1 //===---- IndirectThunks.h - Indirect Thunk Base Class ----------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 ///
9 /// \file
10 /// Contains a base class for Passes that inject an MI thunk.
11 ///
12 //===----------------------------------------------------------------------===//
13
14 #ifndef LLVM_CODEGEN_INDIRECTTHUNKS_H
15 #define LLVM_CODEGEN_INDIRECTTHUNKS_H
16
17 #include "llvm/CodeGen/MachineFunction.h"
18 #include "llvm/CodeGen/MachineModuleInfo.h"
19 #include "llvm/IR/IRBuilder.h"
20 #include "llvm/IR/Module.h"
21
22 namespace llvm {
23
24 template <typename Derived, typename InsertedThunksTy = bool>
25 class ThunkInserter {
getDerived()26 Derived &getDerived() { return *static_cast<Derived *>(this); }
27
28 protected:
29 // A variable used to track whether (and possible which) thunks have been
30 // inserted so far. InsertedThunksTy is usually a bool, but can be other types
31 // to represent more than one type of thunk. Requires an |= operator to
32 // accumulate results.
33 InsertedThunksTy InsertedThunks;
doInitialization(Module & M)34 void doInitialization(Module &M) {}
35 void createThunkFunction(MachineModuleInfo &MMI, StringRef Name,
36 bool Comdat = true, StringRef TargetAttrs = "");
37
38 public:
init(Module & M)39 void init(Module &M) {
40 InsertedThunks = InsertedThunksTy{};
41 getDerived().doInitialization(M);
42 }
43 // return `true` if `MMI` or `MF` was modified
44 bool run(MachineModuleInfo &MMI, MachineFunction &MF);
45 };
46
47 template <typename Derived, typename InsertedThunksTy>
createThunkFunction(MachineModuleInfo & MMI,StringRef Name,bool Comdat,StringRef TargetAttrs)48 void ThunkInserter<Derived, InsertedThunksTy>::createThunkFunction(
49 MachineModuleInfo &MMI, StringRef Name, bool Comdat,
50 StringRef TargetAttrs) {
51 assert(Name.starts_with(getDerived().getThunkPrefix()) &&
52 "Created a thunk with an unexpected prefix!");
53
54 Module &M = const_cast<Module &>(*MMI.getModule());
55 LLVMContext &Ctx = M.getContext();
56 auto Type = FunctionType::get(Type::getVoidTy(Ctx), false);
57 Function *F = Function::Create(Type,
58 Comdat ? GlobalValue::LinkOnceODRLinkage
59 : GlobalValue::InternalLinkage,
60 Name, &M);
61 if (Comdat) {
62 F->setVisibility(GlobalValue::HiddenVisibility);
63 F->setComdat(M.getOrInsertComdat(Name));
64 }
65
66 // Add Attributes so that we don't create a frame, unwind information, or
67 // inline.
68 AttrBuilder B(Ctx);
69 B.addAttribute(llvm::Attribute::NoUnwind);
70 B.addAttribute(llvm::Attribute::Naked);
71 if (TargetAttrs != "")
72 B.addAttribute("target-features", TargetAttrs);
73 F->addFnAttrs(B);
74
75 // Populate our function a bit so that we can verify.
76 BasicBlock *Entry = BasicBlock::Create(Ctx, "entry", F);
77 IRBuilder<> Builder(Entry);
78
79 Builder.CreateRetVoid();
80
81 // MachineFunctions aren't created automatically for the IR-level constructs
82 // we already made. Create them and insert them into the module.
83 MachineFunction &MF = MMI.getOrCreateMachineFunction(*F);
84 // A MachineBasicBlock must not be created for the Entry block; code
85 // generation from an empty naked function in C source code also does not
86 // generate one. At least GlobalISel asserts if this invariant isn't
87 // respected.
88
89 // Set MF properties. We never use vregs...
90 MF.getProperties().set(MachineFunctionProperties::Property::NoVRegs);
91 }
92
93 template <typename Derived, typename InsertedThunksTy>
run(MachineModuleInfo & MMI,MachineFunction & MF)94 bool ThunkInserter<Derived, InsertedThunksTy>::run(MachineModuleInfo &MMI,
95 MachineFunction &MF) {
96 // If MF is not a thunk, check to see if we need to insert a thunk.
97 if (!MF.getName().starts_with(getDerived().getThunkPrefix())) {
98 // Only add a thunk if one of the functions has the corresponding feature
99 // enabled in its subtarget, and doesn't enable external thunks. The target
100 // can use InsertedThunks to detect whether relevant thunks have already
101 // been inserted.
102 // FIXME: Conditionalize on indirect calls so we don't emit a thunk when
103 // nothing will end up calling it.
104 // FIXME: It's a little silly to look at every function just to enumerate
105 // the subtargets, but eventually we'll want to look at them for indirect
106 // calls, so maybe this is OK.
107 if (!getDerived().mayUseThunk(MF, InsertedThunks))
108 return false;
109
110 InsertedThunks |= getDerived().insertThunks(MMI, MF);
111 return true;
112 }
113
114 // If this *is* a thunk function, we need to populate it with the correct MI.
115 getDerived().populateThunk(MF);
116 return true;
117 }
118
119 } // namespace llvm
120
121 #endif
122