Reassociate.cpp revision 9d6565a5b1fbc4286d6ee638d8f47a3171a9ed7e
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/Compiler.h" 33#include "llvm/Support/Debug.h" 34#include "llvm/ADT/PostOrderIterator.h" 35#include "llvm/ADT/Statistic.h" 36#include <algorithm> 37using namespace llvm; 38 39STATISTIC(NumLinear , "Number of insts linearized"); 40STATISTIC(NumChanged, "Number of insts reassociated"); 41STATISTIC(NumAnnihil, "Number of expr tree annihilated"); 42STATISTIC(NumFactor , "Number of multiplies factored"); 43 44namespace { 45 struct VISIBILITY_HIDDEN ValueEntry { 46 unsigned Rank; 47 Value *Op; 48 ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {} 49 }; 50 inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) { 51 return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start. 52 } 53} 54 55/// PrintOps - Print out the expression identified in the Ops list. 56/// 57static void PrintOps(Instruction *I, const std::vector<ValueEntry> &Ops) { 58 Module *M = I->getParent()->getParent()->getParent(); 59 cerr << Instruction::getOpcodeName(I->getOpcode()) << " " 60 << *Ops[0].Op->getType(); 61 for (unsigned i = 0, e = Ops.size(); i != e; ++i) 62 WriteAsOperand(*cerr.stream() << " ", Ops[i].Op, false, M) 63 << "," << Ops[i].Rank; 64} 65 66namespace { 67 class VISIBILITY_HIDDEN Reassociate : public FunctionPass { 68 std::map<BasicBlock*, unsigned> RankMap; 69 std::map<Value*, unsigned> ValueRankMap; 70 bool MadeChange; 71 public: 72 bool runOnFunction(Function &F); 73 74 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 75 AU.setPreservesCFG(); 76 } 77 private: 78 void BuildRankMap(Function &F); 79 unsigned getRank(Value *V); 80 void ReassociateExpression(BinaryOperator *I); 81 void RewriteExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops, 82 unsigned Idx = 0); 83 Value *OptimizeExpression(BinaryOperator *I, std::vector<ValueEntry> &Ops); 84 void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops); 85 void LinearizeExpr(BinaryOperator *I); 86 Value *RemoveFactorFromExpression(Value *V, Value *Factor); 87 void ReassociateBB(BasicBlock *BB); 88 89 void RemoveDeadBinaryOp(Value *V); 90 }; 91 92 RegisterPass<Reassociate> X("reassociate", "Reassociate expressions"); 93} 94 95// Public interface to the Reassociate pass 96FunctionPass *llvm::createReassociatePass() { return new Reassociate(); } 97 98void Reassociate::RemoveDeadBinaryOp(Value *V) { 99 Instruction *Op = dyn_cast<Instruction>(V); 100 if (!Op || !isa<BinaryOperator>(Op) || !isa<CmpInst>(Op) || !Op->use_empty()) 101 return; 102 103 Value *LHS = Op->getOperand(0), *RHS = Op->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()->isInteger() || 169 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I))) 170 ++Rank; 171 172 //DOUT << "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 = ConstantInt::getAllOnesValue(Neg->getType()); 191 192 Instruction *Res = BinaryOperator::createMul(Neg->getOperand(1), Cst, "",Neg); 193 Res->takeName(Neg); 194 Neg->replaceAllUsesWith(Res); 195 Neg->eraseFromParent(); 196 return Res; 197} 198 199// Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'. 200// Note that if D is also part of the expression tree that we recurse to 201// linearize it as well. Besides that case, this does not recurse into A,B, or 202// C. 203void Reassociate::LinearizeExpr(BinaryOperator *I) { 204 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0)); 205 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1)); 206 assert(isReassociableOp(LHS, I->getOpcode()) && 207 isReassociableOp(RHS, I->getOpcode()) && 208 "Not an expression that needs linearization?"); 209 210 DOUT << "Linear" << *LHS << *RHS << *I; 211 212 // Move the RHS instruction to live immediately before I, avoiding breaking 213 // dominator properties. 214 RHS->moveBefore(I); 215 216 // Move operands around to do the linearization. 