--- /dev/null
+//===-- DwarfEHPrepare - Prepare exception handling for code generation ---===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass mulches exception handling code into a form adapted to code
+// 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/Target/TargetLowering.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/PromoteMemToReg.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 VISIBILITY_HIDDEN DwarfEHPrepare : public FunctionPass {
+ const TargetLowering *TLI;
+ bool CompileFast;
+
+ // The eh.exception intrinsic.
+ Function *ExceptionValueIntrinsic;
+
+ // _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);
+ }
+
+ 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) {}
+
+ 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>();
+ }
+
+ 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);
+}
+
+/// 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.
+/// 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) {
+ 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(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;
+ }
+
+ 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() {
+ bool Changed = false;
+
+ for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
+ TerminatorInst *TI = I->getTerminator();
+ if (!isa<UnwindInst>(TI))
+ continue;
+
+ // Replace the unwind instruction with a call to _Unwind_Resume (or the
+ // appropriate target equivalent) followed by an UnreachableInst.
+
+ // Find the rewind function if we didn't already.
+ if (!RewindFunction) {
+ std::vector<const Type*> Params(1, PointerType::getUnqual(Type::Int8Ty));
+ FunctionType *FTy = FunctionType::get(Type::VoidTy, Params, false);
+ const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
+ RewindFunction = F->getParent()->getOrInsertFunction(RewindName, FTy);
+ }
+
+ // Create the call...
+ CallInst::Create(RewindFunction, CreateReadOfExceptionValue(I), "", TI);
+ // ...followed by an UnreachableInst.
+ new UnreachableInst(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;
+ }
+
+ 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);
+ return true;
+ }
+ 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;
+
+ // 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::Int8Ty),
+ "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 = 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();
+
+ return Changed;
+}
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