LICM.cpp revision 245431
1193323Sed//===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===// 2193323Sed// 3193323Sed// The LLVM Compiler Infrastructure 4193323Sed// 5193323Sed// This file is distributed under the University of Illinois Open Source 6193323Sed// License. See LICENSE.TXT for details. 7193323Sed// 8193323Sed//===----------------------------------------------------------------------===// 9193323Sed// 10193323Sed// This pass performs loop invariant code motion, attempting to remove as much 11193323Sed// code from the body of a loop as possible. It does this by either hoisting 12193323Sed// code into the preheader block, or by sinking code to the exit blocks if it is 13193323Sed// safe. This pass also promotes must-aliased memory locations in the loop to 14193323Sed// live in registers, thus hoisting and sinking "invariant" loads and stores. 15193323Sed// 16193323Sed// This pass uses alias analysis for two purposes: 17193323Sed// 18193323Sed// 1. Moving loop invariant loads and calls out of loops. If we can determine 19193323Sed// that a load or call inside of a loop never aliases anything stored to, 20193323Sed// we can hoist it or sink it like any other instruction. 21193323Sed// 2. Scalar Promotion of Memory - If there is a store instruction inside of 22193323Sed// the loop, we try to move the store to happen AFTER the loop instead of 23193323Sed// inside of the loop. This can only happen if a few conditions are true: 24193323Sed// A. The pointer stored through is loop invariant 25193323Sed// B. There are no stores or loads in the loop which _may_ alias the 26193323Sed// pointer. There are no calls in the loop which mod/ref the pointer. 27193323Sed// If these conditions are true, we can promote the loads and stores in the 28193323Sed// loop of the pointer to use a temporary alloca'd variable. We then use 29212904Sdim// the SSAUpdater to construct the appropriate SSA form for the value. 30193323Sed// 31193323Sed//===----------------------------------------------------------------------===// 32193323Sed 33193323Sed#define DEBUG_TYPE "licm" 34193323Sed#include "llvm/Transforms/Scalar.h" 35193323Sed#include "llvm/Constants.h" 36193323Sed#include "llvm/DerivedTypes.h" 37198090Srdivacky#include "llvm/IntrinsicInst.h" 38193323Sed#include "llvm/Instructions.h" 39218893Sdim#include "llvm/LLVMContext.h" 40212904Sdim#include "llvm/Analysis/AliasAnalysis.h" 41212904Sdim#include "llvm/Analysis/AliasSetTracker.h" 42212904Sdim#include "llvm/Analysis/ConstantFolding.h" 43193323Sed#include "llvm/Analysis/LoopInfo.h" 44193323Sed#include "llvm/Analysis/LoopPass.h" 45193323Sed#include "llvm/Analysis/Dominators.h" 46235633Sdim#include "llvm/Analysis/ValueTracking.h" 47212904Sdim#include "llvm/Transforms/Utils/Local.h" 48212904Sdim#include "llvm/Transforms/Utils/SSAUpdater.h" 49245431Sdim#include "llvm/DataLayout.h" 50235633Sdim#include "llvm/Target/TargetLibraryInfo.h" 51193323Sed#include "llvm/Support/CFG.h" 52193323Sed#include "llvm/Support/CommandLine.h" 53198090Srdivacky#include "llvm/Support/raw_ostream.h" 54193323Sed#include "llvm/Support/Debug.h" 55193323Sed#include "llvm/ADT/Statistic.h" 56193323Sed#include <algorithm> 57193323Sedusing namespace llvm; 58193323Sed 59193323SedSTATISTIC(NumSunk , "Number of instructions sunk out of loop"); 60193323SedSTATISTIC(NumHoisted , "Number of instructions hoisted out of loop"); 61193323SedSTATISTIC(NumMovedLoads, "Number of load insts hoisted or sunk"); 62193323SedSTATISTIC(NumMovedCalls, "Number of call insts hoisted or sunk"); 63193323SedSTATISTIC(NumPromoted , "Number of memory locations promoted to registers"); 64193323Sed 65193323Sedstatic cl::opt<bool> 66193323SedDisablePromotion("disable-licm-promotion", cl::Hidden, 67193323Sed cl::desc("Disable memory promotion in LICM pass")); 68193323Sed 69193323Sednamespace { 70198090Srdivacky struct LICM : public LoopPass { 71193323Sed static char ID; // Pass identification, replacement for typeid 72218893Sdim LICM() : LoopPass(ID) { 73218893Sdim initializeLICMPass(*PassRegistry::getPassRegistry()); 74218893Sdim } 75193323Sed 76193323Sed virtual bool runOnLoop(Loop *L, LPPassManager &LPM); 77193323Sed 78193323Sed /// This transformation requires natural loop information & requires that 79193323Sed /// loop preheaders be inserted into the CFG... 80193323Sed /// 81193323Sed virtual void getAnalysisUsage(AnalysisUsage &AU) const { 82193323Sed AU.setPreservesCFG(); 83212904Sdim AU.addRequired<DominatorTree>(); 84212904Sdim AU.addRequired<LoopInfo>(); 85193323Sed AU.addRequiredID(LoopSimplifyID); 86193323Sed AU.addRequired<AliasAnalysis>(); 87212904Sdim AU.addPreserved<AliasAnalysis>(); 88218893Sdim AU.addPreserved("scalar-evolution"); 89198090Srdivacky AU.addPreservedID(LoopSimplifyID); 90235633Sdim AU.addRequired<TargetLibraryInfo>(); 91193323Sed } 92193323Sed 93193323Sed bool doFinalization() { 94212904Sdim assert(LoopToAliasSetMap.empty() && "Didn't free loop alias sets"); 95193323Sed return false; 96193323Sed } 97193323Sed 98193323Sed private: 99193323Sed AliasAnalysis *AA; // Current AliasAnalysis information 100193323Sed LoopInfo *LI; // Current LoopInfo 101212904Sdim DominatorTree *DT; // Dominator Tree for the current Loop. 102193323Sed 103245431Sdim DataLayout *TD; // DataLayout for constant folding. 