diff --git a/clang/lib/AST/ByteCode/Context.cpp b/clang/lib/AST/ByteCode/Context.cppindex a629ff9569428..d8a3368c9d885 100644--- a/clang/lib/AST/ByteCode/Context.cpp+++ b/clang/lib/AST/ByteCode/Context.cpp@@ -52,6 +52,20 @@ bool Context::isPotentialConstantExpr(State &Parent, const FunctionDecl *FD) {   return Func->isValid(); }+bool Context::isPotentialConstantExprUnevaluated(State &Parent, const Expr *E,+                                                 const FunctionDecl *FD) {+  assert(Stk.empty());+  ++EvalID;+  size_t StackSizeBefore = Stk.size();+  Compiler<EvalEmitter> C(*this, *P, Parent, Stk);++  if (!C.interpretCall(FD, E)) {+    C.cleanup();+    Stk.clearTo(StackSizeBefore);+  }+  return true;+}+ bool Context::evaluateAsRValue(State &Parent, const Expr *E, APValue &Result) {   ++EvalID;   bool Recursing = !Stk.empty();diff --git a/clang/lib/AST/ByteCode/Context.h b/clang/lib/AST/ByteCode/Context.hindex 5898ab5e54599..6ab526cec0144 100644--- a/clang/lib/AST/ByteCode/Context.h+++ b/clang/lib/AST/ByteCode/Context.h@@ -47,7 +47,9 @@ class Context final {   ~Context();    /// Checks if a function is a potential constant expression.-  bool isPotentialConstantExpr(State &Parent, const FunctionDecl *FnDecl);+  bool isPotentialConstantExpr(State &Parent, const FunctionDecl *FD);+  bool isPotentialConstantExprUnevaluated(State &Parent, const Expr *E,+                                          const FunctionDecl *FD);    /// Evaluates a toplevel expression as an rvalue.   bool evaluateAsRValue(State &Parent, const Expr *E, APValue &Result);diff --git a/clang/lib/AST/ByteCode/EvalEmitter.cpp b/clang/lib/AST/ByteCode/EvalEmitter.cppindex 5498065657e0a..6e511bc7d2fab 100644--- a/clang/lib/AST/ByteCode/EvalEmitter.cpp+++ b/clang/lib/AST/ByteCode/EvalEmitter.cpp@@ -90,6 +90,19 @@ EvaluationResult EvalEmitter::interpretAsPointer(const Expr *E,   return std::move(this->EvalResult); }+bool EvalEmitter::interpretCall(const FunctionDecl *FD, const Expr *E) {+  // Add parameters to the parameter map. The values in the ParamOffset don't+  // matter in this case as reading from them can't ever work.+  for (const ParmVarDecl *PD : FD->parameters()) {+    this->Params.insert({PD, {0, false}});+  }++  if (!this->visit(E))+    return false;+  PrimType T = Ctx.classify(E).value_or(PT_Ptr);+  return this->emitPop(T, E);+}+ void EvalEmitter::emitLabel(LabelTy Label) { CurrentLabel = Label; }  EvalEmitter::LabelTy EvalEmitter::getLabel() { return NextLabel++; }diff --git a/clang/lib/AST/ByteCode/EvalEmitter.h b/clang/lib/AST/ByteCode/EvalEmitter.hindex 7303adba22af7..2fe7da608c739 100644--- a/clang/lib/AST/ByteCode/EvalEmitter.h+++ b/clang/lib/AST/ByteCode/EvalEmitter.h@@ -40,6 +40,9 @@ class EvalEmitter : public SourceMapper {   EvaluationResult interpretDecl(const VarDecl *VD, bool CheckFullyInitialized);   /// Interpret the given Expr to a Pointer.   EvaluationResult interpretAsPointer(const Expr *E, PtrCallback PtrCB);+  /// Interpret the given expression as if it was in the body of the given+  /// function, i.e. the parameters of the function are available for use.+  bool interpretCall(const FunctionDecl *FD, const Expr *E);    /// Clean up all resources.   void cleanup();diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cppindex 767cc4c3b19eb..6a5dc7a81f4a8 100644--- a/clang/lib/AST/ExprConstant.cpp+++ b/clang/lib/AST/ExprConstant.cpp@@ -18015,6 +18015,11 @@ bool Expr::isPotentialConstantExprUnevaluated(Expr *E,   Info.InConstantContext = true;   Info.CheckingPotentialConstantExpression = true;+  if (Info.EnableNewConstInterp) {+    Info.Ctx.getInterpContext().isPotentialConstantExprUnevaluated(Info, E, FD);+    return Diags.empty();+  }+   // Fabricate a call stack frame to give the arguments a plausible cover story.   CallStackFrame Frame(Info, SourceLocation(), FD, /*This=*/nullptr,                        /*CallExpr=*/nullptr, CallRef());diff --git a/clang/test/Sema/diagnose_if.c b/clang/test/Sema/diagnose_if.cindex e9b8497d5ca4e..a4cf43e9c869f 100644--- a/clang/test/Sema/diagnose_if.c+++ b/clang/test/Sema/diagnose_if.c@@ -1,4 +1,5 @@ // RUN: %clang_cc1 %s -verify -fno-builtin+// RUN: %clang_cc1 %s -verify -fno-builtin -fexperimental-new-constant-interpreter  #define _diagnose_if(...) __attribute__((diagnose_if(__VA_ARGS__)))diff --git a/clang/test/SemaCXX/diagnose_if-ext.cpp b/clang/test/SemaCXX/diagnose_if-ext.cppindex d5625b501322e..e0f73976eea3a 100644--- a/clang/test/SemaCXX/diagnose_if-ext.cpp+++ b/clang/test/SemaCXX/diagnose_if-ext.cpp@@ -1,4 +1,5 @@ // RUN: %clang_cc1 -Wpedantic -fsyntax-only %s -verify+// RUN: %clang_cc1 -Wpedantic -fsyntax-only %s -verify -fexperimental-new-constant-interpreter  void foo() __attribute__((diagnose_if(1, "", "error"))); // expected-warning{{'diagnose_if' is a clang extension}} void foo(int a) __attribute__((diagnose_if(a, "", "error"))); // expected-warning{{'diagnose_if' is a clang extension}}diff --git a/clang/test/SemaCXX/diagnose_if.cpp b/clang/test/SemaCXX/diagnose_if.cppindex 21897c5184b73..1b9e660c4e224 100644--- a/clang/test/SemaCXX/diagnose_if.cpp+++ b/clang/test/SemaCXX/diagnose_if.cpp@@ -1,4 +1,5 @@ // RUN: %clang_cc1 %s -verify -fno-builtin -std=c++14+// RUN: %clang_cc1 %s -verify -fno-builtin -std=c++14 -fexperimental-new-constant-interpreter  #define _diagnose_if(...) __attribute__((diagnose_if(__VA_ARGS__)))