https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53987
--- Comment #4 from Oleg Endo <olegendo at gcc dot gnu.org> ---
It seems that converting unsigned values to signed values, i.e. replacing
zero-extensions with sign-extensions and recombining sign-extensions with loads
could make sense in general.
For example, the following code from CSiBE
mpeg2dec-0.3.1/libmpeg2/motion_comp.s contains sequences like:
_MC_put_x_8_c:
.align 2
.L24:
mov.b @r5,r0
sett
extu.b r0,r1
mov.b @(1,r5),r0
extu.b r0,r0
addc r1,r0
shar r0
mov.b r0,@r4
sett
mov.b @(1,r5),r0
extu.b r0,r3
mov.b @(2,r5),r0
extu.b r0,r1
mov r3,r0
addc r1,r0
shar r0
mov.b r0,@(1,r4)
....
Here effectively only 8 bit values are calculated. The zero-extensions can be
omitted, since the higher bits do not influence the result of the lowest 8 bits
and the higher bits are discarded after the 8 bit stores.