104235633Sdim TargetLibraryInfo *TLI; // TargetLibraryInfo for constant folding. 105235633Sdim 106212904Sdim // State that is updated as we process loops. 107193323Sed bool Changed; // Set to true when we change anything. 108193323Sed BasicBlock *Preheader; // The preheader block of the current loop... 109193323Sed Loop *CurLoop; // The current loop we are working on... 110193323Sed AliasSetTracker *CurAST; // AliasSet information for the current loop... 111245431Sdim bool MayThrow; // The current loop contains an instruction which 112245431Sdim // may throw, thus preventing code motion of 113245431Sdim // instructions with side effects. 114212904Sdim DenseMap<Loop*, AliasSetTracker*> LoopToAliasSetMap; 115193323Sed 116193323Sed /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info. 117193323Sed void cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L); 118193323Sed 119193323Sed /// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias 120193323Sed /// set. 121193323Sed void deleteAnalysisValue(Value *V, Loop *L); 122193323Sed 123193323Sed /// SinkRegion - Walk the specified region of the CFG (defined by all blocks 124193323Sed /// dominated by the specified block, and that are in the current loop) in 125193323Sed /// reverse depth first order w.r.t the DominatorTree. This allows us to 126193323Sed /// visit uses before definitions, allowing us to sink a loop body in one 127193323Sed /// pass without iteration. 128193323Sed /// 129193323Sed void SinkRegion(DomTreeNode *N); 130193323Sed 131193323Sed /// HoistRegion - Walk the specified region of the CFG (defined by all 132193323Sed /// blocks dominated by the specified block, and that are in the current 133193323Sed /// loop) in depth first order w.r.t the DominatorTree. This allows us to 134193323Sed /// visit definitions before uses, allowing us to hoist a loop body in one 135193323Sed /// pass without iteration. 136193323Sed /// 137193323Sed void HoistRegion(DomTreeNode *N); 138193323Sed 139193323Sed /// inSubLoop - Little predicate that returns true if the specified basic 140193323Sed /// block is in a subloop of the current one, not the current one itself. 141193323Sed /// 142193323Sed bool inSubLoop(BasicBlock *BB) { 143193323Sed assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop"); 144218893Sdim return LI->getLoopFor(BB) != CurLoop; 145193323Sed } 146193323Sed 147193323Sed /// sink - When an instruction is found to only be used outside of the loop, 148193323Sed /// this function moves it to the exit blocks and patches up SSA form as 149193323Sed /// needed. 150193323Sed /// 151193323Sed void sink(Instruction &I); 152193323Sed 153193323Sed /// hoist - When an instruction is found to only use loop invariant operands 154193323Sed /// that is safe to hoist, this instruction is called to do the dirty work. 155193323Sed /// 156193323Sed void hoist(Instruction &I); 157193323Sed 158193323Sed /// isSafeToExecuteUnconditionally - Only sink or hoist an instruction if it 159193323Sed /// is not a trapping instruction or if it is a trapping instruction and is 160193323Sed /// guaranteed to execute. 161193323Sed /// 162193323Sed bool isSafeToExecuteUnconditionally(Instruction &I); 163193323Sed 164226890Sdim /// isGuaranteedToExecute - Check that the instruction is guaranteed to 165226890Sdim /// execute. 166226890Sdim /// 167226890Sdim bool isGuaranteedToExecute(Instruction &I); 168226890Sdim 169193323Sed /// pointerInvalidatedByLoop - Return true if the body of this loop may 170193323Sed /// store into the memory location pointed to by V. 171193323Sed /// 172218893Sdim bool pointerInvalidatedByLoop(Value *V, uint64_t Size, 173218893Sdim const MDNode *TBAAInfo) { 174193323Sed // Check to see if any of the basic blocks in CurLoop invalidate *V. 175218893Sdim return CurAST->getAliasSetForPointer(V, Size, TBAAInfo).isMod(); 176193323Sed } 177193323Sed 178193323Sed bool canSinkOrHoistInst(Instruction &I); 179193323Sed bool isNotUsedInLoop(Instruction &I); 180193323Sed 181245431Sdim void PromoteAliasSet(AliasSet &AS, 182245431Sdim SmallVectorImpl<BasicBlock*> &ExitBlocks, 183245431Sdim SmallVectorImpl<Instruction*> &InsertPts); 184193323Sed }; 185193323Sed} 186193323Sed 187193323Sedchar LICM::ID = 0; 188218893SdimINITIALIZE_PASS_BEGIN(LICM, "licm", "Loop Invariant Code Motion", false, false) 189218893SdimINITIALIZE_PASS_DEPENDENCY(DominatorTree) 190218893SdimINITIALIZE_PASS_DEPENDENCY(LoopInfo) 191218893SdimINITIALIZE_PASS_DEPENDENCY(LoopSimplify) 192235633SdimINITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) 193218893SdimINITIALIZE_AG_DEPENDENCY(AliasAnalysis) 194218893SdimINITIALIZE_PASS_END(LICM, "licm", "Loop Invariant Code Motion", false, false) 195193323Sed 196193323SedPass *llvm::createLICMPass() { return new LICM(); } 197193323Sed 198193323Sed/// Hoist expressions out of the specified loop. Note, alias info for inner 199224145Sdim/// loop is not preserved so it is not a good idea to run LICM multiple 200193323Sed/// times on one loop. 201193323Sed/// 202193323Sedbool LICM::runOnLoop(Loop *L, LPPassManager &LPM) { 203193323Sed Changed = false; 204193323Sed 205193323Sed // Get our Loop and Alias Analysis information... 