On Fri, 2015-05-22 at 16:39 -0500, Segher Boessenkool wrote: > On Fri, May 22, 2015 at 02:32:42PM -0500, Scott Wood wrote: > > > I'd also have thought that the 64bit C version above would be generally > > > 'good'. > > > > It doesn't generate the addc/addze sequence. At least with GCC 4.8.2, > > it does something like: > > > > mr tmp0, csum > > li tmp1, 0 > > li tmp2, 0 > > addc tmp3, addend, tmp0 > > adde csum, tmp2, tmp1 > > add csum, csum, tmp3 > > Right. Don't expect older compilers to do sane things here. > > All this begs a question... If it is worth spending so much time > micro-optimising this, why not pick the low-hanging fruit first? > Having a 32-bit accumulator for ones' complement sums, on a 64-bit > system, is not such a great idea.
That would be a more intrusive change -- not (comparatively) low-hanging fruit. Plus, the person submitting these patches is focused on 32-bit. -Scott _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
