Reassociate.cpp revision 0b0803ae1508ff514dd7b471a2a3bcd1e83cb0ef
1//===- Reassociate.cpp - Reassociate binary expressions -------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass reassociates commutative expressions in an order that is designed 11// to promote better constant propagation, GCSE, LICM, PRE... 12// 13// For example: 4 + (x + 5) -> x + (4 + 5) 14// 15// In the implementation of this algorithm, constants are assigned rank = 0, 16// function arguments are rank = 1, and other values are assigned ranks 17// corresponding to the reverse post order traversal of current function 18// (starting at 2), which effectively gives values in deep loops higher rank 19// than values not in loops. 20// 21//===----------------------------------------------------------------------===// 22 23#define DEBUG_TYPE "reassociate" 24#include "llvm/Transforms/Scalar.h" 25#include "llvm/Constants.h" 26#include "llvm/DerivedTypes.h" 27#include "llvm/Function.h" 28#include "llvm/Instructions.h" 29#include "llvm/Pass.h" 30#include "llvm/Assembly/Writer.h" 31#include "llvm/Support/CFG.h" 32#include "llvm/Support/Compiler.h" 33#include "llvm/Support/Debug.h" 34#include "llvm/ADT/PostOrderIterator.h" 35#include "llvm/ADT/Statistic.h" 36#include <algorithm> 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 static char ID; // Pass identification, replacement for typeid 73 Reassociate() : FunctionPass((intptr_t)&ID) {} 74 75 bool runOnFunction(Function &F); 76 77 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 78 AU.setPreservesCFG(); 79 } 80 private: 81 void BuildRankMap(Function &F); 82 unsigned getRank(Value *V); 83 void ReassociateExpression(BinaryOperator *I); 84 void RewriteExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops, 85 unsigned Idx = 0); 86 Value *OptimizeExpression(BinaryOperator *I, std::vector<ValueEntry> &Ops); 87 void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops); 88 void LinearizeExpr(BinaryOperator *I); 89 Value *RemoveFactorFromExpression(Value *V, Value *Factor); 90 void ReassociateBB(BasicBlock *BB); 91 92 void RemoveDeadBinaryOp(Value *V); 93 }; 94 95 char Reassociate::ID = 0; 96 RegisterPass<Reassociate> X("reassociate", "Reassociate expressions"); 97} 98 99// Public interface to the Reassociate pass 100FunctionPass *llvm::createReassociatePass() { return new Reassociate(); } 101 102void Reassociate::RemoveDeadBinaryOp(Value *V) { 103 Instruction *Op = dyn_cast<Instruction>(V); 104 if (!Op || !isa<BinaryOperator>(Op) || !isa<CmpInst>(Op) || !Op->use_empty()) 105 return; 106 107 Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1); 108 RemoveDeadBinaryOp(LHS); 109 RemoveDeadBinaryOp(RHS); 110} 111 112 113static bool isUnmovableInstruction(Instruction *I) { 114 if (I->getOpcode() == Instruction::PHI || 115 I->getOpcode() == Instruction::Alloca || 116 I->getOpcode() == Instruction::Load || 117 I->getOpcode() == Instruction::Malloc || 118 I->getOpcode() == Instruction::Invoke || 119 I->getOpcode() == Instruction::Call || 120 I->getOpcode() == Instruction::UDiv || 121 I->getOpcode() == Instruction::SDiv || 122 I->getOpcode() == Instruction::FDiv || 123 I->getOpcode() == Instruction::URem || 124 I->getOpcode() == Instruction::SRem || 125 I->getOpcode() == Instruction::FRem) 126 return true; 127 return false; 128} 129 130void Reassociate::BuildRankMap(Function &F) { 131 unsigned i = 2; 132 133 // Assign distinct ranks to function arguments 134 for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I) 135 ValueRankMap[I] = ++i; 136 137 ReversePostOrderTraversal<Function*> RPOT(&F); 138 for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(), 139 E = RPOT.end(); I != E; ++I) { 140 BasicBlock *BB = *I; 141 unsigned BBRank = RankMap[BB] = ++i << 16; 142 143 // Walk the basic block, adding precomputed ranks for any instructions that 144 // we cannot move. This ensures that the ranks for these instructions are 145 // all different in the block. 