| //===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass transforms loops that contain branches on loop-invariant conditions |
| // to have multiple loops. For example, it turns the left into the right code: |
| // |
| // for (...) if (lic) |
| // A for (...) |
| // if (lic) A; B; C |
| // B else |
| // C for (...) |
| // A; C |
| // |
| // This can increase the size of the code exponentially (doubling it every time |
| // a loop is unswitched) so we only unswitch if the resultant code will be |
| // smaller than a threshold. |
| // |
| // This pass expects LICM to be run before it to hoist invariant conditions out |
| // of the loop, to make the unswitching opportunity obvious. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/AssumptionCache.h" |
| #include "llvm/Analysis/CodeMetrics.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/LoopPass.h" |
| #include "llvm/Analysis/ScalarEvolution.h" |
| #include "llvm/Analysis/TargetTransformInfo.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/MDBuilder.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/Cloning.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include <algorithm> |
| #include <map> |
| #include <set> |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "loop-unswitch" |
| |
| STATISTIC(NumBranches, "Number of branches unswitched"); |
| STATISTIC(NumSwitches, "Number of switches unswitched"); |
| STATISTIC(NumSelects , "Number of selects unswitched"); |
| STATISTIC(NumTrivial , "Number of unswitches that are trivial"); |
| STATISTIC(NumSimplify, "Number of simplifications of unswitched code"); |
| STATISTIC(TotalInsts, "Total number of instructions analyzed"); |
| |
| // The specific value of 100 here was chosen based only on intuition and a |
| // few specific examples. |
| static cl::opt<unsigned> |
| Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"), |
| cl::init(100), cl::Hidden); |
| |
| namespace { |
| |
| class LUAnalysisCache { |
| |
| typedef DenseMap<const SwitchInst*, SmallPtrSet<const Value *, 8> > |
| UnswitchedValsMap; |
| |
| typedef UnswitchedValsMap::iterator UnswitchedValsIt; |
| |
| struct LoopProperties { |
| unsigned CanBeUnswitchedCount; |
| unsigned WasUnswitchedCount; |
| unsigned SizeEstimation; |
| UnswitchedValsMap UnswitchedVals; |
| }; |
| |
| // Here we use std::map instead of DenseMap, since we need to keep valid |
| // LoopProperties pointer for current loop for better performance. |
| typedef std::map<const Loop*, LoopProperties> LoopPropsMap; |
| typedef LoopPropsMap::iterator LoopPropsMapIt; |
| |
| LoopPropsMap LoopsProperties; |
| UnswitchedValsMap *CurLoopInstructions; |
| LoopProperties *CurrentLoopProperties; |
| |
| // A loop unswitching with an estimated cost above this threshold |
| // is not performed. MaxSize is turned into unswitching quota for |
| // the current loop, and reduced correspondingly, though note that |
| // the quota is returned by releaseMemory() when the loop has been |
| // processed, so that MaxSize will return to its previous |
| // value. So in most cases MaxSize will equal the Threshold flag |
| // when a new loop is processed. An exception to that is that |
| // MaxSize will have a smaller value while processing nested loops |
| // that were introduced due to loop unswitching of an outer loop. |
| // |
| // FIXME: The way that MaxSize works is subtle and depends on the |
| // pass manager processing loops and calling releaseMemory() in a |
| // specific order. It would be good to find a more straightforward |
| // way of doing what MaxSize does. |
| unsigned MaxSize; |
| |
| public: |
| LUAnalysisCache() |
| : CurLoopInstructions(nullptr), CurrentLoopProperties(nullptr), |
| MaxSize(Threshold) {} |
| |
| // Analyze loop. Check its size, calculate is it possible to unswitch |
| // it. Returns true if we can unswitch this loop. |
| bool countLoop(const Loop *L, const TargetTransformInfo &TTI, |
| AssumptionCache *AC); |
| |
| // Clean all data related to given loop. |
| void forgetLoop(const Loop *L); |
| |
| // Mark case value as unswitched. |
| // Since SI instruction can be partly unswitched, in order to avoid |
| // extra unswitching in cloned loops keep track all unswitched values. |
| void setUnswitched(const SwitchInst *SI, const Value *V); |
| |
| // Check was this case value unswitched before or not. |
| bool isUnswitched(const SwitchInst *SI, const Value *V); |
| |
| // Returns true if another unswitching could be done within the cost |
| // threshold. |
| bool CostAllowsUnswitching(); |
| |
| // Clone all loop-unswitch related loop properties. |
| // Redistribute unswitching quotas. |
| // Note, that new loop data is stored inside the VMap. |
| void cloneData(const Loop *NewLoop, const Loop *OldLoop, |
| const ValueToValueMapTy &VMap); |
| }; |
| |
| class LoopUnswitch : public LoopPass { |
| LoopInfo *LI; // Loop information |
| LPPassManager *LPM; |
| AssumptionCache *AC; |
| |
| // LoopProcessWorklist - Used to check if second loop needs processing |
| // after RewriteLoopBodyWithConditionConstant rewrites first loop. |
| std::vector<Loop*> LoopProcessWorklist; |
| |
| LUAnalysisCache BranchesInfo; |
| |
| bool OptimizeForSize; |
| bool redoLoop; |
| |
| Loop *currentLoop; |
