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//===- TypeMetadataUtils.cpp - Utilities related to type metadata ---------===//
//
// 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 file contains functions that make it easier to manipulate type metadata
// for devirtualization.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/TypeMetadataUtils.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
using namespace llvm;
// Search for virtual calls that call FPtr and add them to DevirtCalls.
static void
findCallsAtConstantOffset(SmallVectorImpl<DevirtCallSite> &DevirtCalls,
bool *HasNonCallUses, Value *FPtr, uint64_t Offset,
const CallInst *CI, DominatorTree &DT) {
for (const Use &U : FPtr->uses()) {
Instruction *User = cast<Instruction>(U.getUser());
// Ignore this instruction if it is not dominated by the type intrinsic
// being analyzed. Otherwise we may transform a call sharing the same
// vtable pointer incorrectly. Specifically, this situation can arise
// after indirect call promotion and inlining, where we may have uses
// of the vtable pointer guarded by a function pointer check, and a fallback
// indirect call.
if (!DT.dominates(CI, User))
continue;
if (isa<BitCastInst>(User)) {
findCallsAtConstantOffset(DevirtCalls, HasNonCallUses, User, Offset, CI,
DT);
} else if (auto *CI = dyn_cast<CallInst>(User)) {
DevirtCalls.push_back({Offset, *CI});
} else if (auto *II = dyn_cast<InvokeInst>(User)) {
DevirtCalls.push_back({Offset, *II});
} else if (HasNonCallUses) {
*HasNonCallUses = true;
}
}
}
// Search for virtual calls that load from VPtr and add them to DevirtCalls.
static void findLoadCallsAtConstantOffset(
const Module *M, SmallVectorImpl<DevirtCallSite> &DevirtCalls, Value *VPtr,
int64_t Offset, const CallInst *CI, DominatorTree &DT) {
for (const Use &U : VPtr->uses()) {
Value *User = U.getUser();
if (isa<BitCastInst>(User)) {
findLoadCallsAtConstantOffset(M, DevirtCalls, User, Offset, CI, DT);
} else if (isa<LoadInst>(User)) {
findCallsAtConstantOffset(DevirtCalls, nullptr, User, Offset, CI, DT);
} else if (auto GEP = dyn_cast<GetElementPtrInst>(User)) {
// Take into account the GEP offset.
if (VPtr == GEP->getPointerOperand() && GEP->hasAllConstantIndices()) {
SmallVector<Value *, 8> Indices(drop_begin(GEP->operands()));
int64_t GEPOffset = M->getDataLayout().getIndexedOffsetInType(
GEP->getSourceElementType(), Indices);
findLoadCallsAtConstantOffset(M, DevirtCalls, User, Offset + GEPOffset,
CI, DT);
}
}
}
}
void llvm::findDevirtualizableCallsForTypeTest(
SmallVectorImpl<DevirtCallSite> &DevirtCalls,
SmallVectorImpl<CallInst *> &Assumes, const CallInst *CI,
DominatorTree &DT) {
assert(CI->getCalledFunction()->getIntrinsicID() == Intrinsic::type_test ||
CI->getCalledFunction()->getIntrinsicID() ==
Intrinsic::public_type_test);
const Module *M = CI->getParent()->getParent()->getParent();
// Find llvm.assume intrinsics for this llvm.type.test call.
for (const Use &CIU : CI->uses())
if (auto *Assume = dyn_cast<AssumeInst>(CIU.getUser()))
Assumes.push_back(Assume);
// If we found any, search for virtual calls based on %p and add them to
// DevirtCalls.