146 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 147 if (isUnmovableInstruction(I)) 148 ValueRankMap[I] = ++BBRank; 149 } 150} 151 152unsigned Reassociate::getRank(Value *V) { 153 if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument... 154 155 Instruction *I = dyn_cast<Instruction>(V); 156 if (I == 0) return 0; // Otherwise it's a global or constant, rank 0. 157 158 unsigned &CachedRank = ValueRankMap[I]; 159 if (CachedRank) return CachedRank; // Rank already known? 160 161 // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that 162 // we can reassociate expressions for code motion! Since we do not recurse 163 // for PHI nodes, we cannot have infinite recursion here, because there 164 // cannot be loops in the value graph that do not go through PHI nodes. 165 unsigned Rank = 0, MaxRank = RankMap[I->getParent()]; 166 for (unsigned i = 0, e = I->getNumOperands(); 167 i != e && Rank != MaxRank; ++i) 168 Rank = std::max(Rank, getRank(I->getOperand(i))); 169 170 // If this is a not or neg instruction, do not count it for rank. This 171 // assures us that X and ~X will have the same rank. 172 if (!I->getType()->isInteger() || 173 (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I))) 174 ++Rank; 175 176 //DOUT << "Calculated Rank[" << V->getName() << "] = " 177 // << Rank << "\n"; 178 179 return CachedRank = Rank; 180} 181 182/// isReassociableOp - Return true if V is an instruction of the specified 183/// opcode and if it only has one use. 184static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) { 185 if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) && 186 cast<Instruction>(V)->getOpcode() == Opcode) 187 return cast<BinaryOperator>(V); 188 return 0; 189} 190 191/// LowerNegateToMultiply - Replace 0-X with X*-1. 192/// 193static Instruction *LowerNegateToMultiply(Instruction *Neg) { 194 Constant *Cst = ConstantInt::getAllOnesValue(Neg->getType()); 195 196 Instruction *Res = BinaryOperator::createMul(Neg->getOperand(1), Cst, "",Neg); 197 Res->takeName(Neg); 198 Neg->replaceAllUsesWith(Res); 199 Neg->eraseFromParent(); 200 return Res; 201} 202 203// Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'. 204// Note that if D is also part of the expression tree that we recurse to 205// linearize it as well. Besides that case, this does not recurse into A,B, or 206// C. 207void Reassociate::LinearizeExpr(BinaryOperator *I) { 208 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0)); 209 BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1)); 210 assert(isReassociableOp(LHS, I->getOpcode()) && 211 isReassociableOp(RHS, I->getOpcode()) && 212 "Not an expression that needs linearization?"); 213 214 DOUT << "Linear" << *LHS << *RHS << *I; 215 216 // Move the RHS instruction to live immediately before I, avoiding breaking 217 // dominator properties. 218 RHS->moveBefore(I); 219 220 // Move operands around to do the linearization. 221 I->setOperand(1, RHS->getOperand(0)); 222 RHS->setOperand(0, LHS); 223 I->setOperand(0, RHS); 224 225 ++NumLinear; 226 MadeChange = true; 227 DOUT << "Linearized: " << *I; 228 229 // If D is part of this expression tree, tail recurse. 230 if (isReassociableOp(I->getOperand(1), I->getOpcode())) 231 LinearizeExpr(I); 232} 233 234 235/// LinearizeExprTree - Given an associative binary expression tree, traverse 236/// all of the uses putting it into canonical form. This forces a left-linear 237/// form of the the expression (((a+b)+c)+d), and collects information about the 238/// rank of the non-tree operands. 