Reassociate.cpp revision ac0b6ae358944ae8b2b5a11dc08f52c3ed89f2da
1//===- Reassociate.cpp - Reassociate binary expressions -------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source 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/Debug.h" 33#include "llvm/ADT/PostOrderIterator.h" 34#include "llvm/ADT/Statistic.h" 35#include <algorithm> 36#include <iostream> 37using namespace llvm; 38 39namespace { 40 Statistic NumLinear ("reassociate","Number of insts linearized"); 41 Statistic NumChanged("reassociate","Number of insts reassociated"); 42 Statistic NumSwapped("reassociate","Number of insts with operands swapped"); 43 Statistic NumAnnihil("reassociate","Number of expr tree annihilated"); 44 Statistic NumFactor ("reassociate","Number of multiplies factored"); 45 46 struct 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 std::cerr << Instruction::getOpcodeName(I->getOpcode()) << " " 61 << *Ops[0].Op->getType(); 62 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 63 WriteAsOperand(std::cerr << " ", Ops[i].Op, false, M) 64 << "," << Ops[i].Rank; 65} 66 67namespace { 68 class Reassociate : public FunctionPass { 69 std::map<BasicBlock*, unsigned> RankMap; 70 std::map<Value*, unsigned> ValueRankMap; 71 bool MadeChange; 72 public: 73 bool runOnFunction(Function &F); 74 75 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 76 AU.setPreservesCFG(); 77 } 78 private: 79 void BuildRankMap(Function &F); 80 unsigned getRank(Value *V); 81 void ReassociateExpression(BinaryOperator *I); 82 void RewriteExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops, 83 unsigned Idx = 0); 84 Value *OptimizeExpression(BinaryOperator *I, std::vector<ValueEntry> &Ops); 85 void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops); 86 void LinearizeExpr(BinaryOperator *I); 87 Value *RemoveFactorFromExpression(Value *V, Value *Factor); 88 void ReassociateBB(BasicBlock *BB); 89 90 void RemoveDeadBinaryOp(Value *V); 91 }; 92 93 RegisterPass<Reassociate> X("reassociate", "Reassociate expressions"); 94} 95 96// Public interface to the Reassociate pass 97FunctionPass *llvm::createReassociatePass() { return new Reassociate(); } 98 99void Reassociate::RemoveDeadBinaryOp(Value *V) { 100 BinaryOperator *BOp = dyn_cast<BinaryOperator>(V); 101 if (!BOp || !BOp->use_empty()) return; 102 103 Value *LHS = BOp->getOperand(0), *RHS = BOp->getOperand(1); 104 RemoveDeadBinaryOp(LHS); 105 RemoveDeadBinaryOp(RHS); 106} 107 108 109static bool isUnmovableInstruction(Instruction *I) { 110 if (I->getOpcode() == Instruction::PHI || 111 I->getOpcode() == Instruction::Alloca || 112 I->getOpcode() == Instruction::Load || 113 I->getOpcode() == Instruction::Malloc || 114 I->getOpcode() == Instruction::Invoke || 115 I->getOpcode() == Instruction::Call || 116 I->getOpcode() == Instruction::UDiv || 117 I->getOpcode() == Instruction::SDiv || 118 I->getOpcode() == Instruction::FDiv || 119 I->getOpcode() == Instruction::URem || 120 I->getOpcode() == Instruction::SRem || 121 I->getOpcode() == Instruction::FRem) 122 return true; 123 return false; 124} 125 126void Reassociate::BuildRankMap(Function &F) { 127 unsigned i = 2; 128 129 // Assign distinct ranks to function arguments 130 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I) 131 ValueRankMap[I] = ++i; 132 133 ReversePostOrderTraversal<Function*> RPOT(&F); 134 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(), 135 E = RPOT.end(); I != E; ++I) { 136 BasicBlock *BB = *I; 137 unsigned BBRank = RankMap[BB] = ++i << 16; 138 139 // Walk the basic block, adding precomputed ranks for any instructions that 140 // we cannot move. This ensures that the ranks for these instructions are 141 // all different in the block. 142 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 143 if (isUnmovableInstruction(I)) 144 ValueRankMap[I] = ++BBRank; 145 } 146} 147 148unsigned Reassociate::getRank(Value *V) { 149 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument... 