Reassociate.cpp revision 199481
1//===- Reassociate.cpp - Reassociate binary expressions -------------------===// 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 pass reassociates commutative expressions in an order that is designed 11// to promote better constant propagation, GCSE, LICM, PRE... 12// 13// For example: 4 + (x + 5) -> x + (4 + 5) 14// 15// In the implementation of this algorithm, constants are assigned rank = 0, 16// function arguments are rank = 1, and other values are assigned ranks 17// corresponding to the reverse post order traversal of current function 18// (starting at 2), which effectively gives values in deep loops higher rank 19// than values not in loops. 20// 21//===----------------------------------------------------------------------===// 22 23#define DEBUG_TYPE "reassociate" 24#include "llvm/Transforms/Scalar.h" 25#include "llvm/Constants.h" 26#include "llvm/DerivedTypes.h" 27#include "llvm/Function.h" 28#include "llvm/Instructions.h" 29#include "llvm/IntrinsicInst.h" 30#include "llvm/Pass.h" 31#include "llvm/Assembly/Writer.h" 32#include "llvm/Support/CFG.h" 33#include "llvm/Support/Debug.h" 34#include "llvm/Support/ValueHandle.h" 35#include "llvm/Support/raw_ostream.h" 36#include "llvm/ADT/PostOrderIterator.h" 37#include "llvm/ADT/Statistic.h" 38#include <algorithm> 39#include <map> 40using namespace llvm; 41 42STATISTIC(NumLinear , "Number of insts linearized"); 43STATISTIC(NumChanged, "Number of insts reassociated"); 44STATISTIC(NumAnnihil, "Number of expr tree annihilated"); 45STATISTIC(NumFactor , "Number of multiplies factored"); 46 47namespace { 48 struct ValueEntry { 49 unsigned Rank; 50 Value *Op; 51 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {} 52 }; 53 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) { 54 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start. 55 } 56} 57 58#ifndef NDEBUG 59/// PrintOps - Print out the expression identified in the Ops list. 60/// 61static void PrintOps(Instruction *I, const std::vector<ValueEntry> &Ops) { 62 Module *M = I->getParent()->getParent()->getParent(); 63 errs() << Instruction::getOpcodeName(I->getOpcode()) << " " 64 << *Ops[0].Op->getType(); 65 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 66 WriteAsOperand(errs() << " ", Ops[i].Op, false, M); 67 errs() << "," << Ops[i].Rank; 68 } 69} 70#endif 71 72namespace { 73 class Reassociate : public FunctionPass { 74 std::map<BasicBlock*, unsigned> RankMap; 75 std::map<AssertingVH<>, unsigned> ValueRankMap; 76 bool MadeChange; 77 public: 78 static char ID; // Pass identification, replacement for typeid 79 Reassociate() : FunctionPass(&ID) {} 80 81 bool runOnFunction(Function &F); 82 83 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 84 AU.setPreservesCFG(); 85 } 86 private: 87 void BuildRankMap(Function &F); 88 unsigned getRank(Value *V); 89 void ReassociateExpression(BinaryOperator *I); 90 void RewriteExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops, 91 unsigned Idx = 0); 92 Value *OptimizeExpression(BinaryOperator *I, std::vector<ValueEntry> &Ops); 93 void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops); 94 void LinearizeExpr(BinaryOperator *I); 95 Value *RemoveFactorFromExpression(Value *V, Value *Factor); 96 void ReassociateBB(BasicBlock *BB); 97 98 void RemoveDeadBinaryOp(Value *V); 99 }; 100} 101 102char Reassociate::ID = 0; 103static RegisterPass<Reassociate> X("reassociate", "Reassociate expressions"); 104 105// Public interface to the Reassociate pass 106FunctionPass *llvm::createReassociatePass() { return new Reassociate(); } 107 108void Reassociate::RemoveDeadBinaryOp(Value *V) { 109 Instruction *Op = dyn_cast<Instruction>(V); 110 if (!Op || !isa<BinaryOperator>(Op) || !isa<CmpInst>(Op) || !Op->use_empty()) 111 return; 112 113 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1); 114 RemoveDeadBinaryOp(LHS); 115 RemoveDeadBinaryOp(RHS); 116} 117 118 119static bool isUnmovableInstruction(Instruction *I) { 120 if (I->getOpcode() == Instruction::PHI || 121 I->getOpcode() == Instruction::Alloca || 122 I->getOpcode() == Instruction::Load || 123 I->getOpcode() == Instruction::Invoke || 124 (I->getOpcode() == Instruction::Call && 125 !isa<DbgInfoIntrinsic>(I)) || 126 I->getOpcode() == Instruction::UDiv || 127 I->getOpcode() == Instruction::SDiv || 128 I->getOpcode() == Instruction::FDiv || 129 I->getOpcode() == Instruction::URem || 130 I->getOpcode() == Instruction::SRem || 131 I->getOpcode() == Instruction::FRem) 132 return true; 133 return false; 134} 135 136void Reassociate::BuildRankMap(Function &F) { 137 unsigned i = 2; 138 139 // Assign distinct ranks to function arguments 140 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I) 141 ValueRankMap[&*I] = ++i; 142 143 ReversePostOrderTraversal<Function*> RPOT(&F); 144 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(), 145 E = RPOT.end(); I != E; ++I) { 146 BasicBlock *BB = *I; 147 unsigned BBRank = RankMap[BB] = ++i << 16; 148 149 // Walk the basic block, adding precomputed ranks for any instructions that 150 // we cannot move. This ensures that the ranks for these instructions are 151 // all different in the block. 152 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 153 if (isUnmovableInstruction(I)) 154 ValueRankMap[&*I] = ++BBRank; 155 } 156} 157 158unsigned Reassociate::getRank(Value *V) { 159 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument... 160 161 Instruction *I = dyn_cast<Instruction>(V); 162 if (I == 0) return 0; // Otherwise it's a global or constant, rank 0. 163 164 unsigned &CachedRank = ValueRankMap[I]; 165 if (CachedRank) return CachedRank; // Rank already known? 166 167 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that 168 // we can reassociate expressions for code motion! Since we do not recurse 169 // for PHI nodes, we cannot have infinite recursion here, because there 170 // cannot be loops in the value graph that do not go through PHI nodes. 171 unsigned Rank = 0, MaxRank = RankMap[I->getParent()]; 172 for (unsigned i = 0, e = I->getNumOperands(); 173 i != e && Rank != MaxRank; ++i) 174 Rank = std::max(Rank, getRank(I->getOperand(i))); 175 176 // If this is a not or neg instruction, do not count it for rank. This 177 // assures us that X and ~X will have the same rank. 178 if (!I->getType()->isInteger() || 179 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I))) 180 ++Rank; 181 182 //DEBUG(errs() << "Calculated Rank[" << V->getName() << "] = " 183 // << Rank << "\n"); 184 185 return CachedRank = Rank; 186} 187 188/// isReassociableOp - Return true if V is an instruction of the specified 189/// opcode and if it only has one use. 190static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) { 191 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) && 192 cast<Instruction>(V)->getOpcode() == Opcode) 193 return cast<BinaryOperator>(V); 194 return 0; 195} 196 197/// LowerNegateToMultiply - Replace 0-X with X*-1. 198/// 199static Instruction *LowerNegateToMultiply(Instruction *Neg, 200 std::map<AssertingVH<>, unsigned> &ValueRankMap) { 201 Constant *Cst = Constant::getAllOnesValue(Neg->getType()); 202 203 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg); 204 ValueRankMap.erase(Neg); 205 Res->takeName(Neg); 206 Neg->replaceAllUsesWith(Res); 207 Neg->eraseFromParent(); 208 return Res; 209} 210 211// Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'. 212// Note that if D is also part of the expression tree that we recurse to 213// linearize it as well. Besides that case, this does not recurse into A,B, or 214// C. 215void Reassociate::LinearizeExpr(BinaryOperator *I) { 216 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0)); 217 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1)); 218 assert(isReassociableOp(LHS, I->getOpcode()) && 219 isReassociableOp(RHS, I->getOpcode()) && 220 "Not an expression that needs linearization?"); 221 222 DEBUG(errs() << "Linear" << *LHS << '\n' << *RHS << '\n' << *I << '\n'); 223 224 // Move the RHS instruction to live immediately before I, avoiding breaking 225 // dominator properties. 