https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64015
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Zhenqiang Chen from comment #2)
> 2) How to justify it is valueable (the overhead of ccmp is OK) when
> generating ccmp?
If we ignore the case for swapping.
Try this one:
int
test (int a, int b)
{
return (a > 252) && b > 252;
}
With my patch to do the forcing:
test:
cmp w0, 252
mov w0, 252
ccmp w1, w0, 4, gt
cset w0, gt
ret
Without:
test:
cmp w0, 252
cset w2, gt
cmp w1, 252
cset w0, gt
and w0, w2, w0
ret
Or better yet take:
int
test (int a, int b)
{
return (a > 321223) && b > 321224;
}
Without:
test:
mov w3, 59079
mov w2, 59080
movk w3, 0x4, lsl 16
movk w2, 0x4, lsl 16
cmp w0, w3
cset w3, gt
cmp w1, w2
cset w0, gt
and w0, w3, w0
ret
With forcing:
test:
mov w3, 59079
mov w2, 59080
movk w3, 0x4, lsl 16
movk w2, 0x4, lsl 16
cmp w0, w3
ccmp w1, w2, 4, gt
cset w0, gt
ret
--- CUT ---
Also take:
int
test (int a, int b)
{
return (a > 33) && b > 33;
}
Without:
test:
cmp w0, 33
cset w2, gt
cmp w1, 33
cset w0, gt
and w0, w2, w0
ret
With forcing:
test:
cmp w0, 33
mov w0, 33
ccmp w1, w0, 4, gt
cset w0, gt
ret
See how with forcing is always the same size or smaller?