150 151 Instruction *I = dyn_cast<Instruction>(V); 152 if (I == 0) return 0; // Otherwise it's a global or constant, rank 0. 153 154 unsigned &CachedRank = ValueRankMap[I]; 155 if (CachedRank) return CachedRank; // Rank already known? 156 157 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that 158 // we can reassociate expressions for code motion! Since we do not recurse 159 // for PHI nodes, we cannot have infinite recursion here, because there 160 // cannot be loops in the value graph that do not go through PHI nodes. 161 unsigned Rank = 0, MaxRank = RankMap[I->getParent()]; 162 for (unsigned i = 0, e = I->getNumOperands(); 163 i != e && Rank != MaxRank; ++i) 164 Rank = std::max(Rank, getRank(I->getOperand(i))); 165 166 // If this is a not or neg instruction, do not count it for rank. This 167 // assures us that X and ~X will have the same rank. 168 if (!I->getType()->isIntegral() || 169 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I))) 170 ++Rank; 171 172 //DEBUG(std::cerr << "Calculated Rank[" << V->getName() << "] = " 173 //<< Rank << "\n"); 174 175 return CachedRank = Rank; 176} 177 178/// isReassociableOp - Return true if V is an instruction of the specified 179/// opcode and if it only has one use. 180static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) { 181 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) && 182 cast<Instruction>(V)->getOpcode() == Opcode) 183 return cast<BinaryOperator>(V); 184 return 0; 185} 186 187/// LowerNegateToMultiply - Replace 0-X with X*-1. 188/// 189static Instruction *LowerNegateToMultiply(Instruction *Neg) { 190 Constant *Cst; 191 if (Neg->getType()->isFloatingPoint()) 192 Cst = ConstantFP::get(Neg->getType(), -1); 193 else 194 Cst = ConstantInt::getAllOnesValue(Neg->getType()); 195 196 std::string NegName = Neg->getName(); Neg->setName(""); 197 Instruction *Res = BinaryOperator::createMul(Neg->getOperand(1), Cst, NegName, 198 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 DEBUG(std::cerr << "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 DEBUG(std::cerr << "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 DEBUG(std::cerr << "RA: " << *I); 324 I->setOperand(0, Ops[i].Op); 325 I->setOperand(1, Ops[i+1].Op); 326 DEBUG(std::cerr << "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 DEBUG(std::cerr << "RA: " << *I); 340 I->setOperand(1, Ops[i].Op); 341 DEBUG(std::cerr << "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/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is 396/// only used by an add, transform this into (X+(0-Y)) to promote better 397/// reassociation. 398static Instruction *BreakUpSubtract(Instruction *Sub) { 399 // Don't bother to break this up unless either the LHS is an associable add or 400 // if this is only used by one. 401 if (!isReassociableOp(Sub->getOperand(0), Instruction::Add) && 402 !isReassociableOp(Sub->getOperand(1), Instruction::Add) && 403 !(Sub->hasOneUse() &&isReassociableOp(Sub->use_back(), Instruction::Add))) 404 return 0; 405 406 // Convert a subtract into an add and a neg instruction... so that sub 407 // instructions can be commuted with other add instructions... 408 // 409 // Calculate the negative value of Operand 1 of the sub instruction... 410 // and set it as the RHS of the add instruction we just made... 411 // 412 std::string Name = Sub->getName(); 413 Sub->setName(""); 414 Value *NegVal = NegateValue(Sub->getOperand(1), Sub); 415 Instruction *New = 416 BinaryOperator::createAdd(Sub->getOperand(0), NegVal, Name, Sub); 417 418 // Everyone now refers to the add instruction. 419 Sub->replaceAllUsesWith(New); 420 Sub->eraseFromParent(); 421 422 DEBUG(std::cerr << "Negated: " << *New); 423 return New; 424} 425 426/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used 427/// by one, change this into a multiply by a constant to assist with further 428/// reassociation. 