| DominatorTree *DT; |
| BasicBlock *loopHeader; |
| BasicBlock *loopPreheader; |
| |
| // LoopBlocks contains all of the basic blocks of the loop, including the |
| // preheader of the loop, the body of the loop, and the exit blocks of the |
| // loop, in that order. |
| std::vector<BasicBlock*> LoopBlocks; |
| // NewBlocks contained cloned copy of basic blocks from LoopBlocks. |
| std::vector<BasicBlock*> NewBlocks; |
| |
| public: |
| static char ID; // Pass ID, replacement for typeid |
| explicit LoopUnswitch(bool Os = false) : |
| LoopPass(ID), OptimizeForSize(Os), redoLoop(false), |
| currentLoop(nullptr), DT(nullptr), loopHeader(nullptr), |
| loopPreheader(nullptr) { |
| initializeLoopUnswitchPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnLoop(Loop *L, LPPassManager &LPM) override; |
| bool processCurrentLoop(); |
| |
| /// This transformation requires natural loop information & requires that |
| /// loop preheaders be inserted into the CFG. |
| /// |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequired<AssumptionCacheTracker>(); |
| AU.addRequiredID(LoopSimplifyID); |
| AU.addPreservedID(LoopSimplifyID); |
| AU.addRequired<LoopInfoWrapperPass>(); |
| AU.addPreserved<LoopInfoWrapperPass>(); |
| AU.addRequiredID(LCSSAID); |
| AU.addPreservedID(LCSSAID); |
| AU.addPreserved<DominatorTreeWrapperPass>(); |
| AU.addPreserved<ScalarEvolution>(); |
| AU.addRequired<TargetTransformInfoWrapperPass>(); |
| } |
| |
| private: |
| |
| void releaseMemory() override { |
| BranchesInfo.forgetLoop(currentLoop); |
| } |
| |
| void initLoopData() { |
| loopHeader = currentLoop->getHeader(); |
| loopPreheader = currentLoop->getLoopPreheader(); |
| } |
| |
| /// 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<BasicBlock *> &ExitBlocks); |
| |
| bool UnswitchIfProfitable(Value *LoopCond, Constant *Val, |
| TerminatorInst *TI = nullptr); |
| void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, |
| BasicBlock *ExitBlock, TerminatorInst *TI); |
| void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L, |
| TerminatorInst *TI); |
| |
| void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, |
| Constant *Val, bool isEqual); |
| |
| void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, |
| BasicBlock *TrueDest, |
| BasicBlock *FalseDest, |
| Instruction *InsertPt, |
| TerminatorInst *TI); |
| |
| void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L); |
| bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = nullptr, |
| BasicBlock **LoopExit = nullptr); |
| |
| }; |
| } |
| |
| // Analyze loop. Check its size, calculate is it possible to unswitch |
| // it. Returns true if we can unswitch this loop. |
| bool LUAnalysisCache::countLoop(const Loop *L, const TargetTransformInfo &TTI, |
| AssumptionCache *AC) { |
| |
| LoopPropsMapIt PropsIt; |
| bool Inserted; |
| std::tie(PropsIt, Inserted) = |
| LoopsProperties.insert(std::make_pair(L, LoopProperties())); |
| |
| LoopProperties &Props = PropsIt->second; |
| |
| if (Inserted) { |
| // New loop. |
| |
| // Limit the number of instructions to avoid causing significant code |
| // expansion, and the number of basic blocks, to avoid loops with |
| // large numbers of branches which cause loop unswitching to go crazy. |
| // This is a very ad-hoc heuristic. |
| |
| SmallPtrSet<const Value *, 32> EphValues; |
| CodeMetrics::collectEphemeralValues(L, AC, EphValues); |
| |
| // FIXME: This is overly conservative because it does not take into |
| // consideration code simplification opportunities and code that can |
| // be shared by the resultant unswitched loops. |
| CodeMetrics Metrics; |
| for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); I != E; |
| ++I) |
| Metrics.analyzeBasicBlock(*I, TTI, EphValues); |
| |
| Props.SizeEstimation = Metrics.NumInsts; |
| Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation); |
| Props.WasUnswitchedCount = 0; |
| MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount; |
| |
| if (Metrics.notDuplicatable) { |
| DEBUG(dbgs() << "NOT unswitching loop %" |
| << L->getHeader()->getName() << ", contents cannot be " |
| << "duplicated!\n"); |
| return false; |
| } |
| } |
| |
| // Be careful. This links are good only before new loop addition. |
| CurrentLoopProperties = &Props; |
| CurLoopInstructions = &Props.UnswitchedVals; |
| |
| return true; |
| } |
| |
| // Clean all data related to given loop. |
| void LUAnalysisCache::forgetLoop(const Loop *L) { |
| |
| LoopPropsMapIt LIt = LoopsProperties.find(L); |
| |
| if (LIt != LoopsProperties.end()) { |
| LoopProperties &Props = LIt->second; |
| MaxSize += (Props.CanBeUnswitchedCount + Props.WasUnswitchedCount) * |
| Props.SizeEstimation; |
| LoopsProperties.erase(LIt); |
| } |
| |
| CurrentLoopProperties = nullptr; |
| CurLoopInstructions = nullptr; |
| } |
| |
| // Mark case value as unswitched. |
| // Since SI instruction can be partly unswitched, in order to avoid |
| // extra unswitching in cloned loops keep track all unswitched values. |
| void LUAnalysisCache::setUnswitched(const SwitchInst *SI, const Value *V) { |
| (*CurLoopInstructions)[SI].insert(V); |
| } |
| |
| // Check was this case value unswitched before or not. |
