[Bug target/64844] [5 Regression] Vectorization inhibited in gcc5 when loop starts with elem[1], aarch64 perf regression from 4.9.1

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64844

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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          Component|tree-optimization           |target

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
t.c:8:5: note: === vect_update_slp_costs_according_to_vf ===
t.c:8:5: note: cost model: the vector iteration cost = 26 divided by the scalar
iteration cost = 10 is greater or equal to the vectorization factor = 2.
t.c:8:5: note: not vectorized: vectorization not profitable.
t.c:8:5: note: not vectorized: vector version will never be profitable.
t.c:8:5: note: bad operation or unsupported loop bound.


A cost model issue with cortex-a57.  The cost model changed in GCC 5 for
cortex-a57.  I think this is due to unaligned loads.