X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FTailRecursionElimination.cpp;h=9fb8ddc3d2c1c15475efd0cb73cb66e36c70c8cf;hb=6a565e5be6c3daa69a32d2cf879df8699c7e0f88;hp=1022485a948560f10240b612705572fa13d68c71;hpb=728662f9e869251ff9b5a847b0cb0daa99d1d250;p=oota-llvm.git diff --git a/lib/Transforms/Scalar/TailRecursionElimination.cpp b/lib/Transforms/Scalar/TailRecursionElimination.cpp index 1022485a948..9fb8ddc3d2c 100644 --- a/lib/Transforms/Scalar/TailRecursionElimination.cpp +++ b/lib/Transforms/Scalar/TailRecursionElimination.cpp @@ -52,25 +52,28 @@ #define DEBUG_TYPE "tailcallelim" #include "llvm/Transforms/Scalar.h" -#include "llvm/Transforms/Utils/BasicBlockUtils.h" -#include "llvm/Transforms/Utils/Local.h" -#include "llvm/Constants.h" -#include "llvm/DerivedTypes.h" -#include "llvm/Function.h" -#include "llvm/Instructions.h" -#include "llvm/IntrinsicInst.h" -#include "llvm/Module.h" -#include "llvm/Pass.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/Statistic.h" #include "llvm/Analysis/CaptureTracking.h" #include "llvm/Analysis/InlineCost.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/Loads.h" -#include "llvm/Support/CallSite.h" +#include "llvm/Analysis/TargetTransformInfo.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Module.h" +#include "llvm/Pass.h" #include "llvm/Support/CFG.h" +#include "llvm/Support/CallSite.h" #include "llvm/Support/Debug.h" +#include "llvm/Support/ValueHandle.h" #include "llvm/Support/raw_ostream.h" -#include "llvm/ADT/Statistic.h" -#include "llvm/ADT/STLExtras.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Local.h" using namespace llvm; STATISTIC(NumEliminated, "Number of tail calls removed"); @@ -79,11 +82,15 @@ STATISTIC(NumAccumAdded, "Number of accumulators introduced"); namespace { struct TailCallElim : public FunctionPass { + const TargetTransformInfo *TTI; + static char ID; // Pass identification, replacement for typeid TailCallElim() : FunctionPass(ID) { initializeTailCallElimPass(*PassRegistry::getPassRegistry()); } + virtual void getAnalysisUsage(AnalysisUsage &AU) const; + virtual bool runOnFunction(Function &F); private: @@ -92,16 +99,16 @@ namespace { bool EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret, BasicBlock *&OldEntry, bool &TailCallsAreMarkedTail, - SmallVector &ArgumentPHIs, + SmallVectorImpl &ArgumentPHIs, bool CannotTailCallElimCallsMarkedTail); bool FoldReturnAndProcessPred(BasicBlock *BB, ReturnInst *Ret, BasicBlock *&OldEntry, bool &TailCallsAreMarkedTail, - SmallVector &ArgumentPHIs, + SmallVectorImpl &ArgumentPHIs, bool CannotTailCallElimCallsMarkedTail); bool ProcessReturningBlock(ReturnInst *RI, BasicBlock *&OldEntry, bool &TailCallsAreMarkedTail, - SmallVector &ArgumentPHIs, + SmallVectorImpl &ArgumentPHIs, bool CannotTailCallElimCallsMarkedTail); bool CanMoveAboveCall(Instruction *I, CallInst *CI); Value *CanTransformAccumulatorRecursion(Instruction *I, CallInst *CI); @@ -109,87 +116,108 @@ namespace { } char TailCallElim::ID = 0; -INITIALIZE_PASS(TailCallElim, "tailcallelim", - "Tail Call Elimination", false, false) +INITIALIZE_PASS_BEGIN(TailCallElim, "tailcallelim", + "Tail Call Elimination", false, false) +INITIALIZE_AG_DEPENDENCY(TargetTransformInfo) +INITIALIZE_PASS_END(TailCallElim, "tailcallelim", + "Tail Call Elimination", false, false) // Public interface to the TailCallElimination pass FunctionPass *llvm::createTailCallEliminationPass() { return new TailCallElim(); } -/// AllocaMightEscapeToCalls - Return true if this alloca may be accessed by -/// callees of this function. We only do very simple analysis right now, this -/// could be expanded in the future to use mod/ref information for particular -/// call sites if desired. -static bool AllocaMightEscapeToCalls(AllocaInst *AI) { - // FIXME: do simple 'address taken' analysis. - return true; +void TailCallElim::getAnalysisUsage(AnalysisUsage &AU) const { + AU.addRequired(); } -/// CheckForEscapingAllocas - Scan the specified basic block for alloca -/// instructions. If it contains any that might be accessed by calls, return -/// true. -static bool CheckForEscapingAllocas(BasicBlock *BB, - bool &CannotTCETailMarkedCall) { - bool RetVal = false; - for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) - if (AllocaInst *AI = dyn_cast(I)) { - RetVal |= AllocaMightEscapeToCalls(AI); - - // If this alloca is in the body of the function, or if it is