https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108766
Bug ID: 108766
Summary: unaligned byteswapped 16bit load is just bad
Product: gcc
Version: 13.0
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: riscv
Take:
```
short f(unsigned char *a)
{
return a[0] << 8 | a[1];
}
```
`-O2 -march=rv64iadc_zba_zbb_zbc_zbs_zicsr` produces:
```
lbu a5,1(a0)
lbu a4,0(a0)
slli a0,a5,8
or a0,a0,a4
slliw a5,a0,8
srli a0,a0,8
or a0,a0,a5
sext.h a0,a0
ret
```
That is just horrible.
It should just be:
```
lbu a5,1(a0)
lbu a4,0(a0)
slli a0,a4,8
or a0,a0,a5
sext.h a0,a0
ret
```
It is trying to do an unaligned short load and then a byteswap.
