X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FLoopUnswitch.cpp;h=95d7f8a3beda23b180d350f3835f2e2c187e639e;hp=ad03cded2279601366c682c2118b77ab4171bdc6;hb=2027fcbfdaea79a5486db80a4da7407f50f7f4ec;hpb=f020cb2f752306fa733455085f577e8043de167f diff --git a/lib/Transforms/Scalar/LoopUnswitch.cpp b/lib/Transforms/Scalar/LoopUnswitch.cpp index ad03cded227..95d7f8a3bed 100644 --- a/lib/Transforms/Scalar/LoopUnswitch.cpp +++ b/lib/Transforms/Scalar/LoopUnswitch.cpp @@ -30,6 +30,7 @@ #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/GlobalsModRef.h" #include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/CodeMetrics.h" #include "llvm/Analysis/InstructionSimplify.h" @@ -37,6 +38,10 @@ #include "llvm/Analysis/LoopPass.h" #include "llvm/Analysis/ScalarEvolution.h" #include "llvm/Analysis/TargetTransformInfo.h" +#include "llvm/Analysis/BlockFrequencyInfoImpl.h" +#include "llvm/Analysis/BlockFrequencyInfo.h" +#include "llvm/Analysis/BranchProbabilityInfo.h" +#include "llvm/Support/BranchProbability.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Dominators.h" @@ -70,6 +75,19 @@ static cl::opt Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"), cl::init(100), cl::Hidden); +static cl::opt +LoopUnswitchWithBlockFrequency("loop-unswitch-with-block-frequency", + cl::init(false), cl::Hidden, + cl::desc("Enable the use of the block frequency analysis to access PGO " + "heuristics to minimize code growth in cold regions.")); + +static cl::opt +ColdnessThreshold("loop-unswitch-coldness-threshold", cl::init(1), cl::Hidden, + cl::desc("Coldness threshold in percentage. The loop header frequency " + "(relative to the entry frequency) is compared with this " + "threshold to determine if non-trivial unswitching should be " + "enabled.")); + namespace { class LUAnalysisCache { @@ -148,12 +166,19 @@ namespace { LPPassManager *LPM; AssumptionCache *AC; - // LoopProcessWorklist - Used to check if second loop needs processing - // after RewriteLoopBodyWithConditionConstant rewrites first loop. + // Used to check if second loop needs processing after + // RewriteLoopBodyWithConditionConstant rewrites first loop. std::vector LoopProcessWorklist; LUAnalysisCache BranchesInfo; + bool EnabledPGO; + + // BFI and ColdEntryFreq are only used when PGO and + // LoopUnswitchWithBlockFrequency are enabled. + BlockFrequencyInfo BFI; + BlockFrequency ColdEntryFreq; + bool OptimizeForSize; bool redoLoop; @@ -192,9 +217,11 @@ namespace { AU.addPreserved(); AU.addRequiredID(LCSSAID); AU.addPreservedID(LCSSAID); + AU.addRequired(); AU.addPreserved(); - AU.addPreserved(); + AU.addPreserved(); AU.addRequired(); + AU.addPreserved(); } private: @@ -210,7 +237,8 @@ namespace { /// Split all of the edges from inside the loop to their exit blocks. /// Update the appropriate Phi nodes as we do so. - void SplitExitEdges(Loop *L, const SmallVectorImpl &ExitBlocks); + void SplitExitEdges(Loop *L, + const SmallVectorImpl &ExitBlocks); bool TryTrivialLoopUnswitch(bool &Changed); @@ -366,9 +394,8 @@ Pass *llvm::createLoopUnswitchPass(bool Os) { return new LoopUnswitch(Os); } -/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is -/// invariant in the loop, or has an invariant piece, return the invariant. -/// Otherwise, return null. +/// Cond is a condition that occurs in L. If it is invariant in the loop, or has +/// an invariant piece, return the invariant. Otherwise, return null. static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) { // We started analyze new instruction, increment scanned instructions counter. @@ -410,11 +437,23 @@ bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) { *L->getHeader()->getParent()); LI = &getAnalysis().getLoopInfo(); LPM = &LPM_Ref; - DominatorTreeWrapperPass *DTWP = - getAnalysisIfAvailable(); - DT = DTWP ? &DTWP->getDomTree() : nullptr; + DT = &getAnalysis().getDomTree(); currentLoop = L; Function *F = currentLoop->getHeader()->getParent(); + + EnabledPGO = F->getEntryCount().hasValue(); + + if (LoopUnswitchWithBlockFrequency && EnabledPGO) { + BranchProbabilityInfo BPI(*F, *LI); + BFI.calculate(*L->getHeader()->getParent(), BPI, *LI); + + // Use BranchProbability to compute a minimum frequency based on + // function entry baseline frequency. Loops with headers below this + // frequency are considered as cold. + const BranchProbability ColdProb(ColdnessThreshold, 100); + ColdEntryFreq = BlockFrequency(BFI.getEntryFreq()) * ColdProb; + } + bool Changed = false; do { assert(currentLoop->isLCSSAForm(*DT)); @@ -422,16 +461,13 @@ bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) { Changed |= processCurrentLoop(); } while(redoLoop); - if (Changed) { - // FIXME: Reconstruct dom