[clang][Interp] Support ExpressionTraitExprs

Just push a constant bool value.

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -2051,6 +2051,13 @@ bool ByteCodeExprGen<Emitter>::VisitCXXInheritedCtorInitExpr(
   return this->emitCall(F, E);
 }
 
+template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitExpressionTraitExpr(
+    const ExpressionTraitExpr *E) {
+  assert(Ctx.getLangOpts().CPlusPlus);
+  return this->emitConstBool(E->getValue(), E);
+}
+
 template <class Emitter> bool ByteCodeExprGen<Emitter>::discard(const Expr *E) {
   if (E->containsErrors())
     return false;

clang/lib/AST/Interp/ByteCodeExprGen.h

@@ -112,6 +112,7 @@ class ByteCodeExprGen : public ConstStmtVisitor<ByteCodeExprGen<Emitter>, bool>,
   bool VisitChooseExpr(const ChooseExpr *E);
   bool VisitObjCBoolLiteralExpr(const ObjCBoolLiteralExpr *E);
   bool VisitCXXInheritedCtorInitExpr(const CXXInheritedCtorInitExpr *E);
+  bool VisitExpressionTraitExpr(const ExpressionTraitExpr *E);
 
 protected:
   bool visitExpr(const Expr *E) override;

clang/test/SemaCXX/expression-traits.cpp

@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -std=c++98 -fsyntax-only -verify -fcxx-exceptions %s
+// RUN: %clang_cc1 -std=c++98 -fsyntax-only -verify -fcxx-exceptions %s -fexperimental-new-constant-interpreter
 
 //
 // Tests for "expression traits" intrinsics such as __is_lvalue_expr.