c-family: Fix ICE on __builtin_speculation_safe_value () [PR94755]

When this builtin has no parameters, speculation_safe_value_resolve_call
returns BUILT_IN_NONE, but resolve_overloaded_builtin uselessly
dereferences the first param just to return error_mark_node immediately.

The following patch rearranges it so that we only read the first parameter
if fncode is not BUILT_IN_NONE.

2020-04-27  Jakub Jelinek  <jakub@redhat.com>

	PR c/94755
	* c-common.c (resolve_overloaded_builtin): Return error_mark_node for
	fncode == BUILT_IN_NONE before initialization of first_param.

	* c-c++-common/pr94755.c: New test.

gcc/c-family/ChangeLog

+2020-04-27  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/94755
+	* c-common.c (resolve_overloaded_builtin): Return error_mark_node for
+	fncode == BUILT_IN_NONE before initialization of first_param.
+
 2020-04-23  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/94733

gcc/c-family/c-common.c

@@ -7402,9 +7402,11 @@ resolve_overloaded_builtin (location_t loc, tree function,
 	enum built_in_function fncode
 	  = speculation_safe_value_resolve_call (function, params);;
 
+	if (fncode == BUILT_IN_NONE)
+	  return error_mark_node;
+
 	first_param = (*params)[0];
-	if (fncode == BUILT_IN_NONE
-	    || !speculation_safe_value_resolve_params (loc, function, params))
+	if (!speculation_safe_value_resolve_params (loc, function, params))
 	  return error_mark_node;
 
 	if (targetm.have_speculation_safe_value (true))

gcc/testsuite/ChangeLog

+2020-04-27  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/94755
+	* c-c++-common/pr94755.c: New test.
+
 2020-04-27  Felix Yang  <felix.yang@huawei.com>
 
 	PR tree-optimization/94784

gcc/testsuite/c-c++-common/pr94755.c

+/* PR c/94755 */
+/* { dg-do compile } */
+
+extern void foo (void);
+
+void
+bar (double x)
+{
+  if (x == __builtin_speculation_safe_value ())	/* { dg-error "too few arguments to function" } */
+    foo ();
+}