Reassociate.cpp revision 03afd02ca2486aebb3b29edd2f77920d4e5020fd
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/Compiler.h" 34#include "llvm/Support/Debug.h" 35#include "llvm/ADT/PostOrderIterator.h" 36#include "llvm/ADT/Statistic.h" 37#include <algorithm> 38#include <map> 39using namespace llvm; 40 41STATISTIC(NumLinear , "Number of insts linearized"); 42STATISTIC(NumChanged, "Number of insts reassociated"); 43STATISTIC(NumAnnihil, "Number of expr tree annihilated"); 44STATISTIC(NumFactor , "Number of multiplies factored"); 45 46namespace { 47 struct VISIBILITY_HIDDEN ValueEntry { 48 unsigned Rank; 49 Value *Op; 50 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {} 51 }; 52 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) { 53 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start. 54 } 55} 56 57#ifndef NDEBUG 58/// PrintOps - Print out the expression identified in the Ops list. 59/// 60static void PrintOps(Instruction *I, const std::vector<ValueEntry> &Ops) { 61 Module *M = I->getParent()->getParent()->getParent(); 62 cerr << Instruction::getOpcodeName(I->getOpcode()) << " " 63 << *Ops[0].Op->getType(); 64 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 65 WriteAsOperand(*cerr.stream() << " ", Ops[i].Op, false, M); 66 cerr << "," << Ops[i].Rank; 67 } 68} 69#endif 70 71namespace { 72 class VISIBILITY_HIDDEN Reassociate : public FunctionPass { 73 std::map<BasicBlock*, unsigned> RankMap; 74 std::map<Value*, unsigned> ValueRankMap; 75 bool MadeChange; 76 public: 77 static char ID; // Pass identification, replacement for typeid 78 Reassociate() : FunctionPass(&ID) {} 79 80 bool runOnFunction(Function &F); 81 82 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 83 AU.setPreservesCFG(); 84 } 85 private: 86 void BuildRankMap(Function &F); 87 unsigned getRank(Value *V); 88 void ReassociateExpression(BinaryOperator *I); 89 void RewriteExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops, 90 unsigned Idx = 0); 91 Value *OptimizeExpression(BinaryOperator *I, std::vector<ValueEntry> &Ops); 92 void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops); 93 void LinearizeExpr(BinaryOperator *I); 94 Value *RemoveFactorFromExpression(Value *V, Value *Factor); 95 void ReassociateBB(BasicBlock *BB); 96 97 void RemoveDeadBinaryOp(Value *V); 98 }; 99} 100 101char Reassociate::ID = 0; 102static RegisterPass<Reassociate> X("reassociate", "Reassociate expressions"); 103 104// Public interface to the Reassociate pass 105FunctionPass *llvm::createReassociatePass() { return new Reassociate(); } 106 107void Reassociate::RemoveDeadBinaryOp(Value *V) { 108 Instruction *Op = dyn_cast<Instruction>(V); 109 if (!Op || !isa<BinaryOperator>(Op) || !isa<CmpInst>(Op) || !Op->use_empty()) 110 return; 111 112 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1); 113 RemoveDeadBinaryOp(LHS); 114 RemoveDeadBinaryOp(RHS); 115} 116 117 118static bool isUnmovableInstruction(Instruction *I) { 119 if (I->getOpcode() == Instruction::PHI || 120 I->getOpcode() == Instruction::Alloca || 121 I->getOpcode() == Instruction::Load || 122 I->getOpcode() == Instruction::Malloc || 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 //DOUT << "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 Constant *Cst = ConstantInt::getAllOnesValue(Neg->getType()); 201 202 Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg); 203 Res->takeName(Neg); 204 Neg->replaceAllUsesWith(Res); 205 Neg->eraseFromParent(); 206 return Res; 207} 208 209// Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'. 210// Note that if D is also part of the expression tree that we recurse to 211// linearize it as well. Besides that case, this does not recurse into A,B, or 212// C. 213void Reassociate::LinearizeExpr(BinaryOperator *I) { 214 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0)); 215 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1)); 216 assert(isReassociableOp(LHS, I->getOpcode()) && 217 isReassociableOp(RHS, I->getOpcode()) && 218 "Not an expression that needs linearization?"); 219 220 DOUT << "Linear" << *LHS << *RHS << *I; 221 222 // Move the RHS instruction to live immediately before I, avoiding breaking 223 // dominator properties. 