info, because it is not preserved properly. - if (DT) - DT->recalculate(*F); - } + // FIXME: Reconstruct dom info, because it is not preserved properly. + if (Changed) + DT->recalculate(*F); return Changed; } -/// processCurrentLoop - Do actual work and unswitch loop if possible -/// and profitable. +/// Do actual work and unswitch loop if possible and profitable. bool LoopUnswitch::processCurrentLoop() { bool Changed = false; @@ -451,21 +487,48 @@ bool LoopUnswitch::processCurrentLoop() { LLVMContext &Context = loopHeader->getContext(); - // Probably we reach the quota of branches for this loop. If so - // stop unswitching. + // Analyze loop cost, and stop unswitching if loop content can not be duplicated. if (!BranchesInfo.countLoop( currentLoop, getAnalysis().getTTI( *currentLoop->getHeader()->getParent()), AC)) return false; - // Trivial unswitch condition can only occur at loop header basic block because - // that condition needs to control whether or not the loop does anything at all. // Try trivial unswitch first before loop over other basic blocks in the loop. if (TryTrivialLoopUnswitch(Changed)) { return true; } + // Do not unswitch loops containing convergent operations, as we might be + // making them control dependent on the unswitch value when they were not + // before. + // FIXME: This could be refined to only bail if the convergent operation is + // not already control-dependent on the unswitch value. + for (const auto BB : currentLoop->blocks()) { + for (auto &I : *BB) { + auto CS = CallSite(&I); + if (!CS) continue; + if (CS.hasFnAttr(Attribute::Convergent)) + return false; + } + } + + // Do not do non-trivial unswitch while optimizing for size. + // FIXME: Use Function::optForSize(). + if (OptimizeForSize || + loopHeader->getParent()->hasFnAttribute(Attribute::OptimizeForSize)) + return false; + + if (LoopUnswitchWithBlockFrequency && EnabledPGO) { + // Compute the weighted frequency of the hottest block in the + // loop (loopHeader in this case since inner loops should be + // processed before outer loop). If it is less than ColdFrequency, + // we should not unswitch. + BlockFrequency LoopEntryFreq = BFI.getBlockFreq(loopHeader); + if (LoopEntryFreq < ColdEntryFreq) + return false; + } + // Loop over all of the basic blocks in the loop. If we find an interior // block that is branching on a loop-invariant condition, we can unswitch this // loop. @@ -534,8 +597,8 @@ bool LoopUnswitch::processCurrentLoop() { return Changed; } -/// isTrivialLoopExitBlock - Check to see if all paths from BB exit the -/// loop with no side effects (including infinite loops). +/// Check to see if all paths from BB exit the loop with no side effects +/// (including infinite loops). /// /// If true, we return true and set ExitBB to the block we /// exit through. @@ -572,9 +635,9 @@ static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB, return true; } -/// isTrivialLoopExitBlock - Return true if the specified block unconditionally -/// leads to an exit from the specified loop, and has no side-effects in the -/// process. If so, return the block that is exited to, otherwise return null. +/// Return true if the specified block unconditionally leads to an exit from +/// the specified loop, and has no side-effects in the process. If so, return +/// the block that is exited to, otherwise return null. static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) { std::set Visited; Visited.insert(L->getHeader()); // Branches to header make infinite loops. @@ -584,13 +647,11 @@ static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) { return nullptr; } -/// UnswitchIfProfitable - We have found that we can unswitch currentLoop when -/// LoopCond == Val to simplify the loop. If we decide that this is profitable, +/// We have found that we can unswitch currentLoop when LoopCond == Val to +/// simplify the loop. If we decide that this is profitable, /// unswitch the loop, reprocess the pieces, then return true. bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val, TerminatorInst *TI) { - Function *F = loopHeader->getParent(); - // Check to see if it would be profitable to unswitch current loop. if (!BranchesInfo.CostAllowsUnswitching()) { DEBUG(dbgs() << "NOT unswitching loop %" @@ -601,32 +662,27 @@ bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val, return false; } - // Do not do non-trivial unswitch while optimizing for size. - if (OptimizeForSize || F->hasFnAttribute(Attribute::OptimizeForSize)) - return false; - UnswitchNontrivialCondition(LoopCond, Val, currentLoop, TI); return true; } -/// CloneLoop - Recursively clone the specified loop and all of its children, +/// Recursively clone the specified