CodeGenPrepare.cpp revision 950d3db5f478a84242a90cafce0d8dfc4f8b1152
1//===- CodeGenPrepare.cpp - Prepare a function for code generation --------===// 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 munges the code in the input function to better prepare it for 11// SelectionDAG-based code generation. This works around limitations in it's 12// basic-block-at-a-time approach. It should eventually be removed. 13// 14//===----------------------------------------------------------------------===// 15 16#define DEBUG_TYPE "codegenprepare" 17#include "llvm/Transforms/Scalar.h" 18#include "llvm/Constants.h" 19#include "llvm/DerivedTypes.h" 20#include "llvm/Function.h" 21#include "llvm/InlineAsm.h" 22#include "llvm/Instructions.h" 23#include "llvm/IntrinsicInst.h" 24#include "llvm/Pass.h" 25#include "llvm/Analysis/Dominators.h" 26#include "llvm/Analysis/InstructionSimplify.h" 27#include "llvm/Analysis/ProfileInfo.h" 28#include "llvm/Target/TargetData.h" 29#include "llvm/Target/TargetLowering.h" 30#include "llvm/Transforms/Utils/AddrModeMatcher.h" 31#include "llvm/Transforms/Utils/BasicBlockUtils.h" 32#include "llvm/Transforms/Utils/Local.h" 33#include "llvm/Transforms/Utils/BuildLibCalls.h" 34#include "llvm/ADT/DenseMap.h" 35#include "llvm/ADT/SmallSet.h" 36#include "llvm/ADT/Statistic.h" 37#include "llvm/Assembly/Writer.h" 38#include "llvm/Support/CallSite.h" 39#include "llvm/Support/CommandLine.h" 40#include "llvm/Support/Debug.h" 41#include "llvm/Support/GetElementPtrTypeIterator.h" 42#include "llvm/Support/PatternMatch.h" 43#include "llvm/Support/raw_ostream.h" 44#include "llvm/Support/IRBuilder.h" 45#include "llvm/Support/ValueHandle.h" 46using namespace llvm; 47using namespace llvm::PatternMatch; 48 49STATISTIC(NumBlocksElim, "Number of blocks eliminated"); 50STATISTIC(NumPHIsElim, "Number of trivial PHIs eliminated"); 51STATISTIC(NumGEPsElim, "Number of GEPs converted to casts"); 52STATISTIC(NumCmpUses, "Number of uses of Cmp expressions replaced with uses of " 53 "sunken Cmps"); 54STATISTIC(NumCastUses, "Number of uses of Cast expressions replaced with uses " 55 "of sunken Casts"); 56STATISTIC(NumMemoryInsts, "Number of memory instructions whose address " 57 "computations were sunk"); 58STATISTIC(NumExtsMoved, "Number of [s|z]ext instructions combined with loads"); 59STATISTIC(NumExtUses, "Number of uses of [s|z]ext instructions optimized"); 60 61namespace { 62 class CodeGenPrepare : public FunctionPass { 63 /// TLI - Keep a pointer of a TargetLowering to consult for determining 64 /// transformation profitability. 65 const TargetLowering *TLI; 66 DominatorTree *DT; 67 ProfileInfo *PFI; 68 69 /// CurInstIterator - As we scan instructions optimizing them, this is the 70 /// next instruction to optimize. Xforms that can invalidate this should 71 /// update it. 72 BasicBlock::iterator CurInstIterator; 73 74 // Keeps track of non-local addresses that have been sunk into a block. This 75 // allows us to avoid inserting duplicate code for blocks with multiple 76 // load/stores of the same address. 77 DenseMap<Value*, Value*> SunkAddrs; 78 79 public: 80 static char ID; // Pass identification, replacement for typeid 81 explicit CodeGenPrepare(const TargetLowering *tli = 0) 82 : FunctionPass(ID), TLI(tli) { 83 initializeCodeGenPreparePass(*PassRegistry::getPassRegistry()); 84 } 85 bool runOnFunction(Function &F); 86 87 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 88 AU.addPreserved<DominatorTree>(); 89 AU.addPreserved<ProfileInfo>(); 90 } 91 92 private: 93 bool EliminateMostlyEmptyBlocks(Function &F); 94 bool CanMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const; 95 void EliminateMostlyEmptyBlock(BasicBlock *BB); 96 bool OptimizeBlock(BasicBlock &BB); 97 bool OptimizeInst(Instruction *I); 98 bool OptimizeMemoryInst(Instruction *I, Value *Addr, const Type *AccessTy); 99 bool OptimizeInlineAsmInst(CallInst *CS); 100 bool OptimizeCallInst(CallInst *CI); 101 bool MoveExtToFormExtLoad(Instruction *I); 102 bool OptimizeExtUses(Instruction *I); 103 }; 104} 105 106char CodeGenPrepare::ID = 0; 107INITIALIZE_PASS(CodeGenPrepare, "codegenprepare", 108 "Optimize for code generation", false, false) 109 110FunctionPass *llvm::createCodeGenPreparePass(const TargetLowering *TLI) { 111 return new CodeGenPrepare(TLI); 112} 113 114bool CodeGenPrepare::runOnFunction(Function &F) { 115 bool EverMadeChange = false; 116 117 DT = getAnalysisIfAvailable<DominatorTree>(); 118 PFI = getAnalysisIfAvailable<ProfileInfo>(); 119 // First pass, eliminate blocks that contain only PHI nodes and an 120 // unconditional branch. 