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+//===--- ConstantEmitter.h - IR constant emission ---------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// A helper class for emitting expressions and values as llvm::Constants
+// and as initializers for global variables.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_LIB_CODEGEN_CONSTANTEMITTER_H
+#define LLVM_CLANG_LIB_CODEGEN_CONSTANTEMITTER_H
+
+#include "CodeGenFunction.h"
+#include "CodeGenModule.h"
+
+namespace clang {
+namespace CodeGen {
+
+class ConstantEmitter {
+public:
+  CodeGenModule &CGM;
+  CodeGenFunction *CGF;
+
+private:
+  bool Abstract = false;
+
+  /// Whether non-abstract components of the emitter have been initialized.
+  bool InitializedNonAbstract = false;
+
+  /// Whether the emitter has been finalized.
+  bool Finalized = false;
+
+  /// Whether the constant-emission failed.
+  bool Failed = false;
+
+  /// The AST address space where this (non-abstract) initializer is going.
+  /// Used for generating appropriate placeholders.
+  LangAS DestAddressSpace;
+
+  llvm::SmallVector<std::pair<llvm::Constant *, llvm::GlobalVariable*>, 4>
+    PlaceholderAddresses;
+
+public:
+  ConstantEmitter(CodeGenModule &CGM, CodeGenFunction *CGF = nullptr)
+    : CGM(CGM), CGF(CGF) {}
+
+  /// Initialize this emission in the context of the given function.
+  /// Use this if the expression might contain contextual references like
+  /// block addresses or PredefinedExprs.
+  ConstantEmitter(CodeGenFunction &CGF)
+    : CGM(CGF.CGM), CGF(&CGF) {}
+
+  ConstantEmitter(const ConstantEmitter &other) = delete;
+  ConstantEmitter &operator=(const ConstantEmitter &other) = delete;
+
+  ~ConstantEmitter();
+
+  /// Is the current emission context abstract?
+  bool isAbstract() const {
+    return Abstract;
+  }
+
+  /// Try to emit the initiaizer of the given declaration as an abstract
+  /// constant.  If this succeeds, the emission must be finalized.
+  llvm::Constant *tryEmitForInitializer(const VarDecl &D);
+  llvm::Constant *tryEmitForInitializer(const Expr *E, LangAS destAddrSpace,
+                                        QualType destType);
+  llvm::Constant *emitForInitializer(const APValue &value, LangAS destAddrSpace,
+                                     QualType destType);
+
+  void finalize(llvm::GlobalVariable *global);
+
+  // All of the "abstract" emission methods below permit the emission to
+  // be immediately discarded without finalizing anything.  Therefore, they
+  // must also promise not to do anything that will, in the future, require
+  // finalization:
+  //
+  //   - using the CGF (if present) for anything other than establishing
+  //     semantic context; for example, an expression with ignored
+  //     side-effects must not be emitted as an abstract expression
+  //
+  //   - doing anything that would not be safe to duplicate within an
+  //     initializer or to propagate to another context; for example,
+  //     side effects, or emitting an initialization that requires a
+  //     reference to its current location.
+
+  /// Try to emit the initializer of the given declaration as an abstract
+  /// constant.
+  llvm::Constant *tryEmitAbstractForInitializer(const VarDecl &D);
+
+  /// Emit the result of the given expression as an abstract constant,
+  /// asserting that it succeeded.  This is only safe to do when the
+  /// expression is known to be a constant expression with either a fairly
+  /// simple type or a known simple form.
+  llvm::Constant *emitAbstract(const Expr *E, QualType T);
+  llvm::Constant *emitAbstract(SourceLocation loc, const APValue &value,
+                               QualType T);
+
+  /// Try to emit the result of the given expression as an abstract constant.
+  llvm::Constant *tryEmitAbstract(const Expr *E, QualType T);
+  llvm::Constant *tryEmitAbstractForMemory(const Expr *E, QualType T);
+
+  llvm::Constant *tryEmitAbstract(const APValue &value, QualType T);
+  llvm::Constant *tryEmitAbstractForMemory(const APValue &value, QualType T);
+
+  llvm::Constant *emitNullForMemory(QualType T) {
+    return emitNullForMemory(CGM, T);
+  }
+  llvm::Constant *emitForMemory(llvm::Constant *C, QualType T) {
+    return emitForMemory(CGM, C, T);
+  }
+
+  static llvm::Constant *emitNullForMemory(CodeGenModule &CGM, QualType T);
+  static llvm::Constant *emitForMemory(CodeGenModule &CGM, llvm::Constant *C,
+                                       QualType T);
+
+  // These are private helper routines of the constant emitter that
+  // can't actually be private because things are split out into helper
+  // functions and classes.
+
+  llvm::Constant *tryEmitPrivateForVarInit(const VarDecl &D);
+
+  llvm::Constant *tryEmitPrivate(const Expr *E, QualType T);
+  llvm::Constant *tryEmitPrivateForMemory(const Expr *E, QualType T);
+
+  llvm::Constant *tryEmitPrivate(const APValue &value, QualType T);
+  llvm::Constant *tryEmitPrivateForMemory(const APValue &value, QualType T);
+
+  /// Get the address of the current location.  This is a constant
+  /// that will resolve, after finalization, to the address of the
+  /// 'signal' value that is registered with the emitter later.
+  llvm::GlobalValue *getCurrentAddrPrivate();
+
+  /// Register a 'signal' value with the emitter to inform it where to
+  /// resolve a placeholder.  The signal value must be unique in the
+  /// initializer; it might, for example, be the address of a global that
+  /// refers to the current-address value in its own initializer.
+  ///
+  /// Uses of the placeholder must be properly anchored before finalizing
+  /// the emitter, e.g. by being installed as the initializer of a global
+  /// variable.  That is, it must be possible to replaceAllUsesWith
+  /// the placeholder with the proper address of the signal.
+  void registerCurrentAddrPrivate(llvm::Constant *signal,
+                                  llvm::GlobalValue *placeholder);
+
+private:
+  void initializeNonAbstract(LangAS destAS) {
+    assert(!InitializedNonAbstract);
+    InitializedNonAbstract = true;
+    DestAddressSpace = destAS;
+  }
+  llvm::Constant *markIfFailed(llvm::Constant *init) {
+    if (!init)
+      Failed = true;
+    return init;
+  }
+
+  struct AbstractState {
+    bool OldValue;
+    size_t OldPlaceholdersSize;
+  };
+  AbstractState pushAbstract() {
+    AbstractState saved = { Abstract, PlaceholderAddresses.size() };
+    Abstract = true;
+    return saved;
+  }
+  llvm::Constant *validateAndPopAbstract(llvm::Constant *C, AbstractState save);
+};
+
+}
+}
+
+#endif