Re: [PATCH] s390x: Optimize vector permute with constant indexes

[Stefan Schulze Frielinghaus <stefansf@linux.ibm.com>]

On Tue, Apr 02, 2024 at 09:56:01AM +0200, Juergen Christ wrote:
> Loop vectorizer can generate vector permutes with constant indexes
> where all indexes are equal.  Optimize this case to use vector
> replicate instead of vector permute.
> 
> gcc/ChangeLog:
> 
> 	* config/s390/s390.cc (expand_perm_as_replicate): Implement.
> 	(vectorize_vec_perm_const_1): Call new function.
> 	* config/s390/vx-builtins.md (vec_splat<mode>): Change to...
> 	(@vec_splat<mode>): ...this.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.target/s390/vector/vec-expand-replicate.c: New test.
> 
> Bootstrapped and regtested on s390x.  Ok for trunk?
> 
> Signed-off-by: Juergen Christ <jchrist@linux.ibm.com>
> ---
>  gcc/config/s390/s390.cc                       | 32 +++++++++++++++++++
>  gcc/config/s390/vx-builtins.md                |  2 +-
>  .../s390/vector/vec-expand-replicate.c        | 30 +++++++++++++++++
>  3 files changed, 63 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.target/s390/vector/vec-expand-replicate.c
> 
> diff --git a/gcc/config/s390/s390.cc b/gcc/config/s390/s390.cc
> index 372a23244032..4b4014ebe444 100644
> --- a/gcc/config/s390/s390.cc
> +++ b/gcc/config/s390/s390.cc
> @@ -17923,6 +17923,35 @@ expand_perm_as_a_vlbr_vstbr_candidate (const struct expand_vec_perm_d &d)
>    return false;
>  }
>  
> +static bool expand_perm_as_replicate (const struct expand_vec_perm_d &d)
               ^~~~~~~~~~~~~~~~~~~~~~~~
Function names start on a new line.

> +{
> +  unsigned char i;
> +  unsigned char elem;
> +  rtx base = d.op0;
> +  rtx insn;
> +  /* Needed to silence maybe-uninitialized warning.  */
> +  gcc_assert(d.nelt > 0);
     ~~~~~~~~~~^~~~~~~~~~~~
Between function name and open bracket whitespace is missing.

Curiously enough, the error is about d which is a reference and cannot
be null.  If you are eager you could reduce this and open a PR.

s390.cc:17935:8: warning: ‘d’ may be used uninitialized [-Wmaybe-uninitialized]
17935 |   elem = d.perm[0];
      |   ~~~~~^~~~~~~~~~~

> +  elem = d.perm[0];
> +  for (i = 1; i < d.nelt; ++i)
> +    if (d.perm[i] != elem)
> +      return false;
> +  if (!d.testing_p)
> +    {
> +      if (elem >= d.nelt)
> +	{
> +	  base = d.op1;
> +	  elem -= d.nelt;
> +	}
> +      insn = maybe_gen_vec_splat (d.vmode, d.target, base, GEN_INT (elem));
> +      if (insn == NULL_RTX)
> +	return false;
> +      emit_insn (insn);
> +      return true;
> +    }
> +  else
> +    return maybe_code_for_vec_splat (d.vmode) != CODE_FOR_nothing;
> +}
> +
>  /* Try to find the best sequence for the vector permute operation
>     described by D.  Return true if the operation could be
>     expanded.  */
> @@ -17941,6 +17970,9 @@ vectorize_vec_perm_const_1 (const struct expand_vec_perm_d &d)
>    if (expand_perm_as_a_vlbr_vstbr_candidate (d))
>      return true;
>  
> +  if (expand_perm_as_replicate(d))
         ~~~~~~~~~~~~~~~~~~~~~~~~^~~
Between function name and open bracket whitespace is missing.

> +    return true;
> +
>    return false;
>  }
>  
> diff --git a/gcc/config/s390/vx-builtins.md b/gcc/config/s390/vx-builtins.md
> index 432d81a719fc..93c0d408a43e 100644
> --- a/gcc/config/s390/vx-builtins.md
> +++ b/gcc/config/s390/vx-builtins.md
> @@ -424,7 +424,7 @@
>  
>  
>  ; Replicate from vector element
> -(define_expand "vec_splat<mode>"
> +(define_expand "@vec_splat<mode>"
>    [(set (match_operand:V_HW                      0 "register_operand"  "")
>  	(vec_duplicate:V_HW (vec_select:<non_vec>
>  			     (match_operand:V_HW 1 "register_operand"  "")
> diff --git a/gcc/testsuite/gcc.target/s390/vector/vec-expand-replicate.c b/gcc/testsuite/gcc.target/s390/vector/vec-expand-replicate.c
> new file mode 100644
> index 000000000000..27563a00f22b
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/s390/vector/vec-expand-replicate.c
> @@ -0,0 +1,30 @@
> +/* Check that the vectorize_vec_perm_const expander correctly deals with
> +   replication.  Extracted from spec "nab".  */
> +
> +/* { dg-do compile } */
> +/* { dg-options "-O3 -mzarch -march=z13 -fvect-cost-model=unlimited" } */
> +
> +
> +#define REAL_T  double
> +typedef REAL_T  MATRIX_T[ 4 ][ 4 ];
> +
> +int concat_mat_i, concat_mat_j;
> +static void concat_mat(MATRIX_T m1, MATRIX_T, MATRIX_T m3);
> +MATRIX_T *rot4p() {
> +  MATRIX_T mat3, mat4;
> +  static MATRIX_T mat5;
> +  concat_mat(mat4, mat3, mat5);
> +}
> +void concat_mat(MATRIX_T m1, MATRIX_T, MATRIX_T m3) {
> +  int k;
> +  for (;; concat_mat_i++) {
> +    concat_mat_j = 0;
> +    for (; 4; concat_mat_j++) {
> +      k = 0;
> +      for (; k < 4; k++)
> +        m3[concat_mat_i][concat_mat_j] += m1[concat_mat_i][k];
> +    }

Just nitpicking, if we could come up with a test case which does not
involve integer overflows due to non-terminating loops, I would prefer
that.

Cheers,
Stefan

> +  }
> +}
> +
> +/* { dg-final { scan-assembler-not "vperm" } } */
> -- 
> 2.39.3
>