239/// 240/// NOTE: These intentionally destroys the expression tree operands (turning 241/// them into undef values) to reduce #uses of the values. This means that the 242/// caller MUST use something like RewriteExprTree to put the values back in. 243/// 244void Reassociate::LinearizeExprTree(BinaryOperator *I, 245 std::vector<ValueEntry> &Ops) { 246 Value *LHS = I->getOperand(0), *RHS = I->getOperand(1); 247 unsigned Opcode = I->getOpcode(); 248 249 // First step, linearize the expression if it is in ((A+B)+(C+D)) form. 250 BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode); 251 BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode); 252 253 // If this is a multiply expression tree and it contains internal negations, 254 // transform them into multiplies by -1 so they can be reassociated. 255 if (I->getOpcode() == Instruction::Mul) { 256 if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) { 257 LHS = LowerNegateToMultiply(cast<Instruction>(LHS)); 258 LHSBO = isReassociableOp(LHS, Opcode); 259 } 260 if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) { 261 RHS = LowerNegateToMultiply(cast<Instruction>(RHS)); 262 RHSBO = isReassociableOp(RHS, Opcode); 263 } 264 } 265 266 if (!LHSBO) { 267 if (!RHSBO) { 268 // Neither the LHS or RHS as part of the tree, thus this is a leaf. As 269 // such, just remember these operands and their rank. 270 Ops.push_back(ValueEntry(getRank(LHS), LHS)); 271 Ops.push_back(ValueEntry(getRank(RHS), RHS)); 272 273 // Clear the leaves out. 274 I->setOperand(0, UndefValue::get(I->getType())); 275 I->setOperand(1, UndefValue::get(I->getType())); 276 return; 277 } else { 278 // Turn X+(Y+Z) -> (Y+Z)+X 279 std::swap(LHSBO, RHSBO); 280 std::swap(LHS, RHS); 281 bool Success = !I->swapOperands(); 282 assert(Success && "swapOperands failed"); 283 MadeChange = true; 284 } 285 } else if (RHSBO) { 286 // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not 287 // part of the expression tree. 288 LinearizeExpr(I); 289 LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0)); 290 RHS = I->getOperand(1); 291 RHSBO = 0; 292 } 293 294 // Okay, now we know that the LHS is a nested expression and that the RHS is 295 // not. Perform reassociation. 296 assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!"); 297 298 // Move LHS right before I to make sure that the tree expression dominates all 299 // values. 300 LHSBO->moveBefore(I); 301 302 // Linearize the expression tree on the LHS. 303 LinearizeExprTree(LHSBO, Ops); 304 305 // Remember the RHS operand and its rank. 306 Ops.push_back(ValueEntry(getRank(RHS), RHS)); 307 308 // Clear the RHS leaf out. 309 I->setOperand(1, UndefValue::get(I->getType())); 310} 311 312// RewriteExprTree - Now that the operands for this expression tree are 313// linearized and optimized, emit them in-order. This function is written to be 314// tail recursive. 315void Reassociate::RewriteExprTree(BinaryOperator *I, 316 std::vector<ValueEntry> &Ops, 317 unsigned i) { 318 if (i+2 == Ops.size()) { 319 if (I->getOperand(0) != Ops[i].Op || 320 I->getOperand(1) != Ops[i+1].Op) { 321 Value *OldLHS = I->getOperand(0); 322 DOUT << "RA: " << *I; 323 I->setOperand(0, Ops[i].Op); 324 I->setOperand(1, Ops[i+1].Op); 325 DOUT << "TO: " << *I; 326 MadeChange = true; 327 ++NumChanged; 328 329 // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3) 330 // delete the extra, now dead, nodes. 331 RemoveDeadBinaryOp(OldLHS); 332 } 333 return; 334 } 335 assert(i+2 < Ops.size() && "Ops index out of range!"); 336 337 if (I->getOperand(1) != Ops[i].Op) { 338 DOUT << "RA: " << *I; 339 I->setOperand(1, Ops[i].Op); 340 DOUT << "TO: " << *I; 341 MadeChange = true; 342 ++NumChanged; 343 } 344 345 BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0)); 346 assert(LHS->getOpcode() == I->getOpcode() && 347 "Improper expression tree!"); 348 349 // Compactify the tree instructions together with each other to guarantee 350 // that the expression tree is dominated by all of