226 RHS->moveBefore(I); 227 228 // Move operands around to do the linearization. 229 I->setOperand(1, RHS->getOperand(0)); 230 RHS->setOperand(0, LHS); 231 I->setOperand(0, RHS); 232 233 ++NumLinear; 234 MadeChange = true; 235 DEBUG(errs() << "Linearized: " << *I << '\n'); 236 237 // If D is part of this expression tree, tail recurse. 238 if (isReassociableOp(I->getOperand(1), I->getOpcode())) 239 LinearizeExpr(I); 240} 241 242 243/// LinearizeExprTree - Given an associative binary expression tree, traverse 244/// all of the uses putting it into canonical form. This forces a left-linear 245/// form of the the expression (((a+b)+c)+d), and collects information about the 246/// rank of the non-tree operands. 247/// 248/// NOTE: These intentionally destroys the expression tree operands (turning 249/// them into undef values) to reduce #uses of the values. This means that the 250/// caller MUST use something like RewriteExprTree to put the values back in. 251/// 252void Reassociate::LinearizeExprTree(BinaryOperator *I, 253 std::vector<ValueEntry> &Ops) { 254 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1); 255 unsigned Opcode = I->getOpcode(); 256 257 // First step, linearize the expression if it is in ((A+B)+(C+D)) form. 258 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode); 259 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode); 260 261 // If this is a multiply expression tree and it contains internal negations, 262 // transform them into multiplies by -1 so they can be reassociated. 263 if (I->getOpcode() == Instruction::Mul) { 264 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) { 265 LHS = LowerNegateToMultiply(cast<Instruction>(LHS), ValueRankMap); 266 LHSBO = isReassociableOp(LHS, Opcode); 267 } 268 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) { 269 RHS = LowerNegateToMultiply(cast<Instruction>(RHS), ValueRankMap); 270 RHSBO = isReassociableOp(RHS, Opcode); 271 } 272 } 273 274 if (!LHSBO) { 275 if (!RHSBO) { 276 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As 277 // such, just remember these operands and their rank. 278 Ops.push_back(ValueEntry(getRank(LHS), LHS)); 279 Ops.push_back(ValueEntry(getRank(RHS), RHS)); 280 281 // Clear the leaves out. 282 I->setOperand(0, UndefValue::get(I->getType())); 283 I->setOperand(1, UndefValue::get(I->getType())); 284 return; 285 } else { 286 // Turn X+(Y+Z) -> (Y+Z)+X 287 std::swap(LHSBO, RHSBO); 288 std::swap(LHS, RHS); 289 bool Success = !I->swapOperands(); 290 assert(Success && "swapOperands failed"); 291 Success = false; 292 MadeChange = true; 293 } 294 } else if (RHSBO) { 295 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not 296 // part of the expression tree. 297 LinearizeExpr(I); 298 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0)); 299 RHS = I->getOperand(1); 300 RHSBO = 0; 301 } 302 303 // Okay, now we know that the LHS is a nested expression and that the RHS is 304 // not. Perform reassociation. 305 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!"); 306 307 // Move LHS right before I to make sure that the tree expression dominates all 308 // values. 309 LHSBO->moveBefore(I); 310 311 // Linearize the expression tree on the LHS. 312 LinearizeExprTree(LHSBO, Ops); 313 314 // Remember the RHS operand and its rank. 315 Ops.push_back(ValueEntry(getRank(RHS), RHS)); 316 317 // Clear the RHS leaf out. 318 I->setOperand(1, UndefValue::get(I->getType())); 319} 320 321// RewriteExprTree - Now that the operands for this expression tree are 322// linearized and optimized, emit them in-order. This function is written to be 323// tail recursive. 324void Reassociate::RewriteExprTree(BinaryOperator *I, 325 std::vector<ValueEntry> &Ops, 326 unsigned i) { 327 if (i+2 == Ops.size()) { 328 if (I->getOperand(0) != Ops[i].Op || 329 I->getOperand(1) != Ops[i+1].Op) { 330 Value *OldLHS = I->getOperand(0); 331 DEBUG(errs() << "RA: " << *I << '\n'); 332 I->setOperand(0, Ops[i].Op); 333 I->setOperand(1, Ops[i+1].Op); 334 DEBUG(errs() << "TO: " << *I << '\n'); 335 MadeChange = true; 336 ++NumChanged; 337 338 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3) 339 // delete the extra, now dead, nodes. 