//===--- ConstantEmitter.h - IR constant emission ---------------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// 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 *const 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;

  /// Whether we're in a constant context.

  bool InConstantContext = 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 *tryEmitConstantExpr(const ConstantExpr *CE);

  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