224 RHS->moveBefore(I); 225 226 // Move operands around to do the linearization. 227 I->setOperand(1, RHS->getOperand(0)); 228 RHS->setOperand(0, LHS); 229 I->setOperand(0, RHS); 230 231 ++NumLinear; 232 MadeChange = true; 233 DOUT << "Linearized: " << *I; 234 235 // If D is part of this expression tree, tail recurse. 236 if (isReassociableOp(I->getOperand(1), I->getOpcode())) 237 LinearizeExpr(I); 238} 239 240 241/// LinearizeExprTree - Given an associative binary expression tree, traverse 242/// all of the uses putting it into canonical form. This forces a left-linear 243/// form of the the expression (((a+b)+c)+d), and collects information about the 244/// rank of the non-tree operands. 245/// 246/// NOTE: These intentionally destroys the expression tree operands (turning 247/// them into undef values) to reduce #uses of the values. This means that the 248/// caller MUST use something like RewriteExprTree to put the values back in. 249/// 250void Reassociate::LinearizeExprTree(BinaryOperator *I, 251 std::vector<ValueEntry> &Ops) { 252 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1); 253 unsigned Opcode = I->getOpcode(); 254 255 // First step, linearize the expression if it is in ((A+B)+(C+D)) form. 256 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode); 257 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode); 258 259 // If this is a multiply expression tree and it contains internal negations, 260 // transform them into multiplies by -1 so they can be reassociated. 261 if (I->getOpcode() == Instruction::Mul) { 262 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) { 263 LHS = LowerNegateToMultiply(cast<Instruction>(LHS)); 264 LHSBO = isReassociableOp(LHS, Opcode); 265 } 266 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) { 267 RHS = LowerNegateToMultiply(cast<Instruction>(RHS)); 268 RHSBO = isReassociableOp(RHS, Opcode); 269 } 270 } 271 272 if (!LHSBO) { 273 if (!RHSBO) { 274 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As 275 // such, just remember these operands and their rank. 276 Ops.push_back(ValueEntry(getRank(LHS), LHS)); 277 Ops.push_back(ValueEntry(getRank(RHS), RHS)); 278 279 // Clear the leaves out. 280 I->setOperand(0, UndefValue::get(I->getType())); 281 I->setOperand(1, UndefValue::get(I->getType())); 282 return; 283 } else { 284 // Turn X+(Y+Z) -> (Y+Z)+X 285 std::swap(LHSBO, RHSBO); 286 std::swap(LHS, RHS); 287 bool Success = !I->swapOperands(); 288 assert(Success && "swapOperands failed"); 289 Success = false; 290 MadeChange = true; 291 } 292 } else if (RHSBO) { 293 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not 294 // part of the expression tree. 295 LinearizeExpr(I); 296 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0)); 297 RHS = I->getOperand(1); 298 RHSBO = 0; 299 } 300 301 // Okay, now we know that the LHS is a nested expression and that the RHS is 302 // not. Perform reassociation. 303 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!"); 304 305 // Move LHS right before I to make sure that the tree expression dominates all 306 // values. 307 LHSBO->moveBefore(I); 308 309 // Linearize the expression tree on the LHS. 310 LinearizeExprTree(LHSBO, Ops); 311 312 // Remember the RHS operand and its rank. 313 Ops.push_back(ValueEntry(getRank(RHS), RHS)); 314 315 // Clear the RHS leaf out. 316 I->setOperand(1, UndefValue::get(I->getType())); 317} 318 319// RewriteExprTree - Now that the operands for this expression tree are 320// linearized and optimized, emit them in-order. This function is written to be 321// tail recursive. 