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//===-- 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.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Passes.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
#define DEBUG_TYPE "dwarfehprepare"
STATISTIC(NumResumesLowered, "Number of resume calls lowered");
namespace {
class DwarfEHPrepare : public FunctionPass {
const TargetMachine *TM;
// RewindFunction - _Unwind_Resume or the target equivalent.
Constant *RewindFunction;
bool InsertUnwindResumeCalls(Function &Fn);
Value *GetExceptionObject(ResumeInst *RI);
public:
static char ID; // Pass identification, replacement for typeid.
// INITIALIZE_TM_PASS requires a default constructor, but it isn't used in
// practice.
DwarfEHPrepare() : FunctionPass(ID), TM(nullptr), RewindFunction(nullptr) {}
DwarfEHPrepare(const TargetMachine *TM)
: FunctionPass(ID), TM(TM), RewindFunction(nullptr) {}
bool runOnFunction(Function &Fn) override;
bool doFinalization(Module &M) override {
RewindFunction = nullptr;
return false;
}
const char *getPassName() const override {
return "Exception handling preparation";
}
};
} // end anonymous namespace
char DwarfEHPrepare::ID = 0;
INITIALIZE_TM_PASS(DwarfEHPrepare, "dwarfehprepare", "Prepare DWARF exceptions",
false, false)
FunctionPass *llvm::createDwarfEHPass(const TargetMachine *TM) {
return new DwarfEHPrepare(TM);
}
/// GetExceptionObject - Return the exception object from the value passed into
/// the 'resume' instruction (typically an aggregate). Clean up any dead
/// instructions, including the 'resume' instruction.
Value *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) {
Value *V = RI->getOperand(0);
Value *ExnObj = nullptr;
InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V);
LoadInst *SelLoad = nullptr;
InsertValueInst *ExcIVI = nullptr;
bool EraseIVIs = false;
if (SelIVI) {
if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) {
ExcIVI = dyn_cast<InsertValueInst>(SelIVI->getOperand(0));
if (ExcIVI && isa<UndefValue>(ExcIVI->getOperand(0)) &&
ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) {
ExnObj = ExcIVI->getOperand(1);
SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1));
EraseIVIs = true;
}
}
}
if (!ExnObj)
ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI);
RI->eraseFromParent();
if (EraseIVIs) {
if (SelIVI->use_empty())
SelIVI->eraseFromParent();
if (ExcIVI->use_empty())
ExcIVI->eraseFromParent();
if (SelLoad && SelLoad->use_empty())
SelLoad->eraseFromParent();
}
return ExnObj;
}
/// InsertUnwindResumeCalls - Convert the ResumeInsts that are still present
/// into calls to the appropriate _Unwind_Resume function.
bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
SmallVector<ResumeInst*, 16> Resumes;
for (BasicBlock &BB : Fn) {
if (auto *RI = dyn_cast<ResumeInst>(BB.getTerminator()))
Resumes.push_back(RI);
}
if (Resumes.empty())
return false;
// Find the rewind function if we didn't already.
const TargetLowering *TLI = TM->getSubtargetImpl(Fn)->getTargetLowering();
LLVMContext &Ctx = Fn.getContext();
if (!RewindFunction) {
FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx),
Type::getInt8PtrTy(Ctx), false);
const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
RewindFunction = Fn.getParent()->getOrInsertFunction(RewindName, FTy);
}
// Create the basic block where the _Unwind_Resume call will live.
unsigned ResumesSize = Resumes.size();
if (ResumesSize == 1) {
// Instead of creating a new BB and PHI node, just append the call to
// _Unwind_Resume to the end of the single resume block.
ResumeInst *RI = Resumes.front();
BasicBlock *UnwindBB = RI->getParent();
Value *ExnObj = GetExceptionObject(RI);
// Call the _Unwind_Resume function.
CallInst *CI = CallInst::Create(RewindFunction, ExnObj, "", UnwindBB);
CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
// We never expect _Unwind_Resume to return.
new UnreachableInst(Ctx, UnwindBB);
return true;
}
BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesSize,
"exn.obj", UnwindBB);
// Extract the exception object from the ResumeInst and add it to the PHI node
// that feeds the _Unwind_Resume call.
for (ResumeInst *RI : Resumes) {
BasicBlock *Parent = RI->getParent();
BranchInst::Create(UnwindBB, Parent);
Value *ExnObj = GetExceptionObject(RI);
PN->addIncoming(ExnObj, Parent);
++NumResumesLowered;
}
// Call the function.
CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
// We never expect _Unwind_Resume to return.
new UnreachableInst(Ctx, UnwindBB);
return true;
}
bool DwarfEHPrepare::runOnFunction(Function &Fn) {
assert(TM && "DWARF EH preparation requires a target machine");
bool Changed = InsertUnwindResumeCalls(Fn);
return Changed;
}
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