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llvm-mirror/lib/CodeGen/SjLjEHPrepare.cpp
Eli Friedman ffa26401ac StoreInst should store Align, not MaybeAlign 
This is D77454, except for stores.  All the infrastructure work was done
for loads, so the remaining changes necessary are relatively small.

Differential Revision: https://reviews.llvm.org/D79968
2020-05-15 12:26:58 -07:00

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//===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This transformation is designed for use by code generators which use SjLj
// based exception handling.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
#define DEBUG_TYPE "sjljehprepare"
STATISTIC(NumInvokes, "Number of invokes replaced");
STATISTIC(NumSpilled, "Number of registers live across unwind edges");
namespace {
class SjLjEHPrepare : public FunctionPass {
IntegerType *DataTy;
Type *doubleUnderDataTy;
Type *doubleUnderJBufTy;
Type *FunctionContextTy;
FunctionCallee RegisterFn;
FunctionCallee UnregisterFn;
Function *BuiltinSetupDispatchFn;
Function *FrameAddrFn;
Function *StackAddrFn;
Function *StackRestoreFn;
Function *LSDAAddrFn;
Function *CallSiteFn;
Function *FuncCtxFn;
AllocaInst *FuncCtx;
const TargetMachine *TM;
public:
static char ID; // Pass identification, replacement for typeid
explicit SjLjEHPrepare(const TargetMachine *TM = nullptr)
: FunctionPass(ID), TM(TM) {}
bool doInitialization(Module &M) override;
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {}
StringRef getPassName() const override {
return "SJLJ Exception Handling preparation";
}
private:
bool setupEntryBlockAndCallSites(Function &F);
void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads);
void lowerIncomingArguments(Function &F);
void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
void insertCallSiteStore(Instruction *I, int Number);
};
} // end anonymous namespace
char SjLjEHPrepare::ID = 0;
INITIALIZE_PASS(SjLjEHPrepare, DEBUG_TYPE, "Prepare SjLj exceptions",
false, false)
// Public Interface To the SjLjEHPrepare pass.
FunctionPass *llvm::createSjLjEHPreparePass(const TargetMachine *TM) {
return new SjLjEHPrepare(TM);
}
// doInitialization - Set up decalarations and types needed to process
// exceptions.
bool SjLjEHPrepare::doInitialization(Module &M) {
// Build the function context structure.
// builtin_setjmp uses a five word jbuf
Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
unsigned DataBits =
TM ? TM->getSjLjDataSize() : TargetMachine::DefaultSjLjDataSize;
DataTy = Type::getIntNTy(M.getContext(), DataBits);
doubleUnderDataTy = ArrayType::get(DataTy, 4);
doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
FunctionContextTy = StructType::get(VoidPtrTy, // __prev
DataTy, // call_site
doubleUnderDataTy, // __data
VoidPtrTy, // __personality
VoidPtrTy, // __lsda
doubleUnderJBufTy // __jbuf
);
return true;
}
/// insertCallSiteStore - Insert a store of the call-site value to the
/// function context
void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
IRBuilder<> Builder(I);
// Get a reference to the call_site field.
Type *Int32Ty = Type::getInt32Ty(I->getContext());
Value *Zero = ConstantInt::get(Int32Ty, 0);
Value *One = ConstantInt::get(Int32Ty, 1);
Value *Idxs[2] = { Zero, One };
Value *CallSite =
Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site");
// Insert a store of the call-site number
ConstantInt *CallSiteNoC = ConstantInt::get(DataTy, Number);
Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
}
/// MarkBlocksLiveIn - Insert BB and all of its predecessors into LiveBBs until
/// we reach blocks we've already seen.
static void MarkBlocksLiveIn(BasicBlock *BB,
SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
if (!LiveBBs.insert(BB).second)
return; // already been here.
df_iterator_default_set<BasicBlock*> Visited;
for (BasicBlock *B : inverse_depth_first_ext(BB, Visited))
LiveBBs.insert(B);
}
/// substituteLPadValues - Substitute the values returned by the landingpad
/// instruction with those returned by the personality function.
void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
Value *SelVal) {
SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end());
while (!UseWorkList.empty()) {
Value *Val = UseWorkList.pop_back_val();
auto *EVI = dyn_cast<ExtractValueInst>(Val);
if (!EVI)
continue;
if (EVI->getNumIndices() != 1)
continue;
if (*EVI->idx_begin() == 0)
EVI->replaceAllUsesWith(ExnVal);
else if (*EVI->idx_begin() == 1)
EVI->replaceAllUsesWith(SelVal);
if (EVI->use_empty())
EVI->eraseFromParent();
}
if (LPI->use_empty())
return;
// There are still some uses of LPI. Construct an aggregate with the exception
// values and replace the LPI with that aggregate.
Type *LPadType = LPI->getType();
Value *LPadVal = UndefValue::get(LPadType);
auto *SelI = cast<Instruction>(SelVal);
IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator()));
LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");
LPI->replaceAllUsesWith(LPadVal);
}
/// setupFunctionContext - Allocate the function context on the stack and fill
/// it with all of the data that we know at this point.
