ConstantHoisting.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338
1//===- ConstantHoisting.cpp - Prepare code for expensive constants --------===// 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 identifies expensive constants to hoist and coalesces them to 11// better prepare it for SelectionDAG-based code generation. This works around 12// the limitations of the basic-block-at-a-time approach. 13// 14// First it scans all instructions for integer constants and calculates its 15// cost. If the constant can be folded into the instruction (the cost is 16// TCC_Free) or the cost is just a simple operation (TCC_BASIC), then we don't 17// consider it expensive and leave it alone. This is the default behavior and 18// the default implementation of getIntImmCost will always return TCC_Free. 19// 20// If the cost is more than TCC_BASIC, then the integer constant can't be folded 21// into the instruction and it might be beneficial to hoist the constant. 22// Similar constants are coalesced to reduce register pressure and 23// materialization code. 24// 25// When a constant is hoisted, it is also hidden behind a bitcast to force it to 26// be live-out of the basic block. Otherwise the constant would be just 27// duplicated and each basic block would have its own copy in the SelectionDAG. 28// The SelectionDAG recognizes such constants as opaque and doesn't perform 29// certain transformations on them, which would create a new expensive constant. 30// 31// This optimization is only applied to integer constants in instructions and 32// simple (this means not nested) constant cast expressions. For example: 33// %0 = load i64* inttoptr (i64 big_constant to i64*) 34//===----------------------------------------------------------------------===// 35 36#define DEBUG_TYPE "consthoist" 37#include "llvm/Transforms/Scalar.h" 38#include "llvm/ADT/SmallSet.h" 39#include "llvm/ADT/SmallVector.h" 40#include "llvm/ADT/Statistic.h" 41#include "llvm/Analysis/TargetTransformInfo.h" 42#include "llvm/IR/Constants.h" 43#include "llvm/IR/Dominators.h" 44#include "llvm/IR/IntrinsicInst.h" 45#include "llvm/Pass.h" 46#include "llvm/Support/Debug.h" 47 48using namespace llvm; 49 50STATISTIC(NumConstantsHoisted, "Number of constants hoisted"); 51STATISTIC(NumConstantsRebased, "Number of constants rebased"); 52 53namespace { 54struct ConstantUser; 55struct RebasedConstantInfo; 56 57typedef SmallVector<ConstantUser, 8> ConstantUseListType; 58typedef SmallVector<RebasedConstantInfo, 4> RebasedConstantListType; 59 60/// \brief Keeps track of the user of a constant and the operand index where the 61/// constant is used. 62struct ConstantUser { 63 Instruction *Inst; 64 unsigned OpndIdx; 65 66 ConstantUser(Instruction *Inst, unsigned Idx) : Inst(Inst), OpndIdx(Idx) { } 67}; 68 69/// \brief Keeps track of a constant candidate and its uses. 70struct ConstantCandidate { 71 ConstantUseListType Uses; 72 ConstantInt *ConstInt; 73 unsigned CumulativeCost; 74 75 ConstantCandidate(ConstantInt *ConstInt) 76 : ConstInt(ConstInt), CumulativeCost(0) { } 77 78 /// \brief Add the user to the use list and update the cost. 79 void addUser(Instruction *Inst, unsigned Idx, unsigned Cost) { 80 CumulativeCost += Cost; 81 Uses.push_back(ConstantUser(Inst, Idx)); 82 } 83}; 84 85/// \brief This represents a constant that has been rebased with respect to a 86/// base constant. The difference to the base constant is recorded in Offset. 87struct RebasedConstantInfo { 88 ConstantUseListType Uses; 89 Constant *Offset; 90 91 RebasedConstantInfo(ConstantUseListType &&Uses, Constant *Offset) 92 : Uses(Uses), Offset(Offset) { } 93}; 94 95/// \brief A base constant and all its rebased constants. 