Ops. 351 LHS->moveBefore(I); 352 RewriteExprTree(LHS, Ops, i+1); 353} 354 355 356 357// NegateValue - Insert instructions before the instruction pointed to by BI, 358// that computes the negative version of the value specified. The negative 359// version of the value is returned, and BI is left pointing at the instruction 360// that should be processed next by the reassociation pass. 361// 362static Value *NegateValue(Value *V, Instruction *BI) { 363 // We are trying to expose opportunity for reassociation. One of the things 364 // that we want to do to achieve this is to push a negation as deep into an 365 // expression chain as possible, to expose the add instructions. In practice, 366 // this means that we turn this: 367 // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D 368 // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate 369 // the constants. We assume that instcombine will clean up the mess later if 370 // we introduce tons of unnecessary negation instructions... 371 // 372 if (Instruction *I = dyn_cast<Instruction>(V)) 373 if (I->getOpcode() == Instruction::Add && I->hasOneUse()) { 374 // Push the negates through the add. 375 I->setOperand(0, NegateValue(I->getOperand(0), BI)); 376 I->setOperand(1, NegateValue(I->getOperand(1), BI)); 377 378 // We must move the add instruction here, because the neg instructions do 379 // not dominate the old add instruction in general. By moving it, we are 380 // assured that the neg instructions we just inserted dominate the 381 // instruction we are about to insert after them. 382 // 383 I->moveBefore(BI); 384 I->setName(I->getName()+".neg"); 385 return I; 386 } 387 388 // Insert a 'neg' instruction that subtracts the value from zero to get the 389 // negation. 390 // 391 return BinaryOperator::createNeg(V, V->getName() + ".neg", BI); 392} 393 394/// ShouldBreakUpSubtract - Return true if we should break up this subtract of 395/// X-Y into (X + -Y). 396static bool ShouldBreakUpSubtract(Instruction *Sub) { 397 // If this is a negation, we can't split it up! 398 if (BinaryOperator::isNeg(Sub)) 399 return false; 400 401 // Don't bother to break this up unless either the LHS is an associable add or 402 // subtract or if this is only used by one. 403 if (isReassociableOp(Sub->getOperand(0), Instruction::Add) || 404 isReassociableOp(Sub->getOperand(0), Instruction::Sub)) 405 return true; 406 if (isReassociableOp(Sub->getOperand(1), Instruction::Add) || 407 isReassociableOp(Sub->getOperand(0), Instruction::Sub)) 408 return true; 409 if (Sub->hasOneUse() && 410 (isReassociableOp(Sub->use_back(), Instruction::Add) || 411 isReassociableOp(Sub->use_back(), Instruction::Sub))) 412 return true; 413 414 return false; 415} 416 417/// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is 418/// only used by an add, transform this into (X+(0-Y)) to promote better 419/// reassociation. 420static Instruction *BreakUpSubtract(Instruction *Sub) { 421 // Convert a subtract into an add and a neg instruction... so that sub 422 // instructions can be commuted with other add instructions... 423 // 424 // Calculate the negative value of Operand 1 of the sub instruction... 425 // and set it as the RHS of the add instruction we just made... 426 // 427 Value *NegVal = NegateValue(Sub->getOperand(1), Sub); 428 Instruction *New = 429 BinaryOperator::createAdd(Sub->getOperand(0), NegVal, "", Sub); 430 New->takeName(Sub); 431 432 // Everyone now refers to the add instruction. 433 Sub->replaceAllUsesWith(New); 434 Sub->eraseFromParent(); 435 436 DOUT << "Negated: " << *New; 437 return New; 438} 439 440/// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used 441/// by one, change this into a multiply by a constant to assist with further 442/// reassociation. 