Re: [PATCH-2, rs6000] Enable vector mode for memory equality compare [PR111449]

[David Edelsohn <dje.gcc@gmail.com>]

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On Sun, Oct 8, 2023 at 10:30 PM HAO CHEN GUI <guihaoc@linux.ibm.com> wrote:

> Hi,
>   This patch enables vector mode for memory equality compare by adding
> a new expand cbranchv16qi4 and implementing it. Also the corresponding
> CC reg and compare code is set in rs6000_generate_compare. With the
> patch, 16-byte equality compare can be implemented by one vector compare
> instructions other than 2 8-byte compares with branches.
>
>   The test case is in the second patch which is rs6000 specific.
>
>   Bootstrapped and tested on powerpc64-linux BE and LE with no
> regressions.
>

Thanks for working on this.



>
> Thanks
> Gui Haochen
>
> ChangeLog
> rs6000: Enable vector compare for memory equality compare
>
> gcc/
>         PR target/111449
>         * config/rs6000/altivec.md (cbranchv16qi4): New expand pattern.
>         * config/rs6000/rs6000.cc (rs6000_generate_compare): Generate insn
>         sequence for V16QImode equality compare.
>         * config/rs6000/rs6000.h (MOVE_MAX_PIECES): Define.
>         (COMPARE_MAX_PIECES): Define.
>
> gcc/testsuite/
>         PR target/111449
>         * gcc.target/powerpc/pr111449.c: New.
>
> patch.diff
> diff --git a/gcc/config/rs6000/altivec.md b/gcc/config/rs6000/altivec.md
> index e8a596fb7e9..c69bf266402 100644
> --- a/gcc/config/rs6000/altivec.md
> +++ b/gcc/config/rs6000/altivec.md
> @@ -2605,6 +2605,39 @@ (define_insn "altivec_vupklpx"
>  }
>    [(set_attr "type" "vecperm")])
>
> +(define_expand "cbranchv16qi4"
> +  [(use (match_operator 0 "equality_operator"
> +       [(match_operand:V16QI 1 "gpc_reg_operand")
> +        (match_operand:V16QI 2 "gpc_reg_operand")]))
> +   (use (match_operand 3))]
> +  "VECTOR_UNIT_ALTIVEC_P (V16QImode)"
> +{
> +  if (!TARGET_P9_VECTOR
> +      && MEM_P (operands[1])
> +      && !altivec_indexed_or_indirect_operand (operands[1], V16QImode)
> +      && MEM_P (operands[2])
> +      && !altivec_indexed_or_indirect_operand (operands[2], V16QImode))
> +    {
> +      /* Use direct move as the byte order doesn't matter for equality
> +        compare.  */
> +      rtx reg_op1 = gen_reg_rtx (V16QImode);
> +      rtx reg_op2 = gen_reg_rtx (V16QImode);
> +      rs6000_emit_le_vsx_permute (reg_op1, operands[1], V16QImode);
> +      rs6000_emit_le_vsx_permute (reg_op2, operands[2], V16QImode);
> +      operands[1] = reg_op1;
> +      operands[2] = reg_op2;
> +    }
> +  else
> +    {
> +      operands[1] = force_reg (V16QImode, operands[1]);
> +      operands[2] = force_reg (V16QImode, operands[2]);
> +    }
> +  rtx_code code = GET_CODE (operands[0]);
> +  operands[0] = gen_rtx_fmt_ee (code, V16QImode, operands[1],
> operands[2]);
> +  rs6000_emit_cbranch (V16QImode, operands);
> +  DONE;
> +})
> +
>  ;; Compare vectors producing a vector result and a predicate, setting CR6
> to
>  ;; indicate a combined status
>  (define_insn "altivec_vcmpequ<VI_char>_p"
> diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> index efe9adce1f8..0087d786840 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -15264,6 +15264,15 @@ rs6000_generate_compare (rtx cmp, machine_mode
> mode)
>           else
>             emit_insn (gen_stack_protect_testsi (compare_result, op0,
> op1b));
>         }
> +      else if (mode == V16QImode)
> +       {
> +         gcc_assert (code == EQ || code == NE);
> +
> +         rtx result_vector = gen_reg_rtx (V16QImode);
> +         compare_result = gen_rtx_REG (CCmode, CR6_REGNO);
> +         emit_insn (gen_altivec_vcmpequb_p (result_vector, op0, op1));
> +         code = (code == NE) ? GE : LT;
> +       }
>        else
>         emit_insn (gen_rtx_SET (compare_result,
>                                 gen_rtx_COMPARE (comp_mode, op0, op1)));
> diff --git a/gcc/config/rs6000/rs6000.h b/gcc/config/rs6000/rs6000.h
> index 3503614efbd..dc33bca0802 100644
> --- a/gcc/config/rs6000/rs6000.h
> +++ b/gcc/config/rs6000/rs6000.h
> @@ -1730,6 +1730,8 @@ typedef struct rs6000_args
>     in one reasonably fast instruction.  */
>  #define MOVE_MAX (! TARGET_POWERPC64 ? 4 : 8)
>  #define MAX_MOVE_MAX 8
> +#define MOVE_MAX_PIECES (!TARGET_POWERPC64 ? 4 : 16)
> +#define COMPARE_MAX_PIECES (!TARGET_POWERPC64 ? 4 : 16)
>

How are the definitions of MOVE_MAX_PIECES and COMPARE_MAX_PIECES
determined?  The email does not provide any explanation for the
implementation.  The rest of the patch is related to vector support, but
vector support is not dependent on TARGET_POWERPC64.

Thanks, David


>
>  /* Nonzero if access to memory by bytes is no faster than for words.
>     Also nonzero if doing byte operations (specifically shifts) in
> registers
> diff --git a/gcc/testsuite/gcc.target/powerpc/pr111449.c
> b/gcc/testsuite/gcc.target/powerpc/pr111449.c
> new file mode 100644
> index 00000000000..a8c30b92a41
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/pr111449.c
> @@ -0,0 +1,19 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target powerpc_p8vector_ok } */
> +/* { dg-options "-maltivec -O2" } */
> +/* { dg-require-effective-target has_arch_ppc64 } */
> +
> +/* Ensure vector comparison is used for 16-byte memory equality compare.
> */
> +
> +int compare1 (const char* s1, const char* s2)
> +{
> +  return __builtin_memcmp (s1, s2, 16) == 0;
> +}
> +
> +int compare2 (const char* s1)
> +{
> +  return __builtin_memcmp (s1, "0123456789012345", 16) == 0;
> +}
> +
> +/* { dg-final { scan-assembler-times {\mvcmpequb\.} 2 } } */
> +/* { dg-final { scan-assembler-not {\mcmpd\M} } } */
>