121 EverMadeChange |= EliminateMostlyEmptyBlocks(F); 122 123 bool MadeChange = true; 124 while (MadeChange) { 125 MadeChange = false; 126 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) 127 MadeChange |= OptimizeBlock(*BB); 128 EverMadeChange |= MadeChange; 129 } 130 131 SunkAddrs.clear(); 132 133 return EverMadeChange; 134} 135 136/// EliminateMostlyEmptyBlocks - eliminate blocks that contain only PHI nodes, 137/// debug info directives, and an unconditional branch. Passes before isel 138/// (e.g. LSR/loopsimplify) often split edges in ways that are non-optimal for 139/// isel. Start by eliminating these blocks so we can split them the way we 140/// want them. 141bool CodeGenPrepare::EliminateMostlyEmptyBlocks(Function &F) { 142 bool MadeChange = false; 143 // Note that this intentionally skips the entry block. 144 for (Function::iterator I = ++F.begin(), E = F.end(); I != E; ) { 145 BasicBlock *BB = I++; 146 147 // If this block doesn't end with an uncond branch, ignore it. 148 BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()); 149 if (!BI || !BI->isUnconditional()) 150 continue; 151 152 // If the instruction before the branch (skipping debug info) isn't a phi 153 // node, then other stuff is happening here. 154 BasicBlock::iterator BBI = BI; 155 if (BBI != BB->begin()) { 156 --BBI; 157 while (isa<DbgInfoIntrinsic>(BBI)) { 158 if (BBI == BB->begin()) 159 break; 160 --BBI; 161 } 162 if (!isa<DbgInfoIntrinsic>(BBI) && !isa<PHINode>(BBI)) 163 continue; 164 } 165 166 // Do not break infinite loops. 167 BasicBlock *DestBB = BI->getSuccessor(0); 168 if (DestBB == BB) 169 continue; 170 171 if (!CanMergeBlocks(BB, DestBB)) 172 continue; 173 174 EliminateMostlyEmptyBlock(BB); 175 MadeChange = true; 176 } 177 return MadeChange; 178} 179 180/// CanMergeBlocks - Return true if we can merge BB into DestBB if there is a 181/// single uncond branch between them, and BB contains no other non-phi 182/// instructions. 183bool CodeGenPrepare::CanMergeBlocks(const BasicBlock *BB, 184 const BasicBlock *DestBB) const { 185 // We only want to eliminate blocks whose phi nodes are used by phi nodes in 186 // the successor. If there are more complex condition (e.g. preheaders), 187 // don't mess around with them. 188 BasicBlock::const_iterator BBI = BB->begin(); 189 while (const PHINode *PN = dyn_cast<PHINode>(BBI++)) { 190 for (Value::const_use_iterator UI = PN->use_begin(), E = PN->use_end(); 191 UI != E; ++UI) { 192 const Instruction *User = cast<Instruction>(*UI); 193 if (User->getParent() != DestBB || !isa<PHINode>(User)) 194 return false; 195 // If User is inside DestBB block and it is a PHINode then check 196 // incoming value. If incoming value is not from BB then this is 197 // a complex condition (e.g. preheaders) we want to avoid here. 198 if (User->getParent() == DestBB) { 199 if (const PHINode *UPN = dyn_cast<PHINode>(User)) 200 for (unsigned I = 0, E = UPN->getNumIncomingValues(); I != E; ++I) { 201 Instruction *Insn = dyn_cast<Instruction>(UPN->getIncomingValue(I)); 202 if (Insn && Insn->getParent() == BB && 203 Insn->getParent() != UPN->getIncomingBlock(I)) 204 return false; 205 } 206 } 207 } 208 } 209 210 // If BB and DestBB contain any common predecessors, then the phi nodes in BB 211 // and DestBB may have conflicting incoming values for the block. If so, we 212 // can't merge the block. 213 const PHINode *DestBBPN = dyn_cast<PHINode>(DestBB->begin()); 214 if (!DestBBPN) return true; // no conflict. 215 216 // Collect the preds of BB. 217 SmallPtrSet<const BasicBlock*, 16> BBPreds; 218 if (const PHINode *BBPN = dyn_cast<PHINode>(BB->begin())) { 219 // It is faster to get preds from a PHI than with pred_iterator. 220 for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i) 221 BBPreds.insert(BBPN->getIncomingBlock(i)); 222 } else { 223 BBPreds.insert(pred_begin(BB), pred_end(BB)); 224 } 225 226 // Walk the preds of DestBB. 227 for (unsigned i = 0, e = DestBBPN->getNumIncomingValues(); i != e; ++i) { 228 BasicBlock *Pred = DestBBPN->getIncomingBlock(i); 229 if (BBPreds.count(Pred)) { // Common predecessor? 