[Bug tree-optimization/82604] [8 Regression] SPEC CPU2006 410.bwaves ~50% performance regression with trunk@253679 when ftree-parallelize-loops is used

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82604

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
                 CC|                            |amker at gcc dot gnu.org,
                   |                            |matz at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org
   Target Milestone|---                         |8.0

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I suppose loop distribution inserted a version copy turning this into a
non-perfect nest for outer loops and thus disabling autopar there.

What probably makes sense is to run autoparallelization earlier or to try
-fparallelize-loops-all (using ISL dependence analysis).

Just guesses of course, autopar isn't one of our most elaborate passes...