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From: "felix-gcc at fefe dot de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/105728] New: dead store to static var not optimized out
Date: Wed, 25 May 2022 14:14:24 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105728

            Bug ID: 105728
           Summary: dead store to static var not optimized out
           Product: gcc
           Version: 11.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: felix-gcc at fefe dot de
  Target Milestone: ---

Consider this piece of test code:

int dummy1()
{
  static int removeme =3D 0;
  if (removeme)
  {
      return 0;
  }
  removeme =3D 1;
  return 0;
}

int dummy2()
{
  static int removeme =3D 0;
  if (!removeme)
    removeme =3D 1;
  return 0;
}

int dummy3()
{
  static int removeme =3D 0;
  removeme =3D 1;
  return 0;
}

To me, all of these do the same thing and should generate the same code.
As nobody else can see removeme, and we aren't leaking its address, shouldn=
't
the compiler be able to deduce that all accesses to removeme are
inconsequential and can be removed?

My gcc 11.3 generates a condidion and a store and a return 0 for dummy1, the
same thing for dummy2, but for dummy3 it understands that it only needs to =
emit
a return 0.=