206193323Sed LI = &getAnalysis<LoopInfo>(); 207193323Sed AA = &getAnalysis<AliasAnalysis>(); 208193323Sed DT = &getAnalysis<DominatorTree>(); 209193323Sed 210245431Sdim TD = getAnalysisIfAvailable<DataLayout>(); 211235633Sdim TLI = &getAnalysis<TargetLibraryInfo>(); 212235633Sdim 213193323Sed CurAST = new AliasSetTracker(*AA); 214212904Sdim // Collect Alias info from subloops. 215193323Sed for (Loop::iterator LoopItr = L->begin(), LoopItrE = L->end(); 216193323Sed LoopItr != LoopItrE; ++LoopItr) { 217193323Sed Loop *InnerL = *LoopItr; 218212904Sdim AliasSetTracker *InnerAST = LoopToAliasSetMap[InnerL]; 219212904Sdim assert(InnerAST && "Where is my AST?"); 220193323Sed 221193323Sed // What if InnerLoop was modified by other passes ? 222193323Sed CurAST->add(*InnerAST); 223224145Sdim 224212904Sdim // Once we've incorporated the inner loop's AST into ours, we don't need the 225212904Sdim // subloop's anymore. 226212904Sdim delete InnerAST; 227212904Sdim LoopToAliasSetMap.erase(InnerL); 228193323Sed } 229224145Sdim 230193323Sed CurLoop = L; 231193323Sed 232193323Sed // Get the preheader block to move instructions into... 233193323Sed Preheader = L->getLoopPreheader(); 234193323Sed 235193323Sed // Loop over the body of this loop, looking for calls, invokes, and stores. 236193323Sed // Because subloops have already been incorporated into AST, we skip blocks in 237193323Sed // subloops. 238193323Sed // 239193323Sed for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); 240193323Sed I != E; ++I) { 241193323Sed BasicBlock *BB = *I; 242212904Sdim if (LI->getLoopFor(BB) == L) // Ignore blocks in subloops. 243193323Sed CurAST->add(*BB); // Incorporate the specified basic block 244193323Sed } 245193323Sed 246245431Sdim MayThrow = false; 247245431Sdim // TODO: We've already searched for instructions which may throw in subloops. 248245431Sdim // We may want to reuse this information. 249245431Sdim for (Loop::block_iterator BB = L->block_begin(), BBE = L->block_end(); 250245431Sdim (BB != BBE) && !MayThrow ; ++BB) 251245431Sdim for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); 252245431Sdim (I != E) && !MayThrow; ++I) 253245431Sdim MayThrow |= I->mayThrow(); 254245431Sdim 255193323Sed // We want to visit all of the instructions in this loop... that are not parts 256193323Sed // of our subloops (they have already had their invariants hoisted out of 257193323Sed // their loop, into this loop, so there is no need to process the BODIES of 258193323Sed // the subloops). 259193323Sed // 260193323Sed // Traverse the body of the loop in depth first order on the dominator tree so 261193323Sed // that we are guaranteed to see definitions before we see uses. This allows 262193323Sed // us to sink instructions in one pass, without iteration. After sinking 263193323Sed // instructions, we perform another pass to hoist them out of the loop. 264193323Sed // 265199481Srdivacky if (L->hasDedicatedExits()) 266199481Srdivacky SinkRegion(DT->getNode(L->getHeader())); 267199481Srdivacky if (Preheader) 268199481Srdivacky HoistRegion(DT->getNode(L->getHeader())); 269193323Sed 270193323Sed // Now that all loop invariants have been removed from the loop, promote any 271212904Sdim // memory references to scalars that we can. 272212904Sdim if (!DisablePromotion && Preheader && L->hasDedicatedExits()) { 273245431Sdim SmallVector<BasicBlock *, 8> ExitBlocks; 274245431Sdim SmallVector<Instruction *, 8> InsertPts; 275245431Sdim 276212904Sdim // Loop over all of the alias sets in the tracker object. 277212904Sdim for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end(); 278212904Sdim I != E; ++I) 279245431Sdim PromoteAliasSet(*I, ExitBlocks, InsertPts); 280212904Sdim } 281224145Sdim 282193323Sed // Clear out loops state information for the next iteration 283193323Sed CurLoop = 0; 284193323Sed Preheader = 0; 285193323Sed 286212904Sdim // If this loop is nested inside of another one, save the alias information 287212904Sdim // for when we process the outer loop. 288212904Sdim if (L->getParentLoop()) 289212904Sdim LoopToAliasSetMap[L] = CurAST; 290212904Sdim else 291212904Sdim delete CurAST; 292193323Sed return Changed; 293193323Sed} 294193323Sed 295193323Sed/// SinkRegion - Walk the specified region of the CFG (defined by all blocks 296193323Sed/// dominated by the specified block, and that are in the current loop) in 297193323Sed/// reverse depth first order w.r.t the DominatorTree. This allows us to visit 298193323Sed/// uses before definitions, allowing us to sink a loop body in one pass without 299193323Sed/// iteration. 300193323Sed/// 301193323Sedvoid LICM::SinkRegion(DomTreeNode *N) { 302193323Sed assert(N != 0 && "Null dominator tree node?"); 303193323Sed BasicBlock *BB = N->getBlock(); 304193323Sed 305193323Sed // If this subregion is not in the top level loop at all, exit. 306193323Sed if (!CurLoop->contains(BB)) return; 307193323Sed 308212904Sdim // We are processing blocks in reverse dfo, so process children first. 309193323Sed const std::vector<DomTreeNode*> &Children = N->getChildren(); 310193323Sed for (unsigned i = 0, e = Children.size(); i != e; ++i) 311193323Sed SinkRegion(Children[i]); 312193323Sed 313193323Sed // Only need to process the contents of this block if it is not part of a 314193323Sed // subloop (which would already have been processed). 