "ShouldUseFullStrengthReductionMode should reject this!"); 1345 } while (++i != e && Base == UsersToProcess[i].Base); 1346 } 1347} 1348 1349/// FindIVIncInsertPt - Return the location to insert the increment instruction. 1350/// If the only use if a use of postinc value, (must be the loop termination 1351/// condition), then insert it just before the use. 1352static Instruction *FindIVIncInsertPt(std::vector<BasedUser> &UsersToProcess, 1353 const Loop *L) { 1354 if (UsersToProcess.size() == 1 && 1355 UsersToProcess[0].isUseOfPostIncrementedValue && 1356 L->contains(UsersToProcess[0].Inst)) 1357 return UsersToProcess[0].Inst; 1358 return L->getLoopLatch()->getTerminator(); 1359} 1360 1361/// PrepareToStrengthReduceWithNewPhi - Insert a new induction variable for the 1362/// given users to share. 1363/// 1364void 1365LoopStrengthReduce::PrepareToStrengthReduceWithNewPhi( 1366 std::vector<BasedUser> &UsersToProcess, 1367 const SCEV *Stride, 1368 const SCEV *CommonExprs, 1369 Value *CommonBaseV, 1370 Instruction *IVIncInsertPt, 1371 const Loop *L, 1372 SCEVExpander &PreheaderRewriter) { 1373 DEBUG(dbgs() << " Inserting new PHI:\n"); 1374 1375 PHINode *Phi = InsertAffinePhi(SE->getUnknown(CommonBaseV), 1376 Stride, IVIncInsertPt, L, 1377 PreheaderRewriter); 1378 1379 // Remember this in case a later stride is multiple of this. 1380 IVsByStride[Stride].addIV(Stride, CommonExprs, Phi); 1381 1382 // All the users will share this new IV. 1383 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) 1384 UsersToProcess[i].Phi = Phi; 1385 1386 DEBUG(dbgs() << " IV="); 1387 DEBUG(WriteAsOperand(dbgs(), Phi, /*PrintType=*/false)); 1388 DEBUG(dbgs() << "\n"); 1389} 1390 1391/// PrepareToStrengthReduceFromSmallerStride - Prepare for the given users to 1392/// reuse an induction variable with a stride that is a factor of the current 1393/// induction variable. 1394/// 1395void 1396LoopStrengthReduce::PrepareToStrengthReduceFromSmallerStride( 1397 std::vector<BasedUser> &UsersToProcess, 1398 Value *CommonBaseV, 1399 const IVExpr &ReuseIV, 1400 Instruction *PreInsertPt) { 1401 DEBUG(dbgs() << " Rewriting in terms of existing IV of STRIDE " 1402 << *ReuseIV.Stride << " and BASE " << *ReuseIV.Base << "\n"); 1403 1404 // All the users will share the reused IV. 1405 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) 1406 UsersToProcess[i].Phi = ReuseIV.PHI; 1407 1408 Constant *C = dyn_cast<Constant>(CommonBaseV); 1409 if (C && 1410 (!C->isNullValue() && 1411 !fitsInAddressMode(SE->getUnknown(CommonBaseV), CommonBaseV->getType(), 1412 TLI, false))) 1413 // We want the common base emitted into the preheader! This is just 1414 // using cast as a copy so BitCast (no-op cast) is appropriate 1415 CommonBaseV = new BitCastInst(CommonBaseV, CommonBaseV->getType(), 1416 "commonbase", PreInsertPt); 1417} 1418 1419static bool IsImmFoldedIntoAddrMode(GlobalValue *GV, int64_t Offset, 1420 const Type *AccessTy, 1421 std::vector<BasedUser> &UsersToProcess, 1422 const TargetLowering *TLI) { 1423 SmallVector<Instruction*, 16> AddrModeInsts; 1424 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) { 1425 if (UsersToProcess[i].isUseOfPostIncrementedValue) 1426 continue; 1427 ExtAddrMode AddrMode = 1428 AddressingModeMatcher::Match(UsersToProcess[i].OperandValToReplace, 1429 AccessTy, UsersToProcess[i].Inst, 1430 AddrModeInsts, *TLI); 1431 if (GV && GV != AddrMode.BaseGV) 1432 return false; 1433 if (Offset && !AddrMode.BaseOffs) 1434 // FIXME: How to accurate check it's immediate offset is folded. 1435 return false; 1436 AddrModeInsts.clear(); 1437 } 1438 return true; 1439} 1440 1441/// StrengthReduceIVUsersOfStride - Strength reduce all of the users of a single 1442/// stride of IV. All of the users may have different starting values, and this 1443/// may not be the only stride. 1444void 1445LoopStrengthReduce::StrengthReduceIVUsersOfStride(const SCEV *Stride, 1446 IVUsersOfOneStride &Uses, 1447 Loop *L) { 1448 // If all the users are moved to another stride, then there is nothing to do. 1449 if (Uses.Users.empty()) 1450 return; 1451 1452 // Keep track if every use in UsersToProcess is an address. If they all are, 1453 // we may be able to rewrite the entire collection of them in terms of a 1454 // smaller-stride IV. 1455 bool AllUsesAreAddresses = true; 1456 1457 // Keep track if every use of a single stride is outside the loop. If so, 1458 // we want to be more aggressive about reusing a smaller-stride IV; a 1459 // multiply outside the loop is better than another IV inside. Well, usually. 1460 bool AllUsesAreOutsideLoop = true; 1461 1462 // Transform our list of users and offsets to a bit more complex table. In 1463 // this new vector, each 'BasedUser' contains 'Base' the base of the 1464 // strided accessas well as the old information from Uses. We progressively 1465 // move information from the Base field to the Imm field, until we eventually 1466 // have the full access expression to rewrite the use. 1467 std::vector<BasedUser> UsersToProcess; 1468 const SCEV *CommonExprs = CollectIVUsers(Stride, Uses, L, AllUsesAreAddresses, 1469 AllUsesAreOutsideLoop, 1470 UsersToProcess); 1471 1472 // Sort the UsersToProcess array so that users with common bases are 1473 // next to each other. 1474 SortUsersToProcess(UsersToProcess); 1475 1476 // If we managed to find some expressions in common, we'll need to carry 1477 // their value in a register and add it in for each use. This will take up 1478 // a register operand, which potentially restricts what stride values are 1479 // valid. 1480 bool HaveCommonExprs = !CommonExprs->isZero(); 1481 const Type *ReplacedTy = CommonExprs->getType(); 1482 1483 // If all uses are addresses, consider sinking the immediate part of the 1484 // common expression back into uses if they can fit in the immediate fields. 1485 if (TLI && HaveCommonExprs && AllUsesAreAddresses) { 1486 const SCEV *NewCommon = CommonExprs; 1487 const SCEV *Imm = SE->getIntegerSCEV(0, ReplacedTy); 1488 MoveImmediateValues(TLI, Type::getVoidTy( 1489 L->getLoopPreheader()->getContext()), 1490 NewCommon, Imm, true, L, SE); 1491 if (!Imm->isZero()) { 1492 bool DoSink = true; 1493 1494 // If the immediate part of the common expression is a GV, check if it's 1495 // possible to fold it into the target addressing mode. 1496 GlobalValue *GV = 0; 1497 if (const SCEVUnknown *SU = dyn_cast<SCEVUnknown>(Imm)) 1498 GV = dyn_cast<GlobalValue>(SU->getValue()); 1499 int64_t Offset = 0; 1500 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(Imm)) 1501 Offset = SC->getValue()->getSExtValue(); 1502 if (GV || Offset) 1503 // Pass VoidTy as the AccessTy to be conservative, because 1504 // there could be multiple access types among all the uses. 1505 DoSink = IsImmFoldedIntoAddrMode(GV, Offset, 1506 Type::getVoidTy(L->getLoopPreheader()->getContext()), 1507 UsersToProcess, TLI); 1508 1509 if (DoSink) { 1510 DEBUG(dbgs() << " Sinking " << *Imm << " back down into uses\n"); 1511 for (unsigned i = 0, e = UsersToProcess.size(); i != e; ++i) 1512 UsersToProcess[i].Imm = SE->getAddExpr(UsersToProcess[i].Imm, Imm); 1513 CommonExprs = NewCommon; 1514 HaveCommonExprs = !CommonExprs->isZero(); 1515 ++NumImmSunk; 1516 } 1517 } 1518 } 1519 1520 // Now that we know what we need to do, insert the PHI node itself. 