322void Reassociate::RewriteExprTree(BinaryOperator *I, 323 std::vector<ValueEntry> &Ops, 324 unsigned i) { 325 if (i+2 == Ops.size()) { 326 if (I->getOperand(0) != Ops[i].Op || 327 I->getOperand(1) != Ops[i+1].Op) { 328 Value *OldLHS = I->getOperand(0); 329 DOUT << "RA: " << *I; 330 I->setOperand(0, Ops[i].Op); 331 I->setOperand(1, Ops[i+1].Op); 332 DOUT << "TO: " << *I; 333 MadeChange = true; 334 ++NumChanged; 335 336 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3) 337 // delete the extra, now dead, nodes. 338 RemoveDeadBinaryOp(OldLHS); 339 } 340 return; 341 } 342 assert(i+2 < Ops.size() && "Ops index out of range!"); 343 344 if (I->getOperand(1) != Ops[i].Op) { 345 DOUT << "RA: " << *I; 346 I->setOperand(1, Ops[i].Op); 347 DOUT << "TO: " << *I; 348 MadeChange = true; 349 ++NumChanged; 350 } 351 352 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0)); 353 assert(LHS->getOpcode() == I->getOpcode() && 354 "Improper expression tree!"); 355 356 // Compactify the tree instructions together with each other to guarantee 357 // that the expression tree is dominated by all of Ops. 358 LHS->moveBefore(I); 359 RewriteExprTree(LHS, Ops, i+1); 360} 361 362 363 364// NegateValue - Insert instructions before the instruction pointed to by BI, 365// that computes the negative version of the value specified. The negative 366// version of the value is returned, and BI is left pointing at the instruction 367// that should be processed next by the reassociation pass. 368// 369static Value *NegateValue(Value *V, Instruction *BI) { 370 // We are trying to expose opportunity for reassociation. One of the things 371 // that we want to do to achieve this is to push a negation as deep into an 372 // expression chain as possible, to expose the add instructions. In practice, 373 // this means that we turn this: 374 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D 375 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate 376 // the constants. We assume that instcombine will clean up the mess later if 377 // we introduce tons of unnecessary negation instructions... 378 // 379 if (Instruction *I = dyn_cast<Instruction>(V)) 380 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) { 381 // Push the negates through the add. 382 I->setOperand(0, NegateValue(I->getOperand(0), BI)); 383 I->setOperand(1, NegateValue(I->getOperand(1), BI)); 384 385 // We must move the add instruction here, because the neg instructions do 386 // not dominate the old add instruction in general. By moving it, we are 387 // assured that the neg instructions we just inserted dominate the 388 // instruction we are about to insert after them. 389 // 390 I->moveBefore(BI); 391 I->setName(I->getName()+".neg"); 392 return I; 393 } 394 395 // Insert a 'neg' instruction that subtracts the value from zero to get the 396 // negation. 397 // 398 return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI); 399} 400 401/// ShouldBreakUpSubtract - Return true if we should break up this subtract of 402/// X-Y into (X + -Y). 403static bool ShouldBreakUpSubtract(Instruction *Sub) { 404 // If this is a negation, we can't split it up! 405 if (BinaryOperator::isNeg(Sub)) 406 return false; 407 408 // Don't bother to break this up unless either the LHS is an associable add or 409 // subtract or if this is only used by one. 410 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) || 411 isReassociableOp(Sub->getOperand(0), Instruction::Sub)) 412 return true; 413 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) || 414 isReassociableOp(Sub->getOperand(1), Instruction::Sub)) 415 return true; 416 if (Sub->hasOneUse() && 417 (isReassociableOp(Sub->use_back(), Instruction::Add) || 418 isReassociableOp(Sub->use_back(), Instruction::Sub))) 419 return true; 420 421 return false; 422} 423 424/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is 425/// only used by an add, transform this into (X+(0-Y)) to promote better 426/// reassociation. 427static Instruction *BreakUpSubtract(Instruction *Sub) { 428 // Convert a subtract into an add and a neg instruction... so that sub 429 // instructions can be commuted with other add instructions... 