PR c++/85113 - ICE with constexpr and __builtin_constant_p.

	* constexpr.c (cxx_eval_builtin_function_call): Only defer
	__builtin_constant_p if ctx->quiet.

From-SVN: r259051

gcc/cp/ChangeLog

+2018-04-03  Jason Merrill  <jason@redhat.com>
+
+	PR c++/85113 - ICE with constexpr and __builtin_constant_p.
+	* constexpr.c (cxx_eval_builtin_function_call): Only defer
+	__builtin_constant_p if ctx->quiet.
+
 2018-04-03  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/84768

gcc/cp/constexpr.c

@@ -1171,7 +1171,10 @@ cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun,
   /* Don't fold __builtin_constant_p within a constexpr function.  */
   bool bi_const_p = (DECL_FUNCTION_CODE (fun) == BUILT_IN_CONSTANT_P);
 
+  /* If we aren't requiring a constant expression, defer __builtin_constant_p
+     in a constexpr function until we have values for the parameters.  */
   if (bi_const_p
+      && ctx->quiet
       && current_function_decl
       && DECL_DECLARED_CONSTEXPR_P (current_function_decl))
     {

gcc/testsuite/g++.dg/ext/builtin12.C

+// PR c++/85113
+// { dg-do compile { target c++14 } }
+
+template<bool> struct A {};
+
+constexpr int foo()
+{
+  A<__builtin_constant_p(0)> a{};
+  return 0;
+}