clang/lib/CodeGen/ConstantEmitter.h

   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   bool isInConstantContext() const { return InConstantContext; }
  71   void setInConstantContext(bool var) { InConstantContext = var; }
  72
  73   /// Try to emit the initiaizer of the given declaration as an abstract
  74   /// constant.  If this succeeds, the emission must be finalized.
  75   llvm::Constant *tryEmitForInitializer(const VarDecl &D);
  76   llvm::Constant *tryEmitForInitializer(const Expr *E, LangAS destAddrSpace,
  77                                         QualType destType);
  78   llvm::Constant *emitForInitializer(const APValue &value, LangAS destAddrSpace,
  79                                      QualType destType);
  80
  81   void finalize(llvm::GlobalVariable *global);
  82
  83   // All of the "abstract" emission methods below permit the emission to
  84   // be immediately discarded without finalizing anything.  Therefore, they
  85   // must also promise not to do anything that will, in the future, require
  86   // finalization:
  87   //
  88   //   - using the CGF (if present) for anything other than establishing
  89   //     semantic context; for example, an expression with ignored
  90   //     side-effects must not be emitted as an abstract expression
  91   //
  92   //   - doing anything that would not be safe to duplicate within an
  93   //     initializer or to propagate to another context; for example,
  94   //     side effects, or emitting an initialization that requires a
  95   //     reference to its current location.
  96
  97   /// Try to emit the initializer of the given declaration as an abstract
  98   /// constant.
  99   llvm::Constant *tryEmitAbstractForInitializer(const VarDecl &D);
 100
 101   /// Emit the result of the given expression as an abstract constant,
 102   /// asserting that it succeeded.  This is only safe to do when the
 103   /// expression is known to be a constant expression with either a fairly
 104   /// simple type or a known simple form.
 105   llvm::Constant *emitAbstract(const Expr *E, QualType T);
 106   llvm::Constant *emitAbstract(SourceLocation loc, const APValue &value,
 107                                QualType T);
 108
 109   /// Try to emit the result of the given expression as an abstract constant.
 110   llvm::Constant *tryEmitAbstract(const Expr *E, QualType T);
 111   llvm::Constant *tryEmitAbstractForMemory(const Expr *E, QualType T);
 112
 113   llvm::Constant *tryEmitAbstract(const APValue &value, QualType T);
 114   llvm::Constant *tryEmitAbstractForMemory(const APValue &value, QualType T);
 115
 116   llvm::Constant *tryEmitConstantExpr(const ConstantExpr *CE);
 117
 118   llvm::Constant *emitNullForMemory(QualType T) {
 119     return emitNullForMemory(CGM, T);
 120   }
 121   llvm::Constant *emitForMemory(llvm::Constant *C, QualType T) {
 122     return emitForMemory(CGM, C, T);
 123   }
 124
 125   static llvm::Constant *emitNullForMemory(CodeGenModule &CGM, QualType T);
 126   static llvm::Constant *emitForMemory(CodeGenModule &CGM, llvm::Constant *C,
 127                                        QualType T);
 128
 129   // These are private helper routines of the constant emitter that
 130   // can't actually be private because things are split out into helper
 131   // functions and classes.
 132
 133   llvm::Constant *tryEmitPrivateForVarInit(const VarDecl &D);
 134
 135   llvm::Constant *tryEmitPrivate(const Expr *E, QualType T);
 136   llvm::Constant *tryEmitPrivateForMemory(const Expr *E, QualType T);
 137
 138   llvm::Constant *tryEmitPrivate(const APValue &value, QualType T);
 139   llvm::Constant *tryEmitPrivateForMemory(const APValue &value, QualType T);
 140
 141   /// Get the address of the current location.  This is a constant
 142   /// that will resolve, after finalization, to the address of the
 143   /// 'signal' value that is registered with the emitter later.
 144   llvm::GlobalValue *getCurrentAddrPrivate();
 145
 146   /// Register a 'signal' value with the emitter to inform it where to
 147   /// resolve a placeholder.  The signal value must be unique in the
 148   /// initializer; it might, for example, be the address of a global that
 149   /// refers to the current-address value in its own initializer.
 150   ///
 151   /// Uses of the placeholder must be properly anchored before finalizing
 152   /// the emitter, e.g. by being installed as the initializer of a global
 153   /// variable.  That is, it must be possible to replaceAllUsesWith
 154   /// the placeholder with the proper address of the signal.
 155   void registerCurrentAddrPrivate(llvm::Constant *signal,
 156                                   llvm::GlobalValue *placeholder);
 157
 158 private:
 159   void initializeNonAbstract(LangAS destAS) {
 160     assert(!InitializedNonAbstract);
 161     InitializedNonAbstract = true;
 162     DestAddressSpace = destAS;
 163   }
 164   llvm::Constant *markIfFailed(llvm::Constant *init) {
 165     if (!init)
 166       Failed = true;
 167     return init;
 168   }
 169
 170   struct AbstractState {
 171     bool OldValue;
 172     size_t OldPlaceholdersSize;
 173   };
 174   AbstractState pushAbstract() {
 175     AbstractState saved = { Abstract, PlaceholderAddresses.size() };
 176     Abstract = true;
 177     return saved;
 178   }
 179   llvm::Constant *validateAndPopAbstract(llvm::Constant *C, AbstractState save);
 180 };
 181
 182 }
 183 }
 184
 185 #endif