340 RemoveDeadBinaryOp(OldLHS); 341 } 342 return; 343 } 344 assert(i+2 < Ops.size() && "Ops index out of range!"); 345 346 if (I->getOperand(1) != Ops[i].Op) { 347 DEBUG(errs() << "RA: " << *I << '\n'); 348 I->setOperand(1, Ops[i].Op); 349 DEBUG(errs() << "TO: " << *I << '\n'); 350 MadeChange = true; 351 ++NumChanged; 352 } 353 354 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0)); 355 assert(LHS->getOpcode() == I->getOpcode() && 356 "Improper expression tree!"); 357 358 // Compactify the tree instructions together with each other to guarantee 359 // that the expression tree is dominated by all of Ops. 360 LHS->moveBefore(I); 361 RewriteExprTree(LHS, Ops, i+1); 362} 363 364 365 366// NegateValue - Insert instructions before the instruction pointed to by BI, 367// that computes the negative version of the value specified. The negative 368// version of the value is returned, and BI is left pointing at the instruction 369// that should be processed next by the reassociation pass. 370// 371static Value *NegateValue(Value *V, Instruction *BI) { 372 // We are trying to expose opportunity for reassociation. One of the things 373 // that we want to do to achieve this is to push a negation as deep into an 374 // expression chain as possible, to expose the add instructions. In practice, 375 // this means that we turn this: 376 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D 377 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate 378 // the constants. We assume that instcombine will clean up the mess later if 379 // we introduce tons of unnecessary negation instructions... 380 // 381 if (Instruction *I = dyn_cast<Instruction>(V)) 382 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) { 383 // Push the negates through the add. 384 I->setOperand(0, NegateValue(I->getOperand(0), BI)); 385 I->setOperand(1, NegateValue(I->getOperand(1), BI)); 386 387 // We must move the add instruction here, because the neg instructions do 388 // not dominate the old add instruction in general. By moving it, we are 389 // assured that the neg instructions we just inserted dominate the 390 // instruction we are about to insert after them. 391 // 392 I->moveBefore(BI); 393 I->setName(I->getName()+".neg"); 394 return I; 395 } 396 397 // Insert a 'neg' instruction that subtracts the value from zero to get the 398 // negation. 399 // 400 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI); 401} 402 403/// ShouldBreakUpSubtract - Return true if we should break up this subtract of 404/// X-Y into (X + -Y). 405static bool ShouldBreakUpSubtract(Instruction *Sub) { 406 // If this is a negation, we can't split it up! 407 if (BinaryOperator::isNeg(Sub)) 408 return false; 409 410 // Don't bother to break this up unless either the LHS is an associable add or 411 // subtract or if this is only used by one. 412 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) || 413 isReassociableOp(Sub->getOperand(0), Instruction::Sub)) 414 return true; 415 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) || 416 isReassociableOp(Sub->getOperand(1), Instruction::Sub)) 417 return true; 418 if (Sub->hasOneUse() && 419 (isReassociableOp(Sub->use_back(), Instruction::Add) || 420 isReassociableOp(Sub->use_back(), Instruction::Sub))) 421 return true; 422 423 return false; 424} 425 426/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is 427/// only used by an add, transform this into (X+(0-Y)) to promote better 428/// reassociation. 429static Instruction *BreakUpSubtract(Instruction *Sub, 430 std::map<AssertingVH<>, unsigned> &ValueRankMap) { 431 // Convert a subtract into an add and a neg instruction... so that sub 432 // instructions can be commuted with other add instructions... 