https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88013
--- Comment #9 from krux <hoganmeier at gmail dot com> ---
(In reply to ktkachov from comment #7)
> I tried current trunk (future GCC 9)
> GCC 9 learned to avoid excessive widening during vectorisation, which is
> what accounts for the large number of instructions you see.
Confirmed, the loop is now as described in comment #5 with trunk gcc.
Still with vshr+vmovn as mentioned by Ramana.
But by the way, the tail is completely unrolled, 15x the following, seems quite
excessive to me:
ldrb ip, [r1, #1] @ zero_extendqisi2
movs r6, #151
ldrb lr, [r1] @ zero_extendqisi2
movs r5, #77
ldrb r7, [r1, #2] @ zero_extendqisi2
movs r4, #28
smulbb ip, ip, r6
smlabb lr, r5, lr, ip
add ip, r3, #1
smlabb r7, r4, r7, lr
cmp ip, r2
asr r7, r7, #8
strb r7, [r0]
bge .L1
assert(n >= 16) helps a bit, but n % 16 == 0 doesn't.