430 // 431 // Calculate the negative value of Operand 1 of the sub instruction... 432 // and set it as the RHS of the add instruction we just made... 433 // 434 Value *NegVal = NegateValue(Sub->getOperand(1), Sub); 435 Instruction *New = 436 BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub); 437 New->takeName(Sub); 438 439 // Everyone now refers to the add instruction. 440 Sub->replaceAllUsesWith(New); 441 Sub->eraseFromParent(); 442 443 DOUT << "Negated: " << *New; 444 return New; 445} 446 447/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used 448/// by one, change this into a multiply by a constant to assist with further 449/// reassociation. 450static Instruction *ConvertShiftToMul(Instruction *Shl) { 451 // If an operand of this shift is a reassociable multiply, or if the shift 452 // is used by a reassociable multiply or add, turn into a multiply. 453 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) || 454 (Shl->hasOneUse() && 455 (isReassociableOp(Shl->use_back(), Instruction::Mul) || 456 isReassociableOp(Shl->use_back(), Instruction::Add)))) { 457 Constant *MulCst = ConstantInt::get(Shl->getType(), 1); 458 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1))); 459 460 Instruction *Mul = BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, 461 "", Shl); 462 Mul->takeName(Shl); 463 Shl->replaceAllUsesWith(Mul); 464 Shl->eraseFromParent(); 465 return Mul; 466 } 467 return 0; 468} 469 470// Scan backwards and forwards among values with the same rank as element i to 471// see if X exists. If X does not exist, return i. 472static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i, 473 Value *X) { 474 unsigned XRank = Ops[i].Rank; 475 unsigned e = Ops.size(); 476 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) 477 if (Ops[j].Op == X) 478 return j; 479 // Scan backwards 480 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) 481 if (Ops[j].Op == X) 482 return j; 483 return i; 484} 485 486/// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together 487/// and returning the result. Insert the tree before I. 488static Value *EmitAddTreeOfValues(Instruction *I, std::vector<Value*> &Ops) { 489 if (Ops.size() == 1) return Ops.back(); 490 491 Value *V1 = Ops.back(); 492 Ops.pop_back(); 493 Value *V2 = EmitAddTreeOfValues(I, Ops); 494 return BinaryOperator::CreateAdd(V2, V1, "tmp", I); 495} 496 497/// RemoveFactorFromExpression - If V is an expression tree that is a 498/// multiplication sequence, and if this sequence contains a multiply by Factor, 499/// remove Factor from the tree and return the new tree. 500Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) { 501 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul); 502 if (!BO) return 0; 503 504 std::vector<ValueEntry> Factors; 505 LinearizeExprTree(BO, Factors); 506 507 bool FoundFactor = false; 508 for (unsigned i = 0, e = Factors.size(); i != e; ++i) 509 if (Factors[i].Op == Factor) { 510 FoundFactor = true; 511 Factors.erase(Factors.begin()+i); 512 break; 513 } 514 if (!FoundFactor) { 515 // Make sure to restore the operands to the expression tree. 516 RewriteExprTree(BO, Factors); 517 return 0; 518 } 519 520 if (Factors.size() == 1) return Factors[0].Op; 521 522 RewriteExprTree(BO, Factors); 523 return BO; 524} 525 526/// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively 527/// add its operands as factors, otherwise add V to the list of factors. 528static void FindSingleUseMultiplyFactors(Value *V, 529 std::vector<Value*> &Factors) { 530 BinaryOperator *BO; 531 if ((!V->hasOneUse() && !V->use_empty()) || 532 !(BO = dyn_cast<BinaryOperator>(V)) || 533 BO->getOpcode() != Instruction::Mul) { 534 Factors.push_back(V); 535 return; 536 } 537 538 // Otherwise, add the LHS and RHS to the list of factors. 539 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors); 540 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors); 541} 542 543 544 545Value *Reassociate::OptimizeExpression(BinaryOperator *I, 546 std::vector<ValueEntry> &Ops) { 547 // Now that we have the linearized expression tree, try to optimize it. 548 // Start by folding any constants that we found. 