https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104357
Bug ID: 104357
Summary: [Aarch64] Failure to use csinv instead of mvn+csel
where possible
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: gabravier at gmail dot com
Target Milestone: ---
unsigned char stbi__clamp(int x)
{
if ((unsigned)x > 255) {
if (x < 0) return 0;
if (x > 255) return 255;
}
return x;
}
With -O3, GCC outputs this (on aarch64):
stbi__clamp(int):
mvn w1, w0
cmp w0, 256
and w0, w0, 255
asr w1, w1, 31
and w1, w1, 255
csel w0, w0, w1, cc
ret
LLVM instead outputs this:
stbi__clamp(int):
asr w8, w0, #31
cmp w0, #255
csinv w0, w0, w8, ls
ret
I don't know if the `and`s are there because of ABI differences, but it seems
to me like the `mvn` can definitely be replaced by using `csinv` instead of
`csel`.
