Reassociate.cpp revision 7cbd8a3e92221437048b484d5ef9c0a22d0f8c58
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/Pass.h" 30#include "llvm/Assembly/Writer.h" 31#include "llvm/Support/CFG.h" 32#include "llvm/Support/Compiler.h" 33#include "llvm/Support/Debug.h" 34#include "llvm/ADT/PostOrderIterator.h" 35#include "llvm/ADT/Statistic.h" 36#include <algorithm> 37#include <map> 38using namespace llvm; 39 40STATISTIC(NumLinear , "Number of insts linearized"); 41STATISTIC(NumChanged, "Number of insts reassociated"); 42STATISTIC(NumAnnihil, "Number of expr tree annihilated"); 43STATISTIC(NumFactor , "Number of multiplies factored"); 44 45namespace { 46 struct VISIBILITY_HIDDEN ValueEntry { 47 unsigned Rank; 48 Value *Op; 49 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {} 50 }; 51 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) { 52 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start. 53 } 54} 55 56/// PrintOps - Print out the expression identified in the Ops list. 57/// 58static void PrintOps(Instruction *I, const std::vector<ValueEntry> &Ops) { 59 Module *M = I->getParent()->getParent()->getParent(); 60 cerr << Instruction::getOpcodeName(I->getOpcode()) << " " 61 << *Ops[0].Op->getType(); 62 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 63 WriteAsOperand(*cerr.stream() << " ", Ops[i].Op, false, M) 64 << "," << Ops[i].Rank; 65} 66 67namespace { 68 class VISIBILITY_HIDDEN Reassociate : public FunctionPass { 69 std::map<BasicBlock*, unsigned> RankMap; 70 std::map<Value*, unsigned> ValueRankMap; 71 bool MadeChange; 72 public: 73 static char ID; // Pass identification, replacement for typeid 74 Reassociate() : FunctionPass((intptr_t)&ID) {} 75 76 bool runOnFunction(Function &F); 77 78 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 79 AU.setPreservesCFG(); 80 } 81 private: 82 void BuildRankMap(Function &F); 83 unsigned getRank(Value *V); 84 void ReassociateExpression(BinaryOperator *I); 85 void RewriteExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops, 86 unsigned Idx = 0); 87 Value *OptimizeExpression(BinaryOperator *I, std::vector<ValueEntry> &Ops); 88 void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops); 89 void LinearizeExpr(BinaryOperator *I); 90 Value *RemoveFactorFromExpression(Value *V, Value *Factor); 91 void ReassociateBB(BasicBlock *BB); 92 93 void RemoveDeadBinaryOp(Value *V); 94 }; 95} 96 97char Reassociate::ID = 0; 98static RegisterPass<Reassociate> X("reassociate", "Reassociate expressions"); 99 100// Public interface to the Reassociate pass 101FunctionPass *llvm::createReassociatePass() { return new Reassociate(); } 102 103void Reassociate::RemoveDeadBinaryOp(Value *V) { 104 Instruction *Op = dyn_cast<Instruction>(V); 105 if (!Op || !isa<BinaryOperator>(Op) || !isa<CmpInst>(Op) || !Op->use_empty()) 106 return; 107 108 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1); 109 RemoveDeadBinaryOp(LHS); 110 RemoveDeadBinaryOp(RHS); 111} 112 113 114static bool isUnmovableInstruction(Instruction *I) { 115 if (I->getOpcode() == Instruction::PHI || 116 I->getOpcode() == Instruction::Alloca || 117 I->getOpcode() == Instruction::Load || 118 I->getOpcode() == Instruction::Malloc || 119 I->getOpcode() == Instruction::Invoke || 120 I->getOpcode() == Instruction::Call || 121 I->getOpcode() == Instruction::UDiv || 122 I->getOpcode() == Instruction::SDiv || 123 I->getOpcode() == Instruction::FDiv || 124 I->getOpcode() == Instruction::URem || 125 I->getOpcode() == Instruction::SRem || 126 I->getOpcode() == Instruction::FRem) 127 return true; 128 return false; 129} 130 131void Reassociate::BuildRankMap(Function &F) { 132 unsigned i = 2; 133 134 // Assign distinct ranks to function arguments 135 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I) 136 ValueRankMap[I] = ++i; 137 138 ReversePostOrderTraversal<Function*> RPOT(&F); 139 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(), 140 E = RPOT.end(); I != E; ++I) { 141 BasicBlock *BB = *I; 142 unsigned BBRank = RankMap[BB] = ++i << 16; 143 144 // Walk the basic block, adding precomputed ranks for any instructions that 145 // we cannot move. This ensures that the ranks for these instructions are 146 // all different in the block. 147 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 148 if (isUnmovableInstruction(I)) 149 ValueRankMap[I] = ++BBRank; 150 } 151} 152 153unsigned Reassociate::getRank(Value *V) { 154 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument... 