[Bug target/86073] -O3 arm generates calls to memset even for known at the compile time very small sizes (<=3)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86073

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-06-07
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Probably arm misses the setup to handle this via can_store_by_pieces or
set_storage_via_setmem.  What arm subarchitecture are you creating code for?

On x86 with -m32 the 'size' loop isn't recognized as memset at the GIMPLE
level (it isn't a memset after all) and we expand the 'pro' loop as memset
call but not the 'rem' loop.

Note that pro seems to be MAX(size, <st> & 3) so it isn't really <= 3.

Thus, x86 is working fine but arm isn't.