217 I->setOperand(1, RHS->getOperand(0)); 218 RHS->setOperand(0, LHS); 219 I->setOperand(0, RHS); 220 221 ++NumLinear; 222 MadeChange = true; 223 DOUT << "Linearized: " << *I; 224 225 // If D is part of this expression tree, tail recurse. 226 if (isReassociableOp(I->getOperand(1), I->getOpcode())) 227 LinearizeExpr(I); 228} 229 230 231/// LinearizeExprTree - Given an associative binary expression tree, traverse 232/// all of the uses putting it into canonical form. This forces a left-linear 233/// form of the the expression (((a+b)+c)+d), and collects information about the 234/// rank of the non-tree operands. 235/// 236/// NOTE: These intentionally destroys the expression tree operands (turning 237/// them into undef values) to reduce #uses of the values. This means that the 238/// caller MUST use something like RewriteExprTree to put the values back in. 239/// 240void Reassociate::LinearizeExprTree(BinaryOperator *I, 241 std::vector<ValueEntry> &Ops) { 242 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1); 243 unsigned Opcode = I->getOpcode(); 244 245 // First step, linearize the expression if it is in ((A+B)+(C+D)) form. 246 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode); 247 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode); 248 249 // If this is a multiply expression tree and it contains internal negations, 250 // transform them into multiplies by -1 so they can be reassociated. 251 if (I->getOpcode() == Instruction::Mul) { 252 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) { 253 LHS = LowerNegateToMultiply(cast<Instruction>(LHS)); 254 LHSBO = isReassociableOp(LHS, Opcode); 255 } 256 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) { 257 RHS = LowerNegateToMultiply(cast<Instruction>(RHS)); 258 RHSBO = isReassociableOp(RHS, Opcode); 259 } 260 } 261 262 if (!LHSBO) { 263 if (!RHSBO) { 264 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As 265 // such, just remember these operands and their rank. 266 Ops.push_back(ValueEntry(getRank(LHS), LHS)); 267 Ops.push_back(ValueEntry(getRank(RHS), RHS)); 268 269 // Clear the leaves out. 270 I->setOperand(0, UndefValue::get(I->getType())); 271 I->setOperand(1, UndefValue::get(I->getType())); 272 return; 273 } else { 274 // Turn X+(Y+Z) -> (Y+Z)+X 275 std::swap(LHSBO, RHSBO); 276 std::swap(LHS, RHS); 277 bool Success = !I->swapOperands(); 278 assert(Success && "swapOperands failed"); 279 MadeChange = true; 280 } 281 } else if (RHSBO) { 282 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not 283 // part of the expression tree. 284 LinearizeExpr(I); 285 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0)); 286 RHS = I->getOperand(1); 287 RHSBO = 0; 288 } 289 290 // Okay, now we know that the LHS is a nested expression and that the RHS is 291 // not. Perform reassociation. 292 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!"); 293 294 // Move LHS right before I to make sure that the tree expression dominates all 295 // values. 296 LHSBO->moveBefore(I); 297 298 // Linearize the expression tree on the LHS. 299 LinearizeExprTree(LHSBO, Ops); 300 301 // Remember the RHS operand and its rank. 302 Ops.push_back(ValueEntry(getRank(RHS), RHS)); 303 304 // Clear the RHS leaf out. 305 I->setOperand(1, UndefValue::get(I->getType())); 306} 307 308// RewriteExprTree - Now that the operands for this expression tree are 309// linearized and optimized, emit them in-order. This function is written to be 310// tail recursive. 311void Reassociate::RewriteExprTree(BinaryOperator *I, 312 std::vector<ValueEntry> &Ops, 313 unsigned i) { 314 if (i+2 == Ops.size()) { 315 if (I->getOperand(0) != Ops[i].Op || 316 I->getOperand(1) != Ops[i+1].Op) { 317 Value *OldLHS = I->getOperand(0); 318 DOUT << "RA: " << *I; 319 I->setOperand(0, Ops[i].Op); 320 I->setOperand(1, Ops[i+1].Op); 321 DOUT << "TO: " << *I; 322 MadeChange = true; 323 ++NumChanged; 324 325 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3) 326 // delete the extra, now dead, nodes. 