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.
Steve Ellcey
sell...@mips.com