loop and all of its children, /// mapping the blocks with the specified map. static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM, LoopInfo *LI, LPPassManager *LPM) { - Loop *New = new Loop(); - LPM->insertLoop(New, PL); + Loop &New = LPM->addLoop(PL); // Add all of the blocks in L to the new loop. for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); I != E; ++I) if (LI->getLoopFor(*I) == L) - New->addBasicBlockToLoop(cast(VM[*I]), *LI); + New.addBasicBlockToLoop(cast(VM[*I]), *LI); // Add all of the subloops to the new loop. for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) - CloneLoop(*I, New, VM, LI, LPM); + CloneLoop(*I, &New, VM, LI, LPM); - return New; + return &New; } static void copyMetadata(Instruction *DstInst, const Instruction *SrcInst, @@ -658,15 +714,15 @@ static void copyMetadata(Instruction *DstInst, const Instruction *SrcInst, } } // fallthrough. + case LLVMContext::MD_make_implicit: case LLVMContext::MD_dbg: DstInst->setMetadata(MD.first, MD.second); } } } -/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values -/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the -/// code immediately before InsertPt. +/// Emit a conditional branch on two values if LIC == Val, branch to TrueDst, +/// otherwise branch to FalseDest. Insert the code immediately before InsertPt. void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, BasicBlock *TrueDest, BasicBlock *FalseDest, @@ -696,11 +752,11 @@ void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, SplitCriticalEdge(BI, 1, Options); } -/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable -/// condition in it (a cond branch from its header block to its latch block, -/// where the path through the loop that doesn't execute its body has no -/// side-effects), unswitch it. This doesn't involve any code duplication, just -/// moving the conditional branch outside of the loop and updating loop info. +/// Given a loop that has a trivial unswitchable condition in it (a cond branch +/// from its header block to its latch block, where the path through the loop +/// that doesn't execute its body has no side-effects), unswitch it. This +/// doesn't involve any code duplication, just moving the conditional branch +/// outside of the loop and updating loop info. void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, BasicBlock *ExitBlock, TerminatorInst *TI) { @@ -724,7 +780,7 @@ void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, // without actually branching to it (the exit block should be dominated by the // loop header, not the preheader). assert(!L->contains(ExitBlock) && "Exit block is in the loop?"); - BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), DT, LI); + BasicBlock *NewExit = SplitBlock(ExitBlock, &ExitBlock->front(), DT, LI); // Okay, now we have a position to branch from and a position to branch to, // insert the new conditional branch. @@ -743,31 +799,73 @@ void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, ++NumTrivial; } -/// TryTrivialLoopUnswitch - Check if loop header block's terminator is a trivial -/// unswitch condition: that is, the condition controls whether or not the loop -/// does anything at all (which means it can only occur in loop header). If it is -/// a trivial condition, unswitching produces no code duplications (equivalently, -/// it produces a simpler loop and a new empty loop, which gets deleted). Therefore -/// always unswitch trivial condition. -/// +/// Check if the first non-constant condition starting from the loop header is +/// a trivial unswitch condition: that is, a condition controls whether or not +/// the loop does anything at all. If it is a trivial condition, unswitching +/// produces no code duplications (equivalently, it produces a simpler loop and +/// a new empty loop, which gets deleted). Therefore always unswitch trivial +/// condition. bool LoopUnswitch::TryTrivialLoopUnswitch(bool &Changed) { - BasicBlock *Header = currentLoop->getHeader(); - TerminatorInst *HeaderTerm = Header->getTerminator(); - LLVMContext &Context = Header->getContext(); - - // Check if this loop will execute any side-effecting instructions (e.g. - // stores, calls, volatile loads) in the part of the loop that the code - // *would* execute. Check the header first. - for (BasicBlock::iterator I :*Header) - if (I->mayHaveSideEffects()) + BasicBlock *CurrentBB = currentLoop->getHeader(); + TerminatorInst *CurrentTerm = CurrentBB->getTerminator(); + LLVMContext &Context = CurrentBB->getContext(); + + // If loop header has only one reachable successor (currently via an + // unconditional branch or constant foldable conditional branch, but + // should also