[PATCH] c/69507 - bogus warning: ISO C does not allow ‘__alignof__ (expression)’

[Martin Sebor]

The patch below adjusts the C alignof pedantic warning to avoid
diagnosing the GCC extension (__alignof__) and only diagnose
_Alignof in C99 and prior modes.  This is consistent with how
__attribute__ ((aligned)) and _Alignas is handled (among other
extensions vs standard features).
Martin

PR c/69507 - bogus warning: ISO C does not allow ‘__alignof__ (expression)’

gcc/testsuite/ChangeLog:
2016-05-27  Martin Sebor  <mse...@redhat.com>

        PR c/69507
        * gcc.dg/alignof.c: New test.

gcc/c/ChangeLog:
2016-05-27  Martin Sebor  <mse...@redhat.com>

        PR c/69507
        * c-parser.c (c_parser_alignof_expression): Avoid diagnosing
        __alignof__ (expression).

Index: gcc/c/c-parser.c
===================================================================
--- gcc/c/c-parser.c    (revision 232841)
+++ gcc/c/c-parser.c    (working copy)
@@ -7019,9 +7019,10 @@ c_parser_alignof_expression (c_parser *p
       mark_exp_read (expr.value);
       c_inhibit_evaluation_warnings--;
       in_alignof--;
-      pedwarn (start_loc,
-              OPT_Wpedantic, "ISO C does not allow %<%E (expression)%>",
-              alignof_spelling);
+      if (is_c11_alignof)
+       pedwarn (start_loc,
+                OPT_Wpedantic, "ISO C does not allow %<%E (expression)%>",
+                alignof_spelling);
       ret.value = c_alignof_expr (start_loc, expr.value);
       ret.original_code = ERROR_MARK;
       ret.original_type = NULL;
Index: gcc/testsuite/gcc.dg/alignof.c
===================================================================
--- gcc/testsuite/gcc.dg/alignof.c      (revision 0)
+++ gcc/testsuite/gcc.dg/alignof.c      (working copy)
@@ -0,0 +1,11 @@
+/* PR c/69507 - bogus warning: ISO C does not allow '__alignof__ 
(expression)'
+ */
+/* { dg-do compile } */
+/* { dg-options "-std=c11 -Wno-error -Wpedantic" } */
+
+extern int e;
+
+int a[] = {
+    __alignof__ (e),
+    _Alignof (e)       /* { dg-warning "ISO C does not allow ._Alignof 
\\(expression\\)." } */
+};