96struct ConstantInfo { 97 ConstantInt *BaseConstant; 98 RebasedConstantListType RebasedConstants; 99}; 100 101/// \brief The constant hoisting pass. 102class ConstantHoisting : public FunctionPass { 103 typedef DenseMap<ConstantInt *, unsigned> ConstCandMapType; 104 typedef std::vector<ConstantCandidate> ConstCandVecType; 105 106 const TargetTransformInfo *TTI; 107 DominatorTree *DT; 108 BasicBlock *Entry; 109 110 /// Keeps track of constant candidates found in the function. 111 ConstCandVecType ConstCandVec; 112 113 /// Keep track of cast instructions we already cloned. 114 SmallDenseMap<Instruction *, Instruction *> ClonedCastMap; 115 116 /// These are the final constants we decided to hoist. 117 SmallVector<ConstantInfo, 8> ConstantVec; 118public: 119 static char ID; // Pass identification, replacement for typeid 120 ConstantHoisting() : FunctionPass(ID), TTI(0), DT(0), Entry(0) { 121 initializeConstantHoistingPass(*PassRegistry::getPassRegistry()); 122 } 123 124 bool runOnFunction(Function &Fn) override; 125 126 const char *getPassName() const override { return "Constant Hoisting"; } 127 128 void getAnalysisUsage(AnalysisUsage &AU) const override { 129 AU.setPreservesCFG(); 130 AU.addRequired<DominatorTreeWrapperPass>(); 131 AU.addRequired<TargetTransformInfo>(); 132 } 133 134private: 135 /// \brief Initialize the pass. 136 void setup(Function &Fn) { 137 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); 138 TTI = &getAnalysis<TargetTransformInfo>(); 139 Entry = &Fn.getEntryBlock(); 140 } 141 142 /// \brief Cleanup. 143 void cleanup() { 144 ConstantVec.clear(); 145 ClonedCastMap.clear(); 146 ConstCandVec.clear(); 147 148 TTI = nullptr; 149 DT = nullptr; 150 Entry = nullptr; 151 } 152 153 Instruction *findMatInsertPt(Instruction *Inst, unsigned Idx = ~0U) const; 154 Instruction *findConstantInsertionPoint(const ConstantInfo &ConstInfo) const; 155 void collectConstantCandidates(ConstCandMapType &ConstCandMap, 156 Instruction *Inst, unsigned Idx, 157 ConstantInt *ConstInt); 158 void collectConstantCandidates(ConstCandMapType &ConstCandMap, 159 Instruction *Inst); 160 void collectConstantCandidates(Function &Fn); 161 void findAndMakeBaseConstant(ConstCandVecType::iterator S, 162 ConstCandVecType::iterator E); 163 void findBaseConstants(); 164 void emitBaseConstants(Instruction *Base, Constant *Offset, 165 const ConstantUser &ConstUser); 166 bool emitBaseConstants(); 167 void deleteDeadCastInst() const; 168 bool optimizeConstants(Function &Fn); 169}; 170} 171 172char ConstantHoisting::ID = 0; 173INITIALIZE_PASS_BEGIN(ConstantHoisting, "consthoist", "Constant Hoisting", 174 false, false) 175INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) 176INITIALIZE_AG_DEPENDENCY(TargetTransformInfo) 177INITIALIZE_PASS_END(ConstantHoisting, "consthoist", "Constant Hoisting", 178 false, false) 179 180FunctionPass *llvm::createConstantHoistingPass() { 181 return new ConstantHoisting(); 182} 183 184/// \brief Perform the constant hoisting optimization for the given function. 185bool ConstantHoisting::runOnFunction(Function &Fn) { 186 DEBUG(dbgs() << "********** Begin Constant Hoisting **********\n"); 187 DEBUG(dbgs() << "********** Function: " << Fn.getName() << '\n'); 188 189 setup(Fn); 190 191 bool MadeChange = optimizeConstants(Fn); 192 193 if (MadeChange) { 194 DEBUG(dbgs() << "********** Function after Constant Hoisting: " 195 << Fn.getName() << '\n'); 196 DEBUG(dbgs() << Fn); 197 } 198 DEBUG(dbgs() << "********** End Constant Hoisting **********\n"); 199 200 cleanup(); 201 202 return MadeChange; 203} 204 205 206/// \brief Find the constant materialization insertion point. 