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

["hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.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 :)