Value *SjLjEHPrepare::setupFunctionContext(Function &F,
ArrayRef<LandingPadInst *> LPads) {
BasicBlock *EntryBB = &F.front();
// Create an alloca for the incoming jump buffer ptr and the new jump buffer
// that needs to be restored on all exits from the function. This is an alloca
// because the value needs to be added to the global context list.
auto &DL = F.getParent()->getDataLayout();
const Align Alignment(DL.getPrefTypeAlignment(FunctionContextTy));
FuncCtx = new AllocaInst(FunctionContextTy, DL.getAllocaAddrSpace(), nullptr,
Alignment, "fn_context", &EntryBB->front());
// Fill in the function context structure.
for (LandingPadInst *LPI : LPads) {
IRBuilder<> Builder(LPI->getParent(),
LPI->getParent()->getFirstInsertionPt());
// Reference the __data field.
Value *FCData =
Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data");
// The exception values come back in context->__data[0].
Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
0, 0, "exception_gep");
Value *ExnVal = Builder.CreateLoad(DataTy, ExceptionAddr, true, "exn_val");
ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
0, 1, "exn_selector_gep");
Value *SelVal =
Builder.CreateLoad(DataTy, SelectorAddr, true, "exn_selector_val");
// SelVal must be Int32Ty, so trunc it
SelVal = Builder.CreateTrunc(SelVal, Type::getInt32Ty(F.getContext()));
substituteLPadValues(LPI, ExnVal, SelVal);
}
// Personality function
IRBuilder<> Builder(EntryBB->getTerminator());
Value *PersonalityFn = F.getPersonalityFn();
Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(
FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep");
Builder.CreateStore(
Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
PersonalityFieldPtr, /*isVolatile=*/true);
// LSDA address
Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr");
Value *LSDAFieldPtr =
Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep");
Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);
return FuncCtx;
}
/// lowerIncomingArguments - To avoid having to handle incoming arguments
/// specially, we lower each arg to a copy instruction in the entry block. This
/// ensures that the argument value itself cannot be live out of the entry
/// block.
void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
while (isa<AllocaInst>(AfterAllocaInsPt) &&
cast<AllocaInst>(AfterAllocaInsPt)->isStaticAlloca())
++AfterAllocaInsPt;
assert(AfterAllocaInsPt != F.front().end());
for (auto &AI : F.args()) {
// Swift error really is a register that we model as memory -- instruction
// selection will perform mem-to-reg for us and spill/reload appropriately
// around calls that clobber it. There is no need to spill this
// value to the stack and doing so would not be allowed.
if (AI.isSwiftError())
continue;
Type *Ty = AI.getType();
// Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction.
Value *TrueValue = ConstantInt::getTrue(F.getContext());
Value *UndefValue = UndefValue::get(Ty);
Instruction *SI = SelectInst::Create(
TrueValue, &AI, UndefValue, AI.getName() + ".tmp", &*AfterAllocaInsPt);
AI.replaceAllUsesWith(SI);
// Reset the operand, because it was clobbered by the RAUW above.
SI->setOperand(1, &AI);
}
}
/// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
/// edge and spill them.
void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
ArrayRef<InvokeInst *> Invokes) {
// Finally, scan the code looking for instructions with bad live ranges.
for (BasicBlock &BB : F) {
for (Instruction &Inst : BB) {
// Ignore obvious cases we don't have to handle. In particular, most
// instructions either have no uses or only have a single use inside the
// current block. Ignore them quickly.
if (Inst.use_empty())
continue;
if (Inst.hasOneUse() &&
cast<Instruction>(Inst.user_back())->getParent() == &BB &&
!isa<PHINode>(Inst.user_back()))
continue;
// If this is an alloca in the entry block, it's not a real register
// value.
if (auto *AI = dyn_cast<AllocaInst>(&Inst))
if (AI->isStaticAlloca())
continue;
// Avoid iterator invalidation by copying users to a temporary vector.
SmallVector<Instruction *, 16> Users;
for (User *U : Inst.users()) {
Instruction *UI = cast<Instruction>(U);
if (UI->getParent() != &BB || isa<PHINode>(UI))
Users.push_back(UI);
}
// Find all of the blocks that this value is live in.
SmallPtrSet<BasicBlock *, 32> LiveBBs;
LiveBBs.insert(&BB);
while (!Users.empty()) {
Instruction *U = Users.pop_back_val();
if (!isa<PHINode>(U)) {
MarkBlocksLiveIn(U->getParent(), LiveBBs);
} else {
// Uses for a PHI node occur in their predecessor block.
PHINode *PN = cast<PHINode>(U);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == &Inst)
MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
}
}
// Now that we know all of the blocks that this thing is live in, see if
// it includes any of the unwind locations.
bool NeedsSpill = false;
for (InvokeInst *Invoke : Invokes) {
BasicBlock *UnwindBlock = Invoke->getUnwindDest();
if (UnwindBlock != &BB && LiveBBs.count(UnwindBlock)) {
LLVM_DEBUG(dbgs() << "SJLJ Spill: " << Inst << " around "
<< UnwindBlock->getName() << "\n");
NeedsSpill = true;
break;
}
}
// If we decided we need a spill, do it.