1521 // 1522 DEBUG(dbgs() << "LSR: Examining IVs of TYPE " << *ReplacedTy << " of STRIDE " 1523 << *Stride << ":\n" 1524 << " Common base: " << *CommonExprs << "\n"); 1525 1526 SCEVExpander Rewriter(*SE); 1527 SCEVExpander PreheaderRewriter(*SE); 1528 1529 BasicBlock *Preheader = L->getLoopPreheader(); 1530 Instruction *PreInsertPt = Preheader->getTerminator(); 1531 BasicBlock *LatchBlock = L->getLoopLatch(); 1532 Instruction *IVIncInsertPt = LatchBlock->getTerminator(); 1533 1534 Value *CommonBaseV = Constant::getNullValue(ReplacedTy); 1535 1536 const SCEV *RewriteFactor = SE->getIntegerSCEV(0, ReplacedTy); 1537 IVExpr ReuseIV(SE->getIntegerSCEV(0, 1538 Type::getInt32Ty(Preheader->getContext())), 1539 SE->getIntegerSCEV(0, 1540 Type::getInt32Ty(Preheader->getContext())), 1541 0); 1542 1543 // Choose a strength-reduction strategy and prepare for it by creating 1544 // the necessary PHIs and adjusting the bookkeeping. 1545 if (ShouldUseFullStrengthReductionMode(UsersToProcess, L, 1546 AllUsesAreAddresses, Stride)) { 1547 PrepareToStrengthReduceFully(UsersToProcess, Stride, CommonExprs, L, 1548 PreheaderRewriter); 1549 } else { 1550 // Emit the initial base value into the loop preheader. 1551 CommonBaseV = PreheaderRewriter.expandCodeFor(CommonExprs, ReplacedTy, 1552 PreInsertPt); 1553 1554 // If all uses are addresses, check if it is possible to reuse an IV. The 1555 // new IV must have a stride that is a multiple of the old stride; the 1556 // multiple must be a number that can be encoded in the scale field of the 1557 // target addressing mode; and we must have a valid instruction after this 1558 // substitution, including the immediate field, if any. 1559 RewriteFactor = CheckForIVReuse(HaveCommonExprs, AllUsesAreAddresses, 1560 AllUsesAreOutsideLoop, 1561 Stride, ReuseIV, ReplacedTy, 1562 UsersToProcess); 1563 if (!RewriteFactor->isZero()) 1564 PrepareToStrengthReduceFromSmallerStride(UsersToProcess, CommonBaseV, 1565 ReuseIV, PreInsertPt); 1566 else { 1567 IVIncInsertPt = FindIVIncInsertPt(UsersToProcess, L); 1568 PrepareToStrengthReduceWithNewPhi(UsersToProcess, Stride, CommonExprs, 1569 CommonBaseV, IVIncInsertPt, 1570 L, PreheaderRewriter); 1571 } 1572 } 1573 1574 // Process all the users now, replacing their strided uses with 1575 // strength-reduced forms. This outer loop handles all bases, the inner 1576 // loop handles all users of a particular base. 1577 while (!UsersToProcess.empty()) { 1578 const SCEV *Base = UsersToProcess.back().Base; 1579 Instruction *Inst = UsersToProcess.back().Inst; 1580 1581 // Emit the code for Base into the preheader. 1582 Value *BaseV = 0; 1583 if (!Base->isZero()) { 1584 BaseV = PreheaderRewriter.expandCodeFor(Base, 0, PreInsertPt); 1585 1586 DEBUG(dbgs() << " INSERTING code for BASE = " << *Base << ":"); 1587 if (BaseV->hasName()) 1588 DEBUG(dbgs() << " Result value name = %" << BaseV->getName()); 1589 DEBUG(dbgs() << "\n"); 1590 1591 // If BaseV is a non-zero constant, make sure that it gets inserted into 1592 // the preheader, instead of being forward substituted into the uses. We 1593 // do this by forcing a BitCast (noop cast) to be inserted into the 1594 // preheader in this case. 1595 if (!fitsInAddressMode(Base, getAccessType(Inst), TLI, false) && 1596 isa<Constant>(BaseV)) { 1597 // We want this constant emitted into the preheader! This is just 1598 // using cast as a copy so BitCast (no-op cast) is appropriate 1599 BaseV = new BitCastInst(BaseV, BaseV->getType(), "preheaderinsert", 1600 PreInsertPt); 1601 } 1602 } 1603 1604 // Emit the code to add the immediate offset to the Phi value, just before 1605 // the instructions that we identified as using this stride and base. 1606 do { 1607 // FIXME: Use emitted users to emit other users. 1608 BasedUser &User = UsersToProcess.back(); 1609 1610 DEBUG(dbgs() << " Examining "); 1611 if (User.isUseOfPostIncrementedValue) 1612 DEBUG(dbgs() << "postinc"); 1613 else 1614 DEBUG(dbgs() << "preinc"); 1615 DEBUG(dbgs() << " use "); 1616 DEBUG(WriteAsOperand(dbgs(), UsersToProcess.back().OperandValToReplace, 1617 /*PrintType=*/false)); 1618 DEBUG(dbgs() << " in Inst: " << *User.Inst); 1619 1620 // If this instruction wants to use the post-incremented value, move it 1621 // after the post-inc and use its value instead of the PHI. 1622 Value *RewriteOp = User.Phi; 1623 if (User.isUseOfPostIncrementedValue) { 1624 RewriteOp = User.Phi->getIncomingValueForBlock(LatchBlock); 1625 // If this user is in the loop, make sure it is the last thing in the 1626 // loop to ensure it is dominated by the increment. In case it's the 1627 // only use of the iv, the increment instruction is already before the 1628 // use. 1629 if (L->contains(User.Inst) && User.Inst != IVIncInsertPt) 1630 User.Inst->moveBefore(IVIncInsertPt); 1631 } 1632 1633 const SCEV *RewriteExpr = SE->getUnknown(RewriteOp); 1634 1635 if (SE->getEffectiveSCEVType(RewriteOp->getType()) != 1636 SE->getEffectiveSCEVType(ReplacedTy)) { 1637 assert(SE->getTypeSizeInBits(RewriteOp->getType()) > 1638 SE->getTypeSizeInBits(ReplacedTy) && 1639 "Unexpected widening cast!"); 1640 RewriteExpr = SE->getTruncateExpr(RewriteExpr, ReplacedTy); 1641 } 1642 1643 // If we had to insert new instructions for RewriteOp, we have to 1644 // consider that they may not have been able to end up immediately 1645 // next to RewriteOp, because non-PHI instructions may never precede 1646 // PHI instructions in a block. In this case, remember where the last 1647 // instruction was inserted so that if we're replacing a different 1648 // PHI node, we can use the later point to expand the final 1649 // RewriteExpr. 1650 Instruction *NewBasePt = dyn_cast<Instruction>(RewriteOp); 1651 if (RewriteOp == User.Phi) NewBasePt = 0; 1652 1653 // Clear the SCEVExpander's expression map so that we are guaranteed 1654 // to have the code emitted where we expect it. 1655 Rewriter.clear(); 1656 1657 // If we are reusing the iv, then it must be multiplied by a constant 1658 // factor to take advantage of the addressing mode scale component. 1659 if (!RewriteFactor->isZero()) { 1660 // If we're reusing an IV with a nonzero base (currently this happens 1661 // only when all reuses are outside the loop) subtract that base here. 1662 // The base has been used to initialize the PHI node but we don't want 1663 // it here. 1664 if (!ReuseIV.Base->isZero()) { 1665 const SCEV *typedBase = ReuseIV.Base; 1666 if (SE->getEffectiveSCEVType(RewriteExpr->getType()) != 1667 SE->getEffectiveSCEVType(ReuseIV.Base->getType())) { 1668 // It's possible the original IV is a larger type than the new IV, 1669 // in which case we have to truncate the Base. We checked in 1670 // RequiresTypeConversion that this is valid. 