DwarfEHPrepare.cpp [plain text]
#include "llvm/CodeGen/Passes.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/LibCallSemantics.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Dominators.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"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
#define DEBUG_TYPE "dwarfehprepare"
STATISTIC(NumResumesLowered, "Number of resume calls lowered");
namespace {
class DwarfEHPrepare : public FunctionPass {
const TargetMachine *TM;
Constant *RewindFunction;
DominatorTree *DT;
const TargetLowering *TLI;
bool InsertUnwindResumeCalls(Function &Fn);
Value *GetExceptionObject(ResumeInst *RI);
size_t
pruneUnreachableResumes(Function &Fn,
SmallVectorImpl<ResumeInst *> &Resumes,
SmallVectorImpl<LandingPadInst *> &CleanupLPads);
public:
static char ID;
DwarfEHPrepare()
: FunctionPass(ID), TM(nullptr), RewindFunction(nullptr), DT(nullptr),
TLI(nullptr) {}
DwarfEHPrepare(const TargetMachine *TM)
: FunctionPass(ID), TM(TM), RewindFunction(nullptr), DT(nullptr),
TLI(nullptr) {}
bool runOnFunction(Function &Fn) override;
bool doFinalization(Module &M) override {
RewindFunction = nullptr;
return false;
}
void getAnalysisUsage(AnalysisUsage &AU) const override;
const char *getPassName() const override {
return "Exception handling preparation";
}
};
}
char DwarfEHPrepare::ID = 0;
INITIALIZE_TM_PASS_BEGIN(DwarfEHPrepare, "dwarfehprepare",
"Prepare DWARF exceptions", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_TM_PASS_END(DwarfEHPrepare, "dwarfehprepare",
"Prepare DWARF exceptions", false, false)
FunctionPass *llvm::createDwarfEHPass(const TargetMachine *TM) {
return new DwarfEHPrepare(TM);
}
void DwarfEHPrepare::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
}
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;
}
size_t DwarfEHPrepare::pruneUnreachableResumes(
Function &Fn, SmallVectorImpl<ResumeInst *> &Resumes,
SmallVectorImpl<LandingPadInst *> &CleanupLPads) {
BitVector ResumeReachable(Resumes.size());
size_t ResumeIndex = 0;
for (auto *RI : Resumes) {
for (auto *LP : CleanupLPads) {
if (isPotentiallyReachable(LP, RI, DT)) {
ResumeReachable.set(ResumeIndex);
break;
}
}
++ResumeIndex;
}
if (ResumeReachable.all())
return Resumes.size();
const TargetTransformInfo &TTI =
getAnalysis<TargetTransformInfoWrapperPass>().getTTI(Fn);
LLVMContext &Ctx = Fn.getContext();
size_t ResumesLeft = 0;
for (size_t I = 0, E = Resumes.size(); I < E; ++I) {
ResumeInst *RI = Resumes[I];
if (ResumeReachable[I]) {
Resumes[ResumesLeft++] = RI;
} else {
BasicBlock *BB = RI->getParent();
new UnreachableInst(Ctx, RI);
RI->eraseFromParent();
SimplifyCFG(BB, TTI, 1);
}
}
Resumes.resize(ResumesLeft);
return ResumesLeft;
}
bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
SmallVector<ResumeInst*, 16> Resumes;
SmallVector<LandingPadInst*, 16> CleanupLPads;
for (BasicBlock &BB : Fn) {
if (auto *RI = dyn_cast<ResumeInst>(BB.getTerminator()))
Resumes.push_back(RI);
if (auto *LP = BB.getLandingPadInst())
if (LP->isCleanup())
CleanupLPads.push_back(LP);
}
if (Resumes.empty())
return false;
EHPersonality Pers = classifyEHPersonality(Fn.getPersonalityFn());
if (isFuncletEHPersonality(Pers))
return false;
LLVMContext &Ctx = Fn.getContext();
size_t ResumesLeft = pruneUnreachableResumes(Fn, Resumes, CleanupLPads);
if (ResumesLeft == 0)
return true;
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);
}
if (ResumesLeft == 1) {
ResumeInst *RI = Resumes.front();
BasicBlock *UnwindBB = RI->getParent();
Value *ExnObj = GetExceptionObject(RI);
CallInst *CI = CallInst::Create(RewindFunction, ExnObj, "", UnwindBB);
CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
new UnreachableInst(Ctx, UnwindBB);
return true;
}
BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesLeft,
"exn.obj", UnwindBB);
for (ResumeInst *RI : Resumes) {
BasicBlock *Parent = RI->getParent();
BranchInst::Create(UnwindBB, Parent);
Value *ExnObj = GetExceptionObject(RI);
PN->addIncoming(ExnObj, Parent);
++NumResumesLowered;
}
CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
new UnreachableInst(Ctx, UnwindBB);
return true;
}
bool DwarfEHPrepare::runOnFunction(Function &Fn) {
assert(TM && "DWARF EH preparation requires a target machine");
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
TLI = TM->getSubtargetImpl(Fn)->getTargetLowering();
bool Changed = InsertUnwindResumeCalls(Fn);
DT = nullptr;
TLI = nullptr;
return Changed;
}