https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94643
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Keywords| |missed-optimization
Status|UNCONFIRMED |NEW
Last reconfirmed| |2020-04-18
Summary|[x86_64] gratuitous sign |[sign extension of
|extension of nonnegative |nonnegative value from 32
|value from 32 to 64 bits |to 64 bits
Severity|normal |enhancement
Component|target |tree-optimization
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This could be done on the tree level:
Given (where _1 is short unsigned):
_2 = (int) _1;
_3 = _2 * 16;
_6 = (uint64_t) _3;
We should be able to convert this to:
_7 = (uint64_t) _1;
_6 = _7 << 4;
But there might be a few steps inbetween. I will let someone decide on how it
would work.
This is true even on AARCH64:
adrp x1, a
add x1, x1, :lo12:a
ldrh w0, [x1, w0, sxtw 1]
ubfiz x0, x0, 4, 16
ret
But ubfiz is the the zero extend and shift in one instruction so it does not
matter in the end ...