327 RemoveDeadBinaryOp(OldLHS); 328 } 329 return; 330 } 331 assert(i+2 < Ops.size() && "Ops index out of range!"); 332 333 if (I->getOperand(1) != Ops[i].Op) { 334 DOUT << "RA: " << *I; 335 I->setOperand(1, Ops[i].Op); 336 DOUT << "TO: " << *I; 337 MadeChange = true; 338 ++NumChanged; 339 } 340 341 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0)); 342 assert(LHS->getOpcode() == I->getOpcode() && 343 "Improper expression tree!"); 344 345 // Compactify the tree instructions together with each other to guarantee 346 // that the expression tree is dominated by all of Ops. 347 LHS->moveBefore(I); 348 RewriteExprTree(LHS, Ops, i+1); 349} 350 351 352 353// NegateValue - Insert instructions before the instruction pointed to by BI, 354// that computes the negative version of the value specified. The negative 355// version of the value is returned, and BI is left pointing at the instruction 356// that should be processed next by the reassociation pass. 357// 358static Value *NegateValue(Value *V, Instruction *BI) { 359 // We are trying to expose opportunity for reassociation. One of the things 360 // that we want to do to achieve this is to push a negation as deep into an 361 // expression chain as possible, to expose the add instructions. In practice, 362 // this means that we turn this: 363 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D 364 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate 365 // the constants. We assume that instcombine will clean up the mess later if 366 // we introduce tons of unnecessary negation instructions... 367 // 368 if (Instruction *I = dyn_cast<Instruction>(V)) 369 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) { 370 // Push the negates through the add. 371 I->setOperand(0, NegateValue(I->getOperand(0), BI)); 372 I->setOperand(1, NegateValue(I->getOperand(1), BI)); 373 374 // We must move the add instruction here, because the neg instructions do 375 // not dominate the old add instruction in general. By moving it, we are 376 // assured that the neg instructions we just inserted dominate the 377 // instruction we are about to insert after them. 378 // 379 I->moveBefore(BI); 380 I->setName(I->getName()+".neg"); 381 return I; 382 } 383 384 // Insert a 'neg' instruction that subtracts the value from zero to get the 385 // negation. 386 // 387 return BinaryOperator::createNeg(V, V->getName() + ".neg", BI); 388} 389 390/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is 391/// only used by an add, transform this into (X+(0-Y)) to promote better 392/// reassociation. 393static Instruction *BreakUpSubtract(Instruction *Sub) { 394 // Don't bother to break this up unless either the LHS is an associable add or 395 // if this is only used by one. 396 if (!isReassociableOp(Sub->getOperand(0), Instruction::Add) && 397 !isReassociableOp(Sub->getOperand(1), Instruction::Add) && 398 !(Sub->hasOneUse() &&isReassociableOp(Sub->use_back(), Instruction::Add))) 399 return 0; 400 401 // Convert a subtract into an add and a neg instruction... so that sub 402 // instructions can be commuted with other add instructions... 403 // 404 // Calculate the negative value of Operand 1 of the sub instruction... 405 // and set it as the RHS of the add instruction we just made... 406 // 407 Value *NegVal = NegateValue(Sub->getOperand(1), Sub); 408 Instruction *New = 409 BinaryOperator::createAdd(Sub->getOperand(0), NegVal, "", Sub); 410 New->takeName(Sub); 411 412 // Everyone now refers to the add instruction. 413 Sub->replaceAllUsesWith(New); 414 Sub->eraseFromParent(); 415 416 DOUT << "Negated: " << *New; 417 return New; 418} 419 420/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used 421/// by one, change this into a multiply by a constant to assist with further 422/// reassociation. 