https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111617
Bug ID: 111617
Summary: Unnecessary instructions generated when comparing
mixed-sign small integers
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: davidfromonline at gmail dot com
Target Milestone: ---
Compiling with `-std=c2x -O3`
```c
bool a(signed char x, unsigned char y) {
return x == y;
}
bool b(short x, unsigned short y) {
return x == y;
}
bool c(int x, unsigned y) {
return x == y;
}
bool d(long x, unsigned long y) {
return x == y;
}
bool e(long long x, unsigned long long y) {
return x == y;
}
```
causes gcc to generate
```asm
a:
movsx edi, dil
movzx esi, sil
cmp edi, esi
sete al
ret
b:
movsx edi, di
movzx esi, si
cmp edi, esi
sete al
ret
c:
cmp edi, esi
sete al
ret
d:
cmp rdi, rsi
sete al
ret
e:
cmp rdi, rsi
sete al
ret
```
The `movsx` and `movzx` seem unnecessary, and are not emitted by clang.
See it live: https://godbolt.org/z/dfc93f7Pv