207Instruction *ConstantHoisting::findMatInsertPt(Instruction *Inst, 208 unsigned Idx) const { 209 // The simple and common case. 210 if (!isa<PHINode>(Inst) && !isa<LandingPadInst>(Inst)) 211 return Inst; 212 213 // We can't insert directly before a phi node or landing pad. Insert before 214 // the terminator of the incoming or dominating block. 215 assert(Entry != Inst->getParent() && "PHI or landing pad in entry block!"); 216 if (Idx != ~0U && isa<PHINode>(Inst)) 217 return cast<PHINode>(Inst)->getIncomingBlock(Idx)->getTerminator(); 218 219 BasicBlock *IDom = DT->getNode(Inst->getParent())->getIDom()->getBlock(); 220 return IDom->getTerminator(); 221} 222 223/// \brief Find an insertion point that dominates all uses. 224Instruction *ConstantHoisting:: 225findConstantInsertionPoint(const ConstantInfo &ConstInfo) const { 226 assert(!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry."); 227 // Collect all basic blocks. 228 SmallPtrSet<BasicBlock *, 8> BBs; 229 for (auto const &RCI : ConstInfo.RebasedConstants) 230 for (auto const &U : RCI.Uses) 231 BBs.insert(U.Inst->getParent()); 232 233 if (BBs.count(Entry)) 234 return &Entry->front(); 235 236 while (BBs.size() >= 2) { 237 BasicBlock *BB, *BB1, *BB2; 238 BB1 = *BBs.begin(); 239 BB2 = *std::next(BBs.begin()); 240 BB = DT->findNearestCommonDominator(BB1, BB2); 241 if (BB == Entry) 242 return &Entry->front(); 243 BBs.erase(BB1); 244 BBs.erase(BB2); 245 BBs.insert(BB); 246 } 247 assert((BBs.size() == 1) && "Expected only one element."); 248 Instruction &FirstInst = (*BBs.begin())->front(); 249 return findMatInsertPt(&FirstInst); 250} 251 252 253/// \brief Record constant integer ConstInt for instruction Inst at operand 254/// index Idx. 255/// 256/// The operand at index Idx is not necessarily the constant integer itself. It 257/// could also be a cast instruction or a constant expression that uses the 258// constant integer. 259void ConstantHoisting::collectConstantCandidates(ConstCandMapType &ConstCandMap, 260 Instruction *Inst, 261 unsigned Idx, 262 ConstantInt *ConstInt) { 263 unsigned Cost; 264 // Ask the target about the cost of materializing the constant for the given 265 // instruction and operand index. 266 if (auto IntrInst = dyn_cast<IntrinsicInst>(Inst)) 267 Cost = TTI->getIntImmCost(IntrInst->getIntrinsicID(), Idx, 268 ConstInt->getValue(), ConstInt->getType()); 269 else 270 Cost = TTI->getIntImmCost(Inst->getOpcode(), Idx, ConstInt->getValue(), 271 ConstInt->getType()); 272 273 // Ignore cheap integer constants. 274 if (Cost > TargetTransformInfo::TCC_Basic) { 275 ConstCandMapType::iterator Itr; 276 bool Inserted; 277 std::tie(Itr, Inserted) = ConstCandMap.insert(std::make_pair(ConstInt, 0)); 278 if (Inserted) { 279 ConstCandVec.push_back(ConstantCandidate(ConstInt)); 280 Itr->second = ConstCandVec.size() - 1; 281 } 282 ConstCandVec[Itr->second].addUser(Inst, Idx, Cost); 283 DEBUG(if (isa<ConstantInt>(Inst->getOperand(Idx))) 284 dbgs() << "Collect constant " << *ConstInt << " from " << *Inst 285 << " with cost " << Cost << '\n'; 286 else 287 dbgs() << "Collect constant " << *ConstInt << " indirectly from " 288 << *Inst << " via " << *Inst->getOperand(Idx) << " with cost " 289 << Cost << '\n'; 290 ); 291 } 292} 293 294/// \brief Scan the instruction for expensive integer constants and record them 295/// in the constant candidate vector. 296void ConstantHoisting::collectConstantCandidates(ConstCandMapType &ConstCandMap, 297 Instruction *Inst) { 298 // Skip all cast instructions. They are visited indirectly later on. 299 if (Inst->isCast()) 300 return; 301 302 // Can't handle inline asm. Skip it. 303 if (auto Call = dyn_cast<CallInst>(Inst)) 304 if (isa<InlineAsm>(Call->getCalledValue())) 305 return; 306 307 // Scan all operands. 