230 BBI = DestBB->begin(); 231 while (const PHINode *PN = dyn_cast<PHINode>(BBI++)) { 232 const Value *V1 = PN->getIncomingValueForBlock(Pred); 233 const Value *V2 = PN->getIncomingValueForBlock(BB); 234 235 // If V2 is a phi node in BB, look up what the mapped value will be. 236 if (const PHINode *V2PN = dyn_cast<PHINode>(V2)) 237 if (V2PN->getParent() == BB) 238 V2 = V2PN->getIncomingValueForBlock(Pred); 239 240 // If there is a conflict, bail out. 241 if (V1 != V2) return false; 242 } 243 } 244 } 245 246 return true; 247} 248 249 250/// EliminateMostlyEmptyBlock - Eliminate a basic block that have only phi's and 251/// an unconditional branch in it. 252void CodeGenPrepare::EliminateMostlyEmptyBlock(BasicBlock *BB) { 253 BranchInst *BI = cast<BranchInst>(BB->getTerminator()); 254 BasicBlock *DestBB = BI->getSuccessor(0); 255 256 DEBUG(dbgs() << "MERGING MOSTLY EMPTY BLOCKS - BEFORE:\n" << *BB << *DestBB); 257 258 // If the destination block has a single pred, then this is a trivial edge, 259 // just collapse it. 260 if (BasicBlock *SinglePred = DestBB->getSinglePredecessor()) { 261 if (SinglePred != DestBB) { 262 // Remember if SinglePred was the entry block of the function. If so, we 263 // will need to move BB back to the entry position. 264 bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock(); 265 MergeBasicBlockIntoOnlyPred(DestBB, this); 266 267 if (isEntry && BB != &BB->getParent()->getEntryBlock()) 268 BB->moveBefore(&BB->getParent()->getEntryBlock()); 269 270 DEBUG(dbgs() << "AFTER:\n" << *DestBB << "\n\n\n"); 271 return; 272 } 273 } 274 275 // Otherwise, we have multiple predecessors of BB. Update the PHIs in DestBB 276 // to handle the new incoming edges it is about to have. 277 PHINode *PN; 278 for (BasicBlock::iterator BBI = DestBB->begin(); 279 (PN = dyn_cast<PHINode>(BBI)); ++BBI) { 280 // Remove the incoming value for BB, and remember it. 281 Value *InVal = PN->removeIncomingValue(BB, false); 282 283 // Two options: either the InVal is a phi node defined in BB or it is some 284 // value that dominates BB. 285 PHINode *InValPhi = dyn_cast<PHINode>(InVal); 286 if (InValPhi && InValPhi->getParent() == BB) { 287 // Add all of the input values of the input PHI as inputs of this phi. 288 for (unsigned i = 0, e = InValPhi->getNumIncomingValues(); i != e; ++i) 289 PN->addIncoming(InValPhi->getIncomingValue(i), 290 InValPhi->getIncomingBlock(i)); 291 } else { 292 // Otherwise, add one instance of the dominating value for each edge that 293 // we will be adding. 294 if (PHINode *BBPN = dyn_cast<PHINode>(BB->begin())) { 295 for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i) 296 PN->addIncoming(InVal, BBPN->getIncomingBlock(i)); 297 } else { 298 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 299 PN->addIncoming(InVal, *PI); 300 } 301 } 302 } 303 304 // The PHIs are now updated, change everything that refers to BB to use 305 // DestBB and remove BB. 306 BB->replaceAllUsesWith(DestBB); 307 if (DT) { 308 BasicBlock *BBIDom = DT->getNode(BB)->getIDom()->getBlock(); 309 BasicBlock *DestBBIDom = DT->getNode(DestBB)->getIDom()->getBlock(); 310 BasicBlock *NewIDom = DT->findNearestCommonDominator(BBIDom, DestBBIDom); 311 DT->changeImmediateDominator(DestBB, NewIDom); 312 DT->eraseNode(BB); 313 } 314 if (PFI) { 315 PFI->replaceAllUses(BB, DestBB); 316 PFI->removeEdge(ProfileInfo::getEdge(BB, DestBB)); 317 } 318 BB->eraseFromParent(); 319 ++NumBlocksElim; 320 321 DEBUG(dbgs() << "AFTER:\n" << *DestBB << "\n\n\n"); 322} 323 324/// OptimizeNoopCopyExpression - If the specified cast instruction is a noop 325/// copy (e.g. it's casting from one pointer type to another, i32->i8 on PPC), 326/// sink it into user blocks to reduce the number of virtual 327/// registers that must be created and coalesced. 328/// 329/// Return true if any changes are made. 330/// 331static bool OptimizeNoopCopyExpression(CastInst *CI, const TargetLowering &TLI){ 332 // If this is a noop copy, 333 EVT SrcVT = TLI.getValueType(CI->getOperand(0)->getType()); 334 EVT DstVT = TLI.getValueType(CI->getType()); 335 336 // This is an fp<->int conversion? 