On May 3, 2017 6:46:05 PM GMT+02:00, Jakub Jelinek <ja...@redhat.com> wrote: >On Wed, May 03, 2017 at 06:44:46PM +0200, Richard Biener wrote: >> On May 3, 2017 6:22:14 PM GMT+02:00, Jakub Jelinek <ja...@redhat.com> >wrote: >> >On Wed, May 03, 2017 at 06:18:08PM +0200, Jan Hubicka wrote: >> >> Hi, >> >> my change to sreals makes GCC to be miscompiled with GCC 4.1 and >-O0. >> > This is >> >> related to fact that using sreal implies a non-trivial constructor >> >and thus >> >> ggc_cleared_alloc is no longer standard compliant. I however do >not >> >quite understand >> >> why GCC 4.1 manages to misoptimize this code but I have checked >that >> >this helps >> >> to fix the issue and hopefully will re-start our periodic testers. >> > >> >Is store-merging pass able to optimize that back into reasonable >code >> >(sure, not into ggc_cleared_alloc)? >> >> Whether it is or not, the previous code was buggy. The zeroing does >not >> prevail until after the object construction begins (not sure whether >for >> PODs this would be different). > >Sure, I'm not questioning the patch, just wondering if we shouldn't >improve >store-merging further (we want to do it anyway for e.g. bitop adjacent >operations etc.).
We definitely want to do that. It should also 'nicely' merge with bswap for gathering the load side of a piecewise memory to memory copy. Richard. > > Jakub
