[Bug target/101543] New: extra zeroing of empty struct argument/return value

[Bug target/101543] New: extra zeroing of empty struct argument/return value

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101543

            Bug ID: 101543
           Summary: extra zeroing of empty struct argument/return value
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64-linux-gnu

Take:
struct Tag {
    friend Tag make_tag();
private:
    Tag() {}
};

Tag make_tag() { 
    return Tag{}; 
};

void needs_tag(Tag);

void foo1(void) {
    Tag t = make_tag();
    needs_tag(t);
}


struct Tag1 {};
struct Tag2 {};
struct Tag3 {};
struct Tag4 {};
struct Tag5 {};

void needs_tags(int x, Tag1 t1, Tag2 t2, Tag3 t3, Tag4 t4, Tag5 t5, int y);

void foo2(Tag1 t1, Tag2 t2, Tag3 t3, Tag4 t4, Tag5 t5)
{
needs_tags(12345, t1, t2, t3, t4, t5, t6, t7,t8, 200);
}

---- CUT ---
In make_tag the return register does not need to be zerod.
In foo1, the argument x0 does not need to be zeroed before passing to
needs_tag.
In foo2, argument registers x1-x5 don't need to have been zeroed before passing
to needs_tags.

[Bug target/101543] extra zeroing of empty struct argument/return value

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101543

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=98884

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is similar to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98884 but with
still not skipping the register part.

[Bug target/101543] extra zeroing of empty struct argument/return value

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101543

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note RTL optimizers don't like registers being uninitilized but maybe there is
way to do it ...

[Bug target/101543] extra zeroing of empty struct argument/return value

[belagod at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101543

Tejas Belagod <belagod at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-07-29
                 CC|                            |belagod at gcc dot gnu.org

[Bug target/101543] extra zeroing of empty struct argument/return value

[belagod at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101543

Tejas Belagod <belagod at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |UNCONFIRMED
     Ever confirmed|1                           |0

[Bug target/101543] extra zeroing of empty struct argument/return value

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101543

Gabriel Ravier <gabravier at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gabravier at gmail dot com

--- Comment #3 from Gabriel Ravier <gabravier at gmail dot com> ---
Seems to be fixed on trunk.

[Bug target/101543] extra zeroing of empty struct argument/return value

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101543

--- Comment #4 from Gabriel Ravier <gabravier at gmail dot com> ---
Nevermind, didn't see this was an aarch64 bug