| bool LUAnalysisCache::isUnswitched(const SwitchInst *SI, const Value *V) { |
| return (*CurLoopInstructions)[SI].count(V); |
| } |
| |
| bool LUAnalysisCache::CostAllowsUnswitching() { |
| return CurrentLoopProperties->CanBeUnswitchedCount > 0; |
| } |
| |
| // Clone all loop-unswitch related loop properties. |
| // Redistribute unswitching quotas. |
| // Note, that new loop data is stored inside the VMap. |
| void LUAnalysisCache::cloneData(const Loop *NewLoop, const Loop *OldLoop, |
| const ValueToValueMapTy &VMap) { |
| |
| LoopProperties &NewLoopProps = LoopsProperties[NewLoop]; |
| LoopProperties &OldLoopProps = *CurrentLoopProperties; |
| UnswitchedValsMap &Insts = OldLoopProps.UnswitchedVals; |
| |
| // Reallocate "can-be-unswitched quota" |
| |
| --OldLoopProps.CanBeUnswitchedCount; |
| ++OldLoopProps.WasUnswitchedCount; |
| NewLoopProps.WasUnswitchedCount = 0; |
| unsigned Quota = OldLoopProps.CanBeUnswitchedCount; |
| NewLoopProps.CanBeUnswitchedCount = Quota / 2; |
| OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2; |
| |
| NewLoopProps.SizeEstimation = OldLoopProps.SizeEstimation; |
| |
| // Clone unswitched values info: |
| // for new loop switches we clone info about values that was |
| // already unswitched and has redundant successors. |
| for (UnswitchedValsIt I = Insts.begin(); I != Insts.end(); ++I) { |
| const SwitchInst *OldInst = I->first; |
| Value *NewI = VMap.lookup(OldInst); |
| const SwitchInst *NewInst = cast_or_null<SwitchInst>(NewI); |
| assert(NewInst && "All instructions that are in SrcBB must be in VMap."); |
| |
| NewLoopProps.UnswitchedVals[NewInst] = OldLoopProps.UnswitchedVals[OldInst]; |
| } |
| } |
| |
| char LoopUnswitch::ID = 0; |
| INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops", |
| false, false) |
| INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) |
| INITIALIZE_PASS_DEPENDENCY(LoopSimplify) |
| INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(LCSSA) |
| INITIALIZE_PASS_END(LoopUnswitch, "loop-unswitch", "Unswitch loops", |
| false, false) |
| |
| 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. |
| static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) { |
| |
| // We started analyze new instruction, increment scanned instructions counter. |
| ++TotalInsts; |
| |
| // We can never unswitch on vector conditions. |
| if (Cond->getType()->isVectorTy()) |
| return nullptr; |
| |
| // Constants should be folded, not unswitched on! |
| if (isa<Constant>(Cond)) return nullptr; |
| |
| // TODO: Handle: br (VARIANT|INVARIANT). |
| |
| // Hoist simple values out. |
| if (L->makeLoopInvariant(Cond, Changed)) |
| return Cond; |
| |
| if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond)) |
| if (BO->getOpcode() == Instruction::And || |
| BO->getOpcode() == Instruction::Or) { |
| // If either the left or right side is invariant, we can unswitch on this, |
| // which will cause the branch to go away in one loop and the condition to |
| // simplify in the other one. |
| if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed)) |
| return LHS; |
| if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed)) |
| return RHS; |
| } |
| |
| return nullptr; |
| } |
| |
| bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) { |
| if (skipOptnoneFunction(L)) |
| return false; |
| |
| AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache( |
| *L->getHeader()->getParent()); |
| LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); |
| LPM = &LPM_Ref; |
| DominatorTreeWrapperPass *DTWP = |
| getAnalysisIfAvailable<DominatorTreeWrapperPass>(); |
| DT = DTWP ? &DTWP->getDomTree() : nullptr; |
| currentLoop = L; |
| Function *F = currentLoop->getHeader()->getParent(); |
| bool Changed = false; |
| do { |
| assert(currentLoop->isLCSSAForm(*DT)); |
| redoLoop = false; |
| Changed |= processCurrentLoop(); |
| } while(redoLoop); |
| |
| if (Changed) { |
| // FIXME: Reconstruct dom info, because it is not preserved properly. |
| if (DT) |
| DT->recalculate(*F); |
| } |
| return Changed; |
| } |
| |
| /// processCurrentLoop - Do actual work and unswitch loop if possible |
| /// and profitable. |
| bool LoopUnswitch::processCurrentLoop() { |
| bool Changed = false; |
| |
| initLoopData(); |
| |
| // If LoopSimplify was unable to form a preheader, don't do any unswitching. |
| if (!loopPreheader) |
| return false; |
| |
| // Loops with indirectbr cannot be cloned. |
| if (!currentLoop->isSafeToClone()) |
| return false; |
| |
| // Without dedicated exits, splitting the exit edge may fail. |
| if (!currentLoop->hasDedicatedExits()) |
| return false; |
| |
| LLVMContext &Context = loopHeader->getContext(); |
| |
| // Probably we reach the quota of branches for this loop. If so |
| // stop unswitching. |
| if (!BranchesInfo.countLoop( |
| currentLoop, getAnalysis<TargetTransformInfoWrapperPass>().getTTI( |
| *currentLoop->getHeader()->getParent()), |
| AC)) |
| 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. |
| for (Loop::block_iterator I = currentLoop->block_begin(), |
| E = currentLoop->block_end(); I != E; ++I) { |
| TerminatorInst *TI = (*I)->getTerminator(); |
| if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { |
| // If this isn't branching on an invariant condition, we can't unswitch |