337 if (SrcVT.isInteger() != DstVT.isInteger()) 338 return false; 339 340 // If this is an extension, it will be a zero or sign extension, which 341 // isn't a noop. 342 if (SrcVT.bitsLT(DstVT)) return false; 343 344 // If these values will be promoted, find out what they will be promoted 345 // to. This helps us consider truncates on PPC as noop copies when they 346 // are. 347 if (TLI.getTypeAction(SrcVT) == TargetLowering::Promote) 348 SrcVT = TLI.getTypeToTransformTo(CI->getContext(), SrcVT); 349 if (TLI.getTypeAction(DstVT) == TargetLowering::Promote) 350 DstVT = TLI.getTypeToTransformTo(CI->getContext(), DstVT); 351 352 // If, after promotion, these are the same types, this is a noop copy. 353 if (SrcVT != DstVT) 354 return false; 355 356 BasicBlock *DefBB = CI->getParent(); 357 358 /// InsertedCasts - Only insert a cast in each block once. 359 DenseMap<BasicBlock*, CastInst*> InsertedCasts; 360 361 bool MadeChange = false; 362 for (Value::use_iterator UI = CI->use_begin(), E = CI->use_end(); 363 UI != E; ) { 364 Use &TheUse = UI.getUse(); 365 Instruction *User = cast<Instruction>(*UI); 366 367 // Figure out which BB this cast is used in. For PHI's this is the 368 // appropriate predecessor block. 369 BasicBlock *UserBB = User->getParent(); 370 if (PHINode *PN = dyn_cast<PHINode>(User)) { 371 UserBB = PN->getIncomingBlock(UI); 372 } 373 374 // Preincrement use iterator so we don't invalidate it. 375 ++UI; 376 377 // If this user is in the same block as the cast, don't change the cast. 378 if (UserBB == DefBB) continue; 379 380 // If we have already inserted a cast into this block, use it. 381 CastInst *&InsertedCast = InsertedCasts[UserBB]; 382 383 if (!InsertedCast) { 384 BasicBlock::iterator InsertPt = UserBB->getFirstNonPHI(); 385 386 InsertedCast = 387 CastInst::Create(CI->getOpcode(), CI->getOperand(0), CI->getType(), "", 388 InsertPt); 389 MadeChange = true; 390 } 391 392 // Replace a use of the cast with a use of the new cast. 393 TheUse = InsertedCast; 394 ++NumCastUses; 395 } 396 397 // If we removed all uses, nuke the cast. 398 if (CI->use_empty()) { 399 CI->eraseFromParent(); 400 MadeChange = true; 401 } 402 403 return MadeChange; 404} 405 406/// OptimizeCmpExpression - sink the given CmpInst into user blocks to reduce 407/// the number of virtual registers that must be created and coalesced. This is 408/// a clear win except on targets with multiple condition code registers 409/// (PowerPC), where it might lose; some adjustment may be wanted there. 410/// 411/// Return true if any changes are made. 412static bool OptimizeCmpExpression(CmpInst *CI) { 413 BasicBlock *DefBB = CI->getParent(); 414 415 /// InsertedCmp - Only insert a cmp in each block once. 416 DenseMap<BasicBlock*, CmpInst*> InsertedCmps; 417 418 bool MadeChange = false; 419 for (Value::use_iterator UI = CI->use_begin(), E = CI->use_end(); 420 UI != E; ) { 421 Use &TheUse = UI.getUse(); 422 Instruction *User = cast<Instruction>(*UI); 423 424 // Preincrement use iterator so we don't invalidate it. 425 ++UI; 426 427 // Don't bother for PHI nodes. 428 if (isa<PHINode>(User)) 429 continue; 430 431 // Figure out which BB this cmp is used in. 432 BasicBlock *UserBB = User->getParent(); 433 434 // If this user is in the same block as the cmp, don't change the cmp. 435 if (UserBB == DefBB) continue; 436 437 // If we have already inserted a cmp into this block, use it. 438 CmpInst *&InsertedCmp = InsertedCmps[UserBB]; 439 440 if (!InsertedCmp) { 441 BasicBlock::iterator InsertPt = UserBB->getFirstNonPHI(); 442 443 InsertedCmp = 444 CmpInst::Create(CI->getOpcode(), 445 CI->getPredicate(), CI->getOperand(0), 446 CI->getOperand(1), "", InsertPt); 447 MadeChange = true; 448 } 449 450 // Replace a use of the cmp with a use of the new cmp. 451 TheUse = InsertedCmp; 452 ++NumCmpUses; 453 } 454 455 // If we removed all uses, nuke the cmp. 456 if (CI->use_empty()) 457 CI->eraseFromParent(); 458 459 return MadeChange; 460} 461 462namespace { 463class CodeGenPrepareFortifiedLibCalls : public SimplifyFortifiedLibCalls { 464protected: 465 void replaceCall(Value *With) { 466 CI->replaceAllUsesWith(With); 467 CI->eraseFromParent(); 468 } 469 bool isFoldable(unsigned SizeCIOp, unsigned, bool) const { 470 if (ConstantInt *SizeCI = 471 dyn_cast<ConstantInt>(CI->getArgOperand(SizeCIOp))) 472 return SizeCI->isAllOnesValue(); 473 return false; 474 } 475}; 476} // end anonymous namespace 477 478bool CodeGenPrepare::OptimizeCallInst(CallInst *CI) { 479 BasicBlock *BB = CI->getParent(); 480 481 // Lower inline assembly if we can. 482 // If we found an inline asm expession, and if the target knows how to 483 // lower it to normal LLVM code, do so now. 484 if (TLI && isa<InlineAsm>(CI->getCalledValue())) { 485 if (TLI->ExpandInlineAsm(CI)) { 486 // Avoid invalidating the iterator. 