1671 assert(SE->getTypeSizeInBits(RewriteExpr->getType()) < 1672 SE->getTypeSizeInBits(ReuseIV.Base->getType()) && 1673 "Unexpected lengthening conversion!"); 1674 typedBase = SE->getTruncateExpr(ReuseIV.Base, 1675 RewriteExpr->getType()); 1676 } 1677 RewriteExpr = SE->getMinusSCEV(RewriteExpr, typedBase); 1678 } 1679 1680 // Multiply old variable, with base removed, by new scale factor. 1681 RewriteExpr = SE->getMulExpr(RewriteFactor, 1682 RewriteExpr); 1683 1684 // The common base is emitted in the loop preheader. But since we 1685 // are reusing an IV, it has not been used to initialize the PHI node. 1686 // Add it to the expression used to rewrite the uses. 1687 // When this use is outside the loop, we earlier subtracted the 1688 // common base, and are adding it back here. Use the same expression 1689 // as before, rather than CommonBaseV, so DAGCombiner will zap it. 1690 if (!CommonExprs->isZero()) { 1691 if (L->contains(User.Inst)) 1692 RewriteExpr = SE->getAddExpr(RewriteExpr, 1693 SE->getUnknown(CommonBaseV)); 1694 else 1695 RewriteExpr = SE->getAddExpr(RewriteExpr, CommonExprs); 1696 } 1697 } 1698 1699 // Now that we know what we need to do, insert code before User for the 1700 // immediate and any loop-variant expressions. 1701 if (BaseV) 1702 // Add BaseV to the PHI value if needed. 1703 RewriteExpr = SE->getAddExpr(RewriteExpr, SE->getUnknown(BaseV)); 1704 1705 User.RewriteInstructionToUseNewBase(RewriteExpr, NewBasePt, 1706 Rewriter, L, this, 1707 DeadInsts, SE); 1708 1709 // Mark old value we replaced as possibly dead, so that it is eliminated 1710 // if we just replaced the last use of that value. 1711 DeadInsts.push_back(User.OperandValToReplace); 1712 1713 UsersToProcess.pop_back(); 1714 ++NumReduced; 1715 1716 // If there are any more users to process with the same base, process them 1717 // now. We sorted by base above, so we just have to check the last elt. 1718 } while (!UsersToProcess.empty() && UsersToProcess.back().Base == Base); 1719 // TODO: Next, find out which base index is the most common, pull it out. 1720 } 1721 1722 // IMPORTANT TODO: Figure out how to partition the IV's with this stride, but 1723 // different starting values, into different PHIs. 1724} 1725 1726void LoopStrengthReduce::StrengthReduceIVUsers(Loop *L) { 1727 // Note: this processes each stride/type pair individually. All users 1728 // passed into StrengthReduceIVUsersOfStride have the same type AND stride. 1729 // Also, note that we iterate over IVUsesByStride indirectly by using 1730 // StrideOrder. This extra layer of indirection makes the ordering of 1731 // strides deterministic - not dependent on map order. 1732 for (unsigned Stride = 0, e = IU->StrideOrder.size(); Stride != e; ++Stride) { 1733 std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI = 1734 IU->IVUsesByStride.find(IU->StrideOrder[Stride]); 1735 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!"); 1736 // FIXME: Generalize to non-affine IV's. 1737 if (!SI->first->isLoopInvariant(L)) 1738 continue; 1739 StrengthReduceIVUsersOfStride(SI->first, *SI->second, L); 1740 } 1741} 1742 1743/// FindIVUserForCond - If Cond has an operand that is an expression of an IV, 1744/// set the IV user and stride information and return true, otherwise return 1745/// false. 1746bool LoopStrengthReduce::FindIVUserForCond(ICmpInst *Cond, 1747 IVStrideUse *&CondUse, 1748 const SCEV* &CondStride) { 1749 for (unsigned Stride = 0, e = IU->StrideOrder.size(); 1750 Stride != e && !CondUse; ++Stride) { 1751 std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI = 1752 IU->IVUsesByStride.find(IU->StrideOrder[Stride]); 1753 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!"); 1754 1755 for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(), 1756 E = SI->second->Users.end(); UI != E; ++UI) 1757 if (UI->getUser() == Cond) { 1758 // NOTE: we could handle setcc instructions with multiple uses here, but 1759 // InstCombine does it as well for simple uses, it's not clear that it 1760 // occurs enough in real life to handle. 1761 CondUse = UI; 1762 CondStride = SI->first; 1763 return true; 1764 } 1765 } 1766 return false; 1767} 1768 1769namespace { 1770 // Constant strides come first which in turns are sorted by their absolute 1771 // values. If absolute values are the same, then positive strides comes first. 1772 // e.g. 1773 // 4, -1, X, 1, 2 ==> 1, -1, 2, 4, X 1774 struct StrideCompare { 1775 const ScalarEvolution *SE; 1776 explicit StrideCompare(const ScalarEvolution *se) : SE(se) {} 1777 1778 bool operator()(const SCEV *LHS, const SCEV *RHS) { 1779 const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS); 1780 const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS); 1781 if (LHSC && RHSC) { 1782 int64_t LV = LHSC->getValue()->getSExtValue(); 1783 int64_t RV = RHSC->getValue()->getSExtValue(); 1784 uint64_t ALV = (LV < 0) ? -LV : LV; 1785 uint64_t ARV = (RV < 0) ? -RV : RV; 1786 if (ALV == ARV) { 1787 if (LV != RV) 1788 return LV > RV; 1789 } else { 1790 return ALV < ARV; 1791 } 1792 1793 // If it's the same value but different type, sort by bit width so 1794 // that we emit larger induction variables before smaller 1795 // ones, letting the smaller be re-written in terms of larger ones. 1796 return SE->getTypeSizeInBits(RHS->getType()) < 1797 SE->getTypeSizeInBits(LHS->getType()); 1798 } 1799 return LHSC && !RHSC; 1800 } 1801 }; 1802} 1803 1804/// ChangeCompareStride - If a loop termination compare instruction is the 1805/// only use of its stride, and the compaison is against a constant value, 1806/// try eliminate the stride by moving the compare instruction to another 1807/// stride and change its constant operand accordingly. e.g. 1808/// 1809/// loop: 1810/// ... 1811/// v1 = v1 + 3 1812/// v2 = v2 + 1 1813/// if (v2 < 10) goto loop 1814/// => 1815/// loop: 1816/// ... 1817/// v1 = v1 + 3 1818/// if (v1 < 30) goto loop 1819ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond, 1820 IVStrideUse* &CondUse, 1821 const SCEV* &CondStride, 1822 bool PostPass) { 1823 // If there's only one stride in the loop, there's nothing to do here. 1824 if (IU->StrideOrder.size() < 2) 1825 return Cond; 1826 // If there are other users of the condition's stride, don't bother 1827 // trying to change the condition because the stride will still 1828 // remain. 