[Bug regression/71231] [7 Regression]: 300% runtime increase for rnflow

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71231

Uroš Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |glisse at gcc dot gnu.org

--- Comment #2 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Richard Biener from comment #1)
> Confirmed.  Last time this was Honzas estimation changes, thus CCing Honza
> (aka, I told you so before).
> 
> 160517.34236301 ... 48.68 
> 160518.25236346 ... -1.00 
> 160519.34236434 ... 155.92
> 
> so unfortunately we have one broken run but the above "encodes" the revision
> range 236301 (good) to 236434 (bad).  The other tester constrais the revision
> range to 236299 (good) to 236427 (bad).
> 
> It might be the add-to-multiply reassoc which also applies to x + x,
> producing
> 2 * x which is eventually vectorized to comparatively very slow code (in case
> of integers).  There is a regression bug showing we need to fix this in
> vectorizer pattern recog.

Nope, this time reghunt points to r236338:

Log:
x & C -> x if we know that x & ~C == 0

2016-05-17  Marc Glisse  <marc.glisse@inria.fr>

gcc/
        * match.pd (X & C): New transformation.

Reverting r236338, the -Ofast runtime on my x86_64-linux-gnu box goes from
0m24.650s to 0m15.037s.