433 // 434 // Calculate the negative value of Operand 1 of the sub instruction... 435 // and set it as the RHS of the add instruction we just made... 436 // 437 Value *NegVal = NegateValue(Sub->getOperand(1), Sub); 438 Instruction *New = 439 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub); 440 New->takeName(Sub); 441 442 // Everyone now refers to the add instruction. 443 ValueRankMap.erase(Sub); 444 Sub->replaceAllUsesWith(New); 445 Sub->eraseFromParent(); 446 447 DEBUG(errs() << "Negated: " << *New << '\n'); 448 return New; 449} 450 451/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used 452/// by one, change this into a multiply by a constant to assist with further 453/// reassociation. 454static Instruction *ConvertShiftToMul(Instruction *Shl, 455 std::map<AssertingVH<>, unsigned> &ValueRankMap) { 456 // If an operand of this shift is a reassociable multiply, or if the shift 457 // is used by a reassociable multiply or add, turn into a multiply. 458 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) || 459 (Shl->hasOneUse() && 460 (isReassociableOp(Shl->use_back(), Instruction::Mul) || 461 isReassociableOp(Shl->use_back(), Instruction::Add)))) { 462 Constant *MulCst = ConstantInt::get(Shl->getType(), 1); 463 MulCst = 464 ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1))); 465 466 Instruction *Mul = BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, 467 "", Shl); 468 ValueRankMap.erase(Shl); 469 Mul->takeName(Shl); 470 Shl->replaceAllUsesWith(Mul); 471 Shl->eraseFromParent(); 472 return Mul; 473 } 474 return 0; 475} 476 477// Scan backwards and forwards among values with the same rank as element i to 478// see if X exists. If X does not exist, return i. 479static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i, 480 Value *X) { 481 unsigned XRank = Ops[i].Rank; 482 unsigned e = Ops.size(); 483 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) 484 if (Ops[j].Op == X) 485 return j; 486 // Scan backwards 487 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) 488 if (Ops[j].Op == X) 489 return j; 490 return i; 491} 492 493/// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together 494/// and returning the result. Insert the tree before I. 495static Value *EmitAddTreeOfValues(Instruction *I, std::vector<Value*> &Ops) { 496 if (Ops.size() == 1) return Ops.back(); 497 498 Value *V1 = Ops.back(); 499 Ops.pop_back(); 500 Value *V2 = EmitAddTreeOfValues(I, Ops); 501 return BinaryOperator::CreateAdd(V2, V1, "tmp", I); 502} 503 504/// RemoveFactorFromExpression - If V is an expression tree that is a 505/// multiplication sequence, and if this sequence contains a multiply by Factor, 506/// remove Factor from the tree and return the new tree. 507Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) { 508 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul); 509 if (!BO) return 0; 510 511 std::vector<ValueEntry> Factors; 512 LinearizeExprTree(BO, Factors); 513 514 bool FoundFactor = false; 515 for (unsigned i = 0, e = Factors.size(); i != e; ++i) 516 if (Factors[i].Op == Factor) { 517 FoundFactor = true; 518 Factors.erase(Factors.begin()+i); 519 break; 520 } 521 if (!FoundFactor) { 522 // Make sure to restore the operands to the expression tree. 523 RewriteExprTree(BO, Factors); 524 return 0; 525 } 526 527 if (Factors.size() == 1) return Factors[0].Op; 528 529 RewriteExprTree(BO, Factors); 530 return BO; 531} 532 533/// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively 534/// add its operands as factors, otherwise add V to the list of factors. 535static void FindSingleUseMultiplyFactors(Value *V, 536 std::vector<Value*> &Factors) { 537 BinaryOperator *BO; 538 if ((!V->hasOneUse() && !V->use_empty()) || 539 !(BO = dyn_cast<BinaryOperator>(V)) || 540 BO->getOpcode() != Instruction::Mul) { 541 Factors.push_back(V); 542 return; 543 } 544 545 // Otherwise, add the LHS and RHS to the list of factors. 