308 for (unsigned Idx = 0, E = Inst->getNumOperands(); Idx != E; ++Idx) { 309 Value *Opnd = Inst->getOperand(Idx); 310 311 // Visit constant integers. 312 if (auto ConstInt = dyn_cast<ConstantInt>(Opnd)) { 313 collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt); 314 continue; 315 } 316 317 // Visit cast instructions that have constant integers. 318 if (auto CastInst = dyn_cast<Instruction>(Opnd)) { 319 // Only visit cast instructions, which have been skipped. All other 320 // instructions should have already been visited. 321 if (!CastInst->isCast()) 322 continue; 323 324 if (auto *ConstInt = dyn_cast<ConstantInt>(CastInst->getOperand(0))) { 325 // Pretend the constant is directly used by the instruction and ignore 326 // the cast instruction. 327 collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt); 328 continue; 329 } 330 } 331 332 // Visit constant expressions that have constant integers. 333 if (auto ConstExpr = dyn_cast<ConstantExpr>(Opnd)) { 334 // Only visit constant cast expressions. 335 if (!ConstExpr->isCast()) 336 continue; 337 338 if (auto ConstInt = dyn_cast<ConstantInt>(ConstExpr->getOperand(0))) { 339 // Pretend the constant is directly used by the instruction and ignore 340 // the constant expression. 341 collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt); 342 continue; 343 } 344 } 345 } // end of for all operands 346} 347 348/// \brief Collect all integer constants in the function that cannot be folded 349/// into an instruction itself. 350void ConstantHoisting::collectConstantCandidates(Function &Fn) { 351 ConstCandMapType ConstCandMap; 352 for (Function::iterator BB : Fn) 353 for (BasicBlock::iterator Inst : *BB) 354 collectConstantCandidates(ConstCandMap, Inst); 355} 356 357/// \brief Find the base constant within the given range and rebase all other 358/// constants with respect to the base constant. 359void ConstantHoisting::findAndMakeBaseConstant(ConstCandVecType::iterator S, 360 ConstCandVecType::iterator E) { 361 auto MaxCostItr = S; 362 unsigned NumUses = 0; 363 // Use the constant that has the maximum cost as base constant. 364 for (auto ConstCand = S; ConstCand != E; ++ConstCand) { 365 NumUses += ConstCand->Uses.size(); 366 if (ConstCand->CumulativeCost > MaxCostItr->CumulativeCost) 367 MaxCostItr = ConstCand; 368 } 369 370 // Don't hoist constants that have only one use. 371 if (NumUses <= 1) 372 return; 373 374 ConstantInfo ConstInfo; 375 ConstInfo.BaseConstant = MaxCostItr->ConstInt; 376 Type *Ty = ConstInfo.BaseConstant->getType(); 377 378 // Rebase the constants with respect to the base constant. 379 for (auto ConstCand = S; ConstCand != E; ++ConstCand) { 380 APInt Diff = ConstCand->ConstInt->getValue() - 381 ConstInfo.BaseConstant->getValue(); 382 Constant *Offset = Diff == 0 ? nullptr : ConstantInt::get(Ty, Diff); 383 ConstInfo.RebasedConstants.push_back( 384 RebasedConstantInfo(std::move(ConstCand->Uses), Offset)); 385 } 386 ConstantVec.push_back(ConstInfo); 387} 388 389/// \brief Finds and combines constant candidates that can be easily 390/// rematerialized with an add from a common base constant. 391void ConstantHoisting::findBaseConstants() { 392 // Sort the constants by value and type. This invalidates the mapping! 393 std::sort(ConstCandVec.begin(), ConstCandVec.end(), 394 [](const ConstantCandidate &LHS, const ConstantCandidate &RHS) { 395 if (LHS.ConstInt->getType() != RHS.ConstInt->getType()) 396 return LHS.ConstInt->getType()->getBitWidth() < 397 RHS.ConstInt->getType()->getBitWidth(); 398 return LHS.ConstInt->getValue().ult(RHS.ConstInt->getValue()); 399 }); 400 401 // Simple linear scan through the sorted constant candidate vector for viable 402 // merge candidates. 