[Bug c++/111806] New: g++ generates better code for variant<string, bool> at -Os compared to -O3

["hiraditya at msn dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111806

            Bug ID: 111806
           Summary: g++ generates better code for variant<string, bool> at
                    -Os compared to -O3
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hiraditya at msn dot com
  Target Milestone: ---

#include<variant>
#include<string>
#include<iostream>

int foo() {
    std::variant<std::string, bool> v {"abc"};
    std::cout << std::get<0>(v);
    return 0;
}

g++ -O3 -std=c++20 -g0  -fno-exceptions

foo():
.LFB2484:
        push    rbx
        mov     eax, 25185
        mov     edx, 3
        mov     edi, OFFSET FLAT:_ZSt4cout
        sub     rsp, 48
        lea     rbx, [rsp+16]
        mov     WORD PTR [rsp+16], ax
        mov     rsi, rbx
        mov     QWORD PTR [rsp], rbx
        mov     BYTE PTR [rsp+18], 99
        mov     QWORD PTR [rsp+8], 3
        mov     BYTE PTR [rsp+19], 0
        mov     BYTE PTR [rsp+32], 0
        call    std::basic_ostream<char, std::char_traits<char> >&
std::__ostream_insert<char, std::char_traits<char> >(std::basic_ostream<char,
std::char_traits<char> >&, char const*, long)
        cmp     BYTE PTR [rsp+32], 0
        je      .L5
.L2:
        add     rsp, 48
        xor     eax, eax
        pop     rbx
        ret
.L5:
        mov     rdi, QWORD PTR [rsp]
        cmp     rdi, rbx
        je      .L2
        mov     rax, QWORD PTR [rsp+16]
        lea     rsi, [rax+1]
        call    operator delete(void*, unsigned long)
        add     rsp, 48
        xor     eax, eax
        pop     rbx
        ret
.LFE2484:


g++ -Os -std=c++20 -g0  -fno-exceptions


foo():
.LFB2463:
        push    rbx
        mov     edx, 3
        mov     edi, OFFSET FLAT:_ZSt4cout
        sub     rsp, 48
        lea     rbx, [rsp+24]
        mov     WORD PTR [rsp+24], 25185
        mov     rsi, rbx
        mov     QWORD PTR [rsp+8], rbx
        mov     BYTE PTR [rsp+26], 99
        mov     QWORD PTR [rsp+16], 3
        mov     BYTE PTR [rsp+27], 0
        mov     BYTE PTR [rsp+40], 0
        call    std::basic_ostream<char, std::char_traits<char> >&
std::__ostream_insert<char, std::char_traits<char> >(std::basic_ostream<char,
std::char_traits<char> >&, char const*, long)
        cmp     BYTE PTR [rsp+40], 0
        jne     .L2
        mov     rdi, QWORD PTR [rsp+8]
        cmp     rdi, rbx
        je      .L2
        mov     rax, QWORD PTR [rsp+24]
        lea     rsi, [rax+1]
        call    operator delete(void*, unsigned long)
.L2:
        add     rsp, 48
        xor     eax, eax
        pop     rbx
        ret
.LFE2463:


https://godbolt.org/z/3xKh35Mrv