443static Instruction *ConvertShiftToMul(Instruction *Shl) { 444 // If an operand of this shift is a reassociable multiply, or if the shift 445 // is used by a reassociable multiply or add, turn into a multiply. 446 if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) || 447 (Shl->hasOneUse() && 448 (isReassociableOp(Shl->use_back(), Instruction::Mul) || 449 isReassociableOp(Shl->use_back(), Instruction::Add)))) { 450 Constant *MulCst = ConstantInt::get(Shl->getType(), 1); 451 MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1))); 452 453 Instruction *Mul = BinaryOperator::createMul(Shl->getOperand(0), MulCst, 454 "", Shl); 455 Mul->takeName(Shl); 456 Shl->replaceAllUsesWith(Mul); 457 Shl->eraseFromParent(); 458 return Mul; 459 } 460 return 0; 461} 462 463// Scan backwards and forwards among values with the same rank as element i to 464// see if X exists. If X does not exist, return i. 465static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i, 466 Value *X) { 467 unsigned XRank = Ops[i].Rank; 468 unsigned e = Ops.size(); 469 for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) 470 if (Ops[j].Op == X) 471 return j; 472 // Scan backwards 473 for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) 474 if (Ops[j].Op == X) 475 return j; 476 return i; 477} 478 479/// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together 480/// and returning the result. Insert the tree before I. 481static Value *EmitAddTreeOfValues(Instruction *I, std::vector<Value*> &Ops) { 482 if (Ops.size() == 1) return Ops.back(); 483 484 Value *V1 = Ops.back(); 485 Ops.pop_back(); 486 Value *V2 = EmitAddTreeOfValues(I, Ops); 487 return BinaryOperator::createAdd(V2, V1, "tmp", I); 488} 489 490/// RemoveFactorFromExpression - If V is an expression tree that is a 491/// multiplication sequence, and if this sequence contains a multiply by Factor, 492/// remove Factor from the tree and return the new tree. 493Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) { 494 BinaryOperator *BO = isReassociableOp(V, Instruction::Mul); 495 if (!BO) return 0; 496 497 std::vector<ValueEntry> Factors; 498 LinearizeExprTree(BO, Factors); 499 500 bool FoundFactor = false; 501 for (unsigned i = 0, e = Factors.size(); i != e; ++i) 502 if (Factors[i].Op == Factor) { 503 FoundFactor = true; 504 Factors.erase(Factors.begin()+i); 505 break; 506 } 507 if (!FoundFactor) { 508 // Make sure to restore the operands to the expression tree. 509 RewriteExprTree(BO, Factors); 510 return 0; 511 } 512 513 if (Factors.size() == 1) return Factors[0].Op; 514 515 RewriteExprTree(BO, Factors); 516 return BO; 517} 518 519/// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively 520/// add its operands as factors, otherwise add V to the list of factors. 521static void FindSingleUseMultiplyFactors(Value *V, 522 std::vector<Value*> &Factors) { 523 BinaryOperator *BO; 524 if ((!V->hasOneUse() && !V->use_empty()) || 525 !(BO = dyn_cast<BinaryOperator>(V)) || 526 BO->getOpcode() != Instruction::Mul) { 527 Factors.push_back(V); 528 return; 529 } 530 531 // Otherwise, add the LHS and RHS to the list of factors. 532 FindSingleUseMultiplyFactors(BO->getOperand(1), Factors); 533 FindSingleUseMultiplyFactors(BO->getOperand(0), Factors); 534} 535 536 537 538Value *Reassociate::OptimizeExpression(BinaryOperator *I, 539 std::vector<ValueEntry> &Ops) { 540 // Now that we have the linearized expression tree, try to optimize it. 541 // Start by folding any constants that we found. 542 bool IterateOptimization = false; 543 if (Ops.size() == 1) return Ops[0].Op; 544 545 unsigned Opcode = I->getOpcode(); 546 547 if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op)) 548 if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) { 549 Ops.pop_back(); 550 Ops.back().Op = ConstantExpr::get(Opcode, V1, V2); 551 return OptimizeExpression(I, Ops); 552 } 553 554 // Check for destructive annihilation due to a constant being used. 555 if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op)) 556 switch (Opcode) { 557 default: break; 558 case Instruction::And: 559 if (CstVal->isZero()) { // ... & 0 -> 0 560 ++NumAnnihil; 561 return CstVal; 562 } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ... 