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diff --git a/lib/AST/Interp/Function.h b/lib/AST/Interp/Function.h
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+//===--- Function.h - Bytecode function for the VM --------------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Defines the Function class which holds all bytecode function-specific data.
+//
+// The scope class which describes local variables is also defined here.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_INTERP_FUNCTION_H
+#define LLVM_CLANG_AST_INTERP_FUNCTION_H
+
+#include "Pointer.h"
+#include "Source.h"
+#include "clang/AST/Decl.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace clang {
+namespace interp {
+class Program;
+class ByteCodeEmitter;
+enum PrimType : uint32_t;
+
+/// Describes a scope block.
+///
+/// The block gathers all the descriptors of the locals defined in this block.
+class Scope {
+public:
+  /// Information about a local's storage.
+  struct Local {
+    /// Offset of the local in frame.
+    unsigned Offset;
+    /// Descriptor of the local.
+    Descriptor *Desc;
+  };
+
+  using LocalVectorTy = llvm::SmallVector<Local, 8>;
+
+  Scope(LocalVectorTy &&Descriptors) : Descriptors(std::move(Descriptors)) {}
+
+  llvm::iterator_range<LocalVectorTy::iterator> locals() {
+    return llvm::make_range(Descriptors.begin(), Descriptors.end());
+  }
+
+private:
+  /// Object descriptors in this block.
+  LocalVectorTy Descriptors;
+};
+
+/// Bytecode function.
+///
+/// Contains links to the bytecode of the function, as well as metadata
+/// describing all arguments and stack-local variables.
+class Function {
+public:
+  using ParamDescriptor = std::pair<PrimType, Descriptor *>;
+
+  /// Returns the size of the function's local stack.
+  unsigned getFrameSize() const { return FrameSize; }
+  /// Returns the size of the argument stackx
+  unsigned getArgSize() const { return ArgSize; }
+
+  /// Returns a pointer to the start of the code.
+  CodePtr getCodeBegin() const;
+  /// Returns a pointer to the end of the code.
+  CodePtr getCodeEnd() const;
+
+  /// Returns the original FunctionDecl.
+  const FunctionDecl *getDecl() const { return F; }
+
+  /// Returns the lcoation.
+  SourceLocation getLoc() const { return Loc; }
+
+  /// Returns a parameter descriptor.
+  ParamDescriptor getParamDescriptor(unsigned Offset) const;
+
+  /// Checks if the first argument is a RVO pointer.
+  bool hasRVO() const { return ParamTypes.size() != Params.size(); }
+
+  /// Range over the scope blocks.
+  llvm::iterator_range<llvm::SmallVector<Scope, 2>::iterator> scopes() {
+    return llvm::make_range(Scopes.begin(), Scopes.end());
+  }
+
+  /// Range over argument types.
+  using arg_reverse_iterator = SmallVectorImpl<PrimType>::reverse_iterator;
+  llvm::iterator_range<arg_reverse_iterator> args_reverse() {
+    return llvm::make_range(ParamTypes.rbegin(), ParamTypes.rend());
+  }
+
+  /// Returns a specific scope.
+  Scope &getScope(unsigned Idx) { return Scopes[Idx]; }
+
+  /// Returns the source information at a given PC.
+  SourceInfo getSource(CodePtr PC) const;
+
+  /// Checks if the function is valid to call in constexpr.
+  bool isConstexpr() const { return IsValid; }
+
+  /// Checks if the function is virtual.
+  bool isVirtual() const;
+
+  /// Checks if the function is a constructor.
+  bool isConstructor() const { return isa<CXXConstructorDecl>(F); }
+
+private:
+  /// Construct a function representing an actual function.
+  Function(Program &P, const FunctionDecl *F, unsigned ArgSize,
+           llvm::SmallVector<PrimType, 8> &&ParamTypes,
+           llvm::DenseMap<unsigned, ParamDescriptor> &&Params);
+
+  /// Sets the code of a function.
+  void setCode(unsigned NewFrameSize, std::vector<char> &&NewCode, SourceMap &&NewSrcMap,
+               llvm::SmallVector<Scope, 2> &&NewScopes) {
+    FrameSize = NewFrameSize;
+    Code = std::move(NewCode);
+    SrcMap = std::move(NewSrcMap);
+    Scopes = std::move(NewScopes);
+    IsValid = true;
+  }
+
+private:
+  friend class Program;
+  friend class ByteCodeEmitter;
+
+  /// Program reference.
+  Program &P;
+  /// Location of the executed code.
+  SourceLocation Loc;
+  /// Declaration this function was compiled from.
+  const FunctionDecl *F;
+  /// Local area size: storage + metadata.
+  unsigned FrameSize;
+  /// Size of the argument stack.
+  unsigned ArgSize;
+  /// Program code.
+  std::vector<char> Code;
+  /// Opcode-to-expression mapping.
+  SourceMap SrcMap;
+  /// List of block descriptors.
+  llvm::SmallVector<Scope, 2> Scopes;
+  /// List of argument types.
+  llvm::SmallVector<PrimType, 8> ParamTypes;
+  /// Map from byte offset to parameter descriptor.
+  llvm::DenseMap<unsigned, ParamDescriptor> Params;
+  /// Flag to indicate if the function is valid.
+  bool IsValid = false;
+
+public:
+  /// Dumps the disassembled bytecode to \c llvm::errs().
+  void dump() const;
+  void dump(llvm::raw_ostream &OS) const;
+};
+
+} // namespace interp
+} // namespace clang
+
+#endif