[Bug tree-optimization/39300] vectorizer confused by predictive commoning and PRE

[dorit at gcc dot gnu dot org]

------- Comment #5 from dorit at gcc dot gnu dot org  2009-03-08 14:25 -------
This is a known problem... Indeed when Zdenek introduced predictive-commoning
there was a discussion on whether to schedule it before or after vectorization.
AFAIR, it ended up getting scheduled before the vectorizer just because this
happened to be what Zdenek tested/experimented with, and he didn't have a
problem with scheduling it after vectorization as long as it didn't hurt
performance (of mgrid in particular). Here are related threads:
http://gcc.gnu.org/ml/gcc-patches/2007-02/msg01383.html
http://gcc.gnu.org/ml/gcc-patches/2007-02/msg00555.html
http://gcc.gnu.org/ml/gcc-patches/2007-05/msg00571.html

Regardless of whether we scheudule predcom after vectorization, it will still
be useful to teach the vectorizer to handle such dependence patterns, as they
may (and do) appear in the source code.  


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39300