546 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors); 547 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors); 548} 549 550 551 552Value *Reassociate::OptimizeExpression(BinaryOperator *I, 553 std::vector<ValueEntry> &Ops) { 554 // Now that we have the linearized expression tree, try to optimize it. 555 // Start by folding any constants that we found. 556 bool IterateOptimization = false; 557 if (Ops.size() == 1) return Ops[0].Op; 558 559 unsigned Opcode = I->getOpcode(); 560 561 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op)) 562 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) { 563 Ops.pop_back(); 564 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2); 565 return OptimizeExpression(I, Ops); 566 } 567 568 // Check for destructive annihilation due to a constant being used. 569 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op)) 570 switch (Opcode) { 571 default: break; 572 case Instruction::And: 573 if (CstVal->isZero()) { // ... & 0 -> 0 574 ++NumAnnihil; 575 return CstVal; 576 } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ... 577 Ops.pop_back(); 578 } 579 break; 580 case Instruction::Mul: 581 if (CstVal->isZero()) { // ... * 0 -> 0 582 ++NumAnnihil; 583 return CstVal; 584 } else if (cast<ConstantInt>(CstVal)->isOne()) { 585 Ops.pop_back(); // ... * 1 -> ... 586 } 587 break; 588 case Instruction::Or: 589 if (CstVal->isAllOnesValue()) { // ... | -1 -> -1 590 ++NumAnnihil; 591 return CstVal; 592 } 593 // FALLTHROUGH! 594 case Instruction::Add: 595 case Instruction::Xor: 596 if (CstVal->isZero()) // ... [|^+] 0 -> ... 597 Ops.pop_back(); 598 break; 599 } 600 if (Ops.size() == 1) return Ops[0].Op; 601 602 // Handle destructive annihilation do to identities between elements in the 603 // argument list here. 604 switch (Opcode) { 605 default: break; 606 case Instruction::And: 607 case Instruction::Or: 608 case Instruction::Xor: 609 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs. 610 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1. 611 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 612 // First, check for X and ~X in the operand list. 613 assert(i < Ops.size()); 614 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^. 615 Value *X = BinaryOperator::getNotArgument(Ops[i].Op); 616 unsigned FoundX = FindInOperandList(Ops, i, X); 617 if (FoundX != i) { 618 if (Opcode == Instruction::And) { // ...&X&~X = 0 619 ++NumAnnihil; 620 return Constant::getNullValue(X->getType()); 621 } else if (Opcode == Instruction::Or) { // ...|X|~X = -1 622 ++NumAnnihil; 623 return Constant::getAllOnesValue(X->getType()); 624 } 625 } 626 } 627 628 // Next, check for duplicate pairs of values, which we assume are next to 629 // each other, due to our sorting criteria. 630 assert(i < Ops.size()); 631 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) { 632 if (Opcode == Instruction::And || Opcode == Instruction::Or) { 633 // Drop duplicate values. 634 Ops.erase(Ops.begin()+i); 635 --i; --e; 636 IterateOptimization = true; 637 ++NumAnnihil; 638 } else { 639 assert(Opcode == Instruction::Xor); 640 if (e == 2) { 641 ++NumAnnihil; 642 return Constant::getNullValue(Ops[0].Op->getType()); 643 } 644 // ... X^X -> ... 645 Ops.erase(Ops.begin()+i, Ops.begin()+i+2); 646 i -= 1; e -= 2; 647 IterateOptimization = true; 648 ++NumAnnihil; 649 } 650 } 651 } 652 break; 653 654 case Instruction::Add: 655 // Scan the operand lists looking for X and -X pairs. If we find any, we 656 // can simplify the expression. X+-X == 0. 657 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 658 assert(i < Ops.size()); 659 // Check for X and -X in the operand list. 660 if (BinaryOperator::isNeg(Ops[i].Op)) { 661 Value *X = BinaryOperator::getNegArgument(Ops[i].Op); 662 unsigned FoundX = FindInOperandList(Ops, i, X); 663 if (FoundX != i) { 664 // Remove X and -X from the operand list. 665 if (Ops.size() == 2) { 666 ++NumAnnihil; 667 return Constant::getNullValue(X->getType()); 668 } else { 669 Ops.erase(Ops.begin()+i); 670 if (i < FoundX) 671 --FoundX; 672 else 673 --i; // Need to back up an extra one. 674 Ops.erase(Ops.begin()+FoundX); 675 IterateOptimization = true; 676 ++NumAnnihil; 677 --i; // Revisit element. 