[Bug target/106536] New: P9: gcc does not detect setb pattern

[Bug target/106536] New: P9: gcc does not detect setb pattern

[jens.seifert at de dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106536

            Bug ID: 106536
           Summary: P9: gcc does not detect setb pattern
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jens.seifert at de dot ibm.com
  Target Milestone: ---

int compare2(unsigned long long a, unsigned long long b)
{
    return (a > b ? 1 : (a < b ? -1 : 0));
}

Output:
_Z8compare2yy:
        cmpld 0,3,4
        bgt 0,.L5
        mfcr 3,128
        rlwinm 3,3,1,1
        neg 3,3
        blr
.L5:
        li 3,1
        blr
        .long 0
        .byte 0,9,0,0,0,0,0,0

clang generates:

_Z8compare2yy:                          # @_Z8compare2yy
        cmpld   3, 4
        setb 3, 0
        extsw 3, 3
        blr
        .long   0
        .quad   0

[Bug target/106536] P9: gcc does not detect setb pattern

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106536

Segher Boessenkool <segher at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2022-09-13
             Status|UNCONFIRMED                 |NEW
                 CC|                            |segher at gcc dot gnu.org

--- Comment #1 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Confirmed.

GCC uses conditional branches here in expand already.  It is hard to optimise
this over that.

Using -mcpu=power10 we don't get conditional branches:

        cmpld 7,3,4      # 8    [c=4 l=4]  *cmpdi_unsigned
        li 9,1           # 43   [c=4 l=4]  *movsi_internal1/8
        cmpld 0,3,4      # 45   [c=4 l=4]  *cmpdi_unsigned
        setnbc 10,28     # 44   [c=4 l=4]  *setnbc_unsigned_si
        isel 3,9,10,1    # 46   [c=4 l=4]  isel_unsigned_si/1
        extsw 3,3        # 24   [c=4 l=4]  extendsidi2/1
        blr              # 51   [c=4 l=4]  simple_return

but this of course isn't ideal yet either.  The branches aren't fully optimised
away until ce2, which is *after* combine.  ce1 didn't catch this, perhaps
because
the two conditional assignments are a bit intertwined there?