https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124821
Bug ID: 124821
Summary: Missed optimization for std::string destruction
Product: gcc
Version: 15.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: terra at gnome dot org
Target Milestone: ---
https://godbolt.org/z/YvE7jWd5z
-----------------------------------------------------------------
#include <string>
extern int foo (std::string_view s);
int
bar()
{
return foo(std::string{});
}
-----------------------------------------------------------------
gcc 15.2 compiles this into code that after the call the foo has the full
destructor for std::string including a call to "operator delete":
bar():
push r14
xor edi, edi
push rbx
sub rsp, 56
lea rbx, [rsp+32]
mov BYTE PTR [rsp+32], 0
mov rsi, rbx
mov QWORD PTR [rsp+16], rbx
mov QWORD PTR [rsp+24], 0
call foo(std::basic_string_view<char, std::char_traits<char>>)
mov rdi, QWORD PTR [rsp+16]
cmp rdi, rbx
je .L1
mov DWORD PTR [rsp+12], eax
mov rax, QWORD PTR [rsp+32]
lea rsi, [rax+1]
call operator delete(void*, unsigned long)
mov eax, DWORD PTR [rsp+12]
.L1:
add rsp, 56
pop rbx
pop r14
ret
mov r14, rax
jmp .L3
bar() (.cold):
Since the string wasn't heap allocated to begin with and no-one has had access
to later cause a heap allocation, the branch with operator delete should be
optimized away.
Somewhat related to bug 87502.