155 156 Instruction *I = dyn_cast<Instruction>(V); 157 if (I == 0) return 0; // Otherwise it's a global or constant, rank 0. 158 159 unsigned &CachedRank = ValueRankMap[I]; 160 if (CachedRank) return CachedRank; // Rank already known? 161 162 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that 163 // we can reassociate expressions for code motion! Since we do not recurse 164 // for PHI nodes, we cannot have infinite recursion here, because there 165 // cannot be loops in the value graph that do not go through PHI nodes. 166 unsigned Rank = 0, MaxRank = RankMap[I->getParent()]; 167 for (unsigned i = 0, e = I->getNumOperands(); 168 i != e && Rank != MaxRank; ++i) 169 Rank = std::max(Rank, getRank(I->getOperand(i))); 170 171 // If this is a not or neg instruction, do not count it for rank. This 172 // assures us that X and ~X will have the same rank. 173 if (!I->getType()->isInteger() || 174 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I))) 175 ++Rank; 176 177 //DOUT << "Calculated Rank[" << V->getName() << "] = " 178 // << Rank << "\n"; 179 180 return CachedRank = Rank; 181} 182 183/// isReassociableOp - Return true if V is an instruction of the specified 184/// opcode and if it only has one use. 185static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) { 186 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) && 187 cast<Instruction>(V)->getOpcode() == Opcode) 188 return cast<BinaryOperator>(V); 189 return 0; 190} 191 192/// LowerNegateToMultiply - Replace 0-X with X*-1. 193/// 194static Instruction *LowerNegateToMultiply(Instruction *Neg) { 195 Constant *Cst = ConstantInt::getAllOnesValue(Neg->getType()); 196 197 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg); 198 Res->takeName(Neg); 199 Neg->replaceAllUsesWith(Res); 200 Neg->eraseFromParent(); 201 return Res; 202} 203 204// Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'. 205// Note that if D is also part of the expression tree that we recurse to 206// linearize it as well. Besides that case, this does not recurse into A,B, or 207// C. 208void Reassociate::LinearizeExpr(BinaryOperator *I) { 209 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0)); 210 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1)); 211 assert(isReassociableOp(LHS, I->getOpcode()) && 212 isReassociableOp(RHS, I->getOpcode()) && 213 "Not an expression that needs linearization?"); 214 215 DOUT << "Linear" << *LHS << *RHS << *I; 216 217 // Move the RHS instruction to live immediately before I, avoiding breaking 218 // dominator properties. 219 RHS->moveBefore(I); 220 221 // Move operands around to do the linearization. 222 I->setOperand(1, RHS->getOperand(0)); 223 RHS->setOperand(0, LHS); 224 I->setOperand(0, RHS); 225 226 ++NumLinear; 227 MadeChange = true; 228 DOUT << "Linearized: " << *I; 229 230 // If D is part of this expression tree, tail recurse. 231 if (isReassociableOp(I->getOperand(1), I->getOpcode())) 232 LinearizeExpr(I); 233} 234 235 236/// LinearizeExprTree - Given an associative binary expression tree, traverse 237/// all of the uses putting it into canonical form. This forces a left-linear 238/// form of the the expression (((a+b)+c)+d), and collects information about the 239/// rank of the non-tree operands. 240/// 241/// NOTE: These intentionally destroys the expression tree operands (turning 242/// them into undef values) to reduce #uses of the values. This means that the 243/// caller MUST use something like RewriteExprTree to put the values back in. 244/// 245void Reassociate::LinearizeExprTree(BinaryOperator *I, 246 std::vector<ValueEntry> &Ops) { 247 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1); 248 unsigned Opcode = I->getOpcode(); 249 250 // First step, linearize the expression if it is in ((A+B)+(C+D)) form. 251 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode); 252 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode); 253 254 // If this is a multiply expression tree and it contains internal negations, 255 // transform them into multiplies by -1 so they can be reassociated. 