On Tue, Oct 9, 2018 at 8:41 AM Eric Botcazou <ebotca...@adacore.com> wrote: > > > It's not quite obvious what SSE has to do with this - any hint please? > > SSE introduced alignment constraints into the non-strict-alignment target x86 > so people didn't really want to play by the rules of strict-alignment targets.
Yeah. We've walked back and forth for that very issue though. We now require all targest to play by the same rules -- if you have a *(double *) access then that has to be aligned according to double. We couldn't realistically walk back and rely on alignment of addresses based on their type (like C would allow us to do) because we've thrown away types on addresses. See also the thread about string-length warning stuff where we've posted testcases that show you can get arbitrarily typed addresses into your strlen() calls for example by means of CSE. The middle-end is simply not prepared to preserve that information. It was repeatedly suggested that we _could_ derive alignment info from function parameter types since we rely on precise typing there for example for points-to analysis (albeit only for restrict qualification processing and for DECL_BY_REFERENCE "pointers"). That would fix the simple testcase that was presented here. > > (according to my quick check this changed between gcc-4.5 and gcc-4.6) > > Possibly indeed, I remembered GCC 4.5 as being the turning point. It was really changing over several releases, but yes. Richard. > > -- > Eric Botcazou
