From: Duncan Sands Date: Fri, 3 Sep 2010 08:31:48 +0000 (+0000) Subject: Reapply commit 112702 which was speculatively reverted by echristo. X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=commitdiff_plain;h=850fcd4705177d8630530ea6a18538782eb68a39 Reapply commit 112702 which was speculatively reverted by echristo. Original commit message: Use the SSAUpdator to turn calls to eh.exception that are not in a landing pad into uses of registers rather than loads from a stack slot. Doesn't touch the 'orrible hack code - Bill needs to persuade me harder :) git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112952 91177308-0d34-0410-b5e6-96231b3b80d8 --- diff --git a/lib/CodeGen/DwarfEHPrepare.cpp b/lib/CodeGen/DwarfEHPrepare.cpp index 2522d0b67e3..550fd3e25fb 100644 --- a/lib/CodeGen/DwarfEHPrepare.cpp +++ b/lib/CodeGen/DwarfEHPrepare.cpp @@ -25,12 +25,12 @@ #include "llvm/Support/CallSite.h" #include "llvm/Target/TargetLowering.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/SSAUpdater.h" using namespace llvm; STATISTIC(NumLandingPadsSplit, "Number of landing pads split"); STATISTIC(NumUnwindsLowered, "Number of unwind instructions lowered"); STATISTIC(NumExceptionValuesMoved, "Number of eh.exception calls moved"); -STATISTIC(NumStackTempsIntroduced, "Number of stack temporaries introduced"); namespace { class DwarfEHPrepare : public FunctionPass { @@ -62,24 +62,11 @@ namespace { typedef SmallPtrSet BBSet; BBSet LandingPads; - // Stack temporary used to hold eh.exception values. - AllocaInst *ExceptionValueVar; - bool NormalizeLandingPads(); bool LowerUnwinds(); bool MoveExceptionValueCalls(); - bool FinishStackTemporaries(); Instruction *CreateExceptionValueCall(BasicBlock *BB); - Instruction *CreateValueLoad(BasicBlock *BB); - - /// CreateReadOfExceptionValue - Return the result of the eh.exception - /// intrinsic by calling the intrinsic if in a landing pad, or loading it - /// from the exception value variable otherwise. - Instruction *CreateReadOfExceptionValue(BasicBlock *BB) { - return LandingPads.count(BB) ? - CreateExceptionValueCall(BB) : CreateValueLoad(BB); - } /// CleanupSelectors - Any remaining eh.selector intrinsic calls which still /// use the "llvm.eh.catch.all.value" call need to convert to using its @@ -117,7 +104,7 @@ namespace { virtual bool runOnFunction(Function &Fn); - // getAnalysisUsage - We need dominance frontiers for memory promotion. + // getAnalysisUsage - We need the dominator tree for handling URoR. virtual void getAnalysisUsage(AnalysisUsage &AU) const { AU.addRequired(); AU.addPreserved(); @@ -517,7 +504,7 @@ bool DwarfEHPrepare::LowerUnwinds() { // Create the call... CallInst *CI = CallInst::Create(RewindFunction, - CreateReadOfExceptionValue(TI->getParent()), + CreateExceptionValueCall(TI->getParent()), "", TI); CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME)); // ...followed by an UnreachableInst. @@ -533,9 +520,11 @@ bool DwarfEHPrepare::LowerUnwinds() { } /// MoveExceptionValueCalls - Ensure that eh.exception is only ever called from -/// landing pads by replacing calls outside of landing pads with loads from a -/// stack temporary. Move eh.exception calls inside landing pads to the start -/// of the landing pad (optional, but may make things simpler for later passes). +/// landing pads by replacing calls outside of landing pads with direct use of +/// a register holding the appropriate value; this requires adding calls inside +/// all landing pads to initialize the register. Also, move eh.exception calls +/// inside landing pads to the start of the landing pad (optional, but may make +/// things simpler for later passes). bool DwarfEHPrepare::MoveExceptionValueCalls() { // If the eh.exception intrinsic is not declared in the module then there is // nothing to do. Speed up compilation by checking for this common case. @@ -545,49 +534,87 @@ bool DwarfEHPrepare::MoveExceptionValueCalls() { bool Changed = false; - for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) { - for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) - if (IntrinsicInst *CI = dyn_cast(II++)) - if (CI->getIntrinsicID() == Intrinsic::eh_exception) { - if (!CI->use_empty()) { - Value *ExceptionValue = CreateReadOfExceptionValue(BB); - if (CI == ExceptionValue) { - // The call was at the start of a landing pad - leave it alone. - assert(LandingPads.count(BB) && - "Created eh.exception call outside landing pad!"); - continue; - } - CI->replaceAllUsesWith(ExceptionValue); - } - CI->eraseFromParent(); - ++NumExceptionValuesMoved; - Changed = true; + // Move calls to eh.exception that are inside a landing pad to the start of + // the landing pad. + for (BBSet::const_iterator LI = LandingPads.begin(), LE = LandingPads.end(); + LI != LE; ++LI) { + BasicBlock *LP = *LI; + for (BasicBlock::iterator II = LP->getFirstNonPHIOrDbg(), IE = LP->end(); + II != IE;) + if (EHExceptionInst *EI = dyn_cast(II++)) { + // Found a call to eh.exception. + if (!EI->use_empty()) { + // If there is already a call to eh.exception at the start of the + // landing pad, then get hold of it; otherwise create such a call. + Value *CallAtStart = CreateExceptionValueCall(LP); + + // If the call was at the start of a landing pad then leave it alone. + if (EI == CallAtStart) + continue; + EI->replaceAllUsesWith(CallAtStart); } + EI->eraseFromParent(); + ++NumExceptionValuesMoved; + Changed = true; + } } - return Changed; -} + // Look for calls to eh.exception that are not in a landing pad. If one is + // found, then a register that holds the exception value will be created in + // each landing pad, and the SSAUpdater will be used to compute the values + // returned by eh.exception calls outside of landing pads. + SSAUpdater SSA; + + // Remember where we found the eh.exception call, to avoid rescanning earlier + // basic blocks which we already know contain no eh.exception calls. + bool FoundCallOutsideLandingPad = false; + Function::iterator BB = F->begin(); + for (Function::iterator BE = F->end(); BB != BE; ++BB) { + // Skip over landing pads. + if (LandingPads.count(BB)) + continue; -/// FinishStackTemporaries - If we introduced a stack variable to hold the -/// exception value then initialize it in each landing pad. -bool DwarfEHPrepare::FinishStackTemporaries() { - if (!ExceptionValueVar) - // Nothing to do. - return false; + for (BasicBlock::iterator II = BB->getFirstNonPHIOrDbg(), IE = BB->end(); + II != IE; ++II) + if (isa(II)) { + SSA.Initialize(II->getType(), II->getName()); + FoundCallOutsideLandingPad = true; + break; + } - bool Changed = false; + if (FoundCallOutsideLandingPad) + break; + } + + // If all calls to eh.exception are in landing pads then we are done. + if (!FoundCallOutsideLandingPad) + return Changed; - // Make sure that there is a store of the exception value at the start of - // each landing pad. + // Add a call to eh.exception at the start of each landing pad, and tell the + // SSAUpdater that this is the value produced by the landing pad. for (BBSet::iterator LI = LandingPads.begin(), LE = LandingPads.end(); - LI != LE; ++LI) { - Instruction *ExceptionValue = CreateReadOfExceptionValue(*LI); - Instruction *Store = new StoreInst(ExceptionValue, ExceptionValueVar); - Store->insertAfter(ExceptionValue); - Changed = true; + LI != LE; ++LI) + SSA.AddAvailableValue(*LI, CreateExceptionValueCall(*LI)); + + // Now turn all calls to eh.exception that are not in a landing pad into a use + // of the appropriate register. + for (Function::iterator BE = F->end(); BB != BE; ++BB) { + // Skip over landing pads. + if (LandingPads.count(BB)) + continue; + + for (BasicBlock::iterator II = BB->getFirstNonPHIOrDbg(), IE = BB->end(); + II != IE;) + if (EHExceptionInst *EI = dyn_cast(II++)) { + // Found a call to eh.exception, replace it with the value from any + // upstream landing pad(s). + EI->replaceAllUsesWith(SSA.GetValueAtEndOfBlock(BB)); + EI->eraseFromParent(); + ++NumExceptionValuesMoved; + } } - return Changed; + return true; } /// CreateExceptionValueCall - Insert a call to the eh.exception intrinsic at @@ -610,35 +637,11 @@ Instruction *DwarfEHPrepare::CreateExceptionValueCall(BasicBlock *BB) { return CallInst::Create(ExceptionValueIntrinsic, "eh.value.call", Start); } -/// CreateValueLoad - Insert a load of the exception value stack variable -/// (creating it if necessary) at the start of the basic block (unless -/// there already is a load, in which case the existing load is returned). -Instruction *DwarfEHPrepare::CreateValueLoad(BasicBlock *BB) { - Instruction *Start = BB->getFirstNonPHIOrDbg(); - // Is this a load of the exception temporary? - if (ExceptionValueVar) - if (LoadInst* LI = dyn_cast(Start)) - if (LI->getPointerOperand() == ExceptionValueVar) - // Reuse the existing load. - return Start; - - // Create the temporary if we didn't already. - if (!ExceptionValueVar) { - ExceptionValueVar = new AllocaInst(PointerType::getUnqual( - Type::getInt8Ty(BB->getContext())), "eh.value", F->begin()->begin()); - ++NumStackTempsIntroduced; - } - - // Load the value. - return new LoadInst(ExceptionValueVar, "eh.value.load", Start); -} - bool DwarfEHPrepare::runOnFunction(Function &Fn) { bool Changed = false; // Initialize internal state. DT = &getAnalysis(); - ExceptionValueVar = 0; F = &Fn; // Ensure that only unwind edges end at landing pads (a landing pad is a @@ -653,11 +656,6 @@ bool DwarfEHPrepare::runOnFunction(Function &Fn) { // Move eh.exception calls to landing pads. Changed |= MoveExceptionValueCalls(); - // Initialize any stack temporaries we introduced. - Changed |= FinishStackTemporaries(); - - // TODO: Turn any stack temporaries into registers if possible. - Changed |= HandleURoRInvokes(); LandingPads.clear();