315193323Sed if (inSubLoop(BB)) return; 316193323Sed 317193323Sed for (BasicBlock::iterator II = BB->end(); II != BB->begin(); ) { 318193323Sed Instruction &I = *--II; 319224145Sdim 320212904Sdim // If the instruction is dead, we would try to sink it because it isn't used 321212904Sdim // in the loop, instead, just delete it. 322245431Sdim if (isInstructionTriviallyDead(&I, TLI)) { 323212904Sdim DEBUG(dbgs() << "LICM deleting dead inst: " << I << '\n'); 324212904Sdim ++II; 325212904Sdim CurAST->deleteValue(&I); 326212904Sdim I.eraseFromParent(); 327212904Sdim Changed = true; 328212904Sdim continue; 329212904Sdim } 330193323Sed 331193323Sed // Check to see if we can sink this instruction to the exit blocks 332193323Sed // of the loop. We can do this if the all users of the instruction are 333193323Sed // outside of the loop. In this case, it doesn't even matter if the 334193323Sed // operands of the instruction are loop invariant. 335193323Sed // 336193323Sed if (isNotUsedInLoop(I) && canSinkOrHoistInst(I)) { 337193323Sed ++II; 338193323Sed sink(I); 339193323Sed } 340193323Sed } 341193323Sed} 342193323Sed 343193323Sed/// HoistRegion - Walk the specified region of the CFG (defined by all blocks 344193323Sed/// dominated by the specified block, and that are in the current loop) in depth 345193323Sed/// first order w.r.t the DominatorTree. This allows us to visit definitions 346193323Sed/// before uses, allowing us to hoist a loop body in one pass without iteration. 347193323Sed/// 348193323Sedvoid LICM::HoistRegion(DomTreeNode *N) { 349193323Sed assert(N != 0 && "Null dominator tree node?"); 350193323Sed BasicBlock *BB = N->getBlock(); 351193323Sed 352193323Sed // If this subregion is not in the top level loop at all, exit. 353193323Sed if (!CurLoop->contains(BB)) return; 354193323Sed 355193323Sed // Only need to process the contents of this block if it is not part of a 356193323Sed // subloop (which would already have been processed). 357193323Sed if (!inSubLoop(BB)) 358193323Sed for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ) { 359193323Sed Instruction &I = *II++; 360193323Sed 361212904Sdim // Try constant folding this instruction. If all the operands are 362212904Sdim // constants, it is technically hoistable, but it would be better to just 363212904Sdim // fold it. 364235633Sdim if (Constant *C = ConstantFoldInstruction(&I, TD, TLI)) { 365212904Sdim DEBUG(dbgs() << "LICM folding inst: " << I << " --> " << *C << '\n'); 366212904Sdim CurAST->copyValue(&I, C); 367212904Sdim CurAST->deleteValue(&I); 368212904Sdim I.replaceAllUsesWith(C); 369212904Sdim I.eraseFromParent(); 370212904Sdim continue; 371212904Sdim } 372224145Sdim 373193323Sed // Try hoisting the instruction out to the preheader. We can only do this 374193323Sed // if all of the operands of the instruction are loop invariant and if it 375193323Sed // is safe to hoist the instruction. 376193323Sed // 377218893Sdim if (CurLoop->hasLoopInvariantOperands(&I) && canSinkOrHoistInst(I) && 378193323Sed isSafeToExecuteUnconditionally(I)) 379193323Sed hoist(I); 380212904Sdim } 381193323Sed 382193323Sed const std::vector<DomTreeNode*> &Children = N->getChildren(); 383193323Sed for (unsigned i = 0, e = Children.size(); i != e; ++i) 384193323Sed HoistRegion(Children[i]); 385193323Sed} 386193323Sed 387193323Sed/// canSinkOrHoistInst - Return true if the hoister and sinker can handle this 388193323Sed/// instruction. 389193323Sed/// 390193323Sedbool LICM::canSinkOrHoistInst(Instruction &I) { 391193323Sed // Loads have extra constraints we have to verify before we can hoist them. 392193323Sed if (LoadInst *LI = dyn_cast<LoadInst>(&I)) { 393226890Sdim if (!LI->isUnordered()) 394226890Sdim return false; // Don't hoist volatile/atomic loads! 395193323Sed 396193323Sed // Loads from constant memory are always safe to move, even if they end up 397193323Sed // in the same alias set as something that ends up being modified. 398199989Srdivacky if (AA->pointsToConstantMemory(LI->getOperand(0))) 399193323Sed return true; 400235633Sdim if (LI->getMetadata("invariant.load")) 401235633Sdim return true; 402224145Sdim 403193323Sed // Don't hoist loads which have may-aliased stores in loop. 404218893Sdim uint64_t Size = 0; 405193323Sed if (LI->getType()->isSized()) 406198090Srdivacky Size = AA->getTypeStoreSize(LI->getType()); 407218893Sdim return !pointerInvalidatedByLoop(LI->getOperand(0), Size, 408218893Sdim LI->getMetadata(LLVMContext::MD_tbaa)); 409193323Sed } else if (CallInst *CI = dyn_cast<CallInst>(&I)) { 410223017Sdim // Don't sink or hoist dbg info; it's legal, but not useful. 411223017Sdim if (isa<DbgInfoIntrinsic>(I)) 412223017Sdim return false; 413223017Sdim 414223017Sdim // Handle simple cases by querying alias analysis. 415193323Sed AliasAnalysis::ModRefBehavior Behavior = AA->getModRefBehavior(CI); 416193323Sed if (Behavior == AliasAnalysis::DoesNotAccessMemory) 417193323Sed return true; 418218893Sdim if (AliasAnalysis::onlyReadsMemory(Behavior)) { 419193323Sed // If this call only reads from memory and there are no writes to memory 420193323Sed // in the loop, we can hoist or sink the call as appropriate. 