Fix ICE on conditional expression between DFP and non-DFP float (PR c/71601).

A conditional expression between DFP and non-DFP floating-point
produces an ICE.  This patch fixes this by making
build_conditional_expr return early when c_common_type produces an
error.

Bootstrapped with no regressions on x86_64-pc-linux-gnu.

	PR c/71601
gcc/c:
	* c-typeck.c (build_conditional_expr): Return error_mark_node if
	c_common_type returns error_mark_node.

gcc/testsuite:
	* gcc.dg/dfp/usual-arith-conv-bad-3.c: New test.

From-SVN: r237622

gcc/c/ChangeLog

+2016-06-20  Joseph Myers  <joseph@codesourcery.com>
+
+	PR c/71601
+	* c-typeck.c (build_conditional_expr): Return error_mark_node if
+	c_common_type returns error_mark_node.
+
 2016-06-19 Martin Sebor  <msebor@redhat.com>
 
 	PR c/69507

gcc/c/c-typeck.c

@@ -4846,6 +4846,8 @@ build_conditional_expr (location_t colon_loc, tree ifexp, bool ifexp_bcp,
 	       || code2 == COMPLEX_TYPE))
     {
       result_type = c_common_type (type1, type2);
+      if (result_type == error_mark_node)
+	return error_mark_node;
       do_warn_double_promotion (result_type, type1, type2,
 				"implicit conversion from %qT to %qT to "
 				"match other result of conditional",

gcc/testsuite/ChangeLog

+2016-06-20  Joseph Myers  <joseph@codesourcery.com>
+
+	PR c/71601
+	* gcc.dg/dfp/usual-arith-conv-bad-3.c: New test.
+
 2016-06-20  Jakub Jelinek  <jakub@redhat.com>
 
 	PR middle-end/71581

gcc/testsuite/gcc.dg/dfp/usual-arith-conv-bad-3.c

+/* Test error for conditional expression between DFP and other
+   floating operand.  */
+/* { dg-do compile } */
+
+_Decimal32 a;
+float b;
+int i;
+
+void
+f (void)
+{
+  (void) (i ? a : b); /* { dg-error "mix operands" } */
+}