487 CurInstIterator = BB->begin(); 488 // Avoid processing instructions out of order, which could cause 489 // reuse before a value is defined. 490 SunkAddrs.clear(); 491 return true; 492 } 493 // Sink address computing for memory operands into the block. 494 if (OptimizeInlineAsmInst(CI)) 495 return true; 496 } 497 498 // Lower all uses of llvm.objectsize.* 499 IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI); 500 if (II && II->getIntrinsicID() == Intrinsic::objectsize) { 501 bool Min = (cast<ConstantInt>(II->getArgOperand(1))->getZExtValue() == 1); 502 const Type *ReturnTy = CI->getType(); 503 Constant *RetVal = ConstantInt::get(ReturnTy, Min ? 0 : -1ULL); 504 505 // Substituting this can cause recursive simplifications, which can 506 // invalidate our iterator. Use a WeakVH to hold onto it in case this 507 // happens. 508 WeakVH IterHandle(CurInstIterator); 509 510 ReplaceAndSimplifyAllUses(CI, RetVal, TLI ? TLI->getTargetData() : 0, DT); 511 512 // If the iterator instruction was recursively deleted, start over at the 513 // start of the block. 514 if (IterHandle != CurInstIterator) { 515 CurInstIterator = BB->begin(); 516 SunkAddrs.clear(); 517 } 518 return true; 519 } 520 521 // From here on out we're working with named functions. 522 if (CI->getCalledFunction() == 0) return false; 523 524 // We'll need TargetData from here on out. 525 const TargetData *TD = TLI ? TLI->getTargetData() : 0; 526 if (!TD) return false; 527 528 // Lower all default uses of _chk calls. This is very similar 529 // to what InstCombineCalls does, but here we are only lowering calls 530 // that have the default "don't know" as the objectsize. Anything else 531 // should be left alone. 532 CodeGenPrepareFortifiedLibCalls Simplifier; 533 return Simplifier.fold(CI, TD); 534} 535 536//===----------------------------------------------------------------------===// 537// Memory Optimization 538//===----------------------------------------------------------------------===// 539 540/// IsNonLocalValue - Return true if the specified values are defined in a 541/// different basic block than BB. 542static bool IsNonLocalValue(Value *V, BasicBlock *BB) { 543 if (Instruction *I = dyn_cast<Instruction>(V)) 544 return I->getParent() != BB; 545 return false; 546} 547 548/// OptimizeMemoryInst - Load and Store Instructions often have 549/// addressing modes that can do significant amounts of computation. As such, 550/// instruction selection will try to get the load or store to do as much 551/// computation as possible for the program. The problem is that isel can only 552/// see within a single block. As such, we sink as much legal addressing mode 553/// stuff into the block as possible. 554/// 555/// This method is used to optimize both load/store and inline asms with memory 556/// operands. 557bool CodeGenPrepare::OptimizeMemoryInst(Instruction *MemoryInst, Value *Addr, 558 const Type *AccessTy) { 559 Value *Repl = Addr; 560 561 // Try to collapse single-value PHI nodes. This is necessary to undo 562 // unprofitable PRE transformations. 563 SmallVector<Value*, 8> worklist; 564 SmallPtrSet<Value*, 16> Visited; 565 worklist.push_back(Addr); 566 567 // Use a worklist to iteratively look through PHI nodes, and ensure that 568 // the addressing mode obtained from the non-PHI roots of the graph 569 // are equivalent. 570 Value *Consensus = 0; 571 unsigned NumUsesConsensus = 0; 572 bool IsNumUsesConsensusValid = false; 573 SmallVector<Instruction*, 16> AddrModeInsts; 574 ExtAddrMode AddrMode; 575 while (!worklist.empty()) { 576 Value *V = worklist.back(); 577 worklist.pop_back(); 578 579 // Break use-def graph loops. 580 if (Visited.count(V)) { 581 Consensus = 0; 582 break; 583 } 584 585 Visited.insert(V); 586 587 // For a PHI node, push all of its incoming values. 588 if (PHINode *P = dyn_cast<PHINode>(V)) { 589 for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) 590 worklist.push_back(P->getIncomingValue(i)); 591 continue; 592 } 593 594 // For non-PHIs, determine the addressing mode being computed. 