549 bool IterateOptimization = false; 550 if (Ops.size() == 1) return Ops[0].Op; 551 552 unsigned Opcode = I->getOpcode(); 553 554 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op)) 555 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) { 556 Ops.pop_back(); 557 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2); 558 return OptimizeExpression(I, Ops); 559 } 560 561 // Check for destructive annihilation due to a constant being used. 562 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op)) 563 switch (Opcode) { 564 default: break; 565 case Instruction::And: 566 if (CstVal->isZero()) { // ... & 0 -> 0 567 ++NumAnnihil; 568 return CstVal; 569 } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ... 570 Ops.pop_back(); 571 } 572 break; 573 case Instruction::Mul: 574 if (CstVal->isZero()) { // ... * 0 -> 0 575 ++NumAnnihil; 576 return CstVal; 577 } else if (cast<ConstantInt>(CstVal)->isOne()) { 578 Ops.pop_back(); // ... * 1 -> ... 579 } 580 break; 581 case Instruction::Or: 582 if (CstVal->isAllOnesValue()) { // ... | -1 -> -1 583 ++NumAnnihil; 584 return CstVal; 585 } 586 // FALLTHROUGH! 587 case Instruction::Add: 588 case Instruction::Xor: 589 if (CstVal->isZero()) // ... [|^+] 0 -> ... 590 Ops.pop_back(); 591 break; 592 } 593 if (Ops.size() == 1) return Ops[0].Op; 594 595 // Handle destructive annihilation do to identities between elements in the 596 // argument list here. 597 switch (Opcode) { 598 default: break; 599 case Instruction::And: 600 case Instruction::Or: 601 case Instruction::Xor: 602 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs. 603 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1. 604 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 605 // First, check for X and ~X in the operand list. 606 assert(i < Ops.size()); 607 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^. 608 Value *X = BinaryOperator::getNotArgument(Ops[i].Op); 609 unsigned FoundX = FindInOperandList(Ops, i, X); 610 if (FoundX != i) { 611 if (Opcode == Instruction::And) { // ...&X&~X = 0 612 ++NumAnnihil; 613 return Constant::getNullValue(X->getType()); 614 } else if (Opcode == Instruction::Or) { // ...|X|~X = -1 615 ++NumAnnihil; 616 return ConstantInt::getAllOnesValue(X->getType()); 617 } 618 } 619 } 620 621 // Next, check for duplicate pairs of values, which we assume are next to 622 // each other, due to our sorting criteria. 623 assert(i < Ops.size()); 624 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) { 625 if (Opcode == Instruction::And || Opcode == Instruction::Or) { 626 // Drop duplicate values. 627 Ops.erase(Ops.begin()+i); 628 --i; --e; 629 IterateOptimization = true; 630 ++NumAnnihil; 631 } else { 632 assert(Opcode == Instruction::Xor); 633 if (e == 2) { 634 ++NumAnnihil; 635 return Constant::getNullValue(Ops[0].Op->getType()); 636 } 637 // ... X^X -> ... 638 Ops.erase(Ops.begin()+i, Ops.begin()+i+2); 639 i -= 1; e -= 2; 640 IterateOptimization = true; 641 ++NumAnnihil; 642 } 643 } 644 } 645 break; 646 647 case Instruction::Add: 648 // Scan the operand lists looking for X and -X pairs. If we find any, we 649 // can simplify the expression. X+-X == 0. 650 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 651 assert(i < Ops.size()); 652 // Check for X and -X in the operand list. 653 if (BinaryOperator::isNeg(Ops[i].Op)) { 654 Value *X = BinaryOperator::getNegArgument(Ops[i].Op); 655 unsigned FoundX = FindInOperandList(Ops, i, X); 656 if (FoundX != i) { 657 // Remove X and -X from the operand list. 658 if (Ops.size() == 2) { 659 ++NumAnnihil; 660 return Constant::getNullValue(X->getType()); 661 } else { 662 Ops.erase(Ops.begin()+i); 663 if (i < FoundX) 664 --FoundX; 665 else 666 --i; // Need to back up an extra one. 667 Ops.erase(Ops.begin()+FoundX); 668 IterateOptimization = true; 669 ++NumAnnihil; 670 --i; // Revisit element. 