| // it. |
| if (BI->isConditional()) { |
| // See if this, or some part of it, is loop invariant. If so, we can |
| // unswitch on it if we desire. |
| Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), |
| currentLoop, Changed); |
| if (LoopCond && |
| UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(Context), TI)) { |
| ++NumBranches; |
| return true; |
| } |
| } |
| } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { |
| Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), |
| currentLoop, Changed); |
| unsigned NumCases = SI->getNumCases(); |
| if (LoopCond && NumCases) { |
| // Find a value to unswitch on: |
| // FIXME: this should chose the most expensive case! |
| // FIXME: scan for a case with a non-critical edge? |
| Constant *UnswitchVal = nullptr; |
| |
| // Do not process same value again and again. |
| // At this point we have some cases already unswitched and |
| // some not yet unswitched. Let's find the first not yet unswitched one. |
| for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); |
| i != e; ++i) { |
| Constant *UnswitchValCandidate = i.getCaseValue(); |
| if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) { |
| UnswitchVal = UnswitchValCandidate; |
| break; |
| } |
| } |
| |
| if (!UnswitchVal) |
| continue; |
| |
| if (UnswitchIfProfitable(LoopCond, UnswitchVal)) { |
| ++NumSwitches; |
| return true; |
| } |
| } |
| } |
| |
| // Scan the instructions to check for unswitchable values. |
| for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end(); |
| BBI != E; ++BBI) |
| if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) { |
| Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), |
| currentLoop, Changed); |
| if (LoopCond && UnswitchIfProfitable(LoopCond, |
| ConstantInt::getTrue(Context))) { |
| ++NumSelects; |
| return true; |
| } |
| } |
| } |
| return Changed; |
| } |
| |
| /// isTrivialLoopExitBlock - 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. |
| /// |
| static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB, |
| BasicBlock *&ExitBB, |
| std::set<BasicBlock*> &Visited) { |
| if (!Visited.insert(BB).second) { |
| // Already visited. Without more analysis, this could indicate an infinite |
| // loop. |
| return false; |
| } |
| if (!L->contains(BB)) { |
| // Otherwise, this is a loop exit, this is fine so long as this is the |
| // first exit. |
| if (ExitBB) return false; |
| ExitBB = BB; |
| return true; |
| } |
| |
| // Otherwise, this is an unvisited intra-loop node. Check all successors. |
| for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) { |
| // Check to see if the successor is a trivial loop exit. |
| if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited)) |
| return false; |
| } |
| |
| // Okay, everything after this looks good, check to make sure that this block |
| // doesn't include any side effects. |
| for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) |
| if (I->mayHaveSideEffects()) |
| return false; |
| |
| 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. |
| static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) { |
| std::set<BasicBlock*> Visited; |
| Visited.insert(L->getHeader()); // Branches to header make infinite loops. |
| BasicBlock *ExitBB = nullptr; |
| if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited)) |
| return ExitBB; |
| return nullptr; |
| } |
| |
| /// IsTrivialUnswitchCondition - Check to see if this unswitch condition is |
| /// trivial: that is, that the condition controls whether or not the loop does |
| /// anything at all. If this is a trivial condition, unswitching produces no |
| /// code duplications (equivalently, it produces a simpler loop and a new empty |
| /// loop, which gets deleted). |
| /// |
| /// If this is a trivial condition, return true, otherwise return false. When |
| /// returning true, this sets Cond and Val to the condition that controls the |
| /// trivial condition: when Cond dynamically equals Val, the loop is known to |
| /// exit. Finally, this sets LoopExit to the BB that the loop exits to when |
| /// Cond == Val. |
| /// |
| bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val, |
| BasicBlock **LoopExit) { |
| BasicBlock *Header = currentLoop->getHeader(); |
| TerminatorInst *HeaderTerm = Header->getTerminator(); |
| LLVMContext &Context = Header->getContext(); |
| |
| BasicBlock *LoopExitBB = nullptr; |
| if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) { |
| // If the header block doesn't end with a conditional branch on Cond, we |
| // can't handle it. |
| if (!BI->isConditional() || BI->getCondition() != Cond) |
| return false; |
| |
| // Check to see if a successor of the branch is guaranteed to |
| // exit through a unique exit block without having any |
| // side-effects. If so, determine the value of Cond that causes it to do |
| // this. |
| if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop, |
| BI->getSuccessor(0)))) { |
| if (Val) *Val = ConstantInt::getTrue(Context); |
| } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop, |
| BI->getSuccessor(1)))) { |
| if (Val) *Val = ConstantInt::getFalse(Context); |
| } |
| } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) { |
