PR c++/84424 - ICE with constexpr and __builtin_shuffle.

	* constexpr.c (reduced_constant_expression_p): Handle CONSTRUCTOR of
	VECTOR_TYPE.

From-SVN: r257924

gcc/cp/ChangeLog

+2018-02-22  Jason Merrill  <jason@redhat.com>
+
+	PR c++/84424 - ICE with constexpr and __builtin_shuffle.
+	* constexpr.c (reduced_constant_expression_p): Handle CONSTRUCTOR of
+	VECTOR_TYPE.
+
 2018-02-22  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/84493

gcc/cp/constexpr.c

@@ -1763,7 +1763,13 @@ reduced_constant_expression_p (tree t)
       /* And we need to handle PTRMEM_CST wrapped in a CONSTRUCTOR.  */
       tree idx, val, field; unsigned HOST_WIDE_INT i;
       if (CONSTRUCTOR_NO_IMPLICIT_ZERO (t))
-	field = next_initializable_field (TYPE_FIELDS (TREE_TYPE (t)));
+	{
+	  if (TREE_CODE (TREE_TYPE (t)) == VECTOR_TYPE)
+	    /* An initialized vector would have a VECTOR_CST.  */
+	    return false;
+	  else
+	    field = next_initializable_field (TYPE_FIELDS (TREE_TYPE (t)));
+	}
       else
 	field = NULL_TREE;
       FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (t), i, idx, val)

gcc/testsuite/g++.dg/ext/vector34.C

+// PR c++/84424
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+typedef int vec __attribute__ ((vector_size (2 * sizeof (int))));
+
+constexpr vec u = { 1, 2 };
+constexpr vec v = __builtin_shuffle (v, u); // { dg-error "" }