https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98840
Bug ID: 98840
Summary: Why does baz call the delete operator for moved
unique_ptr
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dmitriy.ovdienko at gmail dot com
Target Milestone: ---
I'm trying to evaluate the overhead of the `unique_ptr` and I do not understand
why does Gcc execute the destructor of the `unique_ptr` passed by value?
Let's assume we have two examples of code:
C style:
```
#include <memory>
void foo(int* ptr);
void baz(int value)
{
int* ptr = new int(value);
try
{
foo(ptr);
}
catch(...)
{
delete ptr;
throw;
}
}
```
The asm (/O3):
```
baz(int):
push rbp
push rbx
mov ebx, edi
mov edi, 4
sub rsp, 8
call operator new(unsigned long)
mov DWORD PTR [rax], ebx
mov rdi, rax
mov rbp, rax
call foo(int*)
add rsp, 8
pop rbx
pop rbp
ret
mov rdi, rax
jmp .L2
baz(int) [clone .cold]:
.L2:
call __cxa_begin_catch
mov esi, 4
mov rdi, rbp
call operator delete(void*, unsigned long)
call __cxa_rethrow
mov rbp, rax
call __cxa_end_catch
mov rdi, rbp
call _Unwind_Resume
```
And C++ style
```
#include <memory>
void foo(std::unique_ptr<int> ptr);
void baz(int value)
{
foo(std::make_unique<int>(value));
}
```
The asm (/O3)
```
baz(int):
push rbp
push rbx
mov ebx, edi
mov edi, 4
sub rsp, 24
call operator new(unsigned long)
lea rdi, [rsp+8]
mov DWORD PTR [rax], ebx
mov QWORD PTR [rsp+8], rax
call foo(std::unique_ptr<int, std::default_delete<int> >)
mov rdi, QWORD PTR [rsp+8]
test rdi, rdi
je .L1
mov esi, 4
call operator delete(void*, unsigned long) <<<<<< Here, why do we
need to call the delete operator. It is `foo` who is responsible for that
.L1:
add rsp, 24
pop rbx
pop rbp
ret
mov rbp, rax
jmp .L3
baz(int) [clone .cold]:
```