678 e -= 2; // Removed two elements. 679 } 680 } 681 } 682 } 683 684 685 // Scan the operand list, checking to see if there are any common factors 686 // between operands. Consider something like A*A+A*B*C+D. We would like to 687 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies. 688 // To efficiently find this, we count the number of times a factor occurs 689 // for any ADD operands that are MULs. 690 std::map<Value*, unsigned> FactorOccurrences; 691 unsigned MaxOcc = 0; 692 Value *MaxOccVal = 0; 693 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 694 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op)) { 695 if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) { 696 // Compute all of the factors of this added value. 697 std::vector<Value*> Factors; 698 FindSingleUseMultiplyFactors(BOp, Factors); 699 assert(Factors.size() > 1 && "Bad linearize!"); 700 701 // Add one to FactorOccurrences for each unique factor in this op. 702 if (Factors.size() == 2) { 703 unsigned Occ = ++FactorOccurrences[Factors[0]]; 704 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; } 705 if (Factors[0] != Factors[1]) { // Don't double count A*A. 706 Occ = ++FactorOccurrences[Factors[1]]; 707 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; } 708 } 709 } else { 710 std::set<Value*> Duplicates; 711 for (unsigned i = 0, e = Factors.size(); i != e; ++i) { 712 if (Duplicates.insert(Factors[i]).second) { 713 unsigned Occ = ++FactorOccurrences[Factors[i]]; 714 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; } 715 } 716 } 717 } 718 } 719 } 720 } 721 722 // If any factor occurred more than one time, we can pull it out. 723 if (MaxOcc > 1) { 724 DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << "\n"); 725 726 // Create a new instruction that uses the MaxOccVal twice. If we don't do 727 // this, we could otherwise run into situations where removing a factor 728 // from an expression will drop a use of maxocc, and this can cause 729 // RemoveFactorFromExpression on successive values to behave differently. 730 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal); 731 std::vector<Value*> NewMulOps; 732 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 733 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) { 734 NewMulOps.push_back(V); 735 Ops.erase(Ops.begin()+i); 736 --i; --e; 737 } 738 } 739 740 // No need for extra uses anymore. 741 delete DummyInst; 742 743 unsigned NumAddedValues = NewMulOps.size(); 744 Value *V = EmitAddTreeOfValues(I, NewMulOps); 745 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I); 746 747 // Now that we have inserted V and its sole use, optimize it. This allows 748 // us to handle cases that require multiple factoring steps, such as this: 749 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C)) 750 if (NumAddedValues > 1) 751 ReassociateExpression(cast<BinaryOperator>(V)); 752 753 ++NumFactor; 754 755 if (Ops.empty()) 756 return V2; 757 758 // Add the new value to the list of things being added. 759 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2)); 760 761 // Rewrite the tree so that there is now a use of V. 762 RewriteExprTree(I, Ops); 763 return OptimizeExpression(I, Ops); 764 } 765 break; 766 //case Instruction::Mul: 767 } 768 769 if (IterateOptimization) 770 return OptimizeExpression(I, Ops); 771 return 0; 772} 773 774 775/// ReassociateBB - Inspect all of the instructions in this basic block, 776/// reassociating them as we go. 777void Reassociate::ReassociateBB(BasicBlock *BB) { 778 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) { 779 Instruction *BI = BBI++; 780 if (BI->getOpcode() == Instruction::Shl && 781 isa<ConstantInt>(BI->getOperand(1))) 782 if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap)) { 783 MadeChange = true; 784 BI = NI; 785 } 786 787 // Reject cases where it is pointless to do this. 788 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() || 789 isa<VectorType>(BI->getType())) 790 continue; // Floating point ops are not associative. 