On 11/03/2010 04:49 PM, Bingfeng Mei wrote:
> Hello,
> I came across an issue with function "optimize" attribute. The code is like:
> __attribute__((optimize("-fno-strict-aliasing")))
> void foo()
> {
> ...
> }
>
> When compiling with -O2, we expect this function is compiled without following
> strict aliasing rule, whereas other code does. However, I found this function
> still
> has strict aliasing flag turned on during compilation. After a little
> investigation,
> I found the following lines of code in parse_optimize_options of c-common.c
> (4.5, 4.6 is similar)
>
> ...
> saved_flag_strict_aliasing = flag_strict_aliasing;
>
> /* Now parse the options. */
> decode_options (opt_argc, opt_argv);
>
> targetm.override_options_after_change();
>
> /* Don't allow changing -fstrict-aliasing. */
> flag_strict_aliasing = saved_flag_strict_aliasing;
> ...
>
> -fstrict-aliasing is excluded from function specific optimize option. I
> checked
> both internal manual and gcc manual. It seems not to be documented. I wonder
> whether there is a good reason for this? If yes, at least we should document
> it.
> BTW, the code certainly works in 4.4.
As far as I can tell the problem was that it didn't work.
See http://gcc.gnu.org/ml/gcc-patches/2008-11/msg00073.html
Andrew.
