[Bug middle-end/114547] New: missed-optimization: use sign flag

[goon.pri.low at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114547

            Bug ID: 114547
           Summary: missed-optimization: use sign flag
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: goon.pri.low at gmail dot com
  Target Milestone: ---

Example functions

int s(int *v, int n) {
        *v -= n;
        return *v < 0;
}

int ns(int *v, int n) {
        *v -= n;
        return *v >= 0;
}

Generated assembly

s:
        mov     eax, DWORD PTR [rdi]
        sub     eax, esi
        mov     DWORD PTR [rdi], eax
        shr     eax, 31
        ret
ns:
        mov     eax, DWORD PTR [rdi]
        sub     eax, esi
        mov     DWORD PTR [rdi], eax
        not     eax
        shr     eax, 31
        ret

Optimal assembly

s:
        xor     eax, eax
        sub     DWORD PTR [rdi], esi
        sets    al
        ret
ns:
        xor     eax, eax
        sub     DWORD PTR [rdi], esi
        setns   al
        ret