423static Instruction *ConvertShiftToMul(Instruction *Shl) { 424 // If an operand of this shift is a reassociable multiply, or if the shift 425 // is used by a reassociable multiply or add, turn into a multiply. 426 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) || 427 (Shl->hasOneUse() && 428 (isReassociableOp(Shl->use_back(), Instruction::Mul) || 429 isReassociableOp(Shl->use_back(), Instruction::Add)))) { 430 Constant *MulCst = ConstantInt::get(Shl->getType(), 1); 431 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1))); 432 433 Instruction *Mul = BinaryOperator::createMul(Shl->getOperand(0), MulCst, 434 "", Shl); 435 Mul->takeName(Shl); 436 Shl->replaceAllUsesWith(Mul); 437 Shl->eraseFromParent(); 438 return Mul; 439 } 440 return 0; 441} 442 443// Scan backwards and forwards among values with the same rank as element i to 444// see if X exists. If X does not exist, return i. 445static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i, 446 Value *X) { 447 unsigned XRank = Ops[i].Rank; 448 unsigned e = Ops.size(); 449 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) 450 if (Ops[j].Op == X) 451 return j; 452 // Scan backwards 453 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) 454 if (Ops[j].Op == X) 455 return j; 456 return i; 457} 458 459/// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together 460/// and returning the result. Insert the tree before I. 461static Value *EmitAddTreeOfValues(Instruction *I, std::vector<Value*> &Ops) { 462 if (Ops.size() == 1) return Ops.back(); 463 464 Value *V1 = Ops.back(); 465 Ops.pop_back(); 466 Value *V2 = EmitAddTreeOfValues(I, Ops); 467 return BinaryOperator::createAdd(V2, V1, "tmp", I); 468} 469 470/// RemoveFactorFromExpression - If V is an expression tree that is a 471/// multiplication sequence, and if this sequence contains a multiply by Factor, 472/// remove Factor from the tree and return the new tree. 473Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) { 474 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul); 475 if (!BO) return 0; 476 477 std::vector<ValueEntry> Factors; 478 LinearizeExprTree(BO, Factors); 479 480 bool FoundFactor = false; 481 for (unsigned i = 0, e = Factors.size(); i != e; ++i) 482 if (Factors[i].Op == Factor) { 483 FoundFactor = true; 484 Factors.erase(Factors.begin()+i); 485 break; 486 } 487 if (!FoundFactor) { 488 // Make sure to restore the operands to the expression tree. 489 RewriteExprTree(BO, Factors); 490 return 0; 491 } 492 493 if (Factors.size() == 1) return Factors[0].Op; 494 495 RewriteExprTree(BO, Factors); 496 return BO; 497} 498 499/// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively 500/// add its operands as factors, otherwise add V to the list of factors. 501static void FindSingleUseMultiplyFactors(Value *V, 502 std::vector<Value*> &Factors) { 503 BinaryOperator *BO; 504 if ((!V->hasOneUse() && !V->use_empty()) || 505 !(BO = dyn_cast<BinaryOperator>(V)) || 506 BO->getOpcode() != Instruction::Mul) { 507 Factors.push_back(V); 508 return; 509 } 510 511 // Otherwise, add the LHS and RHS to the list of factors. 512 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors); 513 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors); 514} 515 516 517 518Value *Reassociate::OptimizeExpression(BinaryOperator *I, 519 std::vector<ValueEntry> &Ops) { 520 // Now that we have the linearized expression tree, try to optimize it. 521 // Start by folding any constants that we found. 