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//===---- IndirectThunks.h - Indirect Thunk Base Class ----------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
///
/// \file
/// Contains a base class for Passes that inject an MI thunk.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_INDIRECTTHUNKS_H
#define LLVM_CODEGEN_INDIRECTTHUNKS_H
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Module.h"
namespace llvm {
template <typename Derived> class ThunkInserter {
Derived &getDerived() { return *static_cast<Derived *>(this); }
protected:
bool InsertedThunks;
void doInitialization(Module &M) {}
void createThunkFunction(MachineModuleInfo &MMI, StringRef Name,
bool Comdat = true);
public:
void init(Module &M) {
InsertedThunks = false;
getDerived().doInitialization(M);
}
// return `true` if `MMI` or `MF` was modified
bool run(MachineModuleInfo &MMI, MachineFunction &MF);
};
template <typename Derived>
void ThunkInserter<Derived>::createThunkFunction(MachineModuleInfo &MMI,
StringRef Name, bool Comdat) {
assert(Name.startswith(getDerived().getThunkPrefix()) &&
"Created a thunk with an unexpected prefix!");
Module &M = const_cast<Module &>(*MMI.getModule());
LLVMContext &Ctx = M.getContext();
auto Type = FunctionType::get(Type::getVoidTy(Ctx), false);
Function *F = Function::Create(Type,
Comdat ? GlobalValue::LinkOnceODRLinkage
: GlobalValue::InternalLinkage,
Name, &M);
if (Comdat) {
F->setVisibility(GlobalValue::HiddenVisibility);
F->setComdat(M.getOrInsertComdat(Name));
}
// Add Attributes so that we don't create a frame, unwind information, or
// inline.
AttrBuilder B;
B.addAttribute(llvm::Attribute::NoUnwind);
B.addAttribute(llvm::Attribute::Naked);
F->addFnAttrs(B);
// Populate our function a bit so that we can verify.
BasicBlock *Entry = BasicBlock::Create(Ctx, "entry", F);
IRBuilder<> Builder(Entry);
Builder.CreateRetVoid();
// MachineFunctions aren't created automatically for the IR-level constructs
// we already made. Create them and insert them into the module.
MachineFunction &MF = MMI.getOrCreateMachineFunction(*F);
// A MachineBasicBlock must not be created for the Entry block; code
// generation from an empty naked function in C source code also does not
// generate one. At least GlobalISel asserts if this invariant isn't
// respected.
// Set MF properties. We never use vregs...
MF.getProperties().set(MachineFunctionProperties::Property::NoVRegs);
}
template <typename Derived>
bool ThunkInserter<Derived>::run(MachineModuleInfo &MMI, MachineFunction &MF) {
// If MF is not a thunk, check to see if we need to insert a thunk.
if (!MF.getName().startswith(getDerived().getThunkPrefix())) {
// If we've already inserted a thunk, nothing else to do.
if (InsertedThunks)
return false;
// Only add a thunk if one of the functions has the corresponding feature
// enabled in its subtarget, and doesn't enable external thunks.
// FIXME: Conditionalize on indirect calls so we don't emit a thunk when
// nothing will end up calling it.
// FIXME: It's a little silly to look at every function just to enumerate
// the subtargets, but eventually we'll want to look at them for indirect
// calls, so maybe this is OK.
if (!getDerived().mayUseThunk(MF))
return false;
getDerived().insertThunks(MMI);
InsertedThunks = true;
return true;
}
// If this *is* a thunk function, we need to populate it with the correct MI.
getDerived().populateThunk(MF);
return true;
}
} // namespace llvm
#endif
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