256 if (I->getOpcode() == Instruction::Mul) { 257 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) { 258 LHS = LowerNegateToMultiply(cast<Instruction>(LHS)); 259 LHSBO = isReassociableOp(LHS, Opcode); 260 } 261 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) { 262 RHS = LowerNegateToMultiply(cast<Instruction>(RHS)); 263 RHSBO = isReassociableOp(RHS, Opcode); 264 } 265 } 266 267 if (!LHSBO) { 268 if (!RHSBO) { 269 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As 270 // such, just remember these operands and their rank. 271 Ops.push_back(ValueEntry(getRank(LHS), LHS)); 272 Ops.push_back(ValueEntry(getRank(RHS), RHS)); 273 274 // Clear the leaves out. 275 I->setOperand(0, UndefValue::get(I->getType())); 276 I->setOperand(1, UndefValue::get(I->getType())); 277 return; 278 } else { 279 // Turn X+(Y+Z) -> (Y+Z)+X 280 std::swap(LHSBO, RHSBO); 281 std::swap(LHS, RHS); 282 bool Success = !I->swapOperands(); 283 assert(Success && "swapOperands failed"); 284 MadeChange = true; 285 } 286 } else if (RHSBO) { 287 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not 288 // part of the expression tree. 289 LinearizeExpr(I); 290 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0)); 291 RHS = I->getOperand(1); 292 RHSBO = 0; 293 } 294 295 // Okay, now we know that the LHS is a nested expression and that the RHS is 296 // not. Perform reassociation. 297 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!"); 298 299 // Move LHS right before I to make sure that the tree expression dominates all 300 // values. 301 LHSBO->moveBefore(I); 302 303 // Linearize the expression tree on the LHS. 304 LinearizeExprTree(LHSBO, Ops); 305 306 // Remember the RHS operand and its rank. 307 Ops.push_back(ValueEntry(getRank(RHS), RHS)); 308 309 // Clear the RHS leaf out. 310 I->setOperand(1, UndefValue::get(I->getType())); 311} 312 313// RewriteExprTree - Now that the operands for this expression tree are 314// linearized and optimized, emit them in-order. This function is written to be 315// tail recursive. 316void Reassociate::RewriteExprTree(BinaryOperator *I, 317 std::vector<ValueEntry> &Ops, 318 unsigned i) { 319 if (i+2 == Ops.size()) { 320 if (I->getOperand(0) != Ops[i].Op || 321 I->getOperand(1) != Ops[i+1].Op) { 322 Value *OldLHS = I->getOperand(0); 323 DOUT << "RA: " << *I; 324 I->setOperand(0, Ops[i].Op); 325 I->setOperand(1, Ops[i+1].Op); 326 DOUT << "TO: " << *I; 327 MadeChange = true; 328 ++NumChanged; 329 330 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3) 331 // delete the extra, now dead, nodes. 332 RemoveDeadBinaryOp(OldLHS); 333 } 334 return; 335 } 336 assert(i+2 < Ops.size() && "Ops index out of range!"); 337 338 if (I->getOperand(1) != Ops[i].Op) { 339 DOUT << "RA: " << *I; 340 I->setOperand(1, Ops[i].Op); 341 DOUT << "TO: " << *I; 342 MadeChange = true; 343 ++NumChanged; 344 } 345 346 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0)); 347 assert(LHS->getOpcode() == I->getOpcode() && 348 "Improper expression tree!"); 349 350 // Compactify the tree instructions together with each other to guarantee 351 // that the expression tree is dominated by all of Ops. 352 LHS->moveBefore(I); 353 RewriteExprTree(LHS, Ops, i+1); 354} 355 356 357 358// NegateValue - Insert instructions before the instruction pointed to by BI, 359// that computes the negative version of the value specified. The negative 360// version of the value is returned, and BI is left pointing at the instruction 361// that should be processed next by the reassociation pass. 362// 363static Value *NegateValue(Value *V, Instruction *BI) { 364 // We are trying to expose opportunity for reassociation. One of the things 365 // that we want to do to achieve this is to push a negation as deep into an 366 // expression chain as possible, to expose the add instructions. In practice, 367 // this means that we turn this: 368 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D 369 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate 370 // the constants. We assume that instcombine will clean up the mess later if 371 // we introduce tons of unnecessary negation instructions... 372 // 373 if (Instruction *I = dyn_cast<Instruction>(V)) 374 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) { 375 // Push the negates through the add. 376 I->setOperand(0, NegateValue(I->getOperand(0), BI)); 377 I->setOperand(1, NegateValue(I->getOperand(1), BI)); 378 379 // We must move the add instruction here, because the neg instructions do 380 // not dominate the old add instruction in general. By moving it, we are 381 // assured that the neg instructions we just inserted dominate the 382 // instruction we are about to insert after them. 383 // 384 I->moveBefore(BI); 385 I->setName(I->getName()+".neg"); 386 return I; 387 } 388 389 // Insert a 'neg' instruction that subtracts the value from zero to get the 390 // negation. 