Re: [PATCH] tree-optimization/104445 - check for vector extraction support

[Richard Sandiford <richard.sandiford@arm.com>]

Richard Biener <rguenther@suse.de> writes:
> This adds a missing check to epilogue reduction re-use, namely
> that we can do hi/lo extracts from the vector when demoting it
> to the epilogue vector size.
>
> I've chosen to add a can_vec_extract helper to optabs-query.h,
> in the future we might want to simplify the vectorizers life by
> handling vector-from-vector extraction via BIT_FIELD_REFs during
> RTL expansion via the mode punning when the vec_extract is not
> directly supported.
>
> I'm not 100% sure we can always do the punning of the
> vec_extract result to a vector mode of the same size, but then
> I'm also not sure how to check for that (the vectorizer doesn't
> in other places it does that at the moment, but I suppose we
> eventually just go through memory there)?
>
> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
>
> Does this look OK?

LGTM.  I guess some of the existing optab checks could be simplified
using the new helper, but that's a separate clean-up.

Thanks,
Richard

>
> Thanks,
> Richard.
>
> 2022-02-09  Richard Biener  <rguenther@suse.de>
>
> 	PR tree-optimization/104445
> 	PR tree-optimization/102832
> 	* optabs-query.h (can_vec_extract): New.
> 	* optabs-query.cc (can_vec_extract): Likewise.
> 	* tree-vect-loop.cc (vect_find_reusable_accumulator): Check
> 	we can extract a hi/lo part from the larger vector.
>
> 	* gcc.dg/vect/pr104445.c: New testcase.
> ---
>  gcc/optabs-query.cc                  | 33 ++++++++++++++++++++++++++++
>  gcc/optabs-query.h                   |  1 +
>  gcc/testsuite/gcc.dg/vect/pr102832.c | 12 ++++++++++
>  gcc/testsuite/gcc.dg/vect/pr104445.c | 16 ++++++++++++++
>  gcc/tree-vect-loop.cc                |  8 +++++--
>  5 files changed, 68 insertions(+), 2 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/vect/pr102832.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/pr104445.c
>
> diff --git a/gcc/optabs-query.cc b/gcc/optabs-query.cc
> index 2ce8d74db16..fa88b4bede0 100644
> --- a/gcc/optabs-query.cc
> +++ b/gcc/optabs-query.cc
> @@ -763,3 +763,36 @@ supports_vec_scatter_store_p (machine_mode mode)
>    return this_fn_optabs->supports_vec_scatter_store[mode] > 0;
>  }
>  
> +/* Whether we can extract part of the vector mode MODE as
> +   (scalar or vector) mode EXTR_MODE.  */
> +
> +bool
> +can_vec_extract (machine_mode mode, machine_mode extr_mode)
> +{
> +  if (!VECTOR_MODE_P (mode))
> +    return false;
> +
> +  unsigned m;
> +  if (!constant_multiple_p (GET_MODE_SIZE (mode),
> +			    GET_MODE_SIZE (extr_mode), &m))
> +    return false;
> +
> +  if (convert_optab_handler (vec_extract_optab, mode, extr_mode)
> +      != CODE_FOR_nothing)
> +    return true;
> +
> +  if (!VECTOR_MODE_P (extr_mode))
> +    return false;
> +
> +  /* Besides a direct vec_extract we can also use an element extract from
> +     an integer vector mode with elements of the size of the extr_mode.  */
> +  scalar_int_mode imode;
> +  machine_mode vmode;
> +  if (!int_mode_for_size (GET_MODE_SIZE (extr_mode), 0).exists (&imode)
> +      || !related_vector_mode (mode, imode, m).exists (&vmode)
> +      || (convert_optab_handler (vec_extract_optab, vmode, imode)
> +	  == CODE_FOR_nothing))
> +    return false;
> +  /* We assume we can pun mode to vmode and imode to extr_mode.  */
> +  return true;
> +}
> diff --git a/gcc/optabs-query.h b/gcc/optabs-query.h
> index 8b768c1797d..b9c9fd6f64d 100644
> --- a/gcc/optabs-query.h
> +++ b/gcc/optabs-query.h
> @@ -195,6 +195,7 @@ bool can_atomic_load_p (machine_mode);
>  bool lshift_cheap_p (bool);
>  bool supports_vec_gather_load_p (machine_mode = E_VOIDmode);
>  bool supports_vec_scatter_store_p (machine_mode = E_VOIDmode);
> +bool can_vec_extract (machine_mode, machine_mode);
>  
>  /* Version of find_widening_optab_handler_and_mode that operates on
>     specific mode types.  */
> diff --git a/gcc/testsuite/gcc.dg/vect/pr102832.c b/gcc/testsuite/gcc.dg/vect/pr102832.c
> new file mode 100644
> index 00000000000..7cb4db5e4c7
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr102832.c
> @@ -0,0 +1,12 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-O3" } */
> +/* { dg-additional-options "-march=armv8.2-a+sve -msve-vector-bits=128" { target aarch64-*-* } } */
> +
> +int a, b;
> +char c;
> +signed char d(int e, int f) { return e - f; }
> +void g() {
> +  a = 0;
> +  for (; a >= -17; a = d(a, 1))
> +    c ^= b;
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/pr104445.c b/gcc/testsuite/gcc.dg/vect/pr104445.c
> new file mode 100644
> index 00000000000..8ec3b3b0f1e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr104445.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-O3" } */
> +/* { dg-additional-options "-mavx -mno-mmx" { target x86_64-*-* i?86-*-* } } */
> +
> +signed char a;
> +signed char f (int i, int j)
> +{
> +  signed char c;
> +  while (i != 0)
> +  {
> +    a ^= j;
> +    ++c;
> +    ++i;
> +  }
> +  return c;
> +}
> diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> index 4860bfd3344..9916ae46460 100644
> --- a/gcc/tree-vect-loop.cc
> +++ b/gcc/tree-vect-loop.cc
> @@ -4997,7 +4997,8 @@ vect_find_reusable_accumulator (loop_vec_info loop_vinfo,
>    if (!constant_multiple_p (TYPE_VECTOR_SUBPARTS (old_vectype),
>  			    TYPE_VECTOR_SUBPARTS (vectype), &m))
>      return false;
> -  /* Check the intermediate vector types are available.  */
> +  /* Check the intermediate vector types and operations are available.  */
> +  tree prev_vectype = old_vectype;
>    while (m > 2)
>      {
>        m /= 2;
> @@ -5006,8 +5007,11 @@ vect_find_reusable_accumulator (loop_vec_info loop_vinfo,
>  	 exact_div (TYPE_VECTOR_SUBPARTS (old_vectype), m));
>        if (!intermediate_vectype
>  	  || !directly_supported_p (STMT_VINFO_REDUC_CODE (reduc_info),
> -				    intermediate_vectype))
> +				    intermediate_vectype)
> +	  || !can_vec_extract (TYPE_MODE (prev_vectype),
> +			       TYPE_MODE (intermediate_vectype)))
>  	return false;
> +      prev_vectype = intermediate_vectype;
>      }
>  
>    /* Non-SLP reductions might apply an adjustment after the reduction