[Bug tree-optimization/74881] New: re-align optimization blocks vectorization on powerpc

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=74881

            Bug ID: 74881
           Summary: re-align optimization blocks vectorization on powerpc
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amker at gcc dot gnu.org
  Target Milestone: ---

Hi,
gcc.dg/vect/vect-117.c starts failing with patch at r238301.  After
investigation I think it exposed a latent vectorizer issue.  Before patch, the
loop is vectorized but guarded by alias check that is always false.  That is,
the vectorized loop will never be executed in reality.  The patch only skips
known to be false alias check.

Detailed analysis and possible fix is at
https://gcc.gnu.org/ml/gcc-patches/2016-08/msg01035.html