671 e -= 2; // Removed two elements. 672 } 673 } 674 } 675 } 676 677 678 // Scan the operand list, checking to see if there are any common factors 679 // between operands. Consider something like A*A+A*B*C+D. We would like to 680 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies. 681 // To efficiently find this, we count the number of times a factor occurs 682 // for any ADD operands that are MULs. 683 std::map<Value*, unsigned> FactorOccurrences; 684 unsigned MaxOcc = 0; 685 Value *MaxOccVal = 0; 686 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 687 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op)) { 688 if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) { 689 // Compute all of the factors of this added value. 690 std::vector<Value*> Factors; 691 FindSingleUseMultiplyFactors(BOp, Factors); 692 assert(Factors.size() > 1 && "Bad linearize!"); 693 694 // Add one to FactorOccurrences for each unique factor in this op. 695 if (Factors.size() == 2) { 696 unsigned Occ = ++FactorOccurrences[Factors[0]]; 697 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; } 698 if (Factors[0] != Factors[1]) { // Don't double count A*A. 699 Occ = ++FactorOccurrences[Factors[1]]; 700 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; } 701 } 702 } else { 703 std::set<Value*> Duplicates; 704 for (unsigned i = 0, e = Factors.size(); i != e; ++i) { 705 if (Duplicates.insert(Factors[i]).second) { 706 unsigned Occ = ++FactorOccurrences[Factors[i]]; 707 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; } 708 } 709 } 710 } 711 } 712 } 713 } 714 715 // If any factor occurred more than one time, we can pull it out. 716 if (MaxOcc > 1) { 717 DOUT << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << "\n"; 718 719 // Create a new instruction that uses the MaxOccVal twice. If we don't do 720 // this, we could otherwise run into situations where removing a factor 721 // from an expression will drop a use of maxocc, and this can cause 722 // RemoveFactorFromExpression on successive values to behave differently. 723 Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal); 724 std::vector<Value*> NewMulOps; 725 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 726 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) { 727 NewMulOps.push_back(V); 728 Ops.erase(Ops.begin()+i); 729 --i; --e; 730 } 731 } 732 733 // No need for extra uses anymore. 734 delete DummyInst; 735 736 unsigned NumAddedValues = NewMulOps.size(); 737 Value *V = EmitAddTreeOfValues(I, NewMulOps); 738 Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I); 739 740 // Now that we have inserted V and its sole use, optimize it. This allows 741 // us to handle cases that require multiple factoring steps, such as this: 742 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C)) 743 if (NumAddedValues > 1) 744 ReassociateExpression(cast<BinaryOperator>(V)); 745 746 ++NumFactor; 747 748 if (Ops.empty()) 749 return V2; 750 751 // Add the new value to the list of things being added. 752 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2)); 753 754 // Rewrite the tree so that there is now a use of V. 755 RewriteExprTree(I, Ops); 756 return OptimizeExpression(I, Ops); 757 } 758 break; 759 //case Instruction::Mul: 760 } 761 762 if (IterateOptimization) 763 return OptimizeExpression(I, Ops); 764 return 0; 765} 766 767 768/// ReassociateBB - Inspect all of the instructions in this basic block, 769/// reassociating them as we go. 770void Reassociate::ReassociateBB(BasicBlock *BB) { 771 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) { 772 Instruction *BI = BBI++; 773 if (BI->getOpcode() == Instruction::Shl && 774 isa<ConstantInt>(BI->getOperand(1))) 775 if (Instruction *NI = ConvertShiftToMul(BI)) { 776 MadeChange = true; 777 BI = NI; 778 } 779 780 // Reject cases where it is pointless to do this. 781 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() || 782 isa<VectorType>(BI->getType())) 783 continue; // Floating point ops are not associative. 