https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65892
--- Comment #24 from rguenther at suse dot de <rguenther at suse dot de> --- On Wed, 2 Nov 2016, txr at alumni dot caltech.edu wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65892 > > --- Comment #22 from Tim Rentsch <txr at alumni dot caltech.edu> --- > [responding to comments from rguent...@suse.de in Comment 20] > > > GCC already implements this if you specify -fno-strict-aliasing. > > The main point of my comments is that the ISO C standard requires > the behavior in this case (and similar cases) be defined and not > subject to any reordering. In other words the result must be the > same as an unoptimized version. If a -fstrict-aliasing gcc /does/ > transform the code so that the behavior is not the same as an > unoptimized version, then gcc is not a conforming implementation. GCC has various optimization options that make it a not strictly conforming implementation (-ffast-math for example), various GNU extensions to the language, etc. > Or is it your position that gcc is conforming only when operated > in the -fno-strict-aliasing mode? That position seems contrary to > the documented description of the -fstrict-aliasing option. Well, N685 is still disputed in this bug. I was just pointing out that GCC has a switch to make it conforming to your interpretation of the standard (and this switch is the default at -O0 and -O1).
