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 20 namespace clang { 21 namespace CodeGen { 22 23 class ConstantEmitter { 24 public: 25 CodeGenModule &CGM; 26 CodeGenFunction *const CGF; 27 28 private: 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 50 public: 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); 154 155 private: 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