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