595 SmallVector<Instruction*, 16> NewAddrModeInsts; 596 ExtAddrMode NewAddrMode = 597 AddressingModeMatcher::Match(V, AccessTy,MemoryInst, 598 NewAddrModeInsts, *TLI); 599 600 // This check is broken into two cases with very similar code to avoid using 601 // getNumUses() as much as possible. Some values have a lot of uses, so 602 // calling getNumUses() unconditionally caused a significant compile-time 603 // regression. 604 if (!Consensus) { 605 Consensus = V; 606 AddrMode = NewAddrMode; 607 AddrModeInsts = NewAddrModeInsts; 608 continue; 609 } else if (NewAddrMode == AddrMode) { 610 if (!IsNumUsesConsensusValid) { 611 NumUsesConsensus = Consensus->getNumUses(); 612 IsNumUsesConsensusValid = true; 613 } 614 615 // Ensure that the obtained addressing mode is equivalent to that obtained 616 // for all other roots of the PHI traversal. Also, when choosing one 617 // such root as representative, select the one with the most uses in order 618 // to keep the cost modeling heuristics in AddressingModeMatcher 619 // applicable. 620 unsigned NumUses = V->getNumUses(); 621 if (NumUses > NumUsesConsensus) { 622 Consensus = V; 623 NumUsesConsensus = NumUses; 624 AddrModeInsts = NewAddrModeInsts; 625 } 626 continue; 627 } 628 629 Consensus = 0; 630 break; 631 } 632 633 // If the addressing mode couldn't be determined, or if multiple different 634 // ones were determined, bail out now. 635 if (!Consensus) return false; 636 637 // Check to see if any of the instructions supersumed by this addr mode are 638 // non-local to I's BB. 639 bool AnyNonLocal = false; 640 for (unsigned i = 0, e = AddrModeInsts.size(); i != e; ++i) { 641 if (IsNonLocalValue(AddrModeInsts[i], MemoryInst->getParent())) { 642 AnyNonLocal = true; 643 break; 644 } 645 } 646 647 // If all the instructions matched are already in this BB, don't do anything. 648 if (!AnyNonLocal) { 649 DEBUG(dbgs() << "CGP: Found local addrmode: " << AddrMode << "\n"); 650 return false; 651 } 652 653 // Insert this computation right after this user. Since our caller is 654 // scanning from the top of the BB to the bottom, reuse of the expr are 655 // guaranteed to happen later. 656 BasicBlock::iterator InsertPt = MemoryInst; 657 658 // Now that we determined the addressing expression we want to use and know 659 // that we have to sink it into this block. Check to see if we have already 660 // done this for some other load/store instr in this block. If so, reuse the 661 // computation. 662 Value *&SunkAddr = SunkAddrs[Addr]; 663 if (SunkAddr) { 664 DEBUG(dbgs() << "CGP: Reusing nonlocal addrmode: " << AddrMode << " for " 665 << *MemoryInst); 666 if (SunkAddr->getType() != Addr->getType()) 667 SunkAddr = new BitCastInst(SunkAddr, Addr->getType(), "tmp", InsertPt); 668 } else { 669 DEBUG(dbgs() << "CGP: SINKING nonlocal addrmode: " << AddrMode << " for " 670 << *MemoryInst); 671 const Type *IntPtrTy = 672 TLI->getTargetData()->getIntPtrType(AccessTy->getContext()); 673 674 Value *Result = 0; 675 676 // Start with the base register. Do this first so that subsequent address 677 // matching finds it last, which will prevent it from trying to match it 678 // as the scaled value in case it happens to be a mul. That would be 679 // problematic if we've sunk a different mul for the scale, because then 680 // we'd end up sinking both muls. 681 if (AddrMode.BaseReg) { 682 Value *V = AddrMode.BaseReg; 683 if (V->getType()->isPointerTy()) 684 V = new PtrToIntInst(V, IntPtrTy, "sunkaddr", InsertPt); 685 if (V->getType() != IntPtrTy) 686 V = CastInst::CreateIntegerCast(V, IntPtrTy, /*isSigned=*/true, 687 "sunkaddr", InsertPt); 688 Result = V; 689 } 690 691 // Add the scale value. 692 if (AddrMode.Scale) { 693 Value *V = AddrMode.ScaledReg; 694 if (V->getType() == IntPtrTy) { 695 // done. 696 } else if (V->getType()->isPointerTy()) { 697 V = new PtrToIntInst(V, IntPtrTy, "sunkaddr", InsertPt); 698 } else if (cast<IntegerType>(IntPtrTy)->getBitWidth() < 699 cast<IntegerType>(V->getType())->getBitWidth()) { 700 V = new TruncInst(V, IntPtrTy, "sunkaddr", InsertPt); 701 } else { 702 V = new SExtInst(V, IntPtrTy, "sunkaddr", InsertPt); 703 } 704 if (AddrMode.Scale != 1) 705 V = BinaryOperator::CreateMul(V, ConstantInt::get(IntPtrTy, 706 AddrMode.Scale), 707 "sunkaddr", InsertPt); 708 if (Result) 709 Result = BinaryOperator::CreateAdd(Result, V, "sunkaddr", InsertPt); 710 else 711 Result = V; 712 } 713 714 // Add in the BaseGV if present. 