if (!Assumes.empty())
findLoadCallsAtConstantOffset(
M, DevirtCalls, CI->getArgOperand(0)->stripPointerCasts(), 0, CI, DT);
}
void llvm::findDevirtualizableCallsForTypeCheckedLoad(
SmallVectorImpl<DevirtCallSite> &DevirtCalls,
SmallVectorImpl<Instruction *> &LoadedPtrs,
SmallVectorImpl<Instruction *> &Preds, bool &HasNonCallUses,
const CallInst *CI, DominatorTree &DT) {
assert(CI->getCalledFunction()->getIntrinsicID() ==
Intrinsic::type_checked_load ||
CI->getCalledFunction()->getIntrinsicID() ==
Intrinsic::type_checked_load_relative);
auto *Offset = dyn_cast<ConstantInt>(CI->getArgOperand(1));
if (!Offset) {
HasNonCallUses = true;
return;
}
for (const Use &U : CI->uses()) {
auto CIU = U.getUser();
if (auto EVI = dyn_cast<ExtractValueInst>(CIU)) {
if (EVI->getNumIndices() == 1 && EVI->getIndices()[0] == 0) {
LoadedPtrs.push_back(EVI);
continue;
}
if (EVI->getNumIndices() == 1 && EVI->getIndices()[0] == 1) {
Preds.push_back(EVI);
continue;
}
}
HasNonCallUses = true;
}
for (Value *LoadedPtr : LoadedPtrs)
findCallsAtConstantOffset(DevirtCalls, &HasNonCallUses, LoadedPtr,
Offset->getZExtValue(), CI, DT);
}
Constant *llvm::getPointerAtOffset(Constant *I, uint64_t Offset, Module &M,
Constant *TopLevelGlobal) {
if (I->getType()->isPointerTy()) {
if (Offset == 0)
return I;
return nullptr;
}
const DataLayout &DL = M.getDataLayout();
if (auto *C = dyn_cast<ConstantStruct>(I)) {
const StructLayout *SL = DL.getStructLayout(C->getType());
if (Offset >= SL->getSizeInBytes())
return nullptr;
unsigned Op = SL->getElementContainingOffset(Offset);
return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
Offset - SL->getElementOffset(Op), M,
TopLevelGlobal);
}
if (auto *C = dyn_cast<ConstantArray>(I)) {
ArrayType *VTableTy = C->getType();
uint64_t ElemSize = DL.getTypeAllocSize(VTableTy->getElementType());
unsigned Op = Offset / ElemSize;
if (Op >= C->getNumOperands())
return nullptr;
return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
Offset % ElemSize, M, TopLevelGlobal);
}
// (Swift-specific) relative-pointer support starts here.
if (auto *CI = dyn_cast<ConstantInt>(I)) {
if (Offset == 0 && CI->isZero()) {
return I;
}
}
if (auto *C = dyn_cast<ConstantExpr>(I)) {
switch (C->getOpcode()) {
case Instruction::Trunc:
case Instruction::PtrToInt:
return getPointerAtOffset(cast<Constant>(C->getOperand(0)), Offset, M,
TopLevelGlobal);
case Instruction::Sub: {
auto *Operand0 = cast<Constant>(C->getOperand(0));
auto *Operand1 = cast<Constant>(C->getOperand(1));
auto StripGEP = [](Constant *C) {
auto *CE = dyn_cast<ConstantExpr>(C);
if (!CE)
return C;
if (CE->getOpcode() != Instruction::GetElementPtr)
return C;
return CE->getOperand(0);
};
auto *Operand1TargetGlobal = StripGEP(getPointerAtOffset(Operand1, 0, M));
// Check that in the "sub (@a, @b)" expression, @b points back to the top
// level global (or a GEP thereof) that we're processing. Otherwise bail.
if (Operand1TargetGlobal != TopLevelGlobal)
return nullptr;
return getPointerAtOffset(Operand0, Offset, M, TopLevelGlobal);
}
default:
return nullptr;
}
}
return nullptr;
}
void llvm::replaceRelativePointerUsersWithZero(Function *F) {
for (auto *U : F->users()) {
auto *PtrExpr = dyn_cast<ConstantExpr>(U);
if (!PtrExpr || PtrExpr->getOpcode() != Instruction::PtrToInt)
continue;
for (auto *PtrToIntUser : PtrExpr->users()) {
auto *SubExpr = dyn_cast<ConstantExpr>(PtrToIntUser);
if (!SubExpr || SubExpr->getOpcode() != Instruction::Sub)
continue;
SubExpr->replaceNonMetadataUsesWith(
ConstantInt::get(SubExpr->getType(), 0));
}
}
}
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