regression on Adobe-C++/loop_unroll

[Chandler Carruth]

I've diffed the IR at -O3 before and after r200067 and it is identical
other than SSA value names that are minutely different.

I think i'll need before/after IR or an exact commandline to produce the
exact same result you're seeing to make much progress here.

On Fri Feb 07 2014 at 1:16:35 AM, Chandler Carruth <chandlerc at gmail.com>
wrote:

> So this doesn't reproduce for me at all when I just compile and
> loop_unroll.cpp from the test suite for x86 (sandybridge). Not really sure
> what all is required to observe this slowdown.
>
> I've also checked and we have no interesting benchmark regressions on our
> internal benchmarks with that revision... Really weird.
>
> Can you provide before/after bitcode? File a bug as well to track it if
> its this severe?
>
> On Fri Feb 07 2014 at 12:32:34 AM, Chandler Carruth <chandlerc at gmail.com>
> wrote:
>
> It's really weird because the public performance bots don't show this
> regression:
>
> http://llvm.org/perf/db_default/v4/nts/21277
>
> It would be really nice to get the stuff that people have hard
> requirements on posted to the LNT dashboard...
>
> It's also particularly weird because this shouldn't really have changed
> the way LICM works. Looking into it though...
>
> On Thu Feb 06 2014 at 11:19:21 AM, Gerolf Hoflehner <ghoflehner at apple.com>
> wrote:
>
> Hi Chandler
>
> your commit seems to cause a major regression (>20%)  on loop_unroll and
> other benchmarks as well. This is ( at least)  on x86 under -O3 -flto and
> seems to be due to the loss of LICM. Please take a look.
>
> Cheers
> Gerolf
>
> ------------------------------------------------------------------------
> r200067 | chandlerc | 2014-01-24 20:07:24 -0800 (Fri, 24 Jan 2014) | 44
> lines
>
> [LPM] Make LCSSA a utility with a FunctionPass that applies it to all
> the loops in a function, and teach LICM to work in the presance of
> LCSSA.
>
>
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