421193323Sed bool FoundMod = false; 422193323Sed for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end(); 423193323Sed I != E; ++I) { 424193323Sed AliasSet &AS = *I; 425193323Sed if (!AS.isForwardingAliasSet() && AS.isMod()) { 426193323Sed FoundMod = true; 427193323Sed break; 428193323Sed } 429193323Sed } 430193323Sed if (!FoundMod) return true; 431193323Sed } 432193323Sed 433245431Sdim // FIXME: This should use mod/ref information to see if we can hoist or 434245431Sdim // sink the call. 435193323Sed 436193323Sed return false; 437193323Sed } 438193323Sed 439245431Sdim // Only these instructions are hoistable/sinkable. 440245431Sdim bool HoistableKind = (isa<BinaryOperator>(I) || isa<CastInst>(I) || 441245431Sdim isa<SelectInst>(I) || isa<GetElementPtrInst>(I) || 442245431Sdim isa<CmpInst>(I) || isa<InsertElementInst>(I) || 443245431Sdim isa<ExtractElementInst>(I) || 444245431Sdim isa<ShuffleVectorInst>(I)); 445245431Sdim if (!HoistableKind) 446245431Sdim return false; 447245431Sdim 448245431Sdim return isSafeToExecuteUnconditionally(I); 449193323Sed} 450193323Sed 451193323Sed/// isNotUsedInLoop - Return true if the only users of this instruction are 452193323Sed/// outside of the loop. If this is true, we can sink the instruction to the 453193323Sed/// exit blocks of the loop. 454193323Sed/// 455193323Sedbool LICM::isNotUsedInLoop(Instruction &I) { 456193323Sed for (Value::use_iterator UI = I.use_begin(), E = I.use_end(); UI != E; ++UI) { 457193323Sed Instruction *User = cast<Instruction>(*UI); 458193323Sed if (PHINode *PN = dyn_cast<PHINode>(User)) { 459193323Sed // PHI node uses occur in predecessor blocks! 460193323Sed for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 461193323Sed if (PN->getIncomingValue(i) == &I) 462193323Sed if (CurLoop->contains(PN->getIncomingBlock(i))) 463193323Sed return false; 464201360Srdivacky } else if (CurLoop->contains(User)) { 465193323Sed return false; 466193323Sed } 467193323Sed } 468193323Sed return true; 469193323Sed} 470193323Sed 471193323Sed 472193323Sed/// sink - When an instruction is found to only be used outside of the loop, 473193323Sed/// this function moves it to the exit blocks and patches up SSA form as needed. 474193323Sed/// This method is guaranteed to remove the original instruction from its 475193323Sed/// position, and may either delete it or move it to outside of the loop. 476193323Sed/// 477193323Sedvoid LICM::sink(Instruction &I) { 478212904Sdim DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n"); 479193323Sed 480193323Sed SmallVector<BasicBlock*, 8> ExitBlocks; 481212904Sdim CurLoop->getUniqueExitBlocks(ExitBlocks); 482193323Sed 483193323Sed if (isa<LoadInst>(I)) ++NumMovedLoads; 484193323Sed else if (isa<CallInst>(I)) ++NumMovedCalls; 485193323Sed ++NumSunk; 486193323Sed Changed = true; 487193323Sed 488193323Sed // The case where there is only a single exit node of this loop is common 489193323Sed // enough that we handle it as a special (more efficient) case. It is more 490193323Sed // efficient to handle because there are no PHI nodes that need to be placed. 491193323Sed if (ExitBlocks.size() == 1) { 492223017Sdim if (!DT->dominates(I.getParent(), ExitBlocks[0])) { 493193323Sed // Instruction is not used, just delete it. 494193323Sed CurAST->deleteValue(&I); 495198090Srdivacky // If I has users in unreachable blocks, eliminate. 496198090Srdivacky // If I is not void type then replaceAllUsesWith undef. 497198090Srdivacky // This allows ValueHandlers and custom metadata to adjust itself. 498212904Sdim if (!I.use_empty()) 499198090Srdivacky I.replaceAllUsesWith(UndefValue::get(I.getType())); 500193323Sed I.eraseFromParent(); 501193323Sed } else { 502193323Sed // Move the instruction to the start of the exit block, after any PHI 503193323Sed // nodes in it. 504226890Sdim I.moveBefore(ExitBlocks[0]->getFirstInsertionPt()); 505212904Sdim 506212904Sdim // This instruction is no longer in the AST for the current loop, because 507212904Sdim // we just sunk it out of the loop. If we just sunk it into an outer 508212904Sdim // loop, we will rediscover the operation when we process it. 509212904Sdim CurAST->deleteValue(&I); 510193323Sed } 511212904Sdim return; 512212904Sdim } 513224145Sdim 514212904Sdim if (ExitBlocks.empty()) { 515193323Sed // The instruction is actually dead if there ARE NO exit blocks. 516193323Sed CurAST->deleteValue(&I); 517198090Srdivacky // If I has users in unreachable blocks, eliminate. 518198090Srdivacky // If I is not void type then replaceAllUsesWith undef. 519198090Srdivacky // This allows ValueHandlers and custom metadata to adjust itself. 520212904Sdim if (!I.use_empty()) 521198090Srdivacky I.replaceAllUsesWith(UndefValue::get(I.getType())); 522193323Sed I.eraseFromParent(); 523212904Sdim return; 524212904Sdim } 525224145Sdim 526212904Sdim // Otherwise, if we have multiple exits, use the SSAUpdater to do all of the 527212904Sdim // hard work of inserting PHI nodes as necessary. 