391 // 392 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI); 393} 394 395/// ShouldBreakUpSubtract - Return true if we should break up this subtract of 396/// X-Y into (X + -Y). 397static bool ShouldBreakUpSubtract(Instruction *Sub) { 398 // If this is a negation, we can't split it up! 399 if (BinaryOperator::isNeg(Sub)) 400 return false; 401 402 // Don't bother to break this up unless either the LHS is an associable add or 403 // subtract or if this is only used by one. 404 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) || 405 isReassociableOp(Sub->getOperand(0), Instruction::Sub)) 406 return true; 407 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) || 408 isReassociableOp(Sub->getOperand(1), Instruction::Sub)) 409 return true; 410 if (Sub->hasOneUse() && 411 (isReassociableOp(Sub->use_back(), Instruction::Add) || 412 isReassociableOp(Sub->use_back(), Instruction::Sub))) 413 return true; 414 415 return false; 416} 417 418/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is 419/// only used by an add, transform this into (X+(0-Y)) to promote better 420/// reassociation. 421static Instruction *BreakUpSubtract(Instruction *Sub) { 422 // Convert a subtract into an add and a neg instruction... so that sub 423 // instructions can be commuted with other add instructions... 424 // 425 // Calculate the negative value of Operand 1 of the sub instruction... 426 // and set it as the RHS of the add instruction we just made... 427 // 428 Value *NegVal = NegateValue(Sub->getOperand(1), Sub); 429 Instruction *New = 430 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub); 431 New->takeName(Sub); 432 433 // Everyone now refers to the add instruction. 434 Sub->replaceAllUsesWith(New); 435 Sub->eraseFromParent(); 436 437 DOUT << "Negated: " << *New; 438 return New; 439} 440 441/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used 442/// by one, change this into a multiply by a constant to assist with further 443/// reassociation. 444static Instruction *ConvertShiftToMul(Instruction *Shl) { 445 // If an operand of this shift is a reassociable multiply, or if the shift 446 // is used by a reassociable multiply or add, turn into a multiply. 447 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) || 448 (Shl->hasOneUse() && 449 (isReassociableOp(Shl->use_back(), Instruction::Mul) || 450 isReassociableOp(Shl->use_back(), Instruction::Add)))) { 451 Constant *MulCst = ConstantInt::get(Shl->getType(), 1); 452 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1))); 453 454 Instruction *Mul = BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, 455 "", Shl); 456 Mul->takeName(Shl); 457 Shl->replaceAllUsesWith(Mul); 458 Shl->eraseFromParent(); 459 return Mul; 460 } 461 return 0; 462} 463 464// Scan backwards and forwards among values with the same rank as element i to 465// see if X exists. If X does not exist, return i. 466static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i, 467 Value *X) { 468 unsigned XRank = Ops[i].Rank; 469 unsigned e = Ops.size(); 470 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) 471 if (Ops[j].Op == X) 472 return j; 473 // Scan backwards 474 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) 475 if (Ops[j].Op == X) 476 return j; 477 return i; 478} 479 480/// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together 481/// and returning the result. Insert the tree before I. 482static Value *EmitAddTreeOfValues(Instruction *I, std::vector<Value*> &Ops) { 483 if (Ops.size() == 1) return Ops.back(); 484 485 Value *V1 = Ops.back(); 486 Ops.pop_back(); 487 Value *V2 = EmitAddTreeOfValues(I, Ops); 488 return BinaryOperator::CreateAdd(V2, V1, "tmp", I); 489} 490 491/// RemoveFactorFromExpression - If V is an expression tree that is a 492/// multiplication sequence, and if this sequence contains a multiply by Factor, 493/// remove Factor from the tree and return the new tree. 494Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) { 495 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul); 496 if (!BO) return 0; 497 498 std::vector<ValueEntry> Factors; 499 LinearizeExprTree(BO, Factors); 500 501 bool FoundFactor = false; 502 for (unsigned i = 0, e = Factors.size(); i != e; ++i) 503 if (Factors[i].Op == Factor) { 504 FoundFactor = true; 505 Factors.erase(Factors.begin()+i); 506 break; 507 } 508 if (!FoundFactor) { 509 // Make sure to restore the operands to the expression tree. 510 RewriteExprTree(BO, Factors); 511 return 0; 512 } 513 514 if (Factors.size() == 1) return Factors[0].Op; 515 516 RewriteExprTree(BO, Factors); 517 return BO; 518} 519 520/// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively 521/// add its operands as factors, otherwise add V to the list of factors. 