//===----------------------------------------------------------------------===//
//
// This pass mulches exception handling code into a form adapted to code
-// generation. Required if using dwarf exception handling.
+// generation. Required if using dwarf exception handling.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "dwarfehprepare"
-#include "llvm/ADT/Statistic.h"
-#include "llvm/Analysis/Dominators.h"
-#include "llvm/CodeGen/Passes.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
-#include "llvm/Support/Compiler.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/Support/CallSite.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
-#include "llvm/Transforms/Utils/PromoteMemToReg.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");
+STATISTIC(NumResumesLowered, "Number of resume calls lowered");
namespace {
class DwarfEHPrepare : public FunctionPass {
+ const TargetMachine *TM;
const TargetLowering *TLI;
- bool CompileFast;
- // The eh.exception intrinsic.
- Function *ExceptionValueIntrinsic;
-
- // _Unwind_Resume or the target equivalent.
+ // RewindFunction - _Unwind_Resume or the target equivalent.
Constant *RewindFunction;
- // Dominator info is used when turning stack temporaries into registers.
- DominatorTree *DT;
- DominanceFrontier *DF;
-
- // The function we are running on.
- Function *F;
-
- // The landing pads for this function.
- typedef SmallPtrSet<BasicBlock*, 8> BBSet;
- BBSet LandingPads;
-
- // Stack temporary used to hold eh.exception values.
- AllocaInst *ExceptionValueVar;
-
- bool NormalizeLandingPads();
- bool LowerUnwinds();
- bool MoveExceptionValueCalls();
- bool FinishStackTemporaries();
- bool PromoteStackTemporaries();
-
- 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);
- }
+ bool InsertUnwindResumeCalls(Function &Fn);
public:
static char ID; // Pass identification, replacement for typeid.
- DwarfEHPrepare(const TargetLowering *tli, bool fast) :
- FunctionPass(&ID), TLI(tli), CompileFast(fast),
- ExceptionValueIntrinsic(0), RewindFunction(0) {}
+ DwarfEHPrepare(const TargetMachine *tm) :
+ FunctionPass(ID), TM(tm), TLI(TM->getTargetLowering()),
+ RewindFunction(0) {
+ initializeDominatorTreePass(*PassRegistry::getPassRegistry());
+ }
virtual bool runOnFunction(Function &Fn);
- // getAnalysisUsage - We need dominance frontiers for memory promotion.
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- if (!CompileFast)
- AU.addRequired<DominatorTree>();
- AU.addPreserved<DominatorTree>();
- if (!CompileFast)
- AU.addRequired<DominanceFrontier>();
- AU.addPreserved<DominanceFrontier>();
- }
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const { }
const char *getPassName() const {
return "Exception handling preparation";
}
-
};
} // end anonymous namespace
char DwarfEHPrepare::ID = 0;
-FunctionPass *llvm::createDwarfEHPass(const TargetLowering *tli, bool fast) {
- return new DwarfEHPrepare(tli, fast);
+FunctionPass *llvm::createDwarfEHPass(const TargetMachine *tm) {
+ return new DwarfEHPrepare(tm);
}
-/// NormalizeLandingPads - Normalize and discover landing pads, noting them
-/// in the LandingPads set. A landing pad is normal if the only CFG edges
-/// that end at it are unwind edges from invoke instructions. If we inlined
-/// through an invoke we could have a normal branch from the previous
-/// unwind block through to the landing pad for the original invoke.
-/// Abnormal landing pads are fixed up by redirecting all unwind edges to
-/// a new basic block which falls through to the original.
-bool DwarfEHPrepare::NormalizeLandingPads() {
- bool Changed = false;
-
- for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
+/// InsertUnwindResumeCalls - Convert the ResumeInsts that are still present
+/// into calls to the appropriate _Unwind_Resume function.
+bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
+ bool UsesNewEH = false;
+ SmallVector<ResumeInst*, 16> Resumes;
+ for (Function::iterator I = Fn.begin(), E = Fn.end(); I != E; ++I) {
TerminatorInst *TI = I->getTerminator();
- if (!isa<InvokeInst>(TI))
- continue;
- BasicBlock *LPad = TI->getSuccessor(1);
- // Skip landing pads that have already been normalized.
- if (LandingPads.count(LPad))
- continue;
-
- // Check that only invoke unwind edges end at the landing pad.
- bool OnlyUnwoundTo = true;
- for (pred_iterator PI = pred_begin(LPad), PE = pred_end(LPad);
- PI != PE; ++PI) {
- TerminatorInst *PT = (*PI)->getTerminator();
- if (!isa<InvokeInst>(PT) || LPad == PT->getSuccessor(0)) {
- OnlyUnwoundTo = false;
- break;
- }
- }
-
- if (OnlyUnwoundTo) {
- // Only unwind edges lead to the landing pad. Remember the landing pad.