563 Ops.pop_back(); 564 } 565 break; 566 case Instruction::Mul: 567 if (CstVal->isZero()) { // ... * 0 -> 0 568 ++NumAnnihil; 569 return CstVal; 570 } else if (cast<ConstantInt>(CstVal)->isOne()) { 571 Ops.pop_back(); // ... * 1 -> ... 572 } 573 break; 574 case Instruction::Or: 575 if (CstVal->isAllOnesValue()) { // ... | -1 -> -1 576 ++NumAnnihil; 577 return CstVal; 578 } 579 // FALLTHROUGH! 580 case Instruction::Add: 581 case Instruction::Xor: 582 if (CstVal->isZero()) // ... [|^+] 0 -> ... 583 Ops.pop_back(); 584 break; 585 } 586 if (Ops.size() == 1) return Ops[0].Op; 587 588 // Handle destructive annihilation do to identities between elements in the 589 // argument list here. 590 switch (Opcode) { 591 default: break; 592 case Instruction::And: 593 case Instruction::Or: 594 case Instruction::Xor: 595 // Scan the operand lists looking for X and ~X pairs, along with X,X pairs. 596 // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1. 597 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 598 // First, check for X and ~X in the operand list. 599 assert(i < Ops.size()); 600 if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^. 601 Value *X = BinaryOperator::getNotArgument(Ops[i].Op); 602 unsigned FoundX = FindInOperandList(Ops, i, X); 603 if (FoundX != i) { 604 if (Opcode == Instruction::And) { // ...&X&~X = 0 605 ++NumAnnihil; 606 return Constant::getNullValue(X->getType()); 607 } else if (Opcode == Instruction::Or) { // ...|X|~X = -1 608 ++NumAnnihil; 609 return ConstantInt::getAllOnesValue(X->getType()); 610 } 611 } 612 } 613 614 // Next, check for duplicate pairs of values, which we assume are next to 615 // each other, due to our sorting criteria. 616 assert(i < Ops.size()); 617 if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) { 618 if (Opcode == Instruction::And || Opcode == Instruction::Or) { 619 // Drop duplicate values. 620 Ops.erase(Ops.begin()+i); 621 --i; --e; 622 IterateOptimization = true; 623 ++NumAnnihil; 624 } else { 625 assert(Opcode == Instruction::Xor); 626 if (e == 2) { 627 ++NumAnnihil; 628 return Constant::getNullValue(Ops[0].Op->getType()); 629 } 630 // ... X^X -> ... 631 Ops.erase(Ops.begin()+i, Ops.begin()+i+2); 632 i -= 1; e -= 2; 633 IterateOptimization = true; 634 ++NumAnnihil; 635 } 636 } 637 } 638 break; 639 640 case Instruction::Add: 641 // Scan the operand lists looking for X and -X pairs. If we find any, we 642 // can simplify the expression. X+-X == 0. 643 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 644 assert(i < Ops.size()); 645 // Check for X and -X in the operand list. 646 if (BinaryOperator::isNeg(Ops[i].Op)) { 647 Value *X = BinaryOperator::getNegArgument(Ops[i].Op); 648 unsigned FoundX = FindInOperandList(Ops, i, X); 649 if (FoundX != i) { 650 // Remove X and -X from the operand list. 651 if (Ops.size() == 2) { 652 ++NumAnnihil; 653 return Constant::getNullValue(X->getType()); 654 } else { 655 Ops.erase(Ops.begin()+i); 656 if (i < FoundX) 657 --FoundX; 658 else 659 --i; // Need to back up an extra one. 660 Ops.erase(Ops.begin()+FoundX); 661 IterateOptimization = true; 662 ++NumAnnihil; 663 --i; // Revisit element. 664 e -= 2; // Removed two elements. 