https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113625
Bug ID: 113625
Summary: Interesting behavior with and without -mcpu=generic
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Target: aarch64
Take:
```
void f(unsigned short * __restrict a, long long * __restrict b)
{
int t = 0;
t += a[0];
t += a[1];
t += a[2];
t += a[3];
b[0] = t;
}
```
Compile this with `-O3 -fno-vect-cost-model` (no extra configure options), GCC
produces:
```
f:
ldr d31, [x0]
sub sp, sp, #16
uaddlv s31, v31.4h
str s31, [sp, 12]
ldrsw x0, [sp, 12]
str x0, [x1]
add sp, sp, 16
```
And then add -mcpu=generic (or -mtune=generic), GCC produces:
```
f:
ldr d31, [x0]
uaddlv s31, v31.4h
fmov w0, s31
sxtw x0, w0
str x0, [x1]
ret
```
I would have expected -mtune=generic be the same as without it but nope.
Maybe I don't understand what the default tuning settings are now vs what
-mtune=generic is supposed to do but also it is not obvious from documentation
either. So this is at min a documentation issue.