// FIXME: Spilling this way is overkill, as it forces all uses of
// the value to be reloaded from the stack slot, even those that aren't
// in the unwind blocks. We should be more selective.
if (NeedsSpill) {
DemoteRegToStack(Inst, true);
++NumSpilled;
}
}
}
// Go through the landing pads and remove any PHIs there.
for (InvokeInst *Invoke : Invokes) {
BasicBlock *UnwindBlock = Invoke->getUnwindDest();
LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
// Place PHIs into a set to avoid invalidating the iterator.
SmallPtrSet<PHINode *, 8> PHIsToDemote;
for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
PHIsToDemote.insert(cast<PHINode>(PN));
if (PHIsToDemote.empty())
continue;
// Demote the PHIs to the stack.
for (PHINode *PN : PHIsToDemote)
DemotePHIToStack(PN);
// Move the landingpad instruction back to the top of the landing pad block.
LPI->moveBefore(&UnwindBlock->front());
}
}
/// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
/// the function context and marking the call sites with the appropriate
/// values. These values are used by the DWARF EH emitter.
bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
SmallVector<ReturnInst *, 16> Returns;
SmallVector<InvokeInst *, 16> Invokes;
SmallSetVector<LandingPadInst *, 16> LPads;
// Look through the terminators of the basic blocks to find invokes.
for (BasicBlock &BB : F)
if (auto *II = dyn_cast<InvokeInst>(BB.getTerminator())) {
if (Function *Callee = II->getCalledFunction())
if (Callee->getIntrinsicID() == Intrinsic::donothing) {
// Remove the NOP invoke.
BranchInst::Create(II->getNormalDest(), II);
II->eraseFromParent();
continue;
}
Invokes.push_back(II);
LPads.insert(II->getUnwindDest()->getLandingPadInst());
} else if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator())) {
Returns.push_back(RI);
}
if (Invokes.empty())
return false;
NumInvokes += Invokes.size();
lowerIncomingArguments(F);
lowerAcrossUnwindEdges(F, Invokes);
Value *FuncCtx =
setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
BasicBlock *EntryBB = &F.front();
IRBuilder<> Builder(EntryBB->getTerminator());
// Get a reference to the jump buffer.
Value *JBufPtr =
Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");
// Save the frame pointer.
Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
"jbuf_fp_gep");
Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
// Save the stack pointer.
Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
"jbuf_sp_gep");
Val = Builder.CreateCall(StackAddrFn, {}, "sp");
Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
// Call the setup_dispatch instrinsic. It fills in the rest of the jmpbuf.
Builder.CreateCall(BuiltinSetupDispatchFn, {});
// Store a pointer to the function context so that the back-end will know
// where to look for it.
Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
Builder.CreateCall(FuncCtxFn, FuncCtxArg);
// At this point, we are all set up, update the invoke instructions to mark
// their call_site values.
for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
insertCallSiteStore(Invokes[I], I + 1);
ConstantInt *CallSiteNum =
ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
// Record the call site value for the back end so it stays associated with
// the invoke.
CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
}
// Mark call instructions that aren't nounwind as no-action (call_site ==
// -1). Skip the entry block, as prior to then, no function context has been
// created for this function and any unexpected exceptions thrown will go
// directly to the caller's context, which is what we want anyway, so no need
// to do anything here.
for (BasicBlock &BB : F) {
if (&BB == &F.front())
continue;
for (Instruction &I : BB)
if (I.mayThrow())
insertCallSiteStore(&I, -1);
}
// Register the function context and make sure it's known to not throw
CallInst *Register =
CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
Register->setDoesNotThrow();
// Following any allocas not in the entry block, update the saved SP in the
// jmpbuf to the new value.
for (BasicBlock &BB : F) {
if (&BB == &F.front())
continue;
for (Instruction &I : BB) {
if (auto *CI = dyn_cast<CallInst>(&I)) {
if (CI->getCalledFunction() != StackRestoreFn)
continue;
} else if (!isa<AllocaInst>(&I)) {
continue;
}
Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
StackAddr->insertAfter(&I);
new StoreInst(StackAddr, StackPtr, true, StackAddr->getNextNode());
}
}
// Finally, for any returns from this function, if this function contains an
// invoke, add a call to unregister the function context.
for (ReturnInst *Return : Returns)
CallInst::Create(UnregisterFn, FuncCtx, "", Return);
return true;
}
bool SjLjEHPrepare::runOnFunction(Function &F) {
Module &M = *F.getParent();
RegisterFn = M.getOrInsertFunction(
"_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
PointerType::getUnqual(FunctionContextTy));
UnregisterFn = M.getOrInsertFunction(
"_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
PointerType::getUnqual(FunctionContextTy));
FrameAddrFn = Intrinsic::getDeclaration(
&M, Intrinsic::frameaddress,
{Type::getInt8PtrTy(M.getContext(),
M.getDataLayout().getAllocaAddrSpace())});
StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
BuiltinSetupDispatchFn =
Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setup_dispatch);
LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
bool Res = setupEntryBlockAndCallSites(F);
return Res;
}
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