| // If this isn't a switch on Cond, we can't handle it. |
| if (SI->getCondition() != Cond) return false; |
| |
| // Check to see if a successor of the switch is guaranteed to go to the |
| // latch block or exit through a one exit block without having any |
| // side-effects. If so, determine the value of Cond that causes it to do |
| // this. |
| // Note that we can't trivially unswitch on the default case or |
| // on already unswitched cases. |
| for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); |
| i != e; ++i) { |
| BasicBlock *LoopExitCandidate; |
| if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop, |
| i.getCaseSuccessor()))) { |
| // Okay, we found a trivial case, remember the value that is trivial. |
| ConstantInt *CaseVal = i.getCaseValue(); |
| |
| // Check that it was not unswitched before, since already unswitched |
| // trivial vals are looks trivial too. |
| if (BranchesInfo.isUnswitched(SI, CaseVal)) |
| continue; |
| LoopExitBB = LoopExitCandidate; |
| if (Val) *Val = CaseVal; |
| break; |
| } |
| } |
| } |
| |
| // 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<PHINode>(LoopExitBB->begin())) |
| return false; // Can't handle this. |
| |
| if (LoopExit) *LoopExit = LoopExitBB; |
| |
| // We already know that nothing uses any scalar values defined inside of this |
| // loop. As such, we just have to check to see 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. We already checked the |
| // tail, check the header now. |
| for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I) |
| if (I->mayHaveSideEffects()) |
| return false; |
| return true; |
| } |
| |
| /// UnswitchIfProfitable - 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(); |
| Constant *CondVal = nullptr; |
| BasicBlock *ExitBlock = nullptr; |
| |
| if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) { |
| // If the condition is trivial, always unswitch. There is no code growth |
| // for this case. |
| UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock, TI); |
| return true; |
| } |
| |
| // Check to see if it would be profitable to unswitch current loop. |
| if (!BranchesInfo.CostAllowsUnswitching()) { |
| DEBUG(dbgs() << "NOT unswitching loop %" |
| << currentLoop->getHeader()->getName() |
| << " at non-trivial condition '" << *Val |
| << "' == " << *LoopCond << "\n" |
| << ". Cost too high.\n"); |
| 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, |
| /// 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); |
| |
| // 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<BasicBlock>(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); |
| |
| return New; |
| } |
| |
| static void copyMetadata(Instruction *DstInst, const Instruction *SrcInst, |
| bool Swapped) { |
| if (!SrcInst || !SrcInst->hasMetadata()) |
| return; |
| |
| SmallVector<std::pair<unsigned, MDNode *>, 4> MDs; |
| SrcInst->getAllMetadata(MDs); |
| for (auto &MD : MDs) { |
| switch (MD.first) { |
| default: |
| break; |
| case LLVMContext::MD_prof: |
| if (Swapped && MD.second->getNumOperands() == 3 && |
| isa<MDString>(MD.second->getOperand(0))) { |
| MDString *MDName = cast<MDString>(MD.second->getOperand(0)); |
| if (MDName->getString() == "branch_weights") { |
| auto *ValT = cast_or_null<ConstantAsMetadata>( |
| MD.second->getOperand(1))->getValue(); |
| auto *ValF = cast_or_null<ConstantAsMetadata>( |
| MD.second->getOperand(2))->getValue(); |
| assert(ValT && ValF && "Invalid Operands of branch_weights"); |
| auto NewMD = |
| MDBuilder(DstInst->getParent()->getContext()) |
| .createBranchWeights(cast<ConstantInt>(ValF)->getZExtValue(), |
| cast<ConstantInt>(ValT)->getZExtValue()); |
| MD.second = NewMD; |
| } |
| } |
| // fallthrough. |
| 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. |
| void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val, |
| BasicBlock *TrueDest, |
| BasicBlock *FalseDest, |
| Instruction *InsertPt, |
| TerminatorInst *TI) { |
| // Insert a conditional branch on LIC to the two preheaders. The original |
| // code is the true version and the new code is the false version. |
| Value *BranchVal = LIC; |
| bool Swapped = false; |
| if (!isa<ConstantInt>(Val) || |
| Val->getType() != Type::getInt1Ty(LIC->getContext())) |
| BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val); |
| else if (Val != ConstantInt::getTrue(Val->getContext())) { |
| // We want to enter the new loop when the condition is true. |
| std::swap(TrueDest, FalseDest); |
| Swapped = true; |
| } |
| |
| // Insert the new branch. |
| BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt); |
| copyMetadata(BI, TI, Swapped); |
| |
| // If either edge is critical, split it. This helps preserve LoopSimplify |
| // form for enclosing loops. |
| auto Options = CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA(); |
| SplitCriticalEdge(BI, 0, Options); |
| 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. |
| void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val, |
| BasicBlock *ExitBlock, |
| TerminatorInst *TI) { |
| DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %" |
| << loopHeader->getName() << " [" << L->getBlocks().size() |
| << " blocks] in Function " |
| << L->getHeader()->getParent()->getName() << " on cond: " << *Val |