a variable - // sized allocation, we cannot tail call eliminate calls marked 'tail' - // with this mechanism. - if (BB != &BB->getParent()->getEntryBlock() || - !isa(AI->getArraySize())) - CannotTCETailMarkedCall = true; - } - return RetVal; +/// CanTRE - Scan the specified basic block for alloca instructions. +/// If it contains any that are variable-sized or not in the entry block, +/// returns false. +static bool CanTRE(AllocaInst *AI) { + // Because of PR962, we don't TRE allocas outside the entry block. + + // If this alloca is in the body of the function, or if it is a variable + // sized allocation, we cannot tail call eliminate calls marked 'tail' + // with this mechanism. + BasicBlock *BB = AI->getParent(); + return BB == &BB->getParent()->getEntryBlock() && + isa(AI->getArraySize()); } +namespace { +struct AllocaCaptureTracker : public CaptureTracker { + AllocaCaptureTracker() : Captured(false) {} + + void tooManyUses() LLVM_OVERRIDE { Captured = true; } + + bool shouldExplore(Use *U) LLVM_OVERRIDE { + Value *V = U->getUser(); + if (isa(V) || isa(V)) + UsesAlloca.insert(V); + return true; + } + + bool captured(Use *U) LLVM_OVERRIDE { + if (isa(U->getUser())) + return false; + Captured = true; + return true; + } + + bool Captured; + SmallPtrSet UsesAlloca; +}; +} // end anonymous namespace + bool TailCallElim::runOnFunction(Function &F) { // If this function is a varargs function, we won't be able to PHI the args // right, so don't even try to convert it... if (F.getFunctionType()->isVarArg()) return false; + TTI = &getAnalysis(); BasicBlock *OldEntry = 0; bool TailCallsAreMarkedTail = false; SmallVector ArgumentPHIs; bool MadeChange = false; - bool FunctionContainsEscapingAllocas = false; - // CannotTCETailMarkedCall - If true, we cannot perform TCE on tail calls + // CanTRETailMarkedCall - If false, we cannot perform TRE on tail calls // marked with the 'tail' attribute, because doing so would cause the stack - // size to increase (real TCE would deallocate variable sized allocas, TCE + // size to increase (real TRE would deallocate variable sized allocas, TRE // doesn't). - bool CannotTCETailMarkedCall = false; - - // Loop over the function, looking for any returning blocks, and keeping track - // of whether this function has any non-trivially used allocas. - for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { - if (FunctionContainsEscapingAllocas && CannotTCETailMarkedCall) - break; - - FunctionContainsEscapingAllocas |= - CheckForEscapingAllocas(BB, CannotTCETailMarkedCall); + bool CanTRETailMarkedCall = true; + + // Find calls that can be marked tail. + AllocaCaptureTracker ACT; + for (Function::iterator BB = F.begin(), EE = F.end(); BB != EE; ++BB) { + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { + if (AllocaInst *AI = dyn_cast(I)) { + CanTRETailMarkedCall &= CanTRE(AI); + PointerMayBeCaptured(AI, &ACT); + // If any allocas are captured, exit. + if (ACT.Captured) + return false; + } + } } - - /// FIXME: The code generator produces really bad code when an 'escaping - /// alloca' is changed from being a static alloca to being a dynamic alloca. - /// Until this is resolved, disable this transformation if that would ever - /// happen. This bug is PR962. - if (FunctionContainsEscapingAllocas) - return false; - // Second pass, change any tail calls to loops. - for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { - if (ReturnInst *Ret = dyn_cast(BB->getTerminator())) { - bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail, - ArgumentPHIs,CannotTCETailMarkedCall); - if (!Change && BB->getFirstNonPHIOrDbg() == Ret) - Change = FoldReturnAndProcessPred(BB, Ret, OldEntry, - TailCallsAreMarkedTail, ArgumentPHIs, - CannotTCETailMarkedCall); - MadeChange |= Change; + // Second pass, change any tail recursive calls to loops. + // + // FIXME: The code generator produces really bad code when an 'escaping + // alloca' is changed from being a static alloca to being a dynamic alloca. + // Until this is resolved, disable this transformation if that would ever + // happen. This bug is PR962. + if (ACT.UsesAlloca.empty()) { + for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { + if (ReturnInst *Ret = dyn_cast(BB->getTerminator())) { + bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail, + ArgumentPHIs, !CanTRETailMarkedCall); + if (!Change && BB->getFirstNonPHIOrDbg() == Ret) + Change = FoldReturnAndProcessPred(BB, Ret, OldEntry, + TailCallsAreMarkedTail, ArgumentPHIs, + !CanTRETailMarkedCall); + MadeChange |= Change; + } } } @@ -210,16 +238,24 @@ bool TailCallElim::runOnFunction(Function &F) { } } - // Finally, if this function contains no non-escaping allocas, or calls - // setjmp, mark all calls in the function as eligible for tail calls - //(there is no stack memory for them to access). - if (!FunctionContainsEscapingAllocas && !F.hasFnAttr(Attribute::ReturnsTwice)) - for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) - for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) + // At this point, we know that the function does not have any captured + // allocas. If additionally the function does not call setjmp, mark all calls + // in the function that do not access stack memory with the tail keyword. This + // implies ensuring that there does not exist any path from a call that takes + // in an alloca but does not capture it and the call which we wish to mark + // with "tail". + if (!F.callsFunctionThatReturnsTwice()) { + for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { if (CallInst *CI = dyn_cast(I)) { - CI->setTailCall(); - MadeChange = true; + if (!ACT.UsesAlloca.count(CI)) { + CI->setTailCall(); + MadeChange = true; + } } + } + } + } return MadeChange; } @@ -234,7 +270,7 @@ bool TailCallElim::CanMoveAboveCall(Instruction *I, CallInst *CI) { // call does not mod/ref the memory location being processed. if (I->mayHaveSideEffects()) // This also handles volatile loads. return false; - + if (LoadInst *L = dyn_cast(I)) { // Loads may always be moved above calls without side effects. if (CI->mayHaveSideEffects()) { @@ -364,7 +400,7 @@ TailCallElim::FindTRECandidate(Instruction *TI, if (&BB->front() == TI) // Make sure there is something before the terminator. return 0; - + // Scan backwards from the return, checking to see if there is a tail call in // this block. If so, set CI to it. CallInst *CI = 0; @@ -388,10 +424,11 @@ TailCallElim::FindTRECandidate(Instruction *TI, // double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call // and disable this xform in this case, because the code generator will // lower the call to fabs into inline code. - if (BB == &F->getEntryBlock() && + if (BB == &F->getEntryBlock() && FirstNonDbg(BB->front()) == CI && FirstNonDbg(llvm::next(BB->begin())) == TI && - callIsSmall(F)) { + CI->getCalledFunction() && + !TTI->isLoweredToCall(CI->getCalledFunction())) { // A single-block function with just a call and a return. Check that // the arguments match. CallSite::arg_iterator I = CallSite(CI).arg_begin(), @@ -410,7 +447,7 @@ TailCallElim::FindTRECandidate(Instruction *TI, bool TailCallElim::EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret, BasicBlock *&OldEntry, bool &TailCallsAreMarkedTail, - SmallVector &ArgumentPHIs, + SmallVectorImpl &ArgumentPHIs, bool CannotTailCallElimCallsMarkedTail) { // If we are introducing accumulator recursion to eliminate operations after // the call instruction that are both associative and commutative, the initial @@ -432,7 +469,7 @@ bool TailCallElim::EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret, BasicBlock::iterator BBI = CI; for (++BBI; &*BBI != Ret; ++BBI) { if (CanMoveAboveCall(BBI, CI)) continue; - + // If we can't move the instruction above the call, it might be because it // is an associative and commutative operation that could be transformed // using accumulator recursion elimination. Check to see if this is the @@ -586,7 +623,7 @@ bool TailCallElim::EliminateRecursiveTailCall(CallInst *CI, ReturnInst *Ret, bool TailCallElim::FoldReturnAndProcessPred(BasicBlock *BB, ReturnInst *Ret, BasicBlock *&OldEntry, bool &TailCallsAreMarkedTail, - SmallVector &ArgumentPHIs, + SmallVectorImpl &ArgumentPHIs, bool CannotTailCallElimCallsMarkedTail) { bool Change = false; @@ -620,10 +657,11 @@ bool TailCallElim::FoldReturnAndProcessPred(BasicBlock *BB, return Change; } -bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry, - bool &TailCallsAreMarkedTail, - SmallVector &ArgumentPHIs, - bool CannotTailCallElimCallsMarkedTail) { +bool +TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry, + bool &TailCallsAreMarkedTail, + SmallVectorImpl &ArgumentPHIs, + bool CannotTailCallElimCallsMarkedTail) { CallInst *CI = FindTRECandidate(Ret, CannotTailCallElimCallsMarkedTail); if (!CI) return false;