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

[pinskia at gcc dot gnu.org via Gcc-bugs]

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.