522 bool IterateOptimization = false; 523 if (Ops.size() == 1) return Ops[0].Op; 524 525 unsigned Opcode = I->getOpcode(); 526 527 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op)) 528 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) { 529 Ops.pop_back(); 530 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2); 531 return OptimizeExpression(I, Ops); 532 } 533 534 // Check for destructive annihilation due to a constant being used. 535 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op)) 536 switch (Opcode) { 537 default: break; 538 case Instruction::And: 539 if (CstVal->isNullValue()) { // ... & 0 -> 0 540 ++NumAnnihil; 541 return CstVal; 542 } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ... 543 Ops.pop_back(); 544 } 545 break; 546 case Instruction::Mul: 547 if (CstVal->isNullValue()) { // ... * 0 -> 0 548 ++NumAnnihil; 549 return CstVal; 550 } else if (cast<ConstantInt>(CstVal)->getZExtValue() == 1) { 551 Ops.pop_back(); // ... * 1 -> ... 552 } 553 break; 554 case Instruction::Or: 555 if (CstVal->isAllOnesValue()) { // ... | -1 -> -1 556 ++NumAnnihil; 557 return CstVal; 558 } 559 // FALLTHROUGH! 560 case Instruction::Add: 561 case Instruction::Xor: 562 if (CstVal->isNullValue()) // ... [|^+] 0 -> ... 563 Ops.pop_back(); 564 break; 565 } 566 if (Ops.size() == 1) return Ops[0].Op; 567 568 // Handle destructive annihilation do to identities between elements in the 569 // argument list here. 570 switch (Opcode) { 571 default: break; 572 case Instruction::And: 573 case Instruction::Or: 574 case Instruction::Xor: 575 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs. 576 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1. 577 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 578 // First, check for X and ~X in the operand list. 579 assert(i < Ops.size()); 580 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^. 581 Value *X = BinaryOperator::getNotArgument(Ops[i].Op); 582 unsigned FoundX = FindInOperandList(Ops, i, X); 583 if (FoundX != i) { 584 if (Opcode == Instruction::And) { // ...&X&~X = 0 585 ++NumAnnihil; 586 return Constant::getNullValue(X->getType()); 587 } else if (Opcode == Instruction::Or) { // ...|X|~X = -1 588 ++NumAnnihil; 589 return ConstantInt::getAllOnesValue(X->getType()); 590 } 591 } 592 } 593 594 // Next, check for duplicate pairs of values, which we assume are next to 595 // each other, due to our sorting criteria. 596 assert(i < Ops.size()); 597 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) { 598 if (Opcode == Instruction::And || Opcode == Instruction::Or) { 599 // Drop duplicate values. 600 Ops.erase(Ops.begin()+i); 601 --i; --e; 602 IterateOptimization = true; 603 ++NumAnnihil; 604 } else { 605 assert(Opcode == Instruction::Xor); 606 if (e == 2) { 607 ++NumAnnihil; 608 return Constant::getNullValue(Ops[0].Op->getType()); 609 } 610 // ... X^X -> ... 611 Ops.erase(Ops.begin()+i, Ops.begin()+i+2); 612 i -= 1; e -= 2; 613 IterateOptimization = true; 614 ++NumAnnihil; 615 } 616 } 617 } 618 break; 619 620 case Instruction::Add: 621 // Scan the operand lists looking for X and -X pairs. If we find any, we 622 // can simplify the expression. X+-X == 0. 623 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 624 assert(i < Ops.size()); 625 // Check for X and -X in the operand list. 626 if (BinaryOperator::isNeg(Ops[i].Op)) { 627 Value *X = BinaryOperator::getNegArgument(Ops[i].Op); 628 unsigned FoundX = FindInOperandList(Ops, i, X); 629 if (FoundX != i) { 630 // Remove X and -X from the operand list. 631 if (Ops.size() == 2) { 632 ++NumAnnihil; 633 return Constant::getNullValue(X->getType()); 634 } else { 635 Ops.erase(Ops.begin()+i); 636 if (i < FoundX) 637 --FoundX; 638 else 639 --i; // Need to back up an extra one. 640 Ops.erase(Ops.begin()+FoundX); 641 IterateOptimization = true; 642 ++NumAnnihil; 643 --i; // Revisit element. 644 e -= 2; // Removed two elements. 