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//===-- IndirectCallVisitor.h - indirect call visitor ---------------------===//
//
// 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 implements defines a visitor class and a helper function that find
// all indirect call-sites in a function.
#ifndef LLVM_ANALYSIS_INDIRECTCALLVISITOR_H
#define LLVM_ANALYSIS_INDIRECTCALLVISITOR_H
#include "llvm/IR/InstVisitor.h"
#include <vector>
namespace llvm {
// Visitor class that finds indirect calls or instructions that gives vtable
// value, depending on Type.
struct PGOIndirectCallVisitor : public InstVisitor<PGOIndirectCallVisitor> {
enum class InstructionType {
kIndirectCall = 0,
kVTableVal = 1,
};
std::vector<CallBase *> IndirectCalls;
std::vector<Instruction *> ProfiledAddresses;
PGOIndirectCallVisitor(InstructionType Type) : Type(Type) {}
// Given an indirect call instruction, try to find the the following pattern
//
// %vtable = load ptr, ptr %obj
// %vfn = getelementptr inbounds ptr, ptr %vtable, i64 1
// %2 = load ptr, ptr %vfn
// $call = tail call i32 %2
//
// A heuristic is used to find the address feeding instructions.
static Instruction *tryGetVTableInstruction(CallBase *CB) {
assert(CB != nullptr && "Caller guaranteed");
if (!CB->isIndirectCall())
return nullptr;
LoadInst *LI = dyn_cast<LoadInst>(CB->getCalledOperand());
if (LI != nullptr) {
Value *FuncPtr = LI->getPointerOperand(); // GEP (or bitcast)
Value *VTablePtr = FuncPtr->stripInBoundsConstantOffsets();
// FIXME: Add support in the frontend so LLVM type intrinsics are
// emitted without LTO. This way, added intrinsics could filter
// non-vtable instructions and reduce instrumentation overhead.
// Since a non-vtable profiled address is not within the address
// range of vtable objects, it's stored as zero in indexed profiles.
// A pass that looks up symbol with an zero hash will (almost) always
// find nullptr and skip the actual transformation (e.g., comparison
// of symbols). So the performance overhead from non-vtable profiled
// address is negligible if exists at all. Comparing loaded address
// with symbol address guarantees correctness.
if (VTablePtr != nullptr && isa<Instruction>(VTablePtr))
return cast<Instruction>(VTablePtr);
}
return nullptr;
}
void visitCallBase(CallBase &Call) {
if (Call.isIndirectCall()) {
IndirectCalls.push_back(&Call);
if (Type != InstructionType::kVTableVal)
return;
Instruction *VPtr =
PGOIndirectCallVisitor::tryGetVTableInstruction(&Call);
if (VPtr)
ProfiledAddresses.push_back(VPtr);
}
}
private:
InstructionType Type;
};
inline std::vector<CallBase *> findIndirectCalls(Function &F) {
PGOIndirectCallVisitor ICV(
PGOIndirectCallVisitor::InstructionType::kIndirectCall);
ICV.visit(F);
return ICV.IndirectCalls;
}
inline std::vector<Instruction *> findVTableAddrs(Function &F) {
PGOIndirectCallVisitor ICV(
PGOIndirectCallVisitor::InstructionType::kVTableVal);
ICV.visit(F);
return ICV.ProfiledAddresses;
}
} // namespace llvm
#endif
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