791 792 // If this is a subtract instruction which is not already in negate form, 793 // see if we can convert it to X+-Y. 794 if (BI->getOpcode() == Instruction::Sub) { 795 if (ShouldBreakUpSubtract(BI)) { 796 BI = BreakUpSubtract(BI, ValueRankMap); 797 MadeChange = true; 798 } else if (BinaryOperator::isNeg(BI)) { 799 // Otherwise, this is a negation. See if the operand is a multiply tree 800 // and if this is not an inner node of a multiply tree. 801 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) && 802 (!BI->hasOneUse() || 803 !isReassociableOp(BI->use_back(), Instruction::Mul))) { 804 BI = LowerNegateToMultiply(BI, ValueRankMap); 805 MadeChange = true; 806 } 807 } 808 } 809 810 // If this instruction is a commutative binary operator, process it. 811 if (!BI->isAssociative()) continue; 812 BinaryOperator *I = cast<BinaryOperator>(BI); 813 814 // If this is an interior node of a reassociable tree, ignore it until we 815 // get to the root of the tree, to avoid N^2 analysis. 816 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode())) 817 continue; 818 819 // If this is an add tree that is used by a sub instruction, ignore it 820 // until we process the subtract. 821 if (I->hasOneUse() && I->getOpcode() == Instruction::Add && 822 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub) 823 continue; 824 825 ReassociateExpression(I); 826 } 827} 828 829void Reassociate::ReassociateExpression(BinaryOperator *I) { 830 831 // First, walk the expression tree, linearizing the tree, collecting 832 std::vector<ValueEntry> Ops; 833 LinearizeExprTree(I, Ops); 834 835 DEBUG(errs() << "RAIn:\t"; PrintOps(I, Ops); errs() << "\n"); 836 837 // Now that we have linearized the tree to a list and have gathered all of 838 // the operands and their ranks, sort the operands by their rank. Use a 839 // stable_sort so that values with equal ranks will have their relative 840 // positions maintained (and so the compiler is deterministic). Note that 841 // this sorts so that the highest ranking values end up at the beginning of 842 // the vector. 843 std::stable_sort(Ops.begin(), Ops.end()); 844 845 // OptimizeExpression - Now that we have the expression tree in a convenient 846 // sorted form, optimize it globally if possible. 847 if (Value *V = OptimizeExpression(I, Ops)) { 848 // This expression tree simplified to something that isn't a tree, 849 // eliminate it. 850 DEBUG(errs() << "Reassoc to scalar: " << *V << "\n"); 851 I->replaceAllUsesWith(V); 852 RemoveDeadBinaryOp(I); 853 return; 854 } 855 856 // We want to sink immediates as deeply as possible except in the case where 857 // this is a multiply tree used only by an add, and the immediate is a -1. 858 // In this case we reassociate to put the negation on the outside so that we 859 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y 860 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() && 861 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add && 862 isa<ConstantInt>(Ops.back().Op) && 863 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) { 864 Ops.insert(Ops.begin(), Ops.back()); 865 Ops.pop_back(); 866 } 867 868 DEBUG(errs() << "RAOut:\t"; PrintOps(I, Ops); errs() << "\n"); 869 870 if (Ops.size() == 1) { 871 // This expression tree simplified to something that isn't a tree, 872 // eliminate it. 873 I->replaceAllUsesWith(Ops[0].Op); 874 RemoveDeadBinaryOp(I); 875 } else { 876 // Now that we ordered and optimized the expressions, splat them back into 877 // the expression tree, removing any unneeded nodes. 878 RewriteExprTree(I, Ops); 879 } 880} 881 882 883bool Reassociate::runOnFunction(Function &F) { 884 // Recalculate the rank map for F 885 BuildRankMap(F); 886 887 MadeChange = false; 888 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 889 ReassociateBB(FI); 890 891 // We are done with the rank map... 892 RankMap.clear(); 893 ValueRankMap.clear(); 894 return MadeChange; 895} 896 897