[Bug tree-optimization/68694] New: SLP loads should be permuted until supported if possible

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68694

            Bug ID: 68694
           Summary: SLP loads should be permuted until supported if
                    possible
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
            Blocks: 53947
  Target Milestone: ---

gcc.dg/vect/pr45752.c FAILs with --param=tree-reassoc-width=2 because the
association lets us arrive with a load permutation we don't support.  With
this testcase it's possible to shuffle the SLP tree (without making it invalid)
making the load permutation supported.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations