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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 for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
/// \file
/// Contains a base class for Passes that inject an MI thunk.
#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, typename InsertedThunksTy = bool>
class ThunkInserter {
Derived &getDerived() { return *static_cast<Derived *>(this); }
// A variable used to track whether (and possible which) thunks have been
// inserted so far. InsertedThunksTy is usually a bool, but can be other types
// to represent more than one type of thunk. Requires an |= operator to
// accumulate results.
InsertedThunksTy InsertedThunks;
void doInitialization(Module &M) {}
void createThunkFunction(MachineModuleInfo &MMI, StringRef Name,
bool Comdat = true, StringRef TargetAttrs = "");
void init(Module &M) {
InsertedThunks = InsertedThunksTy{};
// return `true` if `MMI` or `MF` was modified
bool run(MachineModuleInfo &MMI, MachineFunction &MF);
template <typename Derived, typename InsertedThunksTy>
void ThunkInserter<Derived, InsertedThunksTy>::createThunkFunction(
MachineModuleInfo &MMI, StringRef Name, bool Comdat,
StringRef TargetAttrs) {
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) {
// Add Attributes so that we don't create a frame, unwind information, or
// inline.
AttrBuilder B(Ctx);
if (TargetAttrs != "")
B.addAttribute("target-features", TargetAttrs);
// Populate our function a bit so that we can verify.
BasicBlock *Entry = BasicBlock::Create(Ctx, "entry", F);
IRBuilder<> Builder(Entry);
// 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...
template <typename Derived, typename InsertedThunksTy>
bool ThunkInserter<Derived, InsertedThunksTy>::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())) {
// Only add a thunk if one of the functions has the corresponding feature
// enabled in its subtarget, and doesn't enable external thunks. The target
// can use InsertedThunks to detect whether relevant thunks have already
// been inserted.
// 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, InsertedThunks))
return false;
InsertedThunks |= getDerived().insertThunks(MMI, MF);
return true;
// If this *is* a thunk function, we need to populate it with the correct MI.
return true;
} // namespace llvm