784 785 // If this is a subtract instruction which is not already in negate form, 786 // see if we can convert it to X+-Y. 787 if (BI->getOpcode() == Instruction::Sub) { 788 if (ShouldBreakUpSubtract(BI)) { 789 BI = BreakUpSubtract(BI); 790 MadeChange = true; 791 } else if (BinaryOperator::isNeg(BI)) { 792 // Otherwise, this is a negation. See if the operand is a multiply tree 793 // and if this is not an inner node of a multiply tree. 794 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) && 795 (!BI->hasOneUse() || 796 !isReassociableOp(BI->use_back(), Instruction::Mul))) { 797 BI = LowerNegateToMultiply(BI); 798 MadeChange = true; 799 } 800 } 801 } 802 803 // If this instruction is a commutative binary operator, process it. 804 if (!BI->isAssociative()) continue; 805 BinaryOperator *I = cast<BinaryOperator>(BI); 806 807 // If this is an interior node of a reassociable tree, ignore it until we 808 // get to the root of the tree, to avoid N^2 analysis. 809 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode())) 810 continue; 811 812 // If this is an add tree that is used by a sub instruction, ignore it 813 // until we process the subtract. 814 if (I->hasOneUse() && I->getOpcode() == Instruction::Add && 815 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub) 816 continue; 817 818 ReassociateExpression(I); 819 } 820} 821 822void Reassociate::ReassociateExpression(BinaryOperator *I) { 823 824 // First, walk the expression tree, linearizing the tree, collecting 825 std::vector<ValueEntry> Ops; 826 LinearizeExprTree(I, Ops); 827 828 DOUT << "RAIn:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n"; 829 830 // Now that we have linearized the tree to a list and have gathered all of 831 // the operands and their ranks, sort the operands by their rank. Use a 832 // stable_sort so that values with equal ranks will have their relative 833 // positions maintained (and so the compiler is deterministic). Note that 834 // this sorts so that the highest ranking values end up at the beginning of 835 // the vector. 836 std::stable_sort(Ops.begin(), Ops.end()); 837 838 // OptimizeExpression - Now that we have the expression tree in a convenient 839 // sorted form, optimize it globally if possible. 840 if (Value *V = OptimizeExpression(I, Ops)) { 841 // This expression tree simplified to something that isn't a tree, 842 // eliminate it. 843 DOUT << "Reassoc to scalar: " << *V << "\n"; 844 I->replaceAllUsesWith(V); 845 RemoveDeadBinaryOp(I); 846 return; 847 } 848 849 // We want to sink immediates as deeply as possible except in the case where 850 // this is a multiply tree used only by an add, and the immediate is a -1. 851 // In this case we reassociate to put the negation on the outside so that we 852 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y 853 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() && 854 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add && 855 isa<ConstantInt>(Ops.back().Op) && 856 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) { 857 Ops.insert(Ops.begin(), Ops.back()); 858 Ops.pop_back(); 859 } 860 861 DOUT << "RAOut:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n"; 862 863 if (Ops.size() == 1) { 864 // This expression tree simplified to something that isn't a tree, 865 // eliminate it. 866 I->replaceAllUsesWith(Ops[0].Op); 867 RemoveDeadBinaryOp(I); 868 } else { 869 // Now that we ordered and optimized the expressions, splat them back into 870 // the expression tree, removing any unneeded nodes. 871 RewriteExprTree(I, Ops); 872 } 873} 874 875 876bool Reassociate::runOnFunction(Function &F) { 877 // Recalculate the rank map for F 878 BuildRankMap(F); 879 880 MadeChange = false; 881 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 882 ReassociateBB(FI); 883 884 // We are done with the rank map... 885 RankMap.clear(); 886 ValueRankMap.clear(); 887 return MadeChange; 888} 889 890