https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106323
Bug ID: 106323
Summary: [Suboptimal] memcmp(s1, s2, n) == 0 expansion on
AArch64 compare to llvm
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: zhongyunde at huawei dot com
Target Milestone: ---
test case, see detail https://gcc.godbolt.org/z/PM3jxEM9M
```
#include <string.h>
int src(char* s1, char* s2) {
return memcmp(s1, s2, 3) == 0;
}
```
* llvm doesn't emit branch with instruction cset
```
src: // @src
ldrh w8, [x0]
ldrh w9, [x1]
ldrb w10, [x0, #2]
ldrb w11, [x1, #2]
eor w8, w8, w9
eor w9, w10, w11
orr w8, w8, w9
cmp w8, #0
cset w0, eq
ret
```
* gcc
```
src:
ldrh w3, [x0]
ldrh w2, [x1]
cmp w3, w2
beq .L5
.L2:
mov w0, 1
eor w0, w0, 1
ret
.L5:
ldrb w2, [x0, 2]
ldrb w0, [x1, 2]
cmp w2, w0
bne .L2
mov w0, 0
eor w0, w0, 1
ret
```