645 } 646 } 647 } 648 } 649 650 651 // Scan the operand list, checking to see if there are any common factors 652 // between operands. Consider something like A*A+A*B*C+D. We would like to 653 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies. 654 // To efficiently find this, we count the number of times a factor occurs 655 // for any ADD operands that are MULs. 656 std::map<Value*, unsigned> FactorOccurrences; 657 unsigned MaxOcc = 0; 658 Value *MaxOccVal = 0; 659 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 660 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op)) { 661 if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) { 662 // Compute all of the factors of this added value. 663 std::vector<Value*> Factors; 664 FindSingleUseMultiplyFactors(BOp, Factors); 665 assert(Factors.size() > 1 && "Bad linearize!"); 666 667 // Add one to FactorOccurrences for each unique factor in this op. 668 if (Factors.size() == 2) { 669 unsigned Occ = ++FactorOccurrences[Factors[0]]; 670 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; } 671 if (Factors[0] != Factors[1]) { // Don't double count A*A. 672 Occ = ++FactorOccurrences[Factors[1]]; 673 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; } 674 } 675 } else { 676 std::set<Value*> Duplicates; 677 for (unsigned i = 0, e = Factors.size(); i != e; ++i) { 678 if (Duplicates.insert(Factors[i]).second) { 679 unsigned Occ = ++FactorOccurrences[Factors[i]]; 680 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; } 681 } 682 } 683 } 684 } 685 } 686 } 687 688 // If any factor occurred more than one time, we can pull it out. 689 if (MaxOcc > 1) { 690 DOUT << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << "\n"; 691 692 // Create a new instruction that uses the MaxOccVal twice. If we don't do 693 // this, we could otherwise run into situations where removing a factor 694 // from an expression will drop a use of maxocc, and this can cause 695 // RemoveFactorFromExpression on successive values to behave differently. 696 Instruction *DummyInst = BinaryOperator::createAdd(MaxOccVal, MaxOccVal); 697 std::vector<Value*> NewMulOps; 698 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 699 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) { 700 NewMulOps.push_back(V); 701 Ops.erase(Ops.begin()+i); 702 --i; --e; 703 } 704 } 705 706 // No need for extra uses anymore. 707 delete DummyInst; 708 709 unsigned NumAddedValues = NewMulOps.size(); 710 Value *V = EmitAddTreeOfValues(I, NewMulOps); 711 Value *V2 = BinaryOperator::createMul(V, MaxOccVal, "tmp", I); 712 713 // Now that we have inserted V and its sole use, optimize it. This allows 714 // us to handle cases that require multiple factoring steps, such as this: 715 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C)) 716 if (NumAddedValues > 1) 717 ReassociateExpression(cast<BinaryOperator>(V)); 718 719 ++NumFactor; 720 721 if (Ops.size() == 0) 722 return V2; 723 724 // Add the new value to the list of things being added. 725 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2)); 726 727 // Rewrite the tree so that there is now a use of V. 728 RewriteExprTree(I, Ops); 729 return OptimizeExpression(I, Ops); 730 } 731 break; 732 //case Instruction::Mul: 733 } 734 735 if (IterateOptimization) 736 return OptimizeExpression(I, Ops); 737 return 0; 738} 739 740 741/// ReassociateBB - Inspect all of the instructions in this basic block, 742/// reassociating them as we go. 743void Reassociate::ReassociateBB(BasicBlock *BB) { 744 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) { 745 Instruction *BI = BBI++; 746 if (BI->getOpcode() == Instruction::Shl && 747 isa<ConstantInt>(BI->getOperand(1))) 748 if (Instruction *NI = ConvertShiftToMul(BI)) { 749 MadeChange = true; 750 BI = NI; 751 } 752 753 // Reject cases where it is pointless to do this. 754 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() || 755 isa<VectorType>(BI->getType())) 756 continue; // Floating point ops are not associative. 