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diff --git a/lib/AST/Interp/Context.h b/lib/AST/Interp/Context.h
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+//===--- Context.h - Context for the constexpr 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 constexpr execution context.
+//
+// The execution context manages cached bytecode and the global context.
+// It invokes the compiler and interpreter, propagating errors.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_INTERP_CONTEXT_H
+#define LLVM_CLANG_AST_INTERP_CONTEXT_H
+
+#include "Context.h"
+#include "InterpStack.h"
+#include "clang/AST/APValue.h"
+#include "llvm/ADT/PointerIntPair.h"
+
+namespace clang {
+class ASTContext;
+class LangOptions;
+class Stmt;
+class FunctionDecl;
+class VarDecl;
+
+namespace interp {
+class Function;
+class Program;
+class State;
+enum PrimType : unsigned;
+
+/// Wrapper around interpreter termination results.
+enum class InterpResult {
+  /// Interpreter successfully computed a value.
+  Success,
+  /// Interpreter encountered an error and quit.
+  Fail,
+  /// Interpreter encountered an unimplemented feature, AST fallback.
+  Bail,
+};
+
+/// Holds all information required to evaluate constexpr code in a module.
+class Context {
+public:
+  /// Initialises the constexpr VM.
+  Context(ASTContext &Ctx);
+
+  /// Cleans up the constexpr VM.
+  ~Context();
+
+  /// Checks if a function is a potential constant expression.
+  InterpResult isPotentialConstantExpr(State &Parent,
+                                       const FunctionDecl *FnDecl);
+
+  /// Evaluates a toplevel expression as an rvalue.
+  InterpResult evaluateAsRValue(State &Parent, const Expr *E, APValue &Result);
+
+  /// Evaluates a toplevel initializer.
+  InterpResult evaluateAsInitializer(State &Parent, const VarDecl *VD,
+                                     APValue &Result);
+
+  /// Returns the AST context.
+  ASTContext &getASTContext() const { return Ctx; }
+  /// Returns the language options.
+  const LangOptions &getLangOpts() const;
+  /// Returns the interpreter stack.
+  InterpStack &getStack() { return Stk; }
+  /// Returns CHAR_BIT.
+  unsigned getCharBit() const;
+
+  /// Classifies an expression.
+  llvm::Optional<PrimType> classify(QualType T);
+
+private:
+  /// Runs a function.
+  InterpResult Run(State &Parent, Function *Func, APValue &Result);
+
+  /// Checks a result fromt the interpreter.
+  InterpResult Check(State &Parent, llvm::Expected<bool> &&R);
+
+private:
+  /// Current compilation context.
+  ASTContext &Ctx;
+  /// Flag to indicate if the use of the interpreter is mandatory.
+  bool ForceInterp;
+  /// Interpreter stack, shared across invocations.
+  InterpStack Stk;
+  /// Constexpr program.
+  std::unique_ptr<Program> P;
+};
+
+} // namespace interp
+} // namespace clang
+
+#endif