[Bug rtl-optimization/95891] New: Missing optimization

[Bug rtl-optimization/95891] New: Missing optimization

[jm at bourguet dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95891

            Bug ID: 95891
           Summary: Missing optimization
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jm at bourguet dot org
  Target Milestone: ---

I'm sorry, this is perhaps not the correct component but my knowledge of gcc
internals does not allow me to do more than guess.

For all version of gcc I've tried, the following code:

struct point {
    int x, y;
};

bool f(point a, point b) {
    return a.x == b.x && a.y == b.y;
}

bool f(unsigned long long a, unsigned long long b) {
    return a == b;
}

is compiled to

f(point, point):
        xor     eax, eax
        cmp     edi, esi
        je      .L5
        ret
.L5:
        sar     rdi, 32
        sar     rsi, 32
        cmp     edi, esi
        sete    al
        ret
f(unsigned long long, unsigned long long):
        cmp     rdi, rsi
        sete    al
        ret

I'd expect f(point, point) to have the same assembly as f(unsigned long long,
unsigned long long).

Yours,

-- Jean-Marc Bourguet

[Bug rtl-optimization/95891] Missing optimization

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95891

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-06-25
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.

[Bug tree-optimization/95891] Missing optimization

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95891

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
          Component|rtl-optimization            |tree-optimization

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.  Happens on aarch64 too:
        cmp     w0, w1
        beq     .L5
        mov     w0, 0
        ret
        .p2align 2,,3
.L5:
        asr     x0, x0, 32
        asr     x1, x1, 32
        cmp     w0, w1
        cset    w0, eq
        ret

I wonder if we could expose that point is passed via a 64bit argument at the
tree level and then use BIT_FIELD_REF to do the extraction or lower the field
extractions to BIT_FIELD_REF.

Also we don't optimize:
bool f1(unsigned long long a, unsigned long long b) {
  return (((int)a) == ((int)b)) && ((int)(a>>32) == (int)(b>>32));
}

into just return a==b; either.
Which is another thing which needs to happen after the BIT_FIELD_REF Change ...