| << " == " << *Cond << "\n"); |
| |
| // First step, split the preheader, so that we know that there is a safe place |
| // to insert the conditional branch. We will change loopPreheader to have a |
| // conditional branch on Cond. |
| BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, DT, LI); |
| |
| // Now that we have a place to insert the conditional branch, create a place |
| // to branch to: this is the exit block out of the loop that we should |
| // short-circuit to. |
| |
| // Split this block now, so that the loop maintains its exit block, and so |
| // that the jump from the preheader can execute the contents of the exit block |
| // 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); |
| |
| // Okay, now we have a position to branch from and a position to branch to, |
| // insert the new conditional branch. |
| EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH, |
| loopPreheader->getTerminator(), TI); |
| LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L); |
| loopPreheader->getTerminator()->eraseFromParent(); |
| |
| // We need to reprocess this loop, it could be unswitched again. |
| redoLoop = true; |
| |
| // Now that we know that the loop is never entered when this condition is a |
| // particular value, rewrite the loop with this info. We know that this will |
| // at least eliminate the old branch. |
| RewriteLoopBodyWithConditionConstant(L, Cond, Val, false); |
| ++NumTrivial; |
| } |
| |
| /// SplitExitEdges - 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<BasicBlock *> &ExitBlocks){ |
| |
| for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { |
| BasicBlock *ExitBlock = ExitBlocks[i]; |
| SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock), |
| pred_end(ExitBlock)); |
| |
| // Although SplitBlockPredecessors doesn't preserve loop-simplify in |
| // general, if we call it on all predecessors of all exits then it does. |
| SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", |
| /*AliasAnalysis*/ nullptr, DT, LI, |
| /*PreserveLCSSA*/ true); |
| } |
| } |
| |
| /// 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. |
| void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val, |
| Loop *L, TerminatorInst *TI) { |
| Function *F = loopHeader->getParent(); |
| DEBUG(dbgs() << "loop-unswitch: Unswitching loop %" |
| << loopHeader->getName() << " [" << L->getBlocks().size() |
| << " blocks] in Function " << F->getName() |
| << " when '" << *Val << "' == " << *LIC << "\n"); |
| |
| if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>()) |
| SE->forgetLoop(L); |
| |
| LoopBlocks.clear(); |
| NewBlocks.clear(); |
| |
| // First step, split the preheader and exit blocks, and add these blocks to |
| // the LoopBlocks list. |
| BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, DT, LI); |
| LoopBlocks.push_back(NewPreheader); |
| |
| // We want the loop to come after the preheader, but before the exit blocks. |
| LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end()); |
| |
| SmallVector<BasicBlock*, 8> ExitBlocks; |
| L->getUniqueExitBlocks(ExitBlocks); |
| |
| // Split all of the edges from inside the loop to their exit blocks. Update |
| // the appropriate Phi nodes as we do so. |
| SplitExitEdges(L, ExitBlocks); |
| |
| // The exit blocks may have been changed due to edge splitting, recompute. |
| ExitBlocks.clear(); |
| L->getUniqueExitBlocks(ExitBlocks); |
| |
| // Add exit blocks to the loop blocks. |
| LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end()); |
| |
| // Next step, clone all of the basic blocks that make up the loop (including |
| // the loop preheader and exit blocks), keeping track of the mapping between |
| // the instructions and blocks. |
| NewBlocks.reserve(LoopBlocks.size()); |
| ValueToValueMapTy VMap; |
| for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) { |
| BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F); |
| |
| NewBlocks.push_back(NewBB); |
| VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping. |
| LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L); |
| } |
| |
| // Splice the newly inserted blocks into the function right before the |
| // original preheader. |
| F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(), |
| NewBlocks[0], F->end()); |
| |
| // FIXME: We could register any cloned assumptions instead of clearing the |
| // whole function's cache. |
| AC->clear(); |
| |
| // Now we create the new Loop object for the versioned loop. |
| Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM); |
| |
| // Recalculate unswitching quota, inherit simplified switches info for NewBB, |
| // Probably clone more loop-unswitch related loop properties. |
| BranchesInfo.cloneData(NewLoop, L, VMap); |
| |
| Loop *ParentLoop = L->getParentLoop(); |
| if (ParentLoop) { |
| // Make sure to add the cloned preheader and exit blocks to the parent loop |
| // as well. |
| ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI); |
| } |
| |
| for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { |
| BasicBlock *NewExit = cast<BasicBlock>(VMap[ExitBlocks[i]]); |
| // The new exit block should be in the same loop as the old one. |
| if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i])) |
