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diff --git a/lib/AST/Interp/EvalEmitter.h b/lib/AST/Interp/EvalEmitter.h
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+//===--- EvalEmitter.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_EVALEMITTER_H
+#define LLVM_CLANG_AST_INTERP_EVALEMITTER_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 {
+class FunctionDecl;
+namespace interp {
+class Context;
+class Function;
+class InterpState;
+class Program;
+class SourceInfo;
+enum Opcode : uint32_t;
+
+/// An emitter which evaluates opcodes as they are emitted.
+class EvalEmitter : public SourceMapper {
+public:
+  using LabelTy = uint32_t;
+  using AddrTy = uintptr_t;
+  using Local = Scope::Local;
+
+  llvm::Expected<bool> interpretExpr(const Expr *E);
+  llvm::Expected<bool> interpretDecl(const VarDecl *VD);
+
+protected:
+  EvalEmitter(Context &Ctx, Program &P, State &Parent, InterpStack &Stk,
+              APValue &Result);
+
+  virtual ~EvalEmitter() {}
+
+  /// Define a label.
+  void emitLabel(LabelTy Label);
+  /// Create a label.
+  LabelTy getLabel();
+
+  /// Methods implemented by the compiler.
+  virtual bool visitExpr(const Expr *E) = 0;
+  virtual bool visitDecl(const VarDecl *VD) = 0;
+
+  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 registering a local.
+  Local createLocal(Descriptor *D);
+
+  /// Returns the source location of the current opcode.
+  SourceInfo getSource(Function *F, CodePtr PC) const override {
+    return F ? F->getSource(PC) : CurrentSource;
+  }
+
+  /// Parameter indices.
+  llvm::DenseMap<const ParmVarDecl *, unsigned> Params;
+  /// Local descriptors.
+  llvm::SmallVector<SmallVector<Local, 8>, 2> Descriptors;
+
+private:
+  /// Current compilation context.
+  Context &Ctx;
+  /// Current program.
+  Program &P;
+  /// Callee evaluation state.
+  InterpState S;
+  /// Location to write the result to.
+  APValue &Result;
+
+  /// Temporaries which require storage.
+  llvm::DenseMap<unsigned, std::unique_ptr<char[]>> Locals;
+
+  // The emitter always tracks the current instruction and sets OpPC to a token
+  // value which is mapped to the location of the opcode being evaluated.
+  CodePtr OpPC;
+  /// Location of a failure.
+  llvm::Optional<SourceLocation> BailLocation;
+  /// Location of the current instruction.
+  SourceInfo CurrentSource;
+
+  /// Next label ID to generate - first label is 1.
+  LabelTy NextLabel = 1;
+  /// Label being executed - 0 is the entry label.
+  LabelTy CurrentLabel = 0;
+  /// Active block which should be executed.
+  LabelTy ActiveLabel = 0;
+
+  /// Since expressions can only jump forward, predicated execution is
+  /// used to deal with if-else statements.
+  bool isActive() { return CurrentLabel == ActiveLabel; }
+
+  /// Helper to invoke a method.
+  bool ExecuteCall(Function *F, Pointer &&This, const SourceInfo &Info);
+  /// Helper to emit a diagnostic on a missing method.
+  bool ExecuteNoCall(const FunctionDecl *F, const SourceInfo &Info);
+
+protected:
+#define GET_EVAL_PROTO
+#include "Opcodes.inc"
+#undef GET_EVAL_PROTO
+};
+
+} // namespace interp
+} // namespace clang
+
+#endif