528212904Sdim SmallVector<PHINode*, 8> NewPHIs; 529212904Sdim SSAUpdater SSA(&NewPHIs); 530224145Sdim 531212904Sdim if (!I.use_empty()) 532212904Sdim SSA.Initialize(I.getType(), I.getName()); 533224145Sdim 534212904Sdim // Insert a copy of the instruction in each exit block of the loop that is 535212904Sdim // dominated by the instruction. Each exit block is known to only be in the 536212904Sdim // ExitBlocks list once. 537212904Sdim BasicBlock *InstOrigBB = I.getParent(); 538212904Sdim unsigned NumInserted = 0; 539224145Sdim 540212904Sdim for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 541212904Sdim BasicBlock *ExitBlock = ExitBlocks[i]; 542224145Sdim 543218893Sdim if (!DT->dominates(InstOrigBB, ExitBlock)) 544212904Sdim continue; 545224145Sdim 546212904Sdim // Insert the code after the last PHI node. 547226890Sdim BasicBlock::iterator InsertPt = ExitBlock->getFirstInsertionPt(); 548224145Sdim 549212904Sdim // If this is the first exit block processed, just move the original 550212904Sdim // instruction, otherwise clone the original instruction and insert 551212904Sdim // the copy. 552212904Sdim Instruction *New; 553212904Sdim if (NumInserted++ == 0) { 554212904Sdim I.moveBefore(InsertPt); 555212904Sdim New = &I; 556212904Sdim } else { 557212904Sdim New = I.clone(); 558212904Sdim if (!I.getName().empty()) 559212904Sdim New->setName(I.getName()+".le"); 560212904Sdim ExitBlock->getInstList().insert(InsertPt, New); 561193323Sed } 562224145Sdim 563212904Sdim // Now that we have inserted the instruction, inform SSAUpdater. 564212904Sdim if (!I.use_empty()) 565212904Sdim SSA.AddAvailableValue(ExitBlock, New); 566193323Sed } 567224145Sdim 568212904Sdim // If the instruction doesn't dominate any exit blocks, it must be dead. 569212904Sdim if (NumInserted == 0) { 570212904Sdim CurAST->deleteValue(&I); 571212904Sdim if (!I.use_empty()) 572212904Sdim I.replaceAllUsesWith(UndefValue::get(I.getType())); 573212904Sdim I.eraseFromParent(); 574212904Sdim return; 575212904Sdim } 576224145Sdim 577212904Sdim // Next, rewrite uses of the instruction, inserting PHI nodes as needed. 578212904Sdim for (Value::use_iterator UI = I.use_begin(), UE = I.use_end(); UI != UE; ) { 579212904Sdim // Grab the use before incrementing the iterator. 580212904Sdim Use &U = UI.getUse(); 581212904Sdim // Increment the iterator before removing the use from the list. 582212904Sdim ++UI; 583212904Sdim SSA.RewriteUseAfterInsertions(U); 584212904Sdim } 585224145Sdim 586212904Sdim // Update CurAST for NewPHIs if I had pointer type. 587212904Sdim if (I.getType()->isPointerTy()) 588212904Sdim for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) 589212904Sdim CurAST->copyValue(&I, NewPHIs[i]); 590224145Sdim 591212904Sdim // Finally, remove the instruction from CurAST. It is no longer in the loop. 592212904Sdim CurAST->deleteValue(&I); 593193323Sed} 594193323Sed 595193323Sed/// hoist - When an instruction is found to only use loop invariant operands 596193323Sed/// that is safe to hoist, this instruction is called to do the dirty work. 597193323Sed/// 598193323Sedvoid LICM::hoist(Instruction &I) { 599202375Srdivacky DEBUG(dbgs() << "LICM hoisting to " << Preheader->getName() << ": " 600198090Srdivacky << I << "\n"); 601193323Sed 602212904Sdim // Move the new node to the Preheader, before its terminator. 603212904Sdim I.moveBefore(Preheader->getTerminator()); 604193323Sed 605193323Sed if (isa<LoadInst>(I)) ++NumMovedLoads; 606193323Sed else if (isa<CallInst>(I)) ++NumMovedCalls; 607193323Sed ++NumHoisted; 608193323Sed Changed = true; 609193323Sed} 610193323Sed 611193323Sed/// isSafeToExecuteUnconditionally - Only sink or hoist an instruction if it is 612193323Sed/// not a trapping instruction or if it is a trapping instruction and is 613193323Sed/// guaranteed to execute. 614193323Sed/// 615193323Sedbool LICM::isSafeToExecuteUnconditionally(Instruction &Inst) { 616193323Sed // If it is not a trapping instruction, it is always safe to hoist. 617235633Sdim if (isSafeToSpeculativelyExecute(&Inst)) 618198090Srdivacky return true; 619193323Sed 620226890Sdim return isGuaranteedToExecute(Inst); 621226890Sdim} 622226890Sdim 623226890Sdimbool LICM::isGuaranteedToExecute(Instruction &Inst) { 624245431Sdim 625245431Sdim // Somewhere in this loop there is an instruction which may throw and make us 626245431Sdim // exit the loop. 627245431Sdim if (MayThrow) 628245431Sdim return false; 629245431Sdim 630193323Sed // Otherwise we have to check to make sure that the instruction dominates all 631193323Sed // of the exit blocks. If it doesn't, then there is a path out of the loop 632193323Sed // which does not execute this instruction, so we can't hoist it. 633193323Sed 634193323Sed // If the instruction is in the header block for the loop (which is very 635193323Sed // common), it is always guaranteed to dominate the exit blocks. Since this 636193323Sed // is a common case, and can save some work, check it now. 637193323Sed if (Inst.getParent() == CurLoop->getHeader()) 638193323Sed return true; 639193323Sed 640193323Sed // Get the exit blocks for the current loop. 641193323Sed SmallVector<BasicBlock*, 8> ExitBlocks; 642193323Sed CurLoop->getExitBlocks(ExitBlocks); 643193323Sed 644218893Sdim // Verify that the block dominates each of the exit blocks of the loop. 645193323Sed for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) 646218893Sdim if (!DT->dominates(Inst.getParent(), ExitBlocks[i])) 647193323Sed return false; 648193323Sed 649245431Sdim // As a degenerate case, if the loop is statically infinite then we haven't 650245431Sdim // proven anything since there are no exit blocks. 