[Bug rtl-optimization/56876] New: Combine does not invent new moves

[Bug rtl-optimization/56876] New: Combine does not invent new moves

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56876

             Bug #: 56876
           Summary: Combine does not invent new moves
    Classification: Unclassified
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: glisse@gcc.gnu.org
            Target: x86_64-linux-gnu


Hello,

I am looking at this testcase:

typedef unsigned long long vec __attribute__((vector_size(16)));
vec g;
vec f1(vec a, vec b){
  return ~a&b;
}
vec f2(vec a, vec b){
  return ~g&b;
}

which compiles to:

f1:
    pandn    %xmm1, %xmm0

f2:
    pcmpeqd    %xmm0, %xmm0
    pxor    g(%rip), %xmm0
    pand    %xmm1, %xmm0

whereas I would like to get, like I do with the _mm_andnot_si128 builtin:

    movdqa    g(%rip), %xmm0
    pandn    %xmm1, %xmm0

It seems that combine cannot match the pandn pattern because the first argument
is a memory load and not a register. In this case, it would be better if it
emitted a move to put it in a register so it can match, instead of giving up. I
don't know if there is a good way to characterize such situations where an
extra move is worth it.

[Bug target/56876] Combine does not invent new moves

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56876

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|rtl-optimization            |target

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-04-08 15:53:40 UTC ---
This sounds more like a target issue where prereload instructions are too
strict.

[Bug target/56876] Combine does not invent new moves

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56876

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-12-26
      Known to fail|                            |4.7.3

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

[Bug target/56876] Combine does not invent new moves

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56876

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 53652.

*** This bug has been marked as a duplicate of bug 53652 ***