PR c++/92049 - extra error with -fchecking=2.

The concepts merge brought this bit

@@ -26326,9 +26559,9 @@ build_non_dependent_expr (tree expr)
     unexpected recursive instantiations.  */
       && !parsing_nsdmi ()
       /* Don't do this during concept expansion either and for
-         the same reason.  */
-      && !expanding_concept ())
-    fold_non_dependent_expr (expr, tf_none);
+    the same reason.  */
+      && !parsing_constraint_expression_p ())
+    fold_non_dependent_expr (expr);

   STRIP_ANY_LOCATION_WRAPPER (expr);

(which I'm not finding in the ChangeLog).  Dropping tf_none means that
fold_non_dependent_expr will use tf_warning_or_error by default, and in
this test that causes an error:

  template<bool> struct cond;

  template<int> struct S { 
    void f(int i) {
      cond<__builtin_constant_p(i)>();
    }
  };

  S<1> s;

where it complains that cond<false> is incomplete.  Which it is, but we're
not actually instantiating the function f, so issuing an error seems
overzealous (though not wrong), and it breaks a bunch of tests.  This patch
brings that tf_none back.  We will still complain if we do instantiate f.

	* pt.c (build_non_dependent_expr): Call fold_non_dependent_expr
	with tf_none.

	* g++.dg/template/builtin2.C: New test.

From-SVN: r276906

gcc/cp/ChangeLog

+2019-10-11  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/92049 - extra error with -fchecking=2.
+	* pt.c (build_non_dependent_expr): Call fold_non_dependent_expr
+	with tf_none.
+
 2019-10-11  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	* typeck.c (cp_build_binary_op): Do not handle RROTATE_EXPR and

gcc/cp/pt.c

@@ -27059,7 +27059,7 @@ build_non_dependent_expr (tree expr)
       /* Don't do this during concept processing either and for
          the same reason.  */
       && !processing_constraint_expression_p ())
-    fold_non_dependent_expr (expr);
+    fold_non_dependent_expr (expr, tf_none);
 
   STRIP_ANY_LOCATION_WRAPPER (expr);
 

gcc/testsuite/ChangeLog

+2019-10-11  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/92049 - extra error with -fchecking=2.
+	* g++.dg/template/builtin2.C: New test.
+
 2019-10-11  Jim Wilson  <jimw@sifive.com>
 
 	PR rtl-optimization/91860

gcc/testsuite/g++.dg/template/builtin2.C

+// PR c++/92049 - extra error with -fchecking=2.
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fchecking=2" }
+
+#include "builtin1.C"