522static void FindSingleUseMultiplyFactors(Value *V, 523 std::vector<Value*> &Factors) { 524 BinaryOperator *BO; 525 if ((!V->hasOneUse() && !V->use_empty()) || 526 !(BO = dyn_cast<BinaryOperator>(V)) || 527 BO->getOpcode() != Instruction::Mul) { 528 Factors.push_back(V); 529 return; 530 } 531 532 // Otherwise, add the LHS and RHS to the list of factors. 533 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors); 534 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors); 535} 536 537 538 539Value *Reassociate::OptimizeExpression(BinaryOperator *I, 540 std::vector<ValueEntry> &Ops) { 541 // Now that we have the linearized expression tree, try to optimize it. 542 // Start by folding any constants that we found. 543 bool IterateOptimization = false; 544 if (Ops.size() == 1) return Ops[0].Op; 545 546 unsigned Opcode = I->getOpcode(); 547 548 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op)) 549 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) { 550 Ops.pop_back(); 551 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2); 552 return OptimizeExpression(I, Ops); 553 } 554 555 // Check for destructive annihilation due to a constant being used. 556 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op)) 557 switch (Opcode) { 558 default: break; 559 case Instruction::And: 560 if (CstVal->isZero()) { // ... & 0 -> 0 561 ++NumAnnihil; 562 return CstVal; 563 } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ... 564 Ops.pop_back(); 565 } 566 break; 567 case Instruction::Mul: 568 if (CstVal->isZero()) { // ... * 0 -> 0 569 ++NumAnnihil; 570 return CstVal; 571 } else if (cast<ConstantInt>(CstVal)->isOne()) { 572 Ops.pop_back(); // ... * 1 -> ... 573 } 574 break; 575 case Instruction::Or: 576 if (CstVal->isAllOnesValue()) { // ... | -1 -> -1 577 ++NumAnnihil; 578 return CstVal; 579 } 580 // FALLTHROUGH! 581 case Instruction::Add: 582 case Instruction::Xor: 583 if (CstVal->isZero()) // ... [|^+] 0 -> ... 584 Ops.pop_back(); 585 break; 586 } 587 if (Ops.size() == 1) return Ops[0].Op; 588 589 // Handle destructive annihilation do to identities between elements in the 590 // argument list here. 591 switch (Opcode) { 592 default: break; 593 case Instruction::And: 594 case Instruction::Or: 595 case Instruction::Xor: 596 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs. 597 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1. 598 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 599 // First, check for X and ~X in the operand list. 600 assert(i < Ops.size()); 601 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^. 602 Value *X = BinaryOperator::getNotArgument(Ops[i].Op); 603 unsigned FoundX = FindInOperandList(Ops, i, X); 604 if (FoundX != i) { 605 if (Opcode == Instruction::And) { // ...&X&~X = 0 606 ++NumAnnihil; 607 return Constant::getNullValue(X->getType()); 608 } else if (Opcode == Instruction::Or) { // ...|X|~X = -1 609 ++NumAnnihil; 610 return ConstantInt::getAllOnesValue(X->getType()); 611 } 612 } 613 } 614 615 // Next, check for duplicate pairs of values, which we assume are next to 616 // each other, due to our sorting criteria. 617 assert(i < Ops.size()); 618 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) { 619 if (Opcode == Instruction::And || Opcode == Instruction::Or) { 620 // Drop duplicate values. 621 Ops.erase(Ops.begin()+i); 622 --i; --e; 623 IterateOptimization = true; 624 ++NumAnnihil; 625 } else { 626 assert(Opcode == Instruction::Xor); 627 if (e == 2) { 628 ++NumAnnihil; 629 return Constant::getNullValue(Ops[0].Op->getType()); 630 } 631 // ... X^X -> ... 632 Ops.erase(Ops.begin()+i, Ops.begin()+i+2); 633 i -= 1; e -= 2; 634 IterateOptimization = true; 635 ++NumAnnihil; 636 } 637 } 638 } 639 break; 640 641 case Instruction::Add: 642 // Scan the operand lists looking for X and -X pairs. If we find any, we 643 // can simplify the expression. X+-X == 0. 