715 if (AddrMode.BaseGV) { 716 Value *V = new PtrToIntInst(AddrMode.BaseGV, IntPtrTy, "sunkaddr", 717 InsertPt); 718 if (Result) 719 Result = BinaryOperator::CreateAdd(Result, V, "sunkaddr", InsertPt); 720 else 721 Result = V; 722 } 723 724 // Add in the Base Offset if present. 725 if (AddrMode.BaseOffs) { 726 Value *V = ConstantInt::get(IntPtrTy, AddrMode.BaseOffs); 727 if (Result) 728 Result = BinaryOperator::CreateAdd(Result, V, "sunkaddr", InsertPt); 729 else 730 Result = V; 731 } 732 733 if (Result == 0) 734 SunkAddr = Constant::getNullValue(Addr->getType()); 735 else 736 SunkAddr = new IntToPtrInst(Result, Addr->getType(), "sunkaddr",InsertPt); 737 } 738 739 MemoryInst->replaceUsesOfWith(Repl, SunkAddr); 740 741 if (Repl->use_empty()) { 742 RecursivelyDeleteTriviallyDeadInstructions(Repl); 743 // This address is now available for reassignment, so erase the table entry; 744 // we don't want to match some completely different instruction. 745 SunkAddrs[Addr] = 0; 746 } 747 ++NumMemoryInsts; 748 return true; 749} 750 751/// OptimizeInlineAsmInst - If there are any memory operands, use 752/// OptimizeMemoryInst to sink their address computing into the block when 753/// possible / profitable. 754bool CodeGenPrepare::OptimizeInlineAsmInst(CallInst *CS) { 755 bool MadeChange = false; 756 757 TargetLowering::AsmOperandInfoVector 758 TargetConstraints = TLI->ParseConstraints(CS); 759 unsigned ArgNo = 0; 760 for (unsigned i = 0, e = TargetConstraints.size(); i != e; ++i) { 761 TargetLowering::AsmOperandInfo &OpInfo = TargetConstraints[i]; 762 763 // Compute the constraint code and ConstraintType to use. 764 TLI->ComputeConstraintToUse(OpInfo, SDValue()); 765 766 if (OpInfo.ConstraintType == TargetLowering::C_Memory && 767 OpInfo.isIndirect) { 768 Value *OpVal = CS->getArgOperand(ArgNo++); 769 MadeChange |= OptimizeMemoryInst(CS, OpVal, OpVal->getType()); 770 } else if (OpInfo.Type == InlineAsm::isInput) 771 ArgNo++; 772 } 773 774 return MadeChange; 775} 776 777/// MoveExtToFormExtLoad - Move a zext or sext fed by a load into the same 778/// basic block as the load, unless conditions are unfavorable. This allows 779/// SelectionDAG to fold the extend into the load. 780/// 781bool CodeGenPrepare::MoveExtToFormExtLoad(Instruction *I) { 782 // Look for a load being extended. 783 LoadInst *LI = dyn_cast<LoadInst>(I->getOperand(0)); 784 if (!LI) return false; 785 786 // If they're already in the same block, there's nothing to do. 787 if (LI->getParent() == I->getParent()) 788 return false; 789 790 // If the load has other users and the truncate is not free, this probably 791 // isn't worthwhile. 792 if (!LI->hasOneUse() && 793 TLI && (TLI->isTypeLegal(TLI->getValueType(LI->getType())) || 794 !TLI->isTypeLegal(TLI->getValueType(I->getType()))) && 795 !TLI->isTruncateFree(I->getType(), LI->getType())) 796 return false; 797 798 // Check whether the target supports casts folded into loads. 799 unsigned LType; 800 if (isa<ZExtInst>(I)) 801 LType = ISD::ZEXTLOAD; 802 else { 803 assert(isa<SExtInst>(I) && "Unexpected ext type!"); 804 LType = ISD::SEXTLOAD; 805 } 806 if (TLI && !TLI->isLoadExtLegal(LType, TLI->getValueType(LI->getType()))) 807 return false; 808 809 // Move the extend into the same block as the load, so that SelectionDAG 810 // can fold it. 811 I->removeFromParent(); 812 I->insertAfter(LI); 813 ++NumExtsMoved; 814 return true; 815} 816 817bool CodeGenPrepare::OptimizeExtUses(Instruction *I) { 818 BasicBlock *DefBB = I->getParent(); 819 820 // If the result of a {s|z}ext and its source are both live out, rewrite all 821 // other uses of the source with result of extension. 822 Value *Src = I->getOperand(0); 823 if (Src->hasOneUse()) 824 return false; 825 826 // Only do this xform if truncating is free. 827 if (TLI && !TLI->isTruncateFree(I->getType(), Src->getType())) 828 return false; 829 830 // Only safe to perform the optimization if the source is also defined in 831 // this block. 