429static Instruction *ConvertShiftToMul(Instruction *Shl) { 430 // If an operand of this shift is a reassociable multiply, or if the shift 431 // is used by a reassociable multiply or add, turn into a multiply. 432 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) || 433 (Shl->hasOneUse() && 434 (isReassociableOp(Shl->use_back(), Instruction::Mul) || 435 isReassociableOp(Shl->use_back(), Instruction::Add)))) { 436 Constant *MulCst = ConstantInt::get(Shl->getType(), 1); 437 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1))); 438 439 std::string Name = Shl->getName(); Shl->setName(""); 440 Instruction *Mul = BinaryOperator::createMul(Shl->getOperand(0), MulCst, 441 Name, Shl); 442 Shl->replaceAllUsesWith(Mul); 443 Shl->eraseFromParent(); 444 return Mul; 445 } 446 return 0; 447} 448 449// Scan backwards and forwards among values with the same rank as element i to 450// see if X exists. If X does not exist, return i. 451static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i, 452 Value *X) { 453 unsigned XRank = Ops[i].Rank; 454 unsigned e = Ops.size(); 455 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) 456 if (Ops[j].Op == X) 457 return j; 458 // Scan backwards 459 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) 460 if (Ops[j].Op == X) 461 return j; 462 return i; 463} 464 465/// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together 466/// and returning the result. Insert the tree before I. 467static Value *EmitAddTreeOfValues(Instruction *I, std::vector<Value*> &Ops) { 468 if (Ops.size() == 1) return Ops.back(); 469 470 Value *V1 = Ops.back(); 471 Ops.pop_back(); 472 Value *V2 = EmitAddTreeOfValues(I, Ops); 473 return BinaryOperator::createAdd(V2, V1, "tmp", I); 474} 475 476/// RemoveFactorFromExpression - If V is an expression tree that is a 477/// multiplication sequence, and if this sequence contains a multiply by Factor, 478/// remove Factor from the tree and return the new tree. 479Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) { 480 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul); 481 if (!BO) return 0; 482 483 std::vector<ValueEntry> Factors; 484 LinearizeExprTree(BO, Factors); 485 486 bool FoundFactor = false; 487 for (unsigned i = 0, e = Factors.size(); i != e; ++i) 488 if (Factors[i].Op == Factor) { 489 FoundFactor = true; 490 Factors.erase(Factors.begin()+i); 491 break; 492 } 493 if (!FoundFactor) { 494 // Make sure to restore the operands to the expression tree. 495 RewriteExprTree(BO, Factors); 496 return 0; 497 } 498 499 if (Factors.size() == 1) return Factors[0].Op; 500 501 RewriteExprTree(BO, Factors); 502 return BO; 503} 504 505/// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively 506/// add its operands as factors, otherwise add V to the list of factors. 507static void FindSingleUseMultiplyFactors(Value *V, 508 std::vector<Value*> &Factors) { 509 BinaryOperator *BO; 510 if ((!V->hasOneUse() && !V->use_empty()) || 511 !(BO = dyn_cast<BinaryOperator>(V)) || 512 BO->getOpcode() != Instruction::Mul) { 513 Factors.push_back(V); 514 return; 515 } 516 517 // Otherwise, add the LHS and RHS to the list of factors. 518 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors); 519 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors); 520} 521 522 523 524Value *Reassociate::OptimizeExpression(BinaryOperator *I, 525 std::vector<ValueEntry> &Ops) { 526 // Now that we have the linearized expression tree, try to optimize it. 527 // Start by folding any constants that we found. 