[Bug tree-optimization/70923] [7 regression] gcc.dg/vect/pr60092.c etc. FAIL

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70923

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2016-05-03
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think this is the x + x -> 2 * x canonicalization we now perform.  That's bad
when the target cannot vectorize integer multiplication.

We have vect_recog_mult_pattern that should have triggered here but that
only tries replacement with LSHIFT_EXPR rather than also a simple plus
for 2 * x.

Likely caused by

2016-04-26  Marc Glisse  <marc.glisse@inria.fr>

        * genmatch.c (write_predicate): Add ATTRIBUTE_UNUSED.
        * fold-const.c (fold_binary_loc): Remove 2 transformations
        superseded by match.pd.
        * match.pd (x+x -> x*2): Generalize to integers.