757 758 // If this is a subtract instruction which is not already in negate form, 759 // see if we can convert it to X+-Y. 760 if (BI->getOpcode() == Instruction::Sub) { 761 if (!BinaryOperator::isNeg(BI)) { 762 if (Instruction *NI = BreakUpSubtract(BI)) { 763 MadeChange = true; 764 BI = NI; 765 } 766 } else { 767 // Otherwise, this is a negation. See if the operand is a multiply tree 768 // and if this is not an inner node of a multiply tree. 769 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) && 770 (!BI->hasOneUse() || 771 !isReassociableOp(BI->use_back(), Instruction::Mul))) { 772 BI = LowerNegateToMultiply(BI); 773 MadeChange = true; 774 } 775 } 776 } 777 778 // If this instruction is a commutative binary operator, process it. 779 if (!BI->isAssociative()) continue; 780 BinaryOperator *I = cast<BinaryOperator>(BI); 781 782 // If this is an interior node of a reassociable tree, ignore it until we 783 // get to the root of the tree, to avoid N^2 analysis. 784 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode())) 785 continue; 786 787 // If this is an add tree that is used by a sub instruction, ignore it 788 // until we process the subtract. 789 if (I->hasOneUse() && I->getOpcode() == Instruction::Add && 790 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub) 791 continue; 792 793 ReassociateExpression(I); 794 } 795} 796 797void Reassociate::ReassociateExpression(BinaryOperator *I) { 798 799 // First, walk the expression tree, linearizing the tree, collecting 800 std::vector<ValueEntry> Ops; 801 LinearizeExprTree(I, Ops); 802 803 DOUT << "RAIn:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n"; 804 805 // Now that we have linearized the tree to a list and have gathered all of 806 // the operands and their ranks, sort the operands by their rank. Use a 807 // stable_sort so that values with equal ranks will have their relative 808 // positions maintained (and so the compiler is deterministic). Note that 809 // this sorts so that the highest ranking values end up at the beginning of 810 // the vector. 811 std::stable_sort(Ops.begin(), Ops.end()); 812 813 // OptimizeExpression - Now that we have the expression tree in a convenient 814 // sorted form, optimize it globally if possible. 815 if (Value *V = OptimizeExpression(I, Ops)) { 816 // This expression tree simplified to something that isn't a tree, 817 // eliminate it. 818 DOUT << "Reassoc to scalar: " << *V << "\n"; 819 I->replaceAllUsesWith(V); 820 RemoveDeadBinaryOp(I); 821 return; 822 } 823 824 // We want to sink immediates as deeply as possible except in the case where 825 // this is a multiply tree used only by an add, and the immediate is a -1. 826 // In this case we reassociate to put the negation on the outside so that we 827 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y 828 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() && 829 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add && 830 isa<ConstantInt>(Ops.back().Op) && 831 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) { 832 Ops.insert(Ops.begin(), Ops.back()); 833 Ops.pop_back(); 834 } 835 836 DOUT << "RAOut:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n"; 837 838 if (Ops.size() == 1) { 839 // This expression tree simplified to something that isn't a tree, 840 // eliminate it. 841 I->replaceAllUsesWith(Ops[0].Op); 842 RemoveDeadBinaryOp(I); 843 } else { 844 // Now that we ordered and optimized the expressions, splat them back into 845 // the expression tree, removing any unneeded nodes. 846 RewriteExprTree(I, Ops); 847 } 848} 849 850 851bool Reassociate::runOnFunction(Function &F) { 852 // Recalculate the rank map for F 853 BuildRankMap(F); 854 855 MadeChange = false; 856 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 857 ReassociateBB(FI); 858 859 // We are done with the rank map... 860 RankMap.clear(); 861 ValueRankMap.clear(); 862 return MadeChange; 863} 864 865