| Issue |
117853
|
| Summary |
Missed optimization: per-byte comparisons are not always combined properly
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
purplesyringa
|
Reproducer: https://godbolt.org/z/6caGGoo1e
```c
int is_all_ones(unsigned char *p) {
unsigned char a = p[0];
unsigned char b = p[1];
return a == 255 && b == 255;
}
```
I've expected this to compile to a single read + comparison on platforms that support unaligned accesses. Instead, this happened:
```x86asm
is_all_ones:
movzx ecx, byte ptr [rdi + 1]
and cl, byte ptr [rdi]
xor eax, eax
cmp cl, -1
sete al
ret
```
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