1829 std::map<const SCEV *, IVUsersOfOneStride *>::iterator I = 1830 IU->IVUsesByStride.find(CondStride); 1831 if (I == IU->IVUsesByStride.end()) 1832 return Cond; 1833 if (I->second->Users.size() > 1) { 1834 for (ilist<IVStrideUse>::iterator II = I->second->Users.begin(), 1835 EE = I->second->Users.end(); II != EE; ++II) { 1836 if (II->getUser() == Cond) 1837 continue; 1838 if (!isInstructionTriviallyDead(II->getUser())) 1839 return Cond; 1840 } 1841 } 1842 // Only handle constant strides for now. 1843 const SCEVConstant *SC = dyn_cast<SCEVConstant>(CondStride); 1844 if (!SC) return Cond; 1845 1846 ICmpInst::Predicate Predicate = Cond->getPredicate(); 1847 int64_t CmpSSInt = SC->getValue()->getSExtValue(); 1848 unsigned BitWidth = SE->getTypeSizeInBits(CondStride->getType()); 1849 uint64_t SignBit = 1ULL << (BitWidth-1); 1850 const Type *CmpTy = Cond->getOperand(0)->getType(); 1851 const Type *NewCmpTy = NULL; 1852 unsigned TyBits = SE->getTypeSizeInBits(CmpTy); 1853 unsigned NewTyBits = 0; 1854 const SCEV *NewStride = NULL; 1855 Value *NewCmpLHS = NULL; 1856 Value *NewCmpRHS = NULL; 1857 int64_t Scale = 1; 1858 const SCEV *NewOffset = SE->getIntegerSCEV(0, CmpTy); 1859 1860 if (ConstantInt *C = dyn_cast<ConstantInt>(Cond->getOperand(1))) { 1861 int64_t CmpVal = C->getValue().getSExtValue(); 1862 1863 // Check the relevant induction variable for conformance to 1864 // the pattern. 1865 const SCEV *IV = SE->getSCEV(Cond->getOperand(0)); 1866 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV); 1867 if (!AR || !AR->isAffine()) 1868 return Cond; 1869 1870 const SCEVConstant *StartC = dyn_cast<SCEVConstant>(AR->getStart()); 1871 // Check stride constant and the comparision constant signs to detect 1872 // overflow. 1873 if (StartC) { 1874 if ((StartC->getValue()->getSExtValue() < CmpVal && CmpSSInt < 0) || 1875 (StartC->getValue()->getSExtValue() > CmpVal && CmpSSInt > 0)) 1876 return Cond; 1877 } else { 1878 // More restrictive check for the other cases. 1879 if ((CmpVal & SignBit) != (CmpSSInt & SignBit)) 1880 return Cond; 1881 } 1882 1883 // Look for a suitable stride / iv as replacement. 1884 for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) { 1885 std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI = 1886 IU->IVUsesByStride.find(IU->StrideOrder[i]); 1887 if (!isa<SCEVConstant>(SI->first) || SI->second->Users.empty()) 1888 continue; 1889 int64_t SSInt = cast<SCEVConstant>(SI->first)->getValue()->getSExtValue(); 1890 if (SSInt == CmpSSInt || 1891 abs64(SSInt) < abs64(CmpSSInt) || 1892 (SSInt % CmpSSInt) != 0) 1893 continue; 1894 1895 Scale = SSInt / CmpSSInt; 1896 int64_t NewCmpVal = CmpVal * Scale; 1897 1898 // If old icmp value fits in icmp immediate field, but the new one doesn't 1899 // try something else. 1900 if (TLI && 1901 TLI->isLegalICmpImmediate(CmpVal) && 1902 !TLI->isLegalICmpImmediate(NewCmpVal)) 1903 continue; 1904 1905 APInt Mul = APInt(BitWidth*2, CmpVal, true); 1906 Mul = Mul * APInt(BitWidth*2, Scale, true); 1907 // Check for overflow. 1908 if (!Mul.isSignedIntN(BitWidth)) 1909 continue; 1910 // Check for overflow in the stride's type too. 1911 if (!Mul.isSignedIntN(SE->getTypeSizeInBits(SI->first->getType()))) 1912 continue; 1913 1914 // Watch out for overflow. 1915 if (ICmpInst::isSigned(Predicate) && 1916 (CmpVal & SignBit) != (NewCmpVal & SignBit)) 1917 continue; 1918 1919 // Pick the best iv to use trying to avoid a cast. 1920 NewCmpLHS = NULL; 1921 for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(), 1922 E = SI->second->Users.end(); UI != E; ++UI) { 1923 Value *Op = UI->getOperandValToReplace(); 1924 1925 // If the IVStrideUse implies a cast, check for an actual cast which 1926 // can be used to find the original IV expression. 1927 if (SE->getEffectiveSCEVType(Op->getType()) != 1928 SE->getEffectiveSCEVType(SI->first->getType())) { 1929 CastInst *CI = dyn_cast<CastInst>(Op); 1930 // If it's not a simple cast, it's complicated. 1931 if (!CI) 1932 continue; 1933 // If it's a cast from a type other than the stride type, 1934 // it's complicated. 1935 if (CI->getOperand(0)->getType() != SI->first->getType()) 1936 continue; 1937 // Ok, we found the IV expression in the stride's type. 1938 Op = CI->getOperand(0); 1939 } 1940 1941 NewCmpLHS = Op; 1942 if (NewCmpLHS->getType() == CmpTy) 1943 break; 1944 } 1945 if (!NewCmpLHS) 1946 continue; 1947 1948 NewCmpTy = NewCmpLHS->getType(); 1949 NewTyBits = SE->getTypeSizeInBits(NewCmpTy); 1950 const Type *NewCmpIntTy = IntegerType::get(Cond->getContext(), NewTyBits); 1951 if (RequiresTypeConversion(NewCmpTy, CmpTy)) { 1952 // Check if it is possible to rewrite it using 1953 // an iv / stride of a smaller integer type. 1954 unsigned Bits = NewTyBits; 1955 if (ICmpInst::isSigned(Predicate)) 1956 --Bits; 1957 uint64_t Mask = (1ULL << Bits) - 1; 1958 if (((uint64_t)NewCmpVal & Mask) != (uint64_t)NewCmpVal) 1959 continue; 1960 } 1961 1962 // Don't rewrite if use offset is non-constant and the new type is 1963 // of a different type. 1964 // FIXME: too conservative? 1965 if (NewTyBits != TyBits && !isa<SCEVConstant>(CondUse->getOffset())) 1966 continue; 1967 1968 if (!PostPass) { 1969 bool AllUsesAreAddresses = true; 1970 bool AllUsesAreOutsideLoop = true; 1971 std::vector<BasedUser> UsersToProcess; 1972 const SCEV *CommonExprs = CollectIVUsers(SI->first, *SI->second, L, 1973 AllUsesAreAddresses, 1974 AllUsesAreOutsideLoop, 1975 UsersToProcess); 1976 // Avoid rewriting the compare instruction with an iv of new stride 1977 // if it's likely the new stride uses will be rewritten using the 1978 // stride of the compare instruction. 1979 if (AllUsesAreAddresses && 1980 ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess)) 1981 continue; 1982 } 1983 1984 // Avoid rewriting the compare instruction with an iv which has 1985 // implicit extension or truncation built into it. 1986 // TODO: This is over-conservative. 1987 if (SE->getTypeSizeInBits(CondUse->getOffset()->getType()) != TyBits) 1988 continue; 1989 1990 // If scale is negative, use swapped predicate unless it's testing 1991 // for equality. 1992 if (Scale < 0 && !Cond->isEquality()) 1993 Predicate = ICmpInst::getSwappedPredicate(Predicate); 1994 1995 NewStride = IU->StrideOrder[i]; 1996 if (!isa<PointerType>(NewCmpTy)) 1997 NewCmpRHS = ConstantInt::get(NewCmpTy, NewCmpVal); 1998 else { 1999 Constant *CI = ConstantInt::get(NewCmpIntTy, NewCmpVal); 2000 NewCmpRHS = ConstantExpr::getIntToPtr(CI, NewCmpTy); 2001 } 2002 NewOffset = TyBits == NewTyBits 2003 ? SE->getMulExpr(CondUse->getOffset(), 2004 SE->getConstant(CmpTy, Scale)) 2005 : SE->getConstant(NewCmpIntTy, 2006 cast<SCEVConstant>(CondUse->getOffset())->getValue() 2007 ->getSExtValue()*Scale); 2008 break; 2009 } 2010 } 2011 2012 // Forgo this transformation if it the increment happens to be 2013 // unfortunately positioned after the condition, and the condition 2014 // has multiple uses which prevent it from being moved immediately 2015 // before the branch. See 2016 // test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-*.ll 2017 // for an example of this situation. 