[Bug middle-end/115037] New: Unused std::vector is not optimized away.

[Bug middle-end/115037] New: Unused std::vector is not optimized away.

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115037

            Bug ID: 115037
           Summary: Unused std::vector is not optimized away.
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
  Target Milestone: ---

Compiling 
#include <vector>
void
test()
{
        std::vector<int> test;
        test.push_back (1);
}

leads to

_Z4testv:
.LFB1253:
        .cfi_startproc
        subq    $8, %rsp
        .cfi_def_cfa_offset 16
        movl    $4, %edi
        call    _Znwm
        movl    $4, %esi
        movl    $1, (%rax)
        movq    %rax, %rdi
        addq    $8, %rsp
        .cfi_def_cfa_offset 8
        jmp     _ZdlPvm

while clang optimizes to:

_Z4testv:                               # @_Z4testv
        .cfi_startproc
# %bb.0:
        retq

[Bug middle-end/115037] Unused std::vector is not optimized away.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115037

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This might be a dup of another bug which talks about the same thing.

[Bug middle-end/115037] Unused std::vector is not optimized away.

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115037

Jan Hubicka <hubicka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at redhat dot com,
                   |                            |jwakely at redhat dot com

--- Comment #2 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
I tried to look for duplicates, but did not find one.
However I think the first problem is that we do not optimize away the store of
1 to vector while clang does.  I think this is because we do not believe we can
trust that delete operator is safe?

We get:
void test ()
{
  int * test$D25839$_M_impl$D25146$_M_start;
  struct vector test;
  int * _61;

  <bb 2> [local count: 1073741824]:
  _61 = operator new (4);

  <bb 3> [local count: 1063439392]:
  *_61 = 1;
  operator delete (_61, 4);
  test ={v} {CLOBBER};
  test ={v} {CLOBBER(eol)};
  return;

  <bb 4> [count: 0]:
<L1>:
  test ={v} {CLOBBER};
  resx 2

}
If we can not trust fact that operator delete is good, perhaps we can arrange
explicit clobber before calling it? I think it is up to std::vector to decide
what it will do with the stored array so in this case even instane oprator
delete has no right to expect that the data in vector will be sane :)

[Bug middle-end/115037] Unused std::vector is not optimized away.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115037

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=94294

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Pr 94294

[Bug middle-end/115037] Unused std::vector is not optimized away.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115037

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94293#c4

[Bug middle-end/115037] Unused std::vector is not optimized away.

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115037

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=109442
                 CC|                            |xry111 at gcc dot gnu.org

--- Comment #5 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Isn't this an exact dup of PR109442?

[Bug middle-end/115037] Unused std::vector is not optimized away.

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115037

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes

[Bug middle-end/115037] Unused std::vector is not optimized away.

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115037

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #7 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
.

*** This bug has been marked as a duplicate of bug 109442 ***