528 bool IterateOptimization = false; 529 if (Ops.size() == 1) return Ops[0].Op; 530 531 unsigned Opcode = I->getOpcode(); 532 533 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op)) 534 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) { 535 Ops.pop_back(); 536 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2); 537 return OptimizeExpression(I, Ops); 538 } 539 540 // Check for destructive annihilation due to a constant being used. 541 if (ConstantIntegral *CstVal = dyn_cast<ConstantIntegral>(Ops.back().Op)) 542 switch (Opcode) { 543 default: break; 544 case Instruction::And: 545 if (CstVal->isNullValue()) { // ... & 0 -> 0 546 ++NumAnnihil; 547 return CstVal; 548 } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ... 549 Ops.pop_back(); 550 } 551 break; 552 case Instruction::Mul: 553 if (CstVal->isNullValue()) { // ... * 0 -> 0 554 ++NumAnnihil; 555 return CstVal; 556 } else if (cast<ConstantInt>(CstVal)->getZExtValue() == 1) { 557 Ops.pop_back(); // ... * 1 -> ... 558 } 559 break; 560 case Instruction::Or: 561 if (CstVal->isAllOnesValue()) { // ... | -1 -> -1 562 ++NumAnnihil; 563 return CstVal; 564 } 565 // FALLTHROUGH! 566 case Instruction::Add: 567 case Instruction::Xor: 568 if (CstVal->isNullValue()) // ... [|^+] 0 -> ... 569 Ops.pop_back(); 570 break; 571 } 572 if (Ops.size() == 1) return Ops[0].Op; 573 574 // Handle destructive annihilation do to identities between elements in the 575 // argument list here. 576 switch (Opcode) { 577 default: break; 578 case Instruction::And: 579 case Instruction::Or: 580 case Instruction::Xor: 581 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs. 582 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1. 583 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 584 // First, check for X and ~X in the operand list. 585 assert(i < Ops.size()); 586 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^. 587 Value *X = BinaryOperator::getNotArgument(Ops[i].Op); 588 unsigned FoundX = FindInOperandList(Ops, i, X); 589 if (FoundX != i) { 590 if (Opcode == Instruction::And) { // ...&X&~X = 0 591 ++NumAnnihil; 592 return Constant::getNullValue(X->getType()); 593 } else if (Opcode == Instruction::Or) { // ...|X|~X = -1 594 ++NumAnnihil; 595 return ConstantIntegral::getAllOnesValue(X->getType()); 596 } 597 } 598 } 599 600 // Next, check for duplicate pairs of values, which we assume are next to 601 // each other, due to our sorting criteria. 602 assert(i < Ops.size()); 603 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) { 604 if (Opcode == Instruction::And || Opcode == Instruction::Or) { 605 // Drop duplicate values. 606 Ops.erase(Ops.begin()+i); 607 --i; --e; 608 IterateOptimization = true; 609 ++NumAnnihil; 610 } else { 611 assert(Opcode == Instruction::Xor); 612 if (e == 2) { 613 ++NumAnnihil; 614 return Constant::getNullValue(Ops[0].Op->getType()); 615 } 616 // ... X^X -> ... 617 Ops.erase(Ops.begin()+i, Ops.begin()+i+2); 618 i -= 1; e -= 2; 619 IterateOptimization = true; 620 ++NumAnnihil; 621 } 622 } 623 } 624 break; 625 626 case Instruction::Add: 627 // Scan the operand lists looking for X and -X pairs. If we find any, we 628 // can simplify the expression. X+-X == 0. 629 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 630 assert(i < Ops.size()); 631 // Check for X and -X in the operand list. 632 if (BinaryOperator::isNeg(Ops[i].Op)) { 633 Value *X = BinaryOperator::getNegArgument(Ops[i].Op); 634 unsigned FoundX = FindInOperandList(Ops, i, X); 635 if (FoundX != i) { 636 // Remove X and -X from the operand list. 637 if (Ops.size() == 2) { 638 ++NumAnnihil; 639 return Constant::getNullValue(X->getType()); 640 } else { 641 Ops.erase(Ops.begin()+i); 642 if (i < FoundX) 643 --FoundX; 644 else 645 --i; // Need to back up an extra one. 646 Ops.erase(Ops.begin()+FoundX); 647 IterateOptimization = true; 648 ++NumAnnihil; 649 --i; // Revisit element. 650 e -= 2; // Removed two elements. 