2018 if (!Cond->hasOneUse()) { 2019 for (BasicBlock::iterator I = Cond, E = Cond->getParent()->end(); 2020 I != E; ++I) 2021 if (I == NewCmpLHS) 2022 return Cond; 2023 } 2024 2025 if (NewCmpRHS) { 2026 // Create a new compare instruction using new stride / iv. 2027 ICmpInst *OldCond = Cond; 2028 // Insert new compare instruction. 2029 Cond = new ICmpInst(OldCond, Predicate, NewCmpLHS, NewCmpRHS, 2030 L->getHeader()->getName() + ".termcond"); 2031 2032 DEBUG(dbgs() << " Change compare stride in Inst " << *OldCond); 2033 DEBUG(dbgs() << " to " << *Cond << '\n'); 2034 2035 // Remove the old compare instruction. The old indvar is probably dead too. 2036 DeadInsts.push_back(CondUse->getOperandValToReplace()); 2037 OldCond->replaceAllUsesWith(Cond); 2038 OldCond->eraseFromParent(); 2039 2040 IU->IVUsesByStride[NewStride]->addUser(NewOffset, Cond, NewCmpLHS); 2041 CondUse = &IU->IVUsesByStride[NewStride]->Users.back(); 2042 CondStride = NewStride; 2043 ++NumEliminated; 2044 Changed = true; 2045 } 2046 2047 return Cond; 2048} 2049 2050/// OptimizeMax - Rewrite the loop's terminating condition if it uses 2051/// a max computation. 2052/// 2053/// This is a narrow solution to a specific, but acute, problem. For loops 2054/// like this: 2055/// 2056/// i = 0; 2057/// do { 2058/// p[i] = 0.0; 2059/// } while (++i < n); 2060/// 2061/// the trip count isn't just 'n', because 'n' might not be positive. And 2062/// unfortunately this can come up even for loops where the user didn't use 2063/// a C do-while loop. For example, seemingly well-behaved top-test loops 2064/// will commonly be lowered like this: 2065// 2066/// if (n > 0) { 2067/// i = 0; 2068/// do { 2069/// p[i] = 0.0; 2070/// } while (++i < n); 2071/// } 2072/// 2073/// and then it's possible for subsequent optimization to obscure the if 2074/// test in such a way that indvars can't find it. 2075/// 2076/// When indvars can't find the if test in loops like this, it creates a 2077/// max expression, which allows it to give the loop a canonical 2078/// induction variable: 2079/// 2080/// i = 0; 2081/// max = n < 1 ? 1 : n; 2082/// do { 2083/// p[i] = 0.0; 2084/// } while (++i != max); 2085/// 2086/// Canonical induction variables are necessary because the loop passes 2087/// are designed around them. The most obvious example of this is the 2088/// LoopInfo analysis, which doesn't remember trip count values. It 2089/// expects to be able to rediscover the trip count each time it is 2090/// needed, and it does this using a simple analyis that only succeeds if 2091/// the loop has a canonical induction variable. 2092/// 2093/// However, when it comes time to generate code, the maximum operation 2094/// can be quite costly, especially if it's inside of an outer loop. 2095/// 2096/// This function solves this problem by detecting this type of loop and 2097/// rewriting their conditions from ICMP_NE back to ICMP_SLT, and deleting 2098/// the instructions for the maximum computation. 2099/// 2100ICmpInst *LoopStrengthReduce::OptimizeMax(Loop *L, ICmpInst *Cond, 2101 IVStrideUse* &CondUse) { 2102 // Check that the loop matches the pattern we're looking for. 2103 if (Cond->getPredicate() != CmpInst::ICMP_EQ && 2104 Cond->getPredicate() != CmpInst::ICMP_NE) 2105 return Cond; 2106 2107 SelectInst *Sel = dyn_cast<SelectInst>(Cond->getOperand(1)); 2108 if (!Sel || !Sel->hasOneUse()) return Cond; 2109 2110 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 2111 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount)) 2112 return Cond; 2113 const SCEV *One = SE->getIntegerSCEV(1, BackedgeTakenCount->getType()); 2114 2115 // Add one to the backedge-taken count to get the trip count. 2116 const SCEV *IterationCount = SE->getAddExpr(BackedgeTakenCount, One); 2117 2118 // Check for a max calculation that matches the pattern. 2119 if (!isa<SCEVSMaxExpr>(IterationCount) && !isa<SCEVUMaxExpr>(IterationCount)) 2120 return Cond; 2121 const SCEVNAryExpr *Max = cast<SCEVNAryExpr>(IterationCount); 2122 if (Max != SE->getSCEV(Sel)) return Cond; 2123 2124 // To handle a max with more than two operands, this optimization would 2125 // require additional checking and setup. 2126 if (Max->getNumOperands() != 2) 2127 return Cond; 2128 2129 const SCEV *MaxLHS = Max->getOperand(0); 2130 const SCEV *MaxRHS = Max->getOperand(1); 2131 if (!MaxLHS || MaxLHS != One) return Cond; 2132 2133 // Check the relevant induction variable for conformance to 2134 // the pattern. 2135 const SCEV *IV = SE->getSCEV(Cond->getOperand(0)); 2136 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV); 2137 if (!AR || !AR->isAffine() || 2138 AR->getStart() != One || 2139 AR->getStepRecurrence(*SE) != One) 2140 return Cond; 2141 2142 assert(AR->getLoop() == L && 2143 "Loop condition operand is an addrec in a different loop!"); 2144 2145 // Check the right operand of the select, and remember it, as it will 2146 // be used in the new comparison instruction. 2147 Value *NewRHS = 0; 2148 if (SE->getSCEV(Sel->getOperand(1)) == MaxRHS) 2149 NewRHS = Sel->getOperand(1); 2150 else if (SE->getSCEV(Sel->getOperand(2)) == MaxRHS) 2151 NewRHS = Sel->getOperand(2); 2152 if (!NewRHS) return Cond; 2153 2154 // Determine the new comparison opcode. It may be signed or unsigned, 2155 // and the original comparison may be either equality or inequality. 2156 CmpInst::Predicate Pred = 2157 isa<SCEVSMaxExpr>(Max) ? CmpInst::ICMP_SLT : CmpInst::ICMP_ULT; 2158 if (Cond->getPredicate() == CmpInst::ICMP_EQ) 2159 Pred = CmpInst::getInversePredicate(Pred); 2160 2161 // Ok, everything looks ok to change the condition into an SLT or SGE and 2162 // delete the max calculation. 2163 ICmpInst *NewCond = 2164 new ICmpInst(Cond, Pred, Cond->getOperand(0), NewRHS, "scmp"); 2165 2166 // Delete the max calculation instructions. 2167 Cond->replaceAllUsesWith(NewCond); 2168 CondUse->setUser(NewCond); 2169 Instruction *Cmp = cast<Instruction>(Sel->getOperand(0)); 2170 Cond->eraseFromParent(); 2171 Sel->eraseFromParent(); 2172 if (Cmp->use_empty()) 2173 Cmp->eraseFromParent(); 2174 return NewCond; 2175} 2176 2177/// OptimizeShadowIV - If IV is used in a int-to-float cast 2178/// inside the loop then try to eliminate the cast opeation. 2179void LoopStrengthReduce::OptimizeShadowIV(Loop *L) { 2180 2181 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 2182 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount)) 2183 return; 2184 2185 for (unsigned Stride = 0, e = IU->StrideOrder.size(); Stride != e; 2186 ++Stride) { 2187 std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI = 2188 IU->IVUsesByStride.find(IU->StrideOrder[Stride]); 2189 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!"); 2190 if (!isa<SCEVConstant>(SI->first)) 2191 continue; 2192 2193 for (ilist<IVStrideUse>::iterator UI = SI->second->Users.begin(), 2194 E = SI->second->Users.end(); UI != E; /* empty */) { 2195 ilist<IVStrideUse>::iterator CandidateUI = UI; 2196 ++UI; 2197 Instruction *ShadowUse = CandidateUI->getUser(); 2198 const Type *DestTy = NULL; 2199 2200 /* If shadow use is a int->float cast then insert a second IV 2201 to eliminate this cast. 2202 2203 for (unsigned i = 0; i < n; ++i) 2204 foo((double)i); 2205 2206 is transformed into 2207 2208 double d = 0.0; 2209 for (unsigned i = 0; i < n; ++i, ++d) 2210 foo(d); 2211 */ 2212 if (UIToFPInst *UCast = dyn_cast<UIToFPInst>(CandidateUI->getUser())) 2213 DestTy = UCast->getDestTy(); 2214 else if (SIToFPInst *SCast = dyn_cast<SIToFPInst>(CandidateUI->getUser())) 2215 DestTy = SCast->getDestTy(); 2216 if (!DestTy) continue; 2217 2218 if (TLI) { 2219 // If target does not support DestTy natively then do not apply 2220 // this transformation. 