- LandingPads.insert(LPad);
- continue;
- }
-
- // At least one normal edge ends at the landing pad. Redirect the unwind
- // edges to a new basic block which falls through into this one.
-
- // Create the new basic block.
- BasicBlock *NewBB = BasicBlock::Create(F->getContext(),
- LPad->getName() + "_unwind_edge");
-
- // Insert it into the function right before the original landing pad.
- LPad->getParent()->getBasicBlockList().insert(LPad, NewBB);
-
- // Redirect unwind edges from the original landing pad to NewBB.
- for (pred_iterator PI = pred_begin(LPad), PE = pred_end(LPad); PI != PE; ) {
- TerminatorInst *PT = (*PI++)->getTerminator();
- if (isa<InvokeInst>(PT) && PT->getSuccessor(1) == LPad)
- // Unwind to the new block.
- PT->setSuccessor(1, NewBB);
- }
-
- // If there are any PHI nodes in LPad, we need to update them so that they
- // merge incoming values from NewBB instead.
- for (BasicBlock::iterator II = LPad->begin(); isa<PHINode>(II); ++II) {
- PHINode *PN = cast<PHINode>(II);
- pred_iterator PB = pred_begin(NewBB), PE = pred_end(NewBB);
-
- // Check to see if all of the values coming in via unwind edges are the
- // same. If so, we don't need to create a new PHI node.
- Value *InVal = PN->getIncomingValueForBlock(*PB);
- for (pred_iterator PI = PB; PI != PE; ++PI) {
- if (PI != PB && InVal != PN->getIncomingValueForBlock(*PI)) {
- InVal = 0;
- break;
- }
- }
-
- if (InVal == 0) {
- // Different unwind edges have different values. Create a new PHI node
- // in NewBB.
- PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".unwind",
- NewBB);
- // Add an entry for each unwind edge, using the value from the old PHI.
- for (pred_iterator PI = PB; PI != PE; ++PI)
- NewPN->addIncoming(PN->getIncomingValueForBlock(*PI), *PI);
-
- // Now use this new PHI as the common incoming value for NewBB in PN.
- InVal = NewPN;
- }
-
- // Revector exactly one entry in the PHI node to come from NewBB
- // and delete all other entries that come from unwind edges. If
- // there are both normal and unwind edges from the same predecessor,
- // this leaves an entry for the normal edge.
- for (pred_iterator PI = PB; PI != PE; ++PI)
- PN->removeIncomingValue(*PI);
- PN->addIncoming(InVal, NewBB);
- }
-
- // Add a fallthrough from NewBB to the original landing pad.
- BranchInst::Create(LPad, NewBB);
-
- // Now update DominatorTree and DominanceFrontier analysis information.
- if (DT)
- DT->splitBlock(NewBB);
- if (DF)
- DF->splitBlock(NewBB);
-
- // Remember the newly constructed landing pad. The original landing pad
- // LPad is no longer a landing pad now that all unwind edges have been
- // revectored to NewBB.
- LandingPads.insert(NewBB);
- ++NumLandingPadsSplit;
- Changed = true;
+ if (ResumeInst *RI = dyn_cast<ResumeInst>(TI))
+ Resumes.push_back(RI);
+ else if (InvokeInst *II = dyn_cast<InvokeInst>(TI))
+ UsesNewEH = II->getUnwindDest()->isLandingPad();
}
- return Changed;
-}
-
-/// LowerUnwinds - Turn unwind instructions into calls to _Unwind_Resume,
-/// rethrowing any previously caught exception. This will crash horribly
-/// at runtime if there is no such exception: using unwind to throw a new
-/// exception is currently not supported.
-bool DwarfEHPrepare::LowerUnwinds() {
- SmallVector<TerminatorInst*, 16> UnwindInsts;
-
- for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
- TerminatorInst *TI = I->getTerminator();
- if (isa<UnwindInst>(TI))
- UnwindInsts.push_back(TI);
- }
-
- if (UnwindInsts.empty()) return false;
+ if (Resumes.empty())
+ return UsesNewEH;
// Find the rewind function if we didn't already.
if (!RewindFunction) {
- LLVMContext &Ctx = UnwindInsts[0]->getContext();
- std::vector<const Type*>
- Params(1, Type::getInt8PtrTy(Ctx));
+ LLVMContext &Ctx = Resumes[0]->getContext();
FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx),
- Params, false);
+ Type::getInt8PtrTy(Ctx), false);
const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
- RewindFunction = F->getParent()->getOrInsertFunction(RewindName, FTy);
- }
-
- bool Changed = false;
-
- for (SmallVectorImpl<TerminatorInst*>::iterator
- I = UnwindInsts.begin(), E = UnwindInsts.end(); I != E; ++I) {
- TerminatorInst *TI = *I;
-
- // Replace the unwind instruction with a call to _Unwind_Resume (or the
- // appropriate target equivalent) followed by an UnreachableInst.
