-fstrict-aliasing fixes 3/5: Do not ignore -fstrict-aliasing changes when parsing optimization attribute

[Jan Hubicka]

Hi,
this is third part which enables us to change -fstrict-aliasing using
optimize attribute.  This ought to work safely now because inliner
propagate the flag.

Bootstrapped/regtested x86_64-linux.

Honza

        * gcc.c-torture/execute/alias-1.c: New testcase.
        * c-common.c: Do not silently ignore -fstrict-aliasing changes.
Index: testsuite/gcc.c-torture/execute/alias-1.c
===================================================================
--- testsuite/gcc.c-torture/execute/alias-1.c   (revision 0)
+++ testsuite/gcc.c-torture/execute/alias-1.c   (revision 0)
@@ -0,0 +1,19 @@
+int val;
+
+int *ptr = &val;
+float *ptr2 = &val;
+
+__attribute__((optimize ("-fno-strict-aliasing")))
+typepun ()
+{
+  *ptr2=0;
+}
+
+main()
+{
+  *ptr=1;
+  typepun ();
+  if (*ptr)
+    __builtin_abort ();
+}
+
Index: c-family/c-common.c
===================================================================
--- c-family/c-common.c (revision 231097)
+++ c-family/c-common.c (working copy)
@@ -9988,7 +9988,6 @@ parse_optimize_options (tree args, bool
   bool ret = true;
   unsigned opt_argc;
   unsigned i;
-  int saved_flag_strict_aliasing;
   const char **opt_argv;
   struct cl_decoded_option *decoded_options;
   unsigned int decoded_options_count;
@@ -10081,8 +10080,6 @@ parse_optimize_options (tree args, bool
   for (i = 1; i < opt_argc; i++)
     opt_argv[i] = (*optimize_args)[i];
 
-  saved_flag_strict_aliasing = flag_strict_aliasing;
-
   /* Now parse the options.  */
   decode_cmdline_options_to_array_default_mask (opt_argc, opt_argv,
                                                &decoded_options,
@@ -10093,9 +10090,6 @@ parse_optimize_options (tree args, bool
 
   targetm.override_options_after_change();
 
-  /* Don't allow changing -fstrict-aliasing.  */
-  flag_strict_aliasing = saved_flag_strict_aliasing;
-
   optimize_args->truncate (0);
   return ret;
 }