2221 EVT DVT = TLI->getValueType(DestTy); 2222 if (!TLI->isTypeLegal(DVT)) continue; 2223 } 2224 2225 PHINode *PH = dyn_cast<PHINode>(ShadowUse->getOperand(0)); 2226 if (!PH) continue; 2227 if (PH->getNumIncomingValues() != 2) continue; 2228 2229 const Type *SrcTy = PH->getType(); 2230 int Mantissa = DestTy->getFPMantissaWidth(); 2231 if (Mantissa == -1) continue; 2232 if ((int)SE->getTypeSizeInBits(SrcTy) > Mantissa) 2233 continue; 2234 2235 unsigned Entry, Latch; 2236 if (PH->getIncomingBlock(0) == L->getLoopPreheader()) { 2237 Entry = 0; 2238 Latch = 1; 2239 } else { 2240 Entry = 1; 2241 Latch = 0; 2242 } 2243 2244 ConstantInt *Init = dyn_cast<ConstantInt>(PH->getIncomingValue(Entry)); 2245 if (!Init) continue; 2246 Constant *NewInit = ConstantFP::get(DestTy, Init->getZExtValue()); 2247 2248 BinaryOperator *Incr = 2249 dyn_cast<BinaryOperator>(PH->getIncomingValue(Latch)); 2250 if (!Incr) continue; 2251 if (Incr->getOpcode() != Instruction::Add 2252 && Incr->getOpcode() != Instruction::Sub) 2253 continue; 2254 2255 /* Initialize new IV, double d = 0.0 in above example. */ 2256 ConstantInt *C = NULL; 2257 if (Incr->getOperand(0) == PH) 2258 C = dyn_cast<ConstantInt>(Incr->getOperand(1)); 2259 else if (Incr->getOperand(1) == PH) 2260 C = dyn_cast<ConstantInt>(Incr->getOperand(0)); 2261 else 2262 continue; 2263 2264 if (!C) continue; 2265 2266 // Ignore negative constants, as the code below doesn't handle them 2267 // correctly. TODO: Remove this restriction. 2268 if (!C->getValue().isStrictlyPositive()) continue; 2269 2270 /* Add new PHINode. */ 2271 PHINode *NewPH = PHINode::Create(DestTy, "IV.S.", PH); 2272 2273 /* create new increment. '++d' in above example. */ 2274 Constant *CFP = ConstantFP::get(DestTy, C->getZExtValue()); 2275 BinaryOperator *NewIncr = 2276 BinaryOperator::Create(Incr->getOpcode() == Instruction::Add ? 2277 Instruction::FAdd : Instruction::FSub, 2278 NewPH, CFP, "IV.S.next.", Incr); 2279 2280 NewPH->addIncoming(NewInit, PH->getIncomingBlock(Entry)); 2281 NewPH->addIncoming(NewIncr, PH->getIncomingBlock(Latch)); 2282 2283 /* Remove cast operation */ 2284 ShadowUse->replaceAllUsesWith(NewPH); 2285 ShadowUse->eraseFromParent(); 2286 NumShadow++; 2287 break; 2288 } 2289 } 2290} 2291 2292/// OptimizeIndvars - Now that IVUsesByStride is set up with all of the indvar 2293/// uses in the loop, look to see if we can eliminate some, in favor of using 2294/// common indvars for the different uses. 2295void LoopStrengthReduce::OptimizeIndvars(Loop *L) { 2296 // TODO: implement optzns here. 2297 2298 OptimizeShadowIV(L); 2299} 2300 2301bool LoopStrengthReduce::StrideMightBeShared(const SCEV* Stride, Loop *L, 2302 bool CheckPreInc) { 2303 int64_t SInt = cast<SCEVConstant>(Stride)->getValue()->getSExtValue(); 2304 for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) { 2305 std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI = 2306 IU->IVUsesByStride.find(IU->StrideOrder[i]); 2307 const SCEV *Share = SI->first; 2308 if (!isa<SCEVConstant>(SI->first) || Share == Stride) 2309 continue; 2310 int64_t SSInt = cast<SCEVConstant>(Share)->getValue()->getSExtValue(); 2311 if (SSInt == SInt) 2312 return true; // This can definitely be reused. 2313 if (unsigned(abs64(SSInt)) < SInt || (SSInt % SInt) != 0) 2314 continue; 2315 int64_t Scale = SSInt / SInt; 2316 bool AllUsesAreAddresses = true; 2317 bool AllUsesAreOutsideLoop = true; 2318 std::vector<BasedUser> UsersToProcess; 2319 const SCEV *CommonExprs = CollectIVUsers(SI->first, *SI->second, L, 2320 AllUsesAreAddresses, 2321 AllUsesAreOutsideLoop, 2322 UsersToProcess); 2323 if (AllUsesAreAddresses && 2324 ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess)) { 2325 if (!CheckPreInc) 2326 return true; 2327 // Any pre-inc iv use? 2328 IVUsersOfOneStride &StrideUses = *IU->IVUsesByStride[Share]; 2329 for (ilist<IVStrideUse>::iterator I = StrideUses.Users.begin(), 2330 E = StrideUses.Users.end(); I != E; ++I) { 2331 if (!I->isUseOfPostIncrementedValue()) 2332 return true; 2333 } 2334 } 2335 } 2336 return false; 2337} 2338 2339/// isUsedByExitBranch - Return true if icmp is used by a loop terminating 2340/// conditional branch or it's and / or with other conditions before being used 2341/// as the condition. 2342static bool isUsedByExitBranch(ICmpInst *Cond, Loop *L) { 2343 BasicBlock *CondBB = Cond->getParent(); 2344 if (!L->isLoopExiting(CondBB)) 2345 return false; 2346 BranchInst *TermBr = dyn_cast<BranchInst>(CondBB->getTerminator()); 2347 if (!TermBr || !TermBr->isConditional()) 2348 return false; 2349 2350 Value *User = *Cond->use_begin(); 2351 Instruction *UserInst = dyn_cast<Instruction>(User); 2352 while (UserInst && 2353 (UserInst->getOpcode() == Instruction::And || 2354 UserInst->getOpcode() == Instruction::Or)) { 2355 if (!UserInst->hasOneUse() || UserInst->getParent() != CondBB) 2356 return false; 2357 User = *User->use_begin(); 2358 UserInst = dyn_cast<Instruction>(User); 2359 } 2360 return User == TermBr; 2361} 2362 2363static bool ShouldCountToZero(ICmpInst *Cond, IVStrideUse* &CondUse, 2364 ScalarEvolution *SE, Loop *L, 2365 const TargetLowering *TLI = 0) { 2366 if (!L->contains(Cond)) 2367 return false; 2368 2369 if (!isa<SCEVConstant>(CondUse->getOffset())) 2370 return false; 2371 2372 // Handle only tests for equality for the moment. 2373 if (!Cond->isEquality() || !Cond->hasOneUse()) 2374 return false; 2375 if (!isUsedByExitBranch(Cond, L)) 2376 return false; 2377 2378 Value *CondOp0 = Cond->getOperand(0); 2379 const SCEV *IV = SE->getSCEV(CondOp0); 2380 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(IV); 2381 if (!AR || !AR->isAffine()) 2382 return false; 2383 2384 const SCEVConstant *SC = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*SE)); 2385 if (!SC || SC->getValue()->getSExtValue() < 0) 2386 // If it's already counting down, don't do anything. 2387 return false; 2388 2389 // If the RHS of the comparison is not an loop invariant, the rewrite 2390 // cannot be done. Also bail out if it's already comparing against a zero. 2391 // If we are checking this before cmp stride optimization, check if it's 2392 // comparing against a already legal immediate. 