665 } 666 } 667 } 668 } 669 670 671 // Scan the operand list, checking to see if there are any common factors 672 // between operands. Consider something like A*A+A*B*C+D. We would like to 673 // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies. 674 // To efficiently find this, we count the number of times a factor occurs 675 // for any ADD operands that are MULs. 676 std::map<Value*, unsigned> FactorOccurrences; 677 unsigned MaxOcc = 0; 678 Value *MaxOccVal = 0; 679 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 680 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op)) { 681 if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) { 682 // Compute all of the factors of this added value. 683 std::vector<Value*> Factors; 684 FindSingleUseMultiplyFactors(BOp, Factors); 685 assert(Factors.size() > 1 && "Bad linearize!"); 686 687 // Add one to FactorOccurrences for each unique factor in this op. 688 if (Factors.size() == 2) { 689 unsigned Occ = ++FactorOccurrences[Factors[0]]; 690 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; } 691 if (Factors[0] != Factors[1]) { // Don't double count A*A. 692 Occ = ++FactorOccurrences[Factors[1]]; 693 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; } 694 } 695 } else { 696 std::set<Value*> Duplicates; 697 for (unsigned i = 0, e = Factors.size(); i != e; ++i) { 698 if (Duplicates.insert(Factors[i]).second) { 699 unsigned Occ = ++FactorOccurrences[Factors[i]]; 700 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; } 701 } 702 } 703 } 704 } 705 } 706 } 707 708 // If any factor occurred more than one time, we can pull it out. 709 if (MaxOcc > 1) { 710 DOUT << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << "\n"; 711 712 // Create a new instruction that uses the MaxOccVal twice. If we don't do 713 // this, we could otherwise run into situations where removing a factor 714 // from an expression will drop a use of maxocc, and this can cause 715 // RemoveFactorFromExpression on successive values to behave differently. 716 Instruction *DummyInst = BinaryOperator::createAdd(MaxOccVal, MaxOccVal); 717 std::vector<Value*> NewMulOps; 718 for (unsigned i = 0, e = Ops.size(); i != e; ++i) { 719 if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) { 720 NewMulOps.push_back(V); 721 Ops.erase(Ops.begin()+i); 722 --i; --e; 723 } 724 } 725 726 // No need for extra uses anymore. 727 delete DummyInst; 728 729 unsigned NumAddedValues = NewMulOps.size(); 730 Value *V = EmitAddTreeOfValues(I, NewMulOps); 731 Value *V2 = BinaryOperator::createMul(V, MaxOccVal, "tmp", I); 732 733 // Now that we have inserted V and its sole use, optimize it. This allows 734 // us to handle cases that require multiple factoring steps, such as this: 735 // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C)) 736 if (NumAddedValues > 1) 737 ReassociateExpression(cast<BinaryOperator>(V)); 738 739 ++NumFactor; 740 741 if (Ops.empty()) 742 return V2; 743 744 // Add the new value to the list of things being added. 745 Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2)); 746 747 // Rewrite the tree so that there is now a use of V. 748 RewriteExprTree(I, Ops); 749 return OptimizeExpression(I, Ops); 750 } 751 break; 752 //case Instruction::Mul: 753 } 754 755 if (IterateOptimization) 756 return OptimizeExpression(I, Ops); 757 return 0; 758} 759 760 761/// ReassociateBB - Inspect all of the instructions in this basic block, 762/// reassociating them as we go. 763void Reassociate::ReassociateBB(BasicBlock *BB) { 764 for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) { 765 Instruction *BI = BBI++; 766 if (BI->getOpcode() == Instruction::Shl && 767 isa<ConstantInt>(BI->getOperand(1))) 768 if (Instruction *NI = ConvertShiftToMul(BI)) { 769 MadeChange = true; 770 BI = NI; 771 } 772 773 // Reject cases where it is pointless to do this. 774 if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint() || 775 isa<VectorType>(BI->getType())) 776 continue; // Floating point ops are not associative. 