[FFmpeg-devel] [PATCH 4/7] Use alias-safe types in AV_[RW] macros

[Alexander Strange]

On Feb 18, 2010, at 11:46 AM, Jason Garrett-Glaser wrote:

>> According to Jason, gcc seemed to require those attributes in some
>> cases even with the unions.  Ask him for details.
> 
> I think astrange can probably explain better than I can.
> 
> Dark Shikari

It's documented here:
http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#index-fstrict_002daliasing-785

Their conclusion (from reading some arguments on lists) is that the C99 spec isn't worded well here; it might be rewritten in C1x.

Unfortunate side note, -Wstrict-aliasing doesn't even catch some cases:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42136

llvm doesn't implement strict-aliasing in the first place, so it doesn't provide better warnings here. I don't know how good icc or other compilers are.