https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120434
--- Comment #1 from Kang-Che Sung <Explorer09 at gmail dot com> ---
For signed integers that GCC can detect to be always positive, it uses signed
extension instead of zero extension, even in the "-Os" optimization mode.
For x86-64, sometimes zero extension can produce smaller code.
Test code:
```c
#include <stdint.h>
extern uint64_t subroutine(uint64_t x);
uint64_t func1a(int32_t x) {
if (x < 50)
return 0;
return subroutine(x);
}
uint64_t func1b(int32_t x) {
if (x < 50)
return 0;
__asm__ ("" : "+r" (x)); // Break the (x >= 50) assumption
return subroutine((uint64_t)(uint32_t)x);
}
```
x86_64 gcc 15.1 with "-Os" option produces:
```x86asm
func1a:
cmpl $49, %edi
jle .L2
movslq %edi, %rdi
jmp subroutine
.L2:
xorl %eax, %eax
ret
func1b:
cmpl $49, %edi
jle .L5
movl %edi, %edi
jmp subroutine
.L5:
xorl %eax, %eax
ret
```