consider adding constant foldable switch instruction in + // future), we should keep looking for trivial condition candidates in + // the successor as well. An alternative is to constant fold conditions + // and merge successors into loop header (then we only need to check header's + // terminator). The reason for not doing this in LoopUnswitch pass is that + // it could potentially break LoopPassManager's invariants. Folding dead + // branches could either eliminate the current loop or make other loops + // unreachable. LCSSA form might also not be preserved after deleting + // branches. The following code keeps traversing loop header's successors + // until it finds the trivial condition candidate (condition that is not a + // constant). Since unswitching generates branches with constant conditions, + // this scenario could be very common in practice. + SmallSet Visited; + + while (true) { + // If we exit loop or reach a previous visited block, then + // we can not reach any trivial condition candidates (unfoldable + // branch instructions or switch instructions) and no unswitch + // can happen. Exit and return false. + if (!currentLoop->contains(CurrentBB) || !Visited.insert(CurrentBB).second) return false; + // Check if this loop will execute any side-effecting instructions (e.g. + // stores, calls, volatile loads) in the part of the loop that the code + // *would* execute. Check the header first. + for (Instruction &I : *CurrentBB) + if (I.mayHaveSideEffects()) + return false; + + // FIXME: add check for constant foldable switch instructions. + if (BranchInst *BI = dyn_cast(CurrentTerm)) { + if (BI->isUnconditional()) { + CurrentBB = BI->getSuccessor(0); + } else if (BI->getCondition() == ConstantInt::getTrue(Context)) { + CurrentBB = BI->getSuccessor(0); + } else if (BI->getCondition() == ConstantInt::getFalse(Context)) { + CurrentBB = BI->getSuccessor(1); + } else { + // Found a trivial condition candidate: non-foldable conditional branch. + break; + } + } else { + break; + } + + CurrentTerm = CurrentBB->getTerminator(); + } + // CondVal is the condition that controls the trivial condition. // LoopExitBB is the BasicBlock that loop exits when meets trivial condition. Constant *CondVal = nullptr; BasicBlock *LoopExitBB = nullptr; - if (BranchInst *BI = dyn_cast(HeaderTerm)) { + if (BranchInst *BI = dyn_cast(CurrentTerm)) { // If this isn't branching on an invariant condition, we can't unswitch it. if (!BI->isConditional()) return false; @@ -792,15 +890,16 @@ bool LoopUnswitch::TryTrivialLoopUnswitch(bool &Changed) { CondVal = ConstantInt::getFalse(Context); } - // If we didn't find a single unique LoopExit block, or if the loop exit block - // contains phi nodes, this isn't trivial. + // If we didn't find a single unique LoopExit block, or if the loop exit + // block contains phi nodes, this isn't trivial. if (!LoopExitBB || isa(LoopExitBB->begin())) return false; // Can't handle this. - UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB, HeaderTerm); + UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB, + CurrentTerm); ++NumBranches; return true; - } else if (SwitchInst *SI = dyn_cast(HeaderTerm)) { + } else if (SwitchInst *SI = dyn_cast(CurrentTerm)) { // If this isn't switching on an invariant condition, we can't unswitch it. Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), currentLoop, Changed); @@ -834,20 +933,21 @@ bool LoopUnswitch::TryTrivialLoopUnswitch(bool &Changed) { } } - // If we didn't find a single unique LoopExit block, or if the loop exit block - // contains phi nodes, this isn't trivial. + // If we didn't find a single unique LoopExit block, or if the loop exit + // block contains phi nodes, this isn't trivial. if (!LoopExitBB || isa(LoopExitBB->begin())) return false; // Can't handle this. - UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB, nullptr); + UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB, + nullptr); ++NumSwitches; return true; } return false; } -/// SplitExitEdges - Split all of the edges from inside the loop to their exit -/// blocks. Update the appropriate Phi nodes as we do so. +/// Split all of the edges from inside the loop to their exit blocks. +/// Update the appropriate Phi nodes as we do so. void LoopUnswitch::SplitExitEdges(Loop *L, const SmallVectorImpl &ExitBlocks){ @@ -863,9 +963,9 @@ void LoopUnswitch::SplitExitEdges(Loop *L, } } -/// UnswitchNontrivialCondition - We determined that the loop is profitable -/// to unswitch when LIC equal Val. Split it into loop versions and test the -/// condition outside of either loop. Return the loops created as Out1/Out2. +/// We determined that the loop is profitable to unswitch when