651245431Sdim if (ExitBlocks.empty()) 652245431Sdim return false; 653245431Sdim 654193323Sed return true; 655193323Sed} 656193323Sed 657218893Sdimnamespace { 658218893Sdim class LoopPromoter : public LoadAndStorePromoter { 659218893Sdim Value *SomePtr; // Designated pointer to store to. 660218893Sdim SmallPtrSet<Value*, 4> &PointerMustAliases; 661218893Sdim SmallVectorImpl<BasicBlock*> &LoopExitBlocks; 662245431Sdim SmallVectorImpl<Instruction*> &LoopInsertPts; 663218893Sdim AliasSetTracker &AST; 664223017Sdim DebugLoc DL; 665224145Sdim int Alignment; 666218893Sdim public: 667218893Sdim LoopPromoter(Value *SP, 668218893Sdim const SmallVectorImpl<Instruction*> &Insts, SSAUpdater &S, 669218893Sdim SmallPtrSet<Value*, 4> &PMA, 670245431Sdim SmallVectorImpl<BasicBlock*> &LEB, 671245431Sdim SmallVectorImpl<Instruction*> &LIP, 672245431Sdim AliasSetTracker &ast, DebugLoc dl, int alignment) 673224145Sdim : LoadAndStorePromoter(Insts, S), SomePtr(SP), 674245431Sdim PointerMustAliases(PMA), LoopExitBlocks(LEB), LoopInsertPts(LIP), 675245431Sdim AST(ast), DL(dl), Alignment(alignment) {} 676224145Sdim 677218893Sdim virtual bool isInstInList(Instruction *I, 678218893Sdim const SmallVectorImpl<Instruction*> &) const { 679218893Sdim Value *Ptr; 680218893Sdim if (LoadInst *LI = dyn_cast<LoadInst>(I)) 681218893Sdim Ptr = LI->getOperand(0); 682218893Sdim else 683218893Sdim Ptr = cast<StoreInst>(I)->getPointerOperand(); 684218893Sdim return PointerMustAliases.count(Ptr); 685218893Sdim } 686224145Sdim 687218893Sdim virtual void doExtraRewritesBeforeFinalDeletion() const { 688218893Sdim // Insert stores after in the loop exit blocks. Each exit block gets a 689218893Sdim // store of the live-out values that feed them. Since we've already told 690218893Sdim // the SSA updater about the defs in the loop and the preheader 691218893Sdim // definition, it is all set and we can start using it. 692218893Sdim for (unsigned i = 0, e = LoopExitBlocks.size(); i != e; ++i) { 693218893Sdim BasicBlock *ExitBlock = LoopExitBlocks[i]; 694218893Sdim Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock); 695245431Sdim Instruction *InsertPos = LoopInsertPts[i]; 696223017Sdim StoreInst *NewSI = new StoreInst(LiveInValue, SomePtr, InsertPos); 697224145Sdim NewSI->setAlignment(Alignment); 698223017Sdim NewSI->setDebugLoc(DL); 699218893Sdim } 700218893Sdim } 701218893Sdim 702218893Sdim virtual void replaceLoadWithValue(LoadInst *LI, Value *V) const { 703218893Sdim // Update alias analysis. 704218893Sdim AST.copyValue(LI, V); 705218893Sdim } 706218893Sdim virtual void instructionDeleted(Instruction *I) const { 707218893Sdim AST.deleteValue(I); 708218893Sdim } 709218893Sdim }; 710218893Sdim} // end anon namespace 711218893Sdim 712212904Sdim/// PromoteAliasSet - Try to promote memory values to scalars by sinking 713193323Sed/// stores out of the loop and moving loads to before the loop. We do this by 714193323Sed/// looping over the stores in the loop, looking for stores to Must pointers 715212904Sdim/// which are loop invariant. 716193323Sed/// 717245431Sdimvoid LICM::PromoteAliasSet(AliasSet &AS, 718245431Sdim SmallVectorImpl<BasicBlock*> &ExitBlocks, 719245431Sdim SmallVectorImpl<Instruction*> &InsertPts) { 720212904Sdim // We can promote this alias set if it has a store, if it is a "Must" alias 721212904Sdim // set, if the pointer is loop invariant, and if we are not eliminating any 722212904Sdim // volatile loads or stores. 723212904Sdim if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() || 724212904Sdim AS.isVolatile() || !CurLoop->isLoopInvariant(AS.begin()->getValue())) 725212904Sdim return; 726224145Sdim 727212904Sdim assert(!AS.empty() && 728212904Sdim "Must alias set should have at least one pointer element in it!"); 729212904Sdim Value *SomePtr = AS.begin()->getValue(); 730193323Sed 731212904Sdim // It isn't safe to promote a load/store from the loop if the load/store is 732212904Sdim // conditional. For example, turning: 733193323Sed // 734212904Sdim // for () { if (c) *P += 1; } 735193323Sed // 736212904Sdim // into: 737212904Sdim // 738212904Sdim // tmp = *P; for () { if (c) tmp +=1; } *P = tmp; 739212904Sdim // 740212904Sdim // is not safe, because *P may only be valid to access if 'c' is true. 741224145Sdim // 742212904Sdim // It is safe to promote P if all uses are direct load/stores and if at 743212904Sdim // least one is guaranteed to be executed. 744212904Sdim bool GuaranteedToExecute = false; 745224145Sdim 746212904Sdim SmallVector<Instruction*, 64> LoopUses; 747212904Sdim SmallPtrSet<Value*, 4> PointerMustAliases; 748193323Sed 749224145Sdim // We start with an alignment of one and try to find instructions that allow 750224145Sdim // us to prove better alignment. 751224145Sdim unsigned Alignment = 1; 752224145Sdim 753212904Sdim // Check that all of the pointers in the alias set have the same type. We 754212904Sdim // cannot (yet) promote a memory location that is loaded and stored in 755212904Sdim // different sizes. 756212904Sdim for (AliasSet::iterator ASI = AS.begin(), E = AS.end(); ASI != E; ++ASI) { 757212904Sdim Value *ASIV = ASI->getValue(); 758212904Sdim PointerMustAliases.insert(ASIV); 759224145Sdim 760193323Sed // Check that all of the pointers in the alias set have the same type. We 761193323Sed // cannot (yet) promote a memory location that is loaded and stored in 762193323Sed // different sizes. 