Steve Ellcey <sell...@mips.com> wrote: >On Fri, 2013-12-13 at 11:26 +0100, Richard Biener wrote: >> On Thu, Dec 12, 2013 at 8:19 PM, Steve Ellcey <sell...@mips.com> >wrote: >> > I have a question about the partial pre (-ftree-partial-pre) >optimization >> > that was added in GCC 4.8. I have noticed that this optimization >is slowing >> > down the bitmnp01 benchmark in the EEMBC1.1 suite on MIPS. I see >this with >> > the 4.8 GCC and with ToT GCC. Comparing "-O3 >-fno-tree-partial-pre" vs. >> > just "-O3" on the Tot GCC with MIPS, I see almost a 50% slowdown in >the >> > benchmark due to the partial pre optimization. >> >> Note that partial PRE wasn't added in 4.8 but much earlier. But 4.8 >got an >> option to disable it - which means you have a workaround at your >hands now. >> >> Richard. > >That is interesting because we saw this slowdown on MIPS between 4.7 >and >4.8 and someone tracked it down to this patch: > > >2012-11-16 Jan Hubicka <j...@suse.cz> > > PR tree-optimization/54717 > * tree-ssa-pre.c (do_partial_partial_insertion): Consider also edges > with ANTIC_IN.
That changes a detail in ppre. I suppose you have a testcase and a bug? Richard. >Steve Ellcey >sell...@mips.com