| ExitBBLoop->addBasicBlockToLoop(NewExit, *LI); |
| |
| assert(NewExit->getTerminator()->getNumSuccessors() == 1 && |
| "Exit block should have been split to have one successor!"); |
| BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0); |
| |
| // If the successor of the exit block had PHI nodes, add an entry for |
| // NewExit. |
| for (BasicBlock::iterator I = ExitSucc->begin(); |
| PHINode *PN = dyn_cast<PHINode>(I); ++I) { |
| Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]); |
| ValueToValueMapTy::iterator It = VMap.find(V); |
| if (It != VMap.end()) V = It->second; |
| PN->addIncoming(V, NewExit); |
| } |
| |
| if (LandingPadInst *LPad = NewExit->getLandingPadInst()) { |
| PHINode *PN = PHINode::Create(LPad->getType(), 0, "", |
| ExitSucc->getFirstInsertionPt()); |
| |
| for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc); |
| I != E; ++I) { |
| BasicBlock *BB = *I; |
| LandingPadInst *LPI = BB->getLandingPadInst(); |
| LPI->replaceAllUsesWith(PN); |
| PN->addIncoming(LPI, BB); |
| } |
| } |
| } |
| |
| // Rewrite the code to refer to itself. |
| 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); |
| |
| // Rewrite the original preheader to select between versions of the loop. |
| BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator()); |
| assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] && |
| "Preheader splitting did not work correctly!"); |
| |
| // Emit the new branch that selects between the two versions of this loop. |
| EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR, |
| TI); |
| LPM->deleteSimpleAnalysisValue(OldBR, L); |
| OldBR->eraseFromParent(); |
| |
| LoopProcessWorklist.push_back(NewLoop); |
| redoLoop = true; |
| |
| // Keep a WeakVH holding onto LIC. If the first call to RewriteLoopBody |
| // deletes the instruction (for example by simplifying a PHI that feeds into |
| // the condition that we're unswitching on), we don't rewrite the second |
| // iteration. |
| WeakVH LICHandle(LIC); |
| |
| // Now we rewrite the original code to know that the condition is true and the |
| // new code to know that the condition is false. |
| RewriteLoopBodyWithConditionConstant(L, LIC, Val, false); |
| |
| // It's possible that simplifying one loop could cause the other to be |
| // changed to another value or a constant. If its a constant, don't simplify |
| // it. |
| if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop && |
| LICHandle && !isa<Constant>(LICHandle)) |
| RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true); |
| } |
| |
| /// RemoveFromWorklist - Remove all instances of I from the worklist vector |
| /// specified. |
| static void RemoveFromWorklist(Instruction *I, |
| std::vector<Instruction*> &Worklist) { |
| |
| Worklist.erase(std::remove(Worklist.begin(), Worklist.end(), I), |
| Worklist.end()); |
| } |
| |
| /// ReplaceUsesOfWith - 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<Instruction*> &Worklist, |
| Loop *L, LPPassManager *LPM) { |
| DEBUG(dbgs() << "Replace with '" << *V << "': " << *I); |
| |
| // Add uses to the worklist, which may be dead now. |
| for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) |
| if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i))) |
| Worklist.push_back(Use); |
| |
| // Add users to the worklist which may be simplified now. |
| for (User *U : I->users()) |
| Worklist.push_back(cast<Instruction>(U)); |
| LPM->deleteSimpleAnalysisValue(I, L); |
| RemoveFromWorklist(I, Worklist); |
| I->replaceAllUsesWith(V); |
| I->eraseFromParent(); |
| ++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. |
| void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, |
| Constant *Val, |
| bool IsEqual) { |
| assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?"); |
| |
| // FIXME: Support correlated properties, like: |
| // for (...) |
| // if (li1 < li2) |
| // ... |
| // if (li1 > li2) |
| // ... |
| |
| // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches, |
| // selects, switches. |
| std::vector<Instruction*> Worklist; |
| LLVMContext &Context = Val->getContext(); |
| |
| // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC |
| // in the loop with the appropriate one directly. |
| if (IsEqual || (isa<ConstantInt>(Val) && |
| Val->getType()->isIntegerTy(1))) { |
| Value *Replacement; |
| if (IsEqual) |
| Replacement = Val; |
| else |
| Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()), |
| !cast<ConstantInt>(Val)->getZExtValue()); |
| |
| for (User *U : LIC->users()) { |
| Instruction *UI = dyn_cast<Instruction>(U); |
| if (!UI || !L->contains(UI)) |
| continue; |
| Worklist.push_back(UI); |
| } |
| |
| for (std::vector<Instruction*>::iterator UI = Worklist.begin(), |
| UE = Worklist.end(); UI != UE; ++UI) |
| (*UI)->replaceUsesOfWith(LIC, Replacement); |
| |
| SimplifyCode(Worklist, L); |
| return; |
| } |
| |
| // Otherwise, we don't know the precise value of LIC, but we do know that it |
| // is certainly NOT "Val". As such, simplify any uses in the loop that we |
| // can. This case occurs when we unswitch switch statements. |
| for (User *U : LIC->users()) { |
| Instruction *UI = dyn_cast<Instruction>(U); |
| if (!UI || !L->contains(UI)) |
| continue; |
| |
| Worklist.push_back(UI); |