832 if (!isa<Instruction>(Src) || DefBB != cast<Instruction>(Src)->getParent()) 833 return false; 834 835 bool DefIsLiveOut = false; 836 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); 837 UI != E; ++UI) { 838 Instruction *User = cast<Instruction>(*UI); 839 840 // Figure out which BB this ext is used in. 841 BasicBlock *UserBB = User->getParent(); 842 if (UserBB == DefBB) continue; 843 DefIsLiveOut = true; 844 break; 845 } 846 if (!DefIsLiveOut) 847 return false; 848 849 // Make sure non of the uses are PHI nodes. 850 for (Value::use_iterator UI = Src->use_begin(), E = Src->use_end(); 851 UI != E; ++UI) { 852 Instruction *User = cast<Instruction>(*UI); 853 BasicBlock *UserBB = User->getParent(); 854 if (UserBB == DefBB) continue; 855 // Be conservative. We don't want this xform to end up introducing 856 // reloads just before load / store instructions. 857 if (isa<PHINode>(User) || isa<LoadInst>(User) || isa<StoreInst>(User)) 858 return false; 859 } 860 861 // InsertedTruncs - Only insert one trunc in each block once. 862 DenseMap<BasicBlock*, Instruction*> InsertedTruncs; 863 864 bool MadeChange = false; 865 for (Value::use_iterator UI = Src->use_begin(), E = Src->use_end(); 866 UI != E; ++UI) { 867 Use &TheUse = UI.getUse(); 868 Instruction *User = cast<Instruction>(*UI); 869 870 // Figure out which BB this ext is used in. 871 BasicBlock *UserBB = User->getParent(); 872 if (UserBB == DefBB) continue; 873 874 // Both src and def are live in this block. Rewrite the use. 875 Instruction *&InsertedTrunc = InsertedTruncs[UserBB]; 876 877 if (!InsertedTrunc) { 878 BasicBlock::iterator InsertPt = UserBB->getFirstNonPHI(); 879 880 InsertedTrunc = new TruncInst(I, Src->getType(), "", InsertPt); 881 } 882 883 // Replace a use of the {s|z}ext source with a use of the result. 884 TheUse = InsertedTrunc; 885 ++NumExtUses; 886 MadeChange = true; 887 } 888 889 return MadeChange; 890} 891 892bool CodeGenPrepare::OptimizeInst(Instruction *I) { 893 if (PHINode *P = dyn_cast<PHINode>(I)) { 894 // It is possible for very late stage optimizations (such as SimplifyCFG) 895 // to introduce PHI nodes too late to be cleaned up. If we detect such a 896 // trivial PHI, go ahead and zap it here. 897 if (Value *V = SimplifyInstruction(P)) { 898 P->replaceAllUsesWith(V); 899 P->eraseFromParent(); 900 ++NumPHIsElim; 901 return true; 902 } 903 return false; 904 } 905 906 if (CastInst *CI = dyn_cast<CastInst>(I)) { 907 // If the source of the cast is a constant, then this should have 908 // already been constant folded. The only reason NOT to constant fold 909 // it is if something (e.g. LSR) was careful to place the constant 910 // evaluation in a block other than then one that uses it (e.g. to hoist 911 // the address of globals out of a loop). If this is the case, we don't 912 // want to forward-subst the cast. 913 if (isa<Constant>(CI->getOperand(0))) 914 return false; 915 916 if (TLI && OptimizeNoopCopyExpression(CI, *TLI)) 917 return true; 918 919 if (isa<ZExtInst>(I) || isa<SExtInst>(I)) { 920 bool MadeChange = MoveExtToFormExtLoad(I); 921 return MadeChange | OptimizeExtUses(I); 922 } 923 return false; 924 } 925 926 if (CmpInst *CI = dyn_cast<CmpInst>(I)) 927 return OptimizeCmpExpression(CI); 928 929 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 930 if (TLI) 931 return OptimizeMemoryInst(I, I->getOperand(0), LI->getType()); 932 return false; 933 } 934 935 if (StoreInst *SI = dyn_cast<StoreInst>(I)) { 936 if (TLI) 937 return OptimizeMemoryInst(I, SI->getOperand(1), 938 SI->getOperand(0)->getType()); 939 return false; 940 } 941 942 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) { 943 if (GEPI->hasAllZeroIndices()) { 944 /// The GEP operand must be a pointer, so must its result -> BitCast 945 Instruction *NC = new BitCastInst(GEPI->getOperand(0), GEPI->getType(), 946 GEPI->getName(), GEPI); 947 GEPI->replaceAllUsesWith(NC); 948 GEPI->eraseFromParent(); 949 ++NumGEPsElim; 950 OptimizeInst(NC); 951 return true; 952 } 953 return false; 954 } 955 956 if (CallInst *CI = dyn_cast<CallInst>(I)) 957 return OptimizeCallInst(CI); 958 959 return false; 960} 961 962// In this pass we look for GEP and cast instructions that are used 963// across basic blocks and rewrite them to improve basic-block-at-a-time 964// selection. 965bool CodeGenPrepare::OptimizeBlock(BasicBlock &BB) { 966 SunkAddrs.clear(); 967 bool MadeChange = false; 968 969 CurInstIterator = BB.begin(); 970 for (BasicBlock::iterator E = BB.end(); CurInstIterator != E; ) 971 MadeChange |= OptimizeInst(CurInstIterator++); 972 973 return MadeChange; 974} 975