644 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 645 assert(i < Ops.size()); 646 // Check for X and -X in the operand list. 647 if (BinaryOperator::isNeg(Ops[i].Op)) { 648 Value *X = BinaryOperator::getNegArgument(Ops[i].Op); 649 unsigned FoundX = FindInOperandList(Ops, i, X); 650 if (FoundX != i) { 651 // Remove X and -X from the operand list. 652 if (Ops.size() == 2) { 653 ++NumAnnihil; 654 return Constant::getNullValue(X->getType()); 655 } else { 656 Ops.erase(Ops.begin()+i); 657 if (i < FoundX) 658 --FoundX; 659 else 660 --i; // Need to back up an extra one. 661 Ops.erase(Ops.begin()+FoundX); 662 IterateOptimization = true; 663 ++NumAnnihil; 664 --i; // Revisit element. 665 e -= 2; // Removed two elements. 666 } 667 } 668 } 669 } 670 671 672 // Scan the operand list, checking to see if there are any common factors 673 // between operands. Consider something like A*A+A*B*C+D. We would like to 674 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies. 675 // To efficiently find this, we count the number of times a factor occurs 676 // for any ADD operands that are MULs. 677 std::map<Value*, unsigned> FactorOccurrences; 678 unsigned MaxOcc = 0; 679 Value *MaxOccVal = 0; 680 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 681 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op)) { 682 if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) { 683 // Compute all of the factors of this added value. 684 std::vector<Value*> Factors; 685 FindSingleUseMultiplyFactors(BOp, Factors); 686 assert(Factors.size() > 1 && "Bad linearize!"); 687 688 // Add one to FactorOccurrences for each unique factor in this op. 689 if (Factors.size() == 2) { 690 unsigned Occ = ++FactorOccurrences[Factors[0]]; 691 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; } 692 if (Factors[0] != Factors[1]) { // Don't double count A*A. 693 Occ = ++FactorOccurrences[Factors[1]]; 694 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; } 695 } 696 } else { 697 std::set<Value*> Duplicates; 698 for (unsigned i = 0, e = Factors.size(); i != e; ++i) { 699 if (Duplicates.insert(Factors[i]).second) { 700 unsigned Occ = ++FactorOccurrences[Factors[i]]; 701 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; } 702 } 703 } 704 } 705 } 706 } 707 } 708 709 // If any factor occurred more than one time, we can pull it out. 710 if (MaxOcc > 1) { 711 DOUT << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << "\n"; 712 713 // Create a new instruction that uses the MaxOccVal twice. If we don't do 714 // this, we could otherwise run into situations where removing a factor 715 // from an expression will drop a use of maxocc, and this can cause 716 // RemoveFactorFromExpression on successive values to behave differently. 717 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal); 718 std::vector<Value*> NewMulOps; 719 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 720 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) { 721 NewMulOps.push_back(V); 722 Ops.erase(Ops.begin()+i); 723 --i; --e; 724 } 725 } 726 727 // No need for extra uses anymore. 728 delete DummyInst; 729 730 unsigned NumAddedValues = NewMulOps.size(); 731 Value *V = EmitAddTreeOfValues(I, NewMulOps); 732 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I); 733 734 // Now that we have inserted V and its sole use, optimize it. This allows 735 // us to handle cases that require multiple factoring steps, such as this: 736 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C)) 737 if (NumAddedValues > 1) 738 ReassociateExpression(cast<BinaryOperator>(V)); 739 740 ++NumFactor; 741 742 if (Ops.empty()) 743 return V2; 744 745 // Add the new value to the list of things being added. 746 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2)); 747 748 // Rewrite the tree so that there is now a use of V. 749 RewriteExprTree(I, Ops); 750 return OptimizeExpression(I, Ops); 751 } 752 break; 753 //case Instruction::Mul: 754 } 755 756 if (IterateOptimization) 757 return OptimizeExpression(I, Ops); 758 return 0; 759} 760 761 762/// ReassociateBB - Inspect all of the instructions in this basic block, 763/// reassociating them as we go. 764void Reassociate::ReassociateBB(BasicBlock *BB) { 765 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) { 766 Instruction *BI = BBI++; 767 if (BI->getOpcode() == Instruction::Shl && 768 isa<ConstantInt>(BI->getOperand(1))) 769 if (Instruction *NI = ConvertShiftToMul(BI)) { 770 MadeChange = true; 771 BI = NI; 772 } 773 774 // Reject cases where it is pointless to do this. 775 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() || 776 isa<VectorType>(BI->getType())) 777 continue; // Floating point ops are not associative. 