On Tue, Dec 31, 2013 at 11:04 AM, Jakub Jelinek <ja...@redhat.com> wrote: > Hi! > > As written in the PR, I've been looking why is llvm 3.[34] so much faster > on Scimark2 SOR benchmark and the reason is that it's predictive commoning > or whatever it uses doesn't give up on the inner loop, while our predcom > unnecessarily gives up, because there are reads that could alias the write. > > This simple patch improves the benchmark by 42%. We already ignore > unsuitable dependencies for read/read, the patch extends that for unsuitable > dependencies for read/write by just putting the read (and anything in it's > component) into the bad component which is ignored. pcom doesn't optimize > away the writes and will keep the potentially aliasing reads unmodified as > well. Without the patch we'd merge the two components, and as > !determine_offset between the two DRs, it would mean the whole merged > component would be always unsuitable and thus ignored. With the patch > we'll hopefully have some other reads with known offset to the write > and can optimize that, so the patch should always either handle what > it did before or handle perhaps some more cases. > > The inner loop from the (public domain) benchmark is added in the two tests, > one runtime test and one test looking whether pcom actually optimized it. > > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? > > 2013-12-31 Jakub Jelinek <ja...@redhat.com> > > PR tree-optimization/59643 > * tree-predcom.c (split_data_refs_to_components): If one dr is > read and one write, determine_offset fails and the write isn't > in the bad component, just put the read into the bad component. >
This caused: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59745 -- H.J.