651 } 652 } 653 } 654 } 655 656 657 // Scan the operand list, checking to see if there are any common factors 658 // between operands. Consider something like A*A+A*B*C+D. We would like to 659 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies. 660 // To efficiently find this, we count the number of times a factor occurs 661 // for any ADD operands that are MULs. 662 std::map<Value*, unsigned> FactorOccurrences; 663 unsigned MaxOcc = 0; 664 Value *MaxOccVal = 0; 665 if (!I->getType()->isFloatingPoint()) { 666 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 667 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op)) 668 if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) { 669 // Compute all of the factors of this added value. 670 std::vector<Value*> Factors; 671 FindSingleUseMultiplyFactors(BOp, Factors); 672 assert(Factors.size() > 1 && "Bad linearize!"); 673 674 // Add one to FactorOccurrences for each unique factor in this op. 675 if (Factors.size() == 2) { 676 unsigned Occ = ++FactorOccurrences[Factors[0]]; 677 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; } 678 if (Factors[0] != Factors[1]) { // Don't double count A*A. 679 Occ = ++FactorOccurrences[Factors[1]]; 680 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; } 681 } 682 } else { 683 std::set<Value*> Duplicates; 684 for (unsigned i = 0, e = Factors.size(); i != e; ++i) 685 if (Duplicates.insert(Factors[i]).second) { 686 unsigned Occ = ++FactorOccurrences[Factors[i]]; 687 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; } 688 } 689 } 690 } 691 } 692 } 693 694 // If any factor occurred more than one time, we can pull it out. 695 if (MaxOcc > 1) { 696 DEBUG(std::cerr << "\nFACTORING [" << MaxOcc << "]: " 697 << *MaxOccVal << "\n"); 698 699 // Create a new instruction that uses the MaxOccVal twice. If we don't do 700 // this, we could otherwise run into situations where removing a factor 701 // from an expression will drop a use of maxocc, and this can cause 702 // RemoveFactorFromExpression on successive values to behave differently. 703 Instruction *DummyInst = BinaryOperator::createAdd(MaxOccVal, MaxOccVal); 704 std::vector<Value*> NewMulOps; 705 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 706 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) { 707 NewMulOps.push_back(V); 708 Ops.erase(Ops.begin()+i); 709 --i; --e; 710 } 711 } 712 713 // No need for extra uses anymore. 714 delete DummyInst; 715 716 unsigned NumAddedValues = NewMulOps.size(); 717 Value *V = EmitAddTreeOfValues(I, NewMulOps); 718 Value *V2 = BinaryOperator::createMul(V, MaxOccVal, "tmp", I); 719 720 // Now that we have inserted V and its sole use, optimize it. This allows 721 // us to handle cases that require multiple factoring steps, such as this: 722 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C)) 723 if (NumAddedValues > 1) 724 ReassociateExpression(cast<BinaryOperator>(V)); 725 726 ++NumFactor; 727 728 if (Ops.size() == 0) 729 return V2; 730 731 // Add the new value to the list of things being added. 732 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2)); 733 734 // Rewrite the tree so that there is now a use of V. 735 RewriteExprTree(I, Ops); 736 return OptimizeExpression(I, Ops); 737 } 738 break; 739 //case Instruction::Mul: 740 } 741 742 if (IterateOptimization) 743 return OptimizeExpression(I, Ops); 744 return 0; 745} 746 747 748/// ReassociateBB - Inspect all of the instructions in this basic block, 749/// reassociating them as we go. 750void Reassociate::ReassociateBB(BasicBlock *BB) { 751 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) { 752 Instruction *BI = BBI++; 753 if (BI->getOpcode() == Instruction::Shl && 754 isa<ConstantInt>(BI->getOperand(1))) 755 if (Instruction *NI = ConvertShiftToMul(BI)) { 756 MadeChange = true; 757 BI = NI; 758 } 759 760 // Reject cases where it is pointless to do this. 761 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() || 762 isa<PackedType>(BI->getType())) 763 continue; // Floating point ops are not associative. 