[Bug c/116004] New: PPC64 vector Intrinsic vec_first_mismatch_or_eos_index generates poor code

[Bug c/116004] New: PPC64 vector Intrinsic vec_first_mismatch_or_eos_index generates poor code

[munroesj at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116004

            Bug ID: 116004
           Summary: PPC64 vector Intrinsic vec_first_mismatch_or_eos_index
                    generates poor code
           Product: gcc
           Version: 13.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: munroesj at gcc dot gnu.org
  Target Milestone: ---

GCC13 generates the following code for the intrinsic
vec_first_mismatch_or_eos_index -mcpu=power9 -O3:

00000000000000c0 <test_intrn_first_mismatch_or_eos_index_PWR9>:
      c0:       d1 02 00 f0     xxspltib vs32,0
      c4:       07 00 22 10     vcmpneb v1,v2,v0
      c8:       07 00 03 10     vcmpneb v0,v3,v0
      cc:       07 19 42 10     vcmpnezb v2,v2,v3
      d0:       17 04 21 f0     xxland  vs33,vs33,vs32
      d4:       57 0d 42 f0     xxlorc  vs34,vs34,vs33
      d8:       02 16 61 10     vctzlsbb r3,v2
      dc:       b4 07 63 7c     extsw   r3,r3
      e0:       20 00 80 4e     blr

The use of vcmpneb to compare for EOS is redundant to the vcmpnezb instruction
(which includes the EOS compares). The additional xxland/xxorc logic is only
necessary because of the extra vcmpneb compares.

All you need is a single vcmpnezb as it already handles the a/b mismatch and
EOS tests for both operands. For example:

0000000000000070 <test_vec_first_mismatch_byte_or_eos_index>:
  70:   07 19 42 10     vcmpnezb v2,v2,v3
  74:   02 16 61 10     vctzlsbb r3,v2
  78:   b4 07 63 7c     extsw   r3,r3
  7c:   20 00 80 4e     blr

[Bug target/116004] PPC64 vector Intrinsic vec_first_mismatch_or_eos_index generates poor code

[munroesj at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116004

--- Comment #1 from Steven Munroe <munroesj at gcc dot gnu.org> ---
Compile test code examples:

int
test_intrn_first_mismatch_or_eos_index_PWR9 (vui8_t vra, vui8_t vrb)
{
  return vec_first_mismatch_or_eos_index (vra, vrb);
}

int
test_first_mismatch_byte_or_eos_index_PWR9 (vui8_t vra, vui8_t vrb)
{
  vui8_t abnez;
  int result;

  abnez  = vec_cmpnez (vra, vrb);
  result = vec_cntlz_lsbb (abnez);
  return result;
}

[Bug target/116004] PPC64 vector Intrinsic vec_first_mismatch_or_eos_index generates poor code

[munroesj at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116004

--- Comment #2 from Steven Munroe <munroesj at gcc dot gnu.org> ---
Actually:

  abnez  = (vui8_t) vec_cmpnez (vra, vrb);
  result = vec_cntlz_lsbb (abnez);