2393 Value *RHS = Cond->getOperand(1); 2394 ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS); 2395 if (!L->isLoopInvariant(RHS) || 2396 (RHSC && RHSC->isZero()) || 2397 (RHSC && TLI && TLI->isLegalICmpImmediate(RHSC->getSExtValue()))) 2398 return false; 2399 2400 // Make sure the IV is only used for counting. Value may be preinc or 2401 // postinc; 2 uses in either case. 2402 if (!CondOp0->hasNUses(2)) 2403 return false; 2404 2405 return true; 2406} 2407 2408/// OptimizeLoopTermCond - Change loop terminating condition to use the 2409/// postinc iv when possible. 2410void LoopStrengthReduce::OptimizeLoopTermCond(Loop *L) { 2411 BasicBlock *LatchBlock = L->getLoopLatch(); 2412 bool LatchExit = L->isLoopExiting(LatchBlock); 2413 SmallVector<BasicBlock*, 8> ExitingBlocks; 2414 L->getExitingBlocks(ExitingBlocks); 2415 2416 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) { 2417 BasicBlock *ExitingBlock = ExitingBlocks[i]; 2418 2419 // Finally, get the terminating condition for the loop if possible. If we 2420 // can, we want to change it to use a post-incremented version of its 2421 // induction variable, to allow coalescing the live ranges for the IV into 2422 // one register value. 2423 2424 BranchInst *TermBr = dyn_cast<BranchInst>(ExitingBlock->getTerminator()); 2425 if (!TermBr) 2426 continue; 2427 // FIXME: Overly conservative, termination condition could be an 'or' etc.. 2428 if (TermBr->isUnconditional() || !isa<ICmpInst>(TermBr->getCondition())) 2429 continue; 2430 2431 // Search IVUsesByStride to find Cond's IVUse if there is one. 2432 IVStrideUse *CondUse = 0; 2433 const SCEV *CondStride = 0; 2434 ICmpInst *Cond = cast<ICmpInst>(TermBr->getCondition()); 2435 if (!FindIVUserForCond(Cond, CondUse, CondStride)) 2436 continue; 2437 2438 // If the latch block is exiting and it's not a single block loop, it's 2439 // not safe to use postinc iv in other exiting blocks. FIXME: overly 2440 // conservative? How about icmp stride optimization? 2441 bool UsePostInc = !(e > 1 && LatchExit && ExitingBlock != LatchBlock); 2442 if (UsePostInc && ExitingBlock != LatchBlock) { 2443 if (!Cond->hasOneUse()) 2444 // See below, we don't want the condition to be cloned. 2445 UsePostInc = false; 2446 else { 2447 // If exiting block is the latch block, we know it's safe and profitable 2448 // to transform the icmp to use post-inc iv. Otherwise do so only if it 2449 // would not reuse another iv and its iv would be reused by other uses. 2450 // We are optimizing for the case where the icmp is the only use of the 2451 // iv. 2452 IVUsersOfOneStride &StrideUses = *IU->IVUsesByStride[CondStride]; 2453 for (ilist<IVStrideUse>::iterator I = StrideUses.Users.begin(), 2454 E = StrideUses.Users.end(); I != E; ++I) { 2455 if (I->getUser() == Cond) 2456 continue; 2457 if (!I->isUseOfPostIncrementedValue()) { 2458 UsePostInc = false; 2459 break; 2460 } 2461 } 2462 } 2463 2464 // If iv for the stride might be shared and any of the users use pre-inc 2465 // iv might be used, then it's not safe to use post-inc iv. 2466 if (UsePostInc && 2467 isa<SCEVConstant>(CondStride) && 2468 StrideMightBeShared(CondStride, L, true)) 2469 UsePostInc = false; 2470 } 2471 2472 // If the trip count is computed in terms of a max (due to ScalarEvolution 2473 // being unable to find a sufficient guard, for example), change the loop 2474 // comparison to use SLT or ULT instead of NE. 2475 Cond = OptimizeMax(L, Cond, CondUse); 2476 2477 // If possible, change stride and operands of the compare instruction to 2478 // eliminate one stride. However, avoid rewriting the compare instruction 2479 // with an iv of new stride if it's likely the new stride uses will be 2480 // rewritten using the stride of the compare instruction. 2481 if (ExitingBlock == LatchBlock && isa<SCEVConstant>(CondStride)) { 2482 // If the condition stride is a constant and it's the only use, we might 2483 // want to optimize it first by turning it to count toward zero. 2484 if (!StrideMightBeShared(CondStride, L, false) && 2485 !ShouldCountToZero(Cond, CondUse, SE, L, TLI)) 2486 Cond = ChangeCompareStride(L, Cond, CondUse, CondStride); 2487 } 2488 2489 if (!UsePostInc) 2490 continue; 2491 2492 DEBUG(dbgs() << " Change loop exiting icmp to use postinc iv: " 2493 << *Cond << '\n'); 2494 2495 // It's possible for the setcc instruction to be anywhere in the loop, and 2496 // possible for it to have multiple users. If it is not immediately before 2497 // the exiting block branch, move it. 2498 if (&*++BasicBlock::iterator(Cond) != (Instruction*)TermBr) { 2499 if (Cond->hasOneUse()) { // Condition has a single use, just move it. 2500 Cond->moveBefore(TermBr); 2501 } else { 2502 // Otherwise, clone the terminating condition and insert into the 2503 // loopend. 2504 Cond = cast<ICmpInst>(Cond->clone()); 2505 Cond->setName(L->getHeader()->getName() + ".termcond"); 2506 ExitingBlock->getInstList().insert(TermBr, Cond); 2507 2508 // Clone the IVUse, as the old use still exists! 2509 IU->IVUsesByStride[CondStride]->addUser(CondUse->getOffset(), Cond, 2510 CondUse->getOperandValToReplace()); 2511 CondUse = &IU->IVUsesByStride[CondStride]->Users.back(); 2512 } 2513 } 2514 2515 // If we get to here, we know that we can transform the setcc instruction to 2516 // use the post-incremented version of the IV, allowing us to coalesce the 2517 // live ranges for the IV correctly. 2518 CondUse->setOffset(SE->getMinusSCEV(CondUse->getOffset(), CondStride)); 2519 CondUse->setIsUseOfPostIncrementedValue(true); 2520 Changed = true; 2521 2522 ++NumLoopCond; 2523 } 2524} 2525 2526bool LoopStrengthReduce::OptimizeLoopCountIVOfStride(const SCEV* &Stride, 2527 IVStrideUse* &CondUse, 2528 Loop *L) { 2529 // If the only use is an icmp of a loop exiting conditional branch, then 2530 // attempt the optimization. 2531 BasedUser User = BasedUser(*CondUse, SE); 2532 assert(isa<ICmpInst>(User.Inst) && "Expecting an ICMPInst!"); 2533 ICmpInst *Cond = cast<ICmpInst>(User.Inst); 2534 2535 // Less strict check now that compare stride optimization is done. 2536 if (!ShouldCountToZero(Cond, CondUse, SE, L)) 2537 return false; 2538 2539 Value *CondOp0 = Cond->getOperand(0); 2540 PHINode *PHIExpr = dyn_cast<PHINode>(CondOp0); 2541 Instruction *Incr; 2542 if (!PHIExpr) { 2543 // Value tested is postinc. Find the phi node. 2544 Incr = dyn_cast<BinaryOperator>(CondOp0); 2545 // FIXME: Just use User.OperandValToReplace here? 2546 if (!Incr || Incr->getOpcode() != Instruction::Add) 2547 return false; 2548 2549 PHIExpr = dyn_cast<PHINode>(Incr->getOperand(0)); 2550 if (!PHIExpr) 2551 return false; 2552 // 1 use for preinc value, the increment. 2553 if (!PHIExpr->hasOneUse()) 2554 return false; 2555 } else { 2556 assert(isa<PHINode>(CondOp0) && 2557 "Unexpected loop exiting counting instruction sequence!"); 2558 PHIExpr = cast<PHINode>(CondOp0); 2559 // Value tested is preinc. Find the increment. 