[Bug tree-optimization/81611] [8 Regression] gcc un-learned loop / post-increment optimization

["egallager at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81611

Eric Gallager <egallager at gcc dot gnu.org> changed:

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

--- Comment #22 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Alexandre Oliva from comment #21)
> Author: aoliva
> Date: Tue Jan 30 17:40:50 2018
> New Revision: 257194
> 
> URL: https://gcc.gnu.org/viewcvs?rev=257194&root=gcc&view=rev
> Log:
> [PR81611] accept copies in simple_iv_increment_p
> 
> If there are copies between the GIMPLE_PHI at the loop body and the
> increment that reaches it (presumably through a back edge), still
> regard it as a simple_iv_increment, so that we won't consider the
> value in the back edge eligible for forwprop.  Doing so would risk
> making the phi node and the incremented conflicting value live
> within the loop, and the phi node to be preserved for propagated
> uses after the loop.
> 
> for  gcc/ChangeLog
> 
> 	PR tree-optimization/81611
> 	* tree-ssa-dom.c (simple_iv_increment_p): Skip intervening
> 	copies.
> 
> Modified:
>     trunk/gcc/ChangeLog
>     trunk/gcc/tree-ssa-dom.c

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