403 auto MinValItr = ConstCandVec.begin(); 404 for (auto CC = std::next(ConstCandVec.begin()), E = ConstCandVec.end(); 405 CC != E; ++CC) { 406 if (MinValItr->ConstInt->getType() == CC->ConstInt->getType()) { 407 // Check if the constant is in range of an add with immediate. 408 APInt Diff = CC->ConstInt->getValue() - MinValItr->ConstInt->getValue(); 409 if ((Diff.getBitWidth() <= 64) && 410 TTI->isLegalAddImmediate(Diff.getSExtValue())) 411 continue; 412 } 413 // We either have now a different constant type or the constant is not in 414 // range of an add with immediate anymore. 415 findAndMakeBaseConstant(MinValItr, CC); 416 // Start a new base constant search. 417 MinValItr = CC; 418 } 419 // Finalize the last base constant search. 420 findAndMakeBaseConstant(MinValItr, ConstCandVec.end()); 421} 422 423/// \brief Updates the operand at Idx in instruction Inst with the result of 424/// instruction Mat. If the instruction is a PHI node then special 425/// handling for duplicate values form the same incomming basic block is 426/// required. 427/// \return The update will always succeed, but the return value indicated if 428/// Mat was used for the update or not. 429static bool updateOperand(Instruction *Inst, unsigned Idx, Instruction *Mat) { 430 if (auto PHI = dyn_cast<PHINode>(Inst)) { 431 // Check if any previous operand of the PHI node has the same incoming basic 432 // block. This is a very odd case that happens when the incoming basic block 433 // has a switch statement. In this case use the same value as the previous 434 // operand(s), otherwise we will fail verification due to different values. 435 // The values are actually the same, but the variable names are different 436 // and the verifier doesn't like that. 437 BasicBlock *IncomingBB = PHI->getIncomingBlock(Idx); 438 for (unsigned i = 0; i < Idx; ++i) { 439 if (PHI->getIncomingBlock(i) == IncomingBB) { 440 Value *IncomingVal = PHI->getIncomingValue(i); 441 Inst->setOperand(Idx, IncomingVal); 442 return false; 443 } 444 } 445 } 446 447 Inst->setOperand(Idx, Mat); 448 return true; 449} 450 451/// \brief Emit materialization code for all rebased constants and update their 452/// users. 453void ConstantHoisting::emitBaseConstants(Instruction *Base, Constant *Offset, 454 const ConstantUser &ConstUser) { 455 Instruction *Mat = Base; 456 if (Offset) { 457 Instruction *InsertionPt = findMatInsertPt(ConstUser.Inst, 458 ConstUser.OpndIdx); 459 Mat = BinaryOperator::Create(Instruction::Add, Base, Offset, 460 "const_mat", InsertionPt); 461 462 DEBUG(dbgs() << "Materialize constant (" << *Base->getOperand(0) 463 << " + " << *Offset << ") in BB " 464 << Mat->getParent()->getName() << '\n' << *Mat << '\n'); 465 Mat->setDebugLoc(ConstUser.Inst->getDebugLoc()); 466 } 467 Value *Opnd = ConstUser.Inst->getOperand(ConstUser.OpndIdx); 468 469 // Visit constant integer. 470 if (isa<ConstantInt>(Opnd)) { 471 DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n'); 472 if (!updateOperand(ConstUser.Inst, ConstUser.OpndIdx, Mat) && Offset) 473 Mat->eraseFromParent(); 474 DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n'); 475 return; 476 } 477 478 // Visit cast instruction. 479 if (auto CastInst = dyn_cast<Instruction>(Opnd)) { 480 assert(CastInst->isCast() && "Expected an cast instruction!"); 481 // Check if we already have visited this cast instruction before to avoid 482 // unnecessary cloning. 483 Instruction *&ClonedCastInst = ClonedCastMap[CastInst]; 484 if (!ClonedCastInst) { 485 ClonedCastInst = CastInst->clone(); 486 ClonedCastInst->setOperand(0, Mat); 487 ClonedCastInst->insertAfter(CastInst); 488 // Use the same debug location as the original cast instruction. 