777 778 // If this is a subtract instruction which is not already in negate form, 779 // see if we can convert it to X+-Y. 780 if (BI->getOpcode() == Instruction::Sub) { 781 if (ShouldBreakUpSubtract(BI)) { 782 if (Instruction *NI = BreakUpSubtract(BI)) { 783 MadeChange = true; 784 BI = NI; 785 } 786 } else if (BinaryOperator::isNeg(BI)) { 787 // Otherwise, this is a negation. See if the operand is a multiply tree 788 // and if this is not an inner node of a multiply tree. 789 if (isReassociableOp(BI->getOperand(1), Instruction::Mul) && 790 (!BI->hasOneUse() || 791 !isReassociableOp(BI->use_back(), Instruction::Mul))) { 792 BI = LowerNegateToMultiply(BI); 793 MadeChange = true; 794 } 795 } 796 } 797 798 // If this instruction is a commutative binary operator, process it. 799 if (!BI->isAssociative()) continue; 800 BinaryOperator *I = cast<BinaryOperator>(BI); 801 802 // If this is an interior node of a reassociable tree, ignore it until we 803 // get to the root of the tree, to avoid N^2 analysis. 804 if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode())) 805 continue; 806 807 // If this is an add tree that is used by a sub instruction, ignore it 808 // until we process the subtract. 809 if (I->hasOneUse() && I->getOpcode() == Instruction::Add && 810 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub) 811 continue; 812 813 ReassociateExpression(I); 814 } 815} 816 817void Reassociate::ReassociateExpression(BinaryOperator *I) { 818 819 // First, walk the expression tree, linearizing the tree, collecting 820 std::vector<ValueEntry> Ops; 821 LinearizeExprTree(I, Ops); 822 823 DOUT << "RAIn:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n"; 824 825 // Now that we have linearized the tree to a list and have gathered all of 826 // the operands and their ranks, sort the operands by their rank. Use a 827 // stable_sort so that values with equal ranks will have their relative 828 // positions maintained (and so the compiler is deterministic). Note that 829 // this sorts so that the highest ranking values end up at the beginning of 830 // the vector. 831 std::stable_sort(Ops.begin(), Ops.end()); 832 833 // OptimizeExpression - Now that we have the expression tree in a convenient 834 // sorted form, optimize it globally if possible. 835 if (Value *V = OptimizeExpression(I, Ops)) { 836 // This expression tree simplified to something that isn't a tree, 837 // eliminate it. 838 DOUT << "Reassoc to scalar: " << *V << "\n"; 839 I->replaceAllUsesWith(V); 840 RemoveDeadBinaryOp(I); 841 return; 842 } 843 844 // We want to sink immediates as deeply as possible except in the case where 845 // this is a multiply tree used only by an add, and the immediate is a -1. 846 // In this case we reassociate to put the negation on the outside so that we 847 // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y 848 if (I->getOpcode() == Instruction::Mul && I->hasOneUse() && 849 cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add && 850 isa<ConstantInt>(Ops.back().Op) && 851 cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) { 852 Ops.insert(Ops.begin(), Ops.back()); 853 Ops.pop_back(); 854 } 855 856 DOUT << "RAOut:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n"; 857 858 if (Ops.size() == 1) { 859 // This expression tree simplified to something that isn't a tree, 860 // eliminate it. 861 I->replaceAllUsesWith(Ops[0].Op); 862 RemoveDeadBinaryOp(I); 863 } else { 864 // Now that we ordered and optimized the expressions, splat them back into 865 // the expression tree, removing any unneeded nodes. 866 RewriteExprTree(I, Ops); 867 } 868} 869 870 871bool Reassociate::runOnFunction(Function &F) { 872 // Recalculate the rank map for F 873 BuildRankMap(F); 874 875 MadeChange = false; 876 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) 877 ReassociateBB(FI); 878 879 // We are done with the rank map... 880 RankMap.clear(); 881 ValueRankMap.clear(); 882 return MadeChange; 883} 884 885