2560 // A CmpInst is not a BinaryOperator; we depend on this. 2561 Instruction::use_iterator UI = PHIExpr->use_begin(); 2562 Incr = dyn_cast<BinaryOperator>(UI); 2563 if (!Incr) 2564 Incr = dyn_cast<BinaryOperator>(++UI); 2565 // One use for postinc value, the phi. Unnecessarily conservative? 2566 if (!Incr || !Incr->hasOneUse() || Incr->getOpcode() != Instruction::Add) 2567 return false; 2568 } 2569 2570 // Replace the increment with a decrement. 2571 DEBUG(dbgs() << "LSR: Examining use "); 2572 DEBUG(WriteAsOperand(dbgs(), CondOp0, /*PrintType=*/false)); 2573 DEBUG(dbgs() << " in Inst: " << *Cond << '\n'); 2574 BinaryOperator *Decr = BinaryOperator::Create(Instruction::Sub, 2575 Incr->getOperand(0), Incr->getOperand(1), "tmp", Incr); 2576 Incr->replaceAllUsesWith(Decr); 2577 Incr->eraseFromParent(); 2578 2579 // Substitute endval-startval for the original startval, and 0 for the 2580 // original endval. Since we're only testing for equality this is OK even 2581 // if the computation wraps around. 2582 BasicBlock *Preheader = L->getLoopPreheader(); 2583 Instruction *PreInsertPt = Preheader->getTerminator(); 2584 unsigned InBlock = L->contains(PHIExpr->getIncomingBlock(0)) ? 1 : 0; 2585 Value *StartVal = PHIExpr->getIncomingValue(InBlock); 2586 Value *EndVal = Cond->getOperand(1); 2587 DEBUG(dbgs() << " Optimize loop counting iv to count down [" 2588 << *EndVal << " .. " << *StartVal << "]\n"); 2589 2590 // FIXME: check for case where both are constant. 2591 Constant* Zero = ConstantInt::get(Cond->getOperand(1)->getType(), 0); 2592 BinaryOperator *NewStartVal = BinaryOperator::Create(Instruction::Sub, 2593 EndVal, StartVal, "tmp", PreInsertPt); 2594 PHIExpr->setIncomingValue(InBlock, NewStartVal); 2595 Cond->setOperand(1, Zero); 2596 DEBUG(dbgs() << " New icmp: " << *Cond << "\n"); 2597 2598 int64_t SInt = cast<SCEVConstant>(Stride)->getValue()->getSExtValue(); 2599 const SCEV *NewStride = 0; 2600 bool Found = false; 2601 for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) { 2602 const SCEV *OldStride = IU->StrideOrder[i]; 2603 if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(OldStride)) 2604 if (SC->getValue()->getSExtValue() == -SInt) { 2605 Found = true; 2606 NewStride = OldStride; 2607 break; 2608 } 2609 } 2610 2611 if (!Found) 2612 NewStride = SE->getIntegerSCEV(-SInt, Stride->getType()); 2613 IU->AddUser(NewStride, CondUse->getOffset(), Cond, Cond->getOperand(0)); 2614 IU->IVUsesByStride[Stride]->removeUser(CondUse); 2615 2616 CondUse = &IU->IVUsesByStride[NewStride]->Users.back(); 2617 Stride = NewStride; 2618 2619 ++NumCountZero; 2620 2621 return true; 2622} 2623 2624/// OptimizeLoopCountIV - If, after all sharing of IVs, the IV used for deciding 2625/// when to exit the loop is used only for that purpose, try to rearrange things 2626/// so it counts down to a test against zero. 2627bool LoopStrengthReduce::OptimizeLoopCountIV(Loop *L) { 2628 bool ThisChanged = false; 2629 for (unsigned i = 0, e = IU->StrideOrder.size(); i != e; ++i) { 2630 const SCEV *Stride = IU->StrideOrder[i]; 2631 std::map<const SCEV *, IVUsersOfOneStride *>::iterator SI = 2632 IU->IVUsesByStride.find(Stride); 2633 assert(SI != IU->IVUsesByStride.end() && "Stride doesn't exist!"); 2634 // FIXME: Generalize to non-affine IV's. 2635 if (!SI->first->isLoopInvariant(L)) 2636 continue; 2637 // If stride is a constant and it has an icmpinst use, check if we can 2638 // optimize the loop to count down. 2639 if (isa<SCEVConstant>(Stride) && SI->second->Users.size() == 1) { 2640 Instruction *User = SI->second->Users.begin()->getUser(); 2641 if (!isa<ICmpInst>(User)) 2642 continue; 2643 const SCEV *CondStride = Stride; 2644 IVStrideUse *Use = &*SI->second->Users.begin(); 2645 if (!OptimizeLoopCountIVOfStride(CondStride, Use, L)) 2646 continue; 2647 ThisChanged = true; 2648 2649 // Now check if it's possible to reuse this iv for other stride uses. 2650 for (unsigned j = 0, ee = IU->StrideOrder.size(); j != ee; ++j) { 2651 const SCEV *SStride = IU->StrideOrder[j]; 2652 if (SStride == CondStride) 2653 continue; 2654 std::map<const SCEV *, IVUsersOfOneStride *>::iterator SII = 2655 IU->IVUsesByStride.find(SStride); 2656 assert(SII != IU->IVUsesByStride.end() && "Stride doesn't exist!"); 2657 // FIXME: Generalize to non-affine IV's. 2658 if (!SII->first->isLoopInvariant(L)) 2659 continue; 2660 // FIXME: Rewrite other stride using CondStride. 2661 } 2662 } 2663 } 2664 2665 Changed |= ThisChanged; 2666 return ThisChanged; 2667} 2668 2669bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) { 2670 IU = &getAnalysis<IVUsers>(); 2671 SE = &getAnalysis<ScalarEvolution>(); 2672 Changed = false; 2673 2674 // If LoopSimplify form is not available, stay out of trouble. 2675 if (!L->getLoopPreheader() || !L->getLoopLatch()) 2676 return false; 2677 2678 if (!IU->IVUsesByStride.empty()) { 2679 DEBUG(dbgs() << "\nLSR on \"" << L->getHeader()->getParent()->getName() 2680 << "\" "; 2681 L->print(dbgs())); 2682 2683 // Sort the StrideOrder so we process larger strides first. 2684 std::stable_sort(IU->StrideOrder.begin(), IU->StrideOrder.end(), 2685 StrideCompare(SE)); 2686 2687 // Optimize induction variables. Some indvar uses can be transformed to use 2688 // strides that will be needed for other purposes. A common example of this 2689 // is the exit test for the loop, which can often be rewritten to use the 2690 // computation of some other indvar to decide when to terminate the loop. 2691 OptimizeIndvars(L); 2692 2693 // Change loop terminating condition to use the postinc iv when possible 2694 // and optimize loop terminating compare. FIXME: Move this after 2695 // StrengthReduceIVUsersOfStride? 2696 OptimizeLoopTermCond(L); 2697 2698 // FIXME: We can shrink overlarge IV's here. e.g. if the code has 2699 // computation in i64 values and the target doesn't support i64, demote 2700 // the computation to 32-bit if safe. 2701 2702 // FIXME: Attempt to reuse values across multiple IV's. In particular, we 2703 // could have something like "for(i) { foo(i*8); bar(i*16) }", which should 2704 // be codegened as "for (j = 0;; j+=8) { foo(j); bar(j+j); }" on X86/PPC. 2705 // Need to be careful that IV's are all the same type. Only works for 2706 // intptr_t indvars. 2707 2708 // IVsByStride keeps IVs for one particular loop. 2709 assert(IVsByStride.empty() && "Stale entries in IVsByStride?"); 2710 2711 StrengthReduceIVUsers(L); 2712 2713 // After all sharing is done, see if we can adjust the loop to test against 2714 // zero instead of counting up to a maximum. This is usually faster. 2715 OptimizeLoopCountIV(L); 2716 2717 // We're done analyzing this loop; release all the state we built up for it. 2718 IVsByStride.clear(); 2719 2720 // Clean up after ourselves 2721 DeleteTriviallyDeadInstructions(); 2722 } 2723 2724 // At this point, it is worth checking to see if any recurrence PHIs are also 2725 // dead, so that we can remove them as well. 2726 DeleteDeadPHIs(L->getHeader()); 2727 2728 return Changed; 2729} 2730