764 765 // If this is a subtract instruction which is not already in negate form, 766 // see if we can convert it to X+-Y. 767 if (BI->getOpcode() == Instruction::Sub) { 768 if (!BinaryOperator::isNeg(BI)) { 769 if (Instruction *NI = BreakUpSubtract(BI)) { 770 MadeChange = true; 771 BI = NI; 772 } 773 } else { 774 // Otherwise, this is a negation. See if the operand is a multiply tree 775 // and if this is not an inner node of a multiply tree. 776 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) && 777 (!BI->hasOneUse() || 778 !isReassociableOp(BI->use_back(), Instruction::Mul))) { 779 BI = LowerNegateToMultiply(BI); 780 MadeChange = true; 781 } 782 } 783 } 784 785 // If this instruction is a commutative binary operator, process it. 786 if (!BI->isAssociative()) continue; 787 BinaryOperator *I = cast<BinaryOperator>(BI); 788 789 // If this is an interior node of a reassociable tree, ignore it until we 790 // get to the root of the tree, to avoid N^2 analysis. 791 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode())) 792 continue; 793 794 // If this is an add tree that is used by a sub instruction, ignore it 795 // until we process the subtract. 796 if (I->hasOneUse() && I->getOpcode() == Instruction::Add && 797 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub) 798 continue; 799 800 ReassociateExpression(I); 801 } 802} 803 804void Reassociate::ReassociateExpression(BinaryOperator *I) { 805 806 // First, walk the expression tree, linearizing the tree, collecting 807 std::vector<ValueEntry> Ops; 808 LinearizeExprTree(I, Ops); 809 810 DEBUG(std::cerr << "RAIn:\t"; PrintOps(I, Ops); 811 std::cerr << "\n"); 812 813 // Now that we have linearized the tree to a list and have gathered all of 814 // the operands and their ranks, sort the operands by their rank. Use a 815 // stable_sort so that values with equal ranks will have their relative 816 // positions maintained (and so the compiler is deterministic). Note that 817 // this sorts so that the highest ranking values end up at the beginning of 818 // the vector. 819 std::stable_sort(Ops.begin(), Ops.end()); 820 821 // OptimizeExpression - Now that we have the expression tree in a convenient 822 // sorted form, optimize it globally if possible. 823 if (Value *V = OptimizeExpression(I, Ops)) { 824 // This expression tree simplified to something that isn't a tree, 825 // eliminate it. 826 DEBUG(std::cerr << "Reassoc to scalar: " << *V << "\n"); 827 I->replaceAllUsesWith(V); 828 RemoveDeadBinaryOp(I); 829 return; 830 } 831 832 // We want to sink immediates as deeply as possible except in the case where 833 // this is a multiply tree used only by an add, and the immediate is a -1. 834 // In this case we reassociate to put the negation on the outside so that we 835 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y 836 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() && 837 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add && 838 isa<ConstantInt>(Ops.back().Op) && 839 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) { 840 Ops.insert(Ops.begin(), Ops.back()); 841 Ops.pop_back(); 842 } 843 844 DEBUG(std::cerr << "RAOut:\t"; PrintOps(I, Ops); 845 std::cerr << "\n"); 846 847 if (Ops.size() == 1) { 848 // This expression tree simplified to something that isn't a tree, 849 // eliminate it. 850 I->replaceAllUsesWith(Ops[0].Op); 851 RemoveDeadBinaryOp(I); 852 } else { 853 // Now that we ordered and optimized the expressions, splat them back into 854 // the expression tree, removing any unneeded nodes. 855 RewriteExprTree(I, Ops); 856 } 857} 858 859 860bool Reassociate::runOnFunction(Function &F) { 861 // Recalculate the rank map for F 862 BuildRankMap(F); 863 864 MadeChange = false; 865 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 866 ReassociateBB(FI); 867 868 // We are done with the rank map... 869 RankMap.clear(); 870 ValueRankMap.clear(); 871 return MadeChange; 872} 873 874