778 779 // If this is a subtract instruction which is not already in negate form, 780 // see if we can convert it to X+-Y. 781 if (BI->getOpcode() == Instruction::Sub) { 782 if (ShouldBreakUpSubtract(BI)) { 783 BI = BreakUpSubtract(BI); 784 MadeChange = true; 785 } else if (BinaryOperator::isNeg(BI)) { 786 // Otherwise, this is a negation. See if the operand is a multiply tree 787 // and if this is not an inner node of a multiply tree. 788 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) && 789 (!BI->hasOneUse() || 790 !isReassociableOp(BI->use_back(), Instruction::Mul))) { 791 BI = LowerNegateToMultiply(BI); 792 MadeChange = true; 793 } 794 } 795 } 796 797 // If this instruction is a commutative binary operator, process it. 798 if (!BI->isAssociative()) continue; 799 BinaryOperator *I = cast<BinaryOperator>(BI); 800 801 // If this is an interior node of a reassociable tree, ignore it until we 802 // get to the root of the tree, to avoid N^2 analysis. 803 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode())) 804 continue; 805 806 // If this is an add tree that is used by a sub instruction, ignore it 807 // until we process the subtract. 808 if (I->hasOneUse() && I->getOpcode() == Instruction::Add && 809 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub) 810 continue; 811 812 ReassociateExpression(I); 813 } 814} 815 816void Reassociate::ReassociateExpression(BinaryOperator *I) { 817 818 // First, walk the expression tree, linearizing the tree, collecting 819 std::vector<ValueEntry> Ops; 820 LinearizeExprTree(I, Ops); 821 822 DOUT << "RAIn:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n"; 823 824 // Now that we have linearized the tree to a list and have gathered all of 825 // the operands and their ranks, sort the operands by their rank. Use a 826 // stable_sort so that values with equal ranks will have their relative 827 // positions maintained (and so the compiler is deterministic). Note that 828 // this sorts so that the highest ranking values end up at the beginning of 829 // the vector. 830 std::stable_sort(Ops.begin(), Ops.end()); 831 832 // OptimizeExpression - Now that we have the expression tree in a convenient 833 // sorted form, optimize it globally if possible. 834 if (Value *V = OptimizeExpression(I, Ops)) { 835 // This expression tree simplified to something that isn't a tree, 836 // eliminate it. 837 DOUT << "Reassoc to scalar: " << *V << "\n"; 838 I->replaceAllUsesWith(V); 839 RemoveDeadBinaryOp(I); 840 return; 841 } 842 843 // We want to sink immediates as deeply as possible except in the case where 844 // this is a multiply tree used only by an add, and the immediate is a -1. 845 // In this case we reassociate to put the negation on the outside so that we 846 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y 847 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() && 848 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add && 849 isa<ConstantInt>(Ops.back().Op) && 850 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) { 851 Ops.insert(Ops.begin(), Ops.back()); 852 Ops.pop_back(); 853 } 854 855 DOUT << "RAOut:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n"; 856 857 if (Ops.size() == 1) { 858 // This expression tree simplified to something that isn't a tree, 859 // eliminate it. 860 I->replaceAllUsesWith(Ops[0].Op); 861 RemoveDeadBinaryOp(I); 862 } else { 863 // Now that we ordered and optimized the expressions, splat them back into 864 // the expression tree, removing any unneeded nodes. 865 RewriteExprTree(I, Ops); 866 } 867} 868 869 870bool Reassociate::runOnFunction(Function &F) { 871 // Recalculate the rank map for F 872 BuildRankMap(F); 873 874 MadeChange = false; 875 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 876 ReassociateBB(FI); 877 878 // We are done with the rank map... 879 RankMap.clear(); 880 ValueRankMap.clear(); 881 return MadeChange; 882} 883 884