1//===--- ConstantEmitter.h - IR constant emission ---------------*- 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// A helper class for emitting expressions and values as llvm::Constants
10// and as initializers for global variables.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_CLANG_LIB_CODEGEN_CONSTANTEMITTER_H
15#define LLVM_CLANG_LIB_CODEGEN_CONSTANTEMITTER_H
16
17#include "CodeGenFunction.h"
18#include "CodeGenModule.h"
19
20namespace clang {
21namespace CodeGen {
22
23class ConstantEmitter {
24public:
25 CodeGenModule &CGM;
26 CodeGenFunction *const CGF;
27
28private:
29 bool Abstract = false;
30
31 /// Whether non-abstract components of the emitter have been initialized.
32 bool InitializedNonAbstract = false;
33
34 /// Whether the emitter has been finalized.
35 bool Finalized = false;
36
37 /// Whether the constant-emission failed.
38 bool Failed = false;
39
40 /// Whether we're in a constant context.
41 bool InConstantContext = false;
42
43 /// The AST address space where this (non-abstract) initializer is going.
44 /// Used for generating appropriate placeholders.
45 LangAS DestAddressSpace;
46
47 llvm::SmallVector<std::pair<llvm::Constant *, llvm::GlobalVariable*>, 4>
48 PlaceholderAddresses;
49
50public:
51 ConstantEmitter(CodeGenModule &CGM, CodeGenFunction *CGF = nullptr)
52 : CGM(CGM), CGF(CGF) {}
53
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) {}
59
60 ConstantEmitter(const ConstantEmitter &other) = delete;
61 ConstantEmitter &operator=(const ConstantEmitter &other) = delete;
62
63 ~ConstantEmitter();
64
65 /// Is the current emission context abstract?
66 bool isAbstract() const {
67 return Abstract;
68 }
69
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,
74 QualType destType);
75 llvm::Constant *emitForInitializer(const APValue &value, LangAS destAddrSpace,
76 QualType destType);
77
78 void finalize(llvm::GlobalVariable *global);
79
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
83 // finalization:
84 //
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
88 //
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.
93
94 /// Try to emit the initializer of the given declaration as an abstract
95 /// constant.
96 llvm::Constant *tryEmitAbstractForInitializer(const VarDecl &D);
97
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,
104 QualType T);
105
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);
109
110 llvm::Constant *tryEmitAbstract(const APValue &value, QualType T);
111 llvm::Constant *tryEmitAbstractForMemory(const APValue &value, QualType T);
112
113 llvm::Constant *tryEmitConstantExpr(const ConstantExpr *CE);
114
115 llvm::Constant *emitNullForMemory(QualType T) {
116 return emitNullForMemory(CGM, T);
117 }
118 llvm::Constant *emitForMemory(llvm::Constant *C, QualType T) {
119 return emitForMemory(CGM, C, T);
120 }
121
122 static llvm::Constant *emitNullForMemory(CodeGenModule &CGM, QualType T);
123 static llvm::Constant *emitForMemory(CodeGenModule &CGM, llvm::Constant *C,
124 QualType T);
125
126 // These are private helper routines of the constant emitter that
127 // can't actually be private because things are split out into helper
128 // functions and classes.
129
130 llvm::Constant *tryEmitPrivateForVarInit(const VarDecl &D);
131
132 llvm::Constant *tryEmitPrivate(const Expr *E, QualType T);
133 llvm::Constant *tryEmitPrivateForMemory(const Expr *E, QualType T);
134
135 llvm::Constant *tryEmitPrivate(const APValue &value, QualType T);
136 llvm::Constant *tryEmitPrivateForMemory(const APValue &value, QualType T);
137
138 /// Get the address of the current location. This is a constant
139 /// that will resolve, after finalization, to the address of the
140 /// 'signal' value that is registered with the emitter later.
141 llvm::GlobalValue *getCurrentAddrPrivate();
142
143 /// Register a 'signal' value with the emitter to inform it where to
144 /// resolve a placeholder. The signal value must be unique in the
145 /// initializer; it might, for example, be the address of a global that
146 /// refers to the current-address value in its own initializer.
147 ///
148 /// Uses of the placeholder must be properly anchored before finalizing
149 /// the emitter, e.g. by being installed as the initializer of a global
150 /// variable. That is, it must be possible to replaceAllUsesWith
151 /// the placeholder with the proper address of the signal.
152 void registerCurrentAddrPrivate(llvm::Constant *signal,
153 llvm::GlobalValue *placeholder);
154
155private:
156 void initializeNonAbstract(LangAS destAS) {
157 assert(!InitializedNonAbstract);
158 InitializedNonAbstract = true;
159 DestAddressSpace = destAS;
160 }
161 llvm::Constant *markIfFailed(llvm::Constant *init) {
162 if (!init)
163 Failed = true;
164 return init;
165 }
166
167 struct AbstractState {
168 bool OldValue;
169 size_t OldPlaceholdersSize;
170 };
171 AbstractState pushAbstract() {
172 AbstractState saved = { Abstract, PlaceholderAddresses.size() };
173 Abstract = true;
174 return saved;
175 }
176 llvm::Constant *validateAndPopAbstract(llvm::Constant *C, AbstractState save);
177};
178
179}
180}
181
182#endif
183