Re: [PATCH] fold-const: Handle AND, IOR, XOR with stepped vectors [PR112971].

[Richard Biener <rguenther@suse.de>]

On Mon, 15 Jan 2024, Robin Dapp wrote:

> I gave it another shot now by introducing a separate function as
> Richard suggested.  It's probably not at the location he intended.
> 
> The way I read the discussion there hasn't been any consensus
> on how (or rather where) to properly tackle the problem.  Any
> other ideas still?

I'm happy enough with the patch, esp. at this stage.  OK if
Richard S. doesn't disagree.

Thanks,
Richard.

> Regards
>  Robin
> 
> 
> Found in PR112971 this patch adds folding support for bitwise operations
> of const duplicate zero/one vectors with stepped vectors.
> On riscv we have the situation that a folding would perpetually continue
> without simplifying because e.g. {0, 0, 0, ...} & {7, 6, 5, ...} would
> not be folded to {0, 0, 0, ...}.
> 
> gcc/ChangeLog:
> 
> 	PR middle-end/112971
> 
> 	* fold-const.cc (simplify_const_binop): New function for binop
> 	simplification of two constant vectors when element-wise
> 	handling is not necessary.
> 	(const_binop): Call new function.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.target/riscv/rvv/autovec/pr112971.c: New test.
> ---
>  gcc/fold-const.cc                             | 31 +++++++++++++++++++
>  .../gcc.target/riscv/rvv/autovec/pr112971.c   | 18 +++++++++++
>  2 files changed, 49 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c
> 
> diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
> index 385e4a69ab3..2ef425aec0f 100644
> --- a/gcc/fold-const.cc
> +++ b/gcc/fold-const.cc
> @@ -1343,6 +1343,29 @@ distributes_over_addition_p (tree_code op, int opno)
>      }
>  }
>  
> +/* OP is the INDEXth operand to CODE (counting from zero) and OTHER_OP
> +   is the other operand.  Try to use the value of OP to simplify the
> +   operation in one step, without having to process individual elements.  */
> +static tree
> +simplify_const_binop (tree_code code, tree op, tree other_op,
> +		      int index ATTRIBUTE_UNUSED)
> +{
> +  /* AND, IOR as well as XOR with a zerop can be simplified directly.  */
> +  if (TREE_CODE (op) == VECTOR_CST && TREE_CODE (other_op) == VECTOR_CST)
> +    {
> +      if (integer_zerop (other_op))
> +	{
> +	  if (code == BIT_IOR_EXPR || code == BIT_XOR_EXPR)
> +	    return op;
> +	  else if (code == BIT_AND_EXPR)
> +	    return other_op;
> +	}
> +    }
> +
> +  return NULL_TREE;
> +}
> +
> +
>  /* Combine two constants ARG1 and ARG2 under operation CODE to produce a new
>     constant.  We assume ARG1 and ARG2 have the same data type, or at least
>     are the same kind of constant and the same machine mode.  Return zero if
> @@ -1646,6 +1669,14 @@ const_binop (enum tree_code code, tree arg1, tree arg2)
>  	return build_complex (type, real, imag);
>      }
>  
> +  tree simplified;
> +  if ((simplified = simplify_const_binop (code, arg1, arg2, 0)))
> +    return simplified;
> +
> +  if (commutative_tree_code (code)
> +      && (simplified = simplify_const_binop (code, arg2, arg1, 1)))
> +    return simplified;
> +
>    if (TREE_CODE (arg1) == VECTOR_CST
>        && TREE_CODE (arg2) == VECTOR_CST
>        && known_eq (TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg1)),
> diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c
> new file mode 100644
> index 00000000000..816ebd3c493
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112971.c
> @@ -0,0 +1,18 @@
> +/* { dg-do compile }  */
> +/* { dg-options "-march=rv64gcv_zvl256b -mabi=lp64d -O3 -fno-vect-cost-model" }  */
> +
> +int a;
> +short b[9];
> +char c, d;
> +void e() {
> +  d = 0;
> +  for (;; d++) {
> +    if (b[d])
> +      break;
> +    a = 8;
> +    for (; a >= 0; a--) {
> +      char *f = &c;
> +      *f &= d == (a & d);
> +    }
> +  }
> +}
> 

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