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diff --git a/clang/lib/AST/Interp/ByteCodeEmitter.h b/clang/lib/AST/Interp/ByteCodeEmitter.h
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+++ b/clang/lib/AST/Interp/ByteCodeEmitter.h
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+//===--- ByteCodeEmitter.h - Instruction emitter 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 instruction emitters.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_INTERP_LINKEMITTER_H
+#define LLVM_CLANG_AST_INTERP_LINKEMITTER_H
+
+#include "ByteCodeGenError.h"
+#include "Context.h"
+#include "InterpStack.h"
+#include "InterpState.h"
+#include "PrimType.h"
+#include "Program.h"
+#include "Source.h"
+#include "llvm/Support/Error.h"
+
+namespace clang {
+namespace interp {
+class Context;
+class SourceInfo;
+enum Opcode : uint32_t;
+
+/// An emitter which links the program to bytecode for later use.
+class ByteCodeEmitter {
+protected:
+  using LabelTy = uint32_t;
+  using AddrTy = uintptr_t;
+  using Local = Scope::Local;
+
+public:
+  /// Compiles the function into the module.
+  llvm::Expected<Function *> compileFunc(const FunctionDecl *F);
+
+protected:
+  ByteCodeEmitter(Context &Ctx, Program &P) : Ctx(Ctx), P(P) {}
+
+  virtual ~ByteCodeEmitter() {}
+
+  /// Define a label.
+  void emitLabel(LabelTy Label);
+  /// Create a label.
+  LabelTy getLabel() { return ++NextLabel; }
+
+  /// Methods implemented by the compiler.
+  virtual bool visitFunc(const FunctionDecl *E) = 0;
+  virtual bool visitExpr(const Expr *E) = 0;
+  virtual bool visitDecl(const VarDecl *E) = 0;
+
+  /// Bails out if a given node cannot be compiled.
+  bool bail(const Stmt *S) { return bail(S->getBeginLoc()); }
+  bool bail(const Decl *D) { return bail(D->getBeginLoc()); }
+  bool bail(const SourceLocation &Loc);
+
+  /// Emits jumps.
+  bool jumpTrue(const LabelTy &Label);
+  bool jumpFalse(const LabelTy &Label);
+  bool jump(const LabelTy &Label);
+  bool fallthrough(const LabelTy &Label);
+
+  /// Callback for local registration.
+  Local createLocal(Descriptor *D);
+
+  /// Parameter indices.
+  llvm::DenseMap<const ParmVarDecl *, unsigned> Params;
+  /// Local descriptors.
+  llvm::SmallVector<SmallVector<Local, 8>, 2> Descriptors;
+
+private:
+  /// Current compilation context.
+  Context &Ctx;
+  /// Program to link to.
+  Program &P;
+  /// Index of the next available label.
+  LabelTy NextLabel = 0;
+  /// Offset of the next local variable.
+  unsigned NextLocalOffset = 0;
+  /// Location of a failure.
+  llvm::Optional<SourceLocation> BailLocation;
+  /// Label information for linker.
+  llvm::DenseMap<LabelTy, unsigned> LabelOffsets;
+  /// Location of label relocations.
+  llvm::DenseMap<LabelTy, llvm::SmallVector<unsigned, 5>> LabelRelocs;
+  /// Program code.
+  std::vector<char> Code;
+  /// Opcode to expression mapping.
+  SourceMap SrcMap;
+
+  /// Returns the offset for a jump or records a relocation.
+  int32_t getOffset(LabelTy Label);
+
+  /// Emits an opcode.
+  template <typename... Tys>
+  bool emitOp(Opcode Op, const Tys &... Args, const SourceInfo &L);
+
+protected:
+#define GET_LINK_PROTO
+#include "Opcodes.inc"
+#undef GET_LINK_PROTO
+};
+
+} // namespace interp
+} // namespace clang
+
+#endif