[Bug middle-end/109370] New: Missed optimization for std::optional branchless unwrapping

[andre.schackier at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109370

            Bug ID: 109370
           Summary: Missed optimization for std::optional branchless
                    unwrapping
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: andre.schackier at gmail dot com
  Target Milestone: ---

Given the following source code godbolt: https://godbolt.org/z/vW6ebqafK

#include <optional>

int f(std::optional<int>&& o) {
    if (!o) return -1;

    return *o;
}

gcc with '-O3' generates:
f(std::optional<int>&&):
        cmp     BYTE PTR [rdi+4], 0
        je      .L3
        mov     eax, DWORD PTR [rdi]
        ret
.L3:
        mov     eax, -1
        ret

while clang generates:
f(std::optional<int>&&):                    # @f(std::optional<int>&&)
        xor     eax, eax
        cmp     byte ptr [rdi + 4], 1
        sbb     eax, eax
        or      eax, dword ptr [rdi]
        ret