-
- // Create the call...
- CallInst *CI = CallInst::Create(RewindFunction,
- CreateReadOfExceptionValue(TI->getParent()),
- "", TI);
- CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
- // ...followed by an UnreachableInst.
- new UnreachableInst(TI->getContext(), TI);
-
- // Nuke the unwind instruction.
- TI->eraseFromParent();
- ++NumUnwindsLowered;
- Changed = true;
- }
-
- return Changed;
-}
-
-/// 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).
-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.
- if (!ExceptionValueIntrinsic &&
- !F->getParent()->getFunction(Intrinsic::getName(Intrinsic::eh_exception)))
- return false;
-
- 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<IntrinsicInst>(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;
- }
- }
-
- return Changed;
-}
-
-/// 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;
-
- bool Changed = false;
-
- // Make sure that there is a store of the exception value at the start of
- // each 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;
+ RewindFunction = Fn.getParent()->getOrInsertFunction(RewindName, FTy);
}
- return Changed;
-}
-
-/// PromoteStackTemporaries - Turn any stack temporaries we introduced into
-/// registers if possible.
-bool DwarfEHPrepare::PromoteStackTemporaries() {
- if (ExceptionValueVar && DT && DF && isAllocaPromotable(ExceptionValueVar)) {
- // Turn the exception temporary into registers and phi nodes if possible.
- std::vector<AllocaInst*> Allocas(1, ExceptionValueVar);
- PromoteMemToReg(Allocas, *DT, *DF, ExceptionValueVar->getContext());
- return true;
+ // Create the basic block where the _Unwind_Resume call will live.
+ LLVMContext &Ctx = Fn.getContext();
+ BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
+ PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), Resumes.size(),
+ "exn.obj", UnwindBB);
+
+ // Extract the exception object from the ResumeInst and add it to the PHI node
+ // that feeds the _Unwind_Resume call.
+ for (SmallVectorImpl<ResumeInst*>::iterator
+ I = Resumes.begin(), E = Resumes.end(); I != E; ++I) {
+ ResumeInst *RI = *I;
+ BranchInst::Create(UnwindBB, RI->getParent());
+ ExtractValueInst *ExnObj = ExtractValueInst::Create(RI->getOperand(0),
+ 0, "exn.obj", RI);
+ PN->addIncoming(ExnObj, RI->getParent());
+ RI->eraseFromParent();
+ ++NumResumesLowered;
}
- return false;
-}
-/// CreateExceptionValueCall - Insert a call to the eh.exception intrinsic at
-/// the start of the basic block (unless there already is one, in which case
-/// the existing call is returned).
-Instruction *DwarfEHPrepare::CreateExceptionValueCall(BasicBlock *BB) {
- Instruction *Start = BB->getFirstNonPHI();
- // Is this a call to eh.exception?
- if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(Start))
- if (CI->getIntrinsicID() == Intrinsic::eh_exception)
- // Reuse the existing call.
- return Start;
+ // Call the function.
+ CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
+ CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
- // Find the eh.exception intrinsic if we didn't already.
- if (!ExceptionValueIntrinsic)
- ExceptionValueIntrinsic = Intrinsic::getDeclaration(F->getParent(),
- Intrinsic::eh_exception);
-
- // Create the call.
- 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->getFirstNonPHI();
- // Is this a load of the exception temporary?
- if (ExceptionValueVar)
- if (LoadInst* LI = dyn_cast<LoadInst>(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);
+ // We never expect _Unwind_Resume to return.
+ new UnreachableInst(Ctx, UnwindBB);
+ return true;
}
bool DwarfEHPrepare::runOnFunction(Function &Fn) {
- bool Changed = false;
-
- // Initialize internal state.
- DT = getAnalysisIfAvailable<DominatorTree>();
- DF = getAnalysisIfAvailable<DominanceFrontier>();
- ExceptionValueVar = 0;
- F = &Fn;
-
- // Ensure that only unwind edges end at landing pads (a landing pad is a
- // basic block where an invoke unwind edge ends).
- Changed |= NormalizeLandingPads();
-
- // Turn unwind instructions into libcalls.
- Changed |= LowerUnwinds();
-
- // TODO: Move eh.selector calls to landing pads and combine them.
-
- // Move eh.exception calls to landing pads.
- Changed |= MoveExceptionValueCalls();
-
- // Initialize any stack temporaries we introduced.
- Changed |= FinishStackTemporaries();
-
- // Turn any stack temporaries into registers if possible.
- if (!CompileFast)
- Changed |= PromoteStackTemporaries();
-
- LandingPads.clear();
-
+ bool Changed = InsertUnwindResumeCalls(Fn);
return Changed;
}