489 ClonedCastInst->setDebugLoc(CastInst->getDebugLoc()); 490 DEBUG(dbgs() << "Clone instruction: " << *ClonedCastInst << '\n' 491 << "To : " << *CastInst << '\n'); 492 } 493 494 DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n'); 495 updateOperand(ConstUser.Inst, ConstUser.OpndIdx, ClonedCastInst); 496 DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n'); 497 return; 498 } 499 500 // Visit constant expression. 501 if (auto ConstExpr = dyn_cast<ConstantExpr>(Opnd)) { 502 Instruction *ConstExprInst = ConstExpr->getAsInstruction(); 503 ConstExprInst->setOperand(0, Mat); 504 ConstExprInst->insertBefore(findMatInsertPt(ConstUser.Inst, 505 ConstUser.OpndIdx)); 506 507 // Use the same debug location as the instruction we are about to update. 508 ConstExprInst->setDebugLoc(ConstUser.Inst->getDebugLoc()); 509 510 DEBUG(dbgs() << "Create instruction: " << *ConstExprInst << '\n' 511 << "From : " << *ConstExpr << '\n'); 512 DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n'); 513 if (!updateOperand(ConstUser.Inst, ConstUser.OpndIdx, ConstExprInst)) { 514 ConstExprInst->eraseFromParent(); 515 if (Offset) 516 Mat->eraseFromParent(); 517 } 518 DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n'); 519 return; 520 } 521} 522 523/// \brief Hoist and hide the base constant behind a bitcast and emit 524/// materialization code for derived constants. 525bool ConstantHoisting::emitBaseConstants() { 526 bool MadeChange = false; 527 for (auto const &ConstInfo : ConstantVec) { 528 // Hoist and hide the base constant behind a bitcast. 529 Instruction *IP = findConstantInsertionPoint(ConstInfo); 530 IntegerType *Ty = ConstInfo.BaseConstant->getType(); 531 Instruction *Base = 532 new BitCastInst(ConstInfo.BaseConstant, Ty, "const", IP); 533 DEBUG(dbgs() << "Hoist constant (" << *ConstInfo.BaseConstant << ") to BB " 534 << IP->getParent()->getName() << '\n' << *Base << '\n'); 535 NumConstantsHoisted++; 536 537 // Emit materialization code for all rebased constants. 538 for (auto const &RCI : ConstInfo.RebasedConstants) { 539 NumConstantsRebased++; 540 for (auto const &U : RCI.Uses) 541 emitBaseConstants(Base, RCI.Offset, U); 542 } 543 544 // Use the same debug location as the last user of the constant. 545 assert(!Base->use_empty() && "The use list is empty!?"); 546 assert(isa<Instruction>(Base->user_back()) && 547 "All uses should be instructions."); 548 Base->setDebugLoc(cast<Instruction>(Base->user_back())->getDebugLoc()); 549 550 // Correct for base constant, which we counted above too. 551 NumConstantsRebased--; 552 MadeChange = true; 553 } 554 return MadeChange; 555} 556 557/// \brief Check all cast instructions we made a copy of and remove them if they 558/// have no more users. 559void ConstantHoisting::deleteDeadCastInst() const { 560 for (auto const &I : ClonedCastMap) 561 if (I.first->use_empty()) 562 I.first->eraseFromParent(); 563} 564 565/// \brief Optimize expensive integer constants in the given function. 566bool ConstantHoisting::optimizeConstants(Function &Fn) { 567 // Collect all constant candidates. 568 collectConstantCandidates(Fn); 569 570 // There are no constant candidates to worry about. 571 if (ConstCandVec.empty()) 572 return false; 573 574 // Combine constants that can be easily materialized with an add from a common 575 // base constant. 576 findBaseConstants(); 577 578 // There are no constants to emit. 579 if (ConstantVec.empty()) 580 return false; 581 582 // Finally hoist the base constant and emit materialization code for dependent 583 // constants. 584 bool MadeChange = emitBaseConstants(); 585 586 // Cleanup dead instructions. 587 deleteDeadCastInst(); 588 589 return MadeChange; 590} 591