LIC equal Val. +/// Split it into loop versions and test the condition outside of either loop. +/// Return the loops created as Out1/Out2. void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, Loop *L, TerminatorInst *TI) { Function *F = loopHeader->getParent(); @@ -874,8 +974,8 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, << " blocks] in Function " << F->getName() << " when '" << *Val << "' == " << *LIC << "\n"); - if (ScalarEvolution *SE = getAnalysisIfAvailable()) - SE->forgetLoop(L); + if (auto *SEWP = getAnalysisIfAvailable()) + SEWP->getSE().forgetLoop(L); LoopBlocks.clear(); NewBlocks.clear(); @@ -917,8 +1017,9 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, // Splice the newly inserted blocks into the function right before the // original preheader. - F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(), - NewBlocks[0], F->end()); + F->getBasicBlockList().splice(NewPreheader->getIterator(), + F->getBasicBlockList(), + NewBlocks[0]->getIterator(), F->end()); // FIXME: We could register any cloned assumptions instead of clearing the // whole function's cache. @@ -960,7 +1061,7 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, if (LandingPadInst *LPad = NewExit->getLandingPadInst()) { PHINode *PN = PHINode::Create(LPad->getType(), 0, "", - ExitSucc->getFirstInsertionPt()); + &*ExitSucc->getFirstInsertionPt()); for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc); I != E; ++I) { @@ -976,7 +1077,8 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i) for (BasicBlock::iterator I = NewBlocks[i]->begin(), E = NewBlocks[i]->end(); I != E; ++I) - RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries); + RemapInstruction(&*I, VMap, + RF_NoModuleLevelChanges | RF_IgnoreMissingEntries); // Rewrite the original preheader to select between versions of the loop. BranchInst *OldBR = cast(loopPreheader->getTerminator()); @@ -1010,8 +1112,7 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true); } -/// RemoveFromWorklist - Remove all instances of I from the worklist vector -/// specified. +/// Remove all instances of I from the worklist vector specified. static void RemoveFromWorklist(Instruction *I, std::vector &Worklist) { @@ -1019,7 +1120,7 @@ static void RemoveFromWorklist(Instruction *I, Worklist.end()); } -/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the +/// When we find that I really equals V, remove I from the /// program, replacing all uses with V and update the worklist. static void ReplaceUsesOfWith(Instruction *I, Value *V, std::vector &Worklist, @@ -1041,9 +1142,9 @@ static void ReplaceUsesOfWith(Instruction *I, Value *V, ++NumSimplify; } -// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has -// the value specified by Val in the specified loop, or we know it does NOT have -// that value. Rewrite any uses of LIC or of properties correlated to it. +/// We know either that the value LIC has the value specified by Val in the +/// specified loop, or we know it does NOT have that value. +/// Rewrite any uses of LIC or of properties correlated to it. void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, Constant *Val, bool IsEqual) { @@ -1154,18 +1255,16 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, // domtree here -- instead we force it to do a full recomputation // after the pass is complete -- but we do need to inform it of // new blocks. - if (DT) - DT->addNewBlock(Abort, NewSISucc); + DT->addNewBlock(Abort, NewSISucc); } SimplifyCode(Worklist, L); } -/// SimplifyCode - Okay, now that we have simplified some instructions in the -/// loop, walk over it and constant prop, dce, and fold control flow where -/// possible. Note that this is effectively a very simple loop-structure-aware -/// optimizer. During processing of this loop, L could very well be deleted, so -/// it must not be used. +/// Now that we have simplified some instructions in the loop, walk over it and +/// constant prop, dce, and fold control flow where possible. Note that this is +/// effectively a very simple loop-structure-aware optimizer. During processing +/// of this loop, L could very well be deleted, so it must not be used. /// /// FIXME: When the loop optimizer is more mature, separate this out to a new /// pass. @@ -1223,8 +1322,8 @@ void LoopUnswitch::SimplifyCode(std::vector &Worklist, Loop *L) { Succ->replaceAllUsesWith(Pred); // Move all of the successor contents from Succ to Pred. - Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(), - Succ->end()); + Pred->getInstList().splice(BI->getIterator(), Succ->getInstList(), + Succ->begin(), Succ->end()); LPM->deleteSimpleAnalysisValue(BI, L); BI->eraseFromParent(); RemoveFromWorklist(BI, Worklist);