| |
| // TODO: We could do other simplifications, for example, turning |
| // 'icmp eq LIC, Val' -> false. |
| |
| // If we know that LIC is not Val, use this info to simplify code. |
| SwitchInst *SI = dyn_cast<SwitchInst>(UI); |
| if (!SI || !isa<ConstantInt>(Val)) continue; |
| |
| SwitchInst::CaseIt DeadCase = SI->findCaseValue(cast<ConstantInt>(Val)); |
| // Default case is live for multiple values. |
| if (DeadCase == SI->case_default()) continue; |
| |
| // Found a dead case value. Don't remove PHI nodes in the |
| // successor if they become single-entry, those PHI nodes may |
| // be in the Users list. |
| |
| BasicBlock *Switch = SI->getParent(); |
| BasicBlock *SISucc = DeadCase.getCaseSuccessor(); |
| BasicBlock *Latch = L->getLoopLatch(); |
| |
| BranchesInfo.setUnswitched(SI, Val); |
| |
| if (!SI->findCaseDest(SISucc)) continue; // Edge is critical. |
| // If the DeadCase successor dominates the loop latch, then the |
| // transformation isn't safe since it will delete the sole predecessor edge |
| // to the latch. |
| if (Latch && DT->dominates(SISucc, Latch)) |
| continue; |
| |
| // FIXME: This is a hack. We need to keep the successor around |
| // and hooked up so as to preserve the loop structure, because |
| // trying to update it is complicated. So instead we preserve the |
| // loop structure and put the block on a dead code path. |
| SplitEdge(Switch, SISucc, DT, LI); |
| // Compute the successors instead of relying on the return value |
| // of SplitEdge, since it may have split the switch successor |
| // after PHI nodes. |
| BasicBlock *NewSISucc = DeadCase.getCaseSuccessor(); |
| BasicBlock *OldSISucc = *succ_begin(NewSISucc); |
| // Create an "unreachable" destination. |
| BasicBlock *Abort = BasicBlock::Create(Context, "us-unreachable", |
| Switch->getParent(), |
| OldSISucc); |
| new UnreachableInst(Context, Abort); |
| // Force the new case destination to branch to the "unreachable" |
| // block while maintaining a (dead) CFG edge to the old block. |
| NewSISucc->getTerminator()->eraseFromParent(); |
| BranchInst::Create(Abort, OldSISucc, |
| ConstantInt::getTrue(Context), NewSISucc); |
| // Release the PHI operands for this edge. |
| for (BasicBlock::iterator II = NewSISucc->begin(); |
| PHINode *PN = dyn_cast<PHINode>(II); ++II) |
| PN->setIncomingValue(PN->getBasicBlockIndex(Switch), |
| UndefValue::get(PN->getType())); |
| // Tell the domtree about the new block. We don't fully update the |
| // 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); |
| } |
| |
| 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. |
| /// |
| /// FIXME: When the loop optimizer is more mature, separate this out to a new |
| /// pass. |
| /// |
| void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) { |
| const DataLayout &DL = L->getHeader()->getModule()->getDataLayout(); |
| while (!Worklist.empty()) { |
| Instruction *I = Worklist.back(); |
| Worklist.pop_back(); |
| |
| // Simple DCE. |
| if (isInstructionTriviallyDead(I)) { |
| DEBUG(dbgs() << "Remove dead instruction '" << *I); |
| |
| // Add uses to the worklist, which may be dead now. |
| for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) |
| if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i))) |
| Worklist.push_back(Use); |
| LPM->deleteSimpleAnalysisValue(I, L); |
| RemoveFromWorklist(I, Worklist); |
| I->eraseFromParent(); |
| ++NumSimplify; |
| continue; |
| } |
| |
| // See if instruction simplification can hack this up. This is common for |
| // things like "select false, X, Y" after unswitching made the condition be |
| // 'false'. TODO: update the domtree properly so we can pass it here. |
| if (Value *V = SimplifyInstruction(I, DL)) |
| if (LI->replacementPreservesLCSSAForm(I, V)) { |
| ReplaceUsesOfWith(I, V, Worklist, L, LPM); |
| continue; |
| } |
| |
| // Special case hacks that appear commonly in unswitched code. |
| if (BranchInst *BI = dyn_cast<BranchInst>(I)) { |
| if (BI->isUnconditional()) { |
| // If BI's parent is the only pred of the successor, fold the two blocks |
| // together. |
| BasicBlock *Pred = BI->getParent(); |
| BasicBlock *Succ = BI->getSuccessor(0); |
| BasicBlock *SinglePred = Succ->getSinglePredecessor(); |
| if (!SinglePred) continue; // Nothing to do. |
| assert(SinglePred == Pred && "CFG broken"); |
| |
| DEBUG(dbgs() << "Merging blocks: " << Pred->getName() << " <- " |
| << Succ->getName() << "\n"); |
| |
| // Resolve any single entry PHI nodes in Succ. |
| while (PHINode *PN = dyn_cast<PHINode>(Succ->begin())) |
| ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM); |
| |
| // If Succ has any successors with PHI nodes, update them to have |
| // entries coming from Pred instead of Succ. |
| Succ->replaceAllUsesWith(Pred); |
| |
| // Move all of the successor contents from Succ to Pred. |
| Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(), |
| Succ->end()); |
| LPM->deleteSimpleAnalysisValue(BI, L); |
| BI->eraseFromParent(); |
| RemoveFromWorklist(BI, Worklist); |
| |
| // Remove Succ from the loop tree. |
| LI->removeBlock(Succ); |
| LPM->deleteSimpleAnalysisValue(Succ, L); |
| Succ->eraseFromParent(); |
| ++NumSimplify; |
| continue; |
| } |
| |
| continue; |
| } |
| } |
| } |