763212904Sdim if (SomePtr->getType() != ASIV->getType()) 764212904Sdim return; 765224145Sdim 766212904Sdim for (Value::use_iterator UI = ASIV->use_begin(), UE = ASIV->use_end(); 767193323Sed UI != UE; ++UI) { 768212904Sdim // Ignore instructions that are outside the loop. 769193323Sed Instruction *Use = dyn_cast<Instruction>(*UI); 770201360Srdivacky if (!Use || !CurLoop->contains(Use)) 771193323Sed continue; 772224145Sdim 773212904Sdim // If there is an non-load/store instruction in the loop, we can't promote 774212904Sdim // it. 775224145Sdim if (LoadInst *load = dyn_cast<LoadInst>(Use)) { 776226890Sdim assert(!load->isVolatile() && "AST broken"); 777226890Sdim if (!load->isSimple()) 778226890Sdim return; 779224145Sdim } else if (StoreInst *store = dyn_cast<StoreInst>(Use)) { 780218893Sdim // Stores *of* the pointer are not interesting, only stores *to* the 781218893Sdim // pointer. 782218893Sdim if (Use->getOperand(1) != ASIV) 783218893Sdim continue; 784226890Sdim assert(!store->isVolatile() && "AST broken"); 785226890Sdim if (!store->isSimple()) 786226890Sdim return; 787226890Sdim 788226890Sdim // Note that we only check GuaranteedToExecute inside the store case 789226890Sdim // so that we do not introduce stores where they did not exist before 790226890Sdim // (which would break the LLVM concurrency model). 791226890Sdim 792226890Sdim // If the alignment of this instruction allows us to specify a more 793226890Sdim // restrictive (and performant) alignment and if we are sure this 794226890Sdim // instruction will be executed, update the alignment. 795226890Sdim // Larger is better, with the exception of 0 being the best alignment. 796226890Sdim unsigned InstAlignment = store->getAlignment(); 797226890Sdim if ((InstAlignment > Alignment || InstAlignment == 0) 798226890Sdim && (Alignment != 0)) 799226890Sdim if (isGuaranteedToExecute(*Use)) { 800226890Sdim GuaranteedToExecute = true; 801226890Sdim Alignment = InstAlignment; 802226890Sdim } 803226890Sdim 804226890Sdim if (!GuaranteedToExecute) 805226890Sdim GuaranteedToExecute = isGuaranteedToExecute(*Use); 806226890Sdim 807212904Sdim } else 808212904Sdim return; // Not a load or store. 809224145Sdim 810212904Sdim LoopUses.push_back(Use); 811193323Sed } 812212904Sdim } 813224145Sdim 814212904Sdim // If there isn't a guaranteed-to-execute instruction, we can't promote. 815212904Sdim if (!GuaranteedToExecute) 816212904Sdim return; 817224145Sdim 818212904Sdim // Otherwise, this is safe to promote, lets do it! 819224145Sdim DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " <<*SomePtr<<'\n'); 820212904Sdim Changed = true; 821212904Sdim ++NumPromoted; 822193323Sed 823223017Sdim // Grab a debug location for the inserted loads/stores; given that the 824223017Sdim // inserted loads/stores have little relation to the original loads/stores, 825223017Sdim // this code just arbitrarily picks a location from one, since any debug 826223017Sdim // location is better than none. 827223017Sdim DebugLoc DL = LoopUses[0]->getDebugLoc(); 828223017Sdim 829245431Sdim // Figure out the loop exits and their insertion points, if this is the 830245431Sdim // first promotion. 831245431Sdim if (ExitBlocks.empty()) { 832245431Sdim CurLoop->getUniqueExitBlocks(ExitBlocks); 833245431Sdim InsertPts.resize(ExitBlocks.size()); 834245431Sdim for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) 835245431Sdim InsertPts[i] = ExitBlocks[i]->getFirstInsertionPt(); 836245431Sdim } 837224145Sdim 838212904Sdim // We use the SSAUpdater interface to insert phi nodes as required. 839212904Sdim SmallVector<PHINode*, 16> NewPHIs; 840212904Sdim SSAUpdater SSA(&NewPHIs); 841218893Sdim LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks, 842245431Sdim InsertPts, *CurAST, DL, Alignment); 843224145Sdim 844218893Sdim // Set up the preheader to have a definition of the value. It is the live-out 845218893Sdim // value from the preheader that uses in the loop will use. 846218893Sdim LoadInst *PreheaderLoad = 847218893Sdim new LoadInst(SomePtr, SomePtr->getName()+".promoted", 848218893Sdim Preheader->getTerminator()); 849224145Sdim PreheaderLoad->setAlignment(Alignment); 850223017Sdim PreheaderLoad->setDebugLoc(DL); 851218893Sdim SSA.AddAvailableValue(Preheader, PreheaderLoad); 852212904Sdim 853218893Sdim // Rewrite all the loads in the loop and remember all the definitions from 854218893Sdim // stores in the loop. 855218893Sdim Promoter.run(LoopUses); 856221345Sdim 857221345Sdim // If the SSAUpdater didn't use the load in the preheader, just zap it now. 858221345Sdim if (PreheaderLoad->use_empty()) 859221345Sdim PreheaderLoad->eraseFromParent(); 860193323Sed} 861193323Sed 862212904Sdim 863193323Sed/// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info. 864193323Sedvoid LICM::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L) { 865212904Sdim AliasSetTracker *AST = LoopToAliasSetMap.lookup(L); 866193323Sed if (!AST) 867193323Sed return; 868193323Sed 869193323Sed AST->copyValue(From, To); 870193323Sed} 871193323Sed 872193323Sed/// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias 873193323Sed/// set. 874193323Sedvoid LICM::deleteAnalysisValue(Value *V, Loop *L) { 875212904Sdim AliasSetTracker *AST = LoopToAliasSetMap.lookup(L); 876193323Sed if (!AST) 877193323Sed return; 878193323Sed 879193323Sed AST->deleteValue(V); 880193323Sed} 881