1 //===--- ConstantEmitter.h - IR constant emission ---------------*- C++ -*-===//
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
7 //===----------------------------------------------------------------------===//
9 // A helper class for emitting expressions and values as llvm::Constants
10 // and as initializers for global variables.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_CLANG_LIB_CODEGEN_CONSTANTEMITTER_H
15 #define LLVM_CLANG_LIB_CODEGEN_CONSTANTEMITTER_H
17 #include "CodeGenFunction.h"
18 #include "CodeGenModule.h"
23 class ConstantEmitter {
29 bool Abstract = false;
31 /// Whether non-abstract components of the emitter have been initialized.
32 bool InitializedNonAbstract = false;
34 /// Whether the emitter has been finalized.
35 bool Finalized = false;
37 /// Whether the constant-emission failed.
40 /// Whether we're in a constant context.
41 bool InConstantContext = false;
43 /// The AST address space where this (non-abstract) initializer is going.
44 /// Used for generating appropriate placeholders.
45 LangAS DestAddressSpace;
47 llvm::SmallVector<std::pair<llvm::Constant *, llvm::GlobalVariable*>, 4>
51 ConstantEmitter(CodeGenModule &CGM, CodeGenFunction *CGF = nullptr)
52 : CGM(CGM), CGF(CGF) {}
54 /// Initialize this emission in the context of the given function.
55 /// Use this if the expression might contain contextual references like
56 /// block addresses or PredefinedExprs.
57 ConstantEmitter(CodeGenFunction &CGF)
58 : CGM(CGF.CGM), CGF(&CGF) {}
60 ConstantEmitter(const ConstantEmitter &other) = delete;
61 ConstantEmitter &operator=(const ConstantEmitter &other) = delete;
65 /// Is the current emission context abstract?
66 bool isAbstract() const {
70 /// Try to emit the initiaizer of the given declaration as an abstract
71 /// constant. If this succeeds, the emission must be finalized.
72 llvm::Constant *tryEmitForInitializer(const VarDecl &D);
73 llvm::Constant *tryEmitForInitializer(const Expr *E, LangAS destAddrSpace,
75 llvm::Constant *emitForInitializer(const APValue &value, LangAS destAddrSpace,
78 void finalize(llvm::GlobalVariable *global);
80 // All of the "abstract" emission methods below permit the emission to
81 // be immediately discarded without finalizing anything. Therefore, they
82 // must also promise not to do anything that will, in the future, require
85 // - using the CGF (if present) for anything other than establishing
86 // semantic context; for example, an expression with ignored
87 // side-effects must not be emitted as an abstract expression
89 // - doing anything that would not be safe to duplicate within an
90 // initializer or to propagate to another context; for example,
91 // side effects, or emitting an initialization that requires a
92 // reference to its current location.
94 /// Try to emit the initializer of the given declaration as an abstract
96 llvm::Constant *tryEmitAbstractForInitializer(const VarDecl &D);
98 /// Emit the result of the given expression as an abstract constant,
99 /// asserting that it succeeded. This is only safe to do when the
100 /// expression is known to be a constant expression with either a fairly
101 /// simple type or a known simple form.
102 llvm::Constant *emitAbstract(const Expr *E, QualType T);
103 llvm::Constant *emitAbstract(SourceLocation loc, const APValue &value,
106 /// Try to emit the result of the given expression as an abstract constant.
107 llvm::Constant *tryEmitAbstract(const Expr *E, QualType T);
108 llvm::Constant *tryEmitAbstractForMemory(const Expr *E, QualType T);
110 llvm::Constant *tryEmitAbstract(const APValue &value, QualType T);
111 llvm::Constant *tryEmitAbstractForMemory(const APValue &value, QualType T);
113 llvm::Constant *emitNullForMemory(QualType T) {
114 return emitNullForMemory(CGM, T);
116 llvm::Constant *emitForMemory(llvm::Constant *C, QualType T) {
117 return emitForMemory(CGM, C, T);
120 static llvm::Constant *emitNullForMemory(CodeGenModule &CGM, QualType T);
121 static llvm::Constant *emitForMemory(CodeGenModule &CGM, llvm::Constant *C,
124 // These are private helper routines of the constant emitter that
125 // can't actually be private because things are split out into helper
126 // functions and classes.
128 llvm::Constant *tryEmitPrivateForVarInit(const VarDecl &D);
130 llvm::Constant *tryEmitPrivate(const Expr *E, QualType T);
131 llvm::Constant *tryEmitPrivateForMemory(const Expr *E, QualType T);
133 llvm::Constant *tryEmitPrivate(const APValue &value, QualType T);
134 llvm::Constant *tryEmitPrivateForMemory(const APValue &value, QualType T);
136 /// Get the address of the current location. This is a constant
137 /// that will resolve, after finalization, to the address of the
138 /// 'signal' value that is registered with the emitter later.
139 llvm::GlobalValue *getCurrentAddrPrivate();
141 /// Register a 'signal' value with the emitter to inform it where to
142 /// resolve a placeholder. The signal value must be unique in the
143 /// initializer; it might, for example, be the address of a global that
144 /// refers to the current-address value in its own initializer.
146 /// Uses of the placeholder must be properly anchored before finalizing
147 /// the emitter, e.g. by being installed as the initializer of a global
148 /// variable. That is, it must be possible to replaceAllUsesWith
149 /// the placeholder with the proper address of the signal.
150 void registerCurrentAddrPrivate(llvm::Constant *signal,
151 llvm::GlobalValue *placeholder);
154 void initializeNonAbstract(LangAS destAS) {
155 assert(!InitializedNonAbstract);
156 InitializedNonAbstract = true;
157 DestAddressSpace = destAS;
159 llvm::Constant *markIfFailed(llvm::Constant *init) {
165 struct AbstractState {
167 size_t OldPlaceholdersSize;
169 AbstractState pushAbstract() {
170 AbstractState saved = { Abstract, PlaceholderAddresses.size() };
174 llvm::Constant *validateAndPopAbstract(llvm::Constant *C, AbstractState save);