Re: [PATCH V4] SCCVN: Add LEN_MASK_STORE and fix LEN_STORE

[Richard Biener <rguenther@suse.de>]

On Tue, 27 Jun 2023, juzhe.zhong@rivai.ai wrote:

> From: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
> 
> Hi, Richi.
> 
> I tried to understand your last email and to refactor the do-while loop using VECTOR_CST_NELTS.
> 
> This patch works fine for LEN_MASK_STORE and compiler can CSE redundant store.
> I have appended testcase in this patch to test VN for LEN_MASK_STORE.
> 
> I am not sure whether I am on the same page with you.
> 
> Feel free to correct me, Thanks.
> 
> gcc/ChangeLog:
> 
>         * tree-ssa-sccvn.cc (vn_reference_lookup_3): Add LEN_MASK_STORE and fix LEN_STORE
> 
> gcc/testsuite/ChangeLog:
> 
>         * gcc.target/riscv/rvv/autovec/partial/len_maskstore_vn-1.c: New test.
> 
> ---
>  .../rvv/autovec/partial/len_maskstore_vn-1.c  | 30 +++++++++++++++++++
>  gcc/tree-ssa-sccvn.cc                         | 24 +++++++++++----
>  2 files changed, 49 insertions(+), 5 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/partial/len_maskstore_vn-1.c
> 
> diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/partial/len_maskstore_vn-1.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/partial/len_maskstore_vn-1.c
> new file mode 100644
> index 00000000000..0b2d03693dc
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/partial/len_maskstore_vn-1.c
> @@ -0,0 +1,30 @@
> +/* { dg-do compile } */
> +/* { dg-options "-march=rv32gcv_zvl256b -mabi=ilp32d --param riscv-autovec-preference=fixed-vlmax -O3 -fdump-tree-fre5" } */
> +
> +void __attribute__((noinline,noclone))
> +foo (int *out, int *res)
> +{
> +  int mask[] = { 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1 };
> +  int i;
> +  for (i = 0; i < 16; ++i)
> +    {
> +      if (mask[i])
> +        out[i] = i;
> +    }
> +  int o0 = out[0];
> +  int o7 = out[7];
> +  int o14 = out[14];
> +  int o15 = out[15];
> +  res[0] = o0;
> +  res[2] = o7;
> +  res[4] = o14;
> +  res[6] = o15;
> +}
> +
> +/* Vectorization produces .LEN_MASK_STORE, unrolling will unroll the two
> +   vector iterations.  FRE5 after that should be able to CSE
> +   out[7] and out[15], but leave out[0] and out[14] alone.  */
> +/* { dg-final { scan-tree-dump " = o0_\[0-9\]+;" "fre5" } } */
> +/* { dg-final { scan-tree-dump " = 7;" "fre5" } } */
> +/* { dg-final { scan-tree-dump " = o14_\[0-9\]+;" "fre5" } } */
> +/* { dg-final { scan-tree-dump " = 15;" "fre5" } } */
> diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
> index 11061a374a2..242d82d6274 100644
> --- a/gcc/tree-ssa-sccvn.cc
> +++ b/gcc/tree-ssa-sccvn.cc
> @@ -3304,6 +3304,16 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
>  	  if (!tree_fits_uhwi_p (len) || !tree_fits_shwi_p (bias))
>  	    return (void *)-1;
>  	  break;
> +	case IFN_LEN_MASK_STORE:
> +	  len = gimple_call_arg (call, 2);
> +	  bias = gimple_call_arg (call, 5);
> +	  if (!tree_fits_uhwi_p (len) || !tree_fits_shwi_p (bias))
> +	    return (void *)-1;
> +	  mask = gimple_call_arg (call, internal_fn_mask_index (fn));
> +	  mask = vn_valueize (mask);
> +	  if (TREE_CODE (mask) != VECTOR_CST)
> +	    return (void *)-1;
> +	  break;
>  	default:
>  	  return (void *)-1;
>  	}
> @@ -3344,11 +3354,17 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
>  	      tree vectype = TREE_TYPE (def_rhs);
>  	      unsigned HOST_WIDE_INT elsz
>  		= tree_to_uhwi (TYPE_SIZE (TREE_TYPE (vectype)));
> +	      /* Set initial len value is the UINT_MAX, so mask_idx < actual_len
> +		 is always true for MASK_STORE.  */
> +	      unsigned actual_len = UINT_MAX;
> +	      if (len)
> +		actual_len = tree_to_uhwi (len) + tree_to_shwi (bias);
> +	      unsigned nunits
> +		= MIN (actual_len, VECTOR_CST_NELTS (mask).coeffs[0]);

No, that's not correct and what I meant.  There's
vector_cst_encoded_nelts (mask), but for example for an
all-ones mask that would be 1.  You'd then also not access
VECTOR_CST_ELT but VECTOR_CST_ENCODED_ELT.  What I'm not sure
is how to recover the implicit walk over all elements for the
purpose of computing start/length and how generally this will
work for variable-length vectors where enumerating "all"
elements touched is required for correctness.

The most simple thing would be to make this all conditional
to constant TYPE_VECTOR_SUBPARTS.  Which is also why I was
asking for VL vector testcases.

Richard.

>  	      if (mask)
>  		{
>  		  HOST_WIDE_INT start = 0, length = 0;
> -		  unsigned mask_idx = 0;
> -		  do
> +		  for (unsigned mask_idx = 0; mask_idx < nunits; mask_idx++)
>  		    {
>  		      if (integer_zerop (VECTOR_CST_ELT (mask, mask_idx)))
>  			{
> @@ -3371,9 +3387,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
>  			}
>  		      else
>  			length += elsz;
> -		      mask_idx++;
>  		    }
> -		  while (known_lt (mask_idx, TYPE_VECTOR_SUBPARTS (vectype)));
>  		  if (length != 0)
>  		    {
>  		      pd.rhs_off = start;
> @@ -3389,7 +3403,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
>  		{
>  		  pd.offset = offset2i;
>  		  pd.size = (tree_to_uhwi (len)
> -			     + -tree_to_shwi (bias)) * BITS_PER_UNIT;
> +			     + tree_to_shwi (bias)) * BITS_PER_UNIT;
>  		  if (BYTES_BIG_ENDIAN)
>  		    pd.rhs_off = pd.size - tree_to_uhwi (TYPE_SIZE (vectype));
>  		  else
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)