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

[Richard Biener <rguenther@suse.de>]

On Tue, 19 Dec 2023, ??? wrote:

> Thanks Robin send initial patch to fix this ICE bug.
> 
> CC to Richard S, Richard B, and Andrew.

Just one comment, it seems that VECTOR_CST_STEPPED_P should
implicitly include VECTOR_CST_DUPLICATE_P since it would be
a step of zero (but as implemented it doesn't catch this).
Looking at the implementation it's odd that we can handle
VECTOR_CST_NELTS_PER_PATTERN == 1 (duplicate) and
== 3 (stepped) but not == 2 (not sure what that would be).

Maybe the tests can be re-formulated in terms of
VECTOR_CST_NELTS_PER_PATTERN?

Richard.

> Thanks.
> 
> 
> 
> juzhe.zhong@rivai.ai
>  
> From: Robin Dapp
> Date: 2023-12-19 03:50
> To: gcc-patches
> CC: rdapp.gcc; Li, Pan2; juzhe.zhong@rivai.ai
> Subject: [PATCH] fold-const: Handle AND, IOR, XOR with stepped vectors [PR112971].
> Hi,
>  
> found in PR112971, this patch adds folding support for bitwise operations
> of const duplicate zero vectors and 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 fold to {0, 0, 0, ...}.
>  
> Bootstrapped and regtested on x86 and aarch64, regtested on riscv.
>  
> I won't be available to respond quickly until next year.  Pan or Juzhe,
> as discussed, feel free to continue with possible revisions.
>  
> Regards
> Robin
>  
>  
> gcc/ChangeLog:
>  
> PR middle-end/112971
>  
> * fold-const.cc (const_binop): Handle
> zerop@1  AND/IOR/XOR  VECT_CST_STEPPED_P@2
>  
> gcc/testsuite/ChangeLog:
>  
> * gcc.target/riscv/rvv/autovec/pr112971.c: New test.
> ---
> gcc/fold-const.cc                              | 14 +++++++++++++-
> .../gcc.target/riscv/rvv/autovec/pr112971.c    | 18 ++++++++++++++++++
> 2 files changed, 31 insertions(+), 1 deletion(-)
> 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 f5d68ac323a..43ed097bf5c 100644
> --- a/gcc/fold-const.cc
> +++ b/gcc/fold-const.cc
> @@ -1653,8 +1653,20 @@ const_binop (enum tree_code code, tree arg1, tree arg2)
>      {
>        tree type = TREE_TYPE (arg1);
>        bool step_ok_p;
> +
> +      /* AND, IOR as well as XOR with a zerop can be handled directly.  */
>        if (VECTOR_CST_STEPPED_P (arg1)
> -   && VECTOR_CST_STEPPED_P (arg2))
> +   && VECTOR_CST_DUPLICATE_P (arg2)
> +   && integer_zerop (VECTOR_CST_ELT (arg2, 0)))
> + step_ok_p = code == BIT_AND_EXPR || code == BIT_IOR_EXPR
> +   || code == BIT_XOR_EXPR;
> +      else if (VECTOR_CST_STEPPED_P (arg2)
> +        && VECTOR_CST_DUPLICATE_P (arg1)
> +        && integer_zerop (VECTOR_CST_ELT (arg1, 0)))
> + step_ok_p = code == BIT_AND_EXPR || code == BIT_IOR_EXPR
> +   || code == BIT_XOR_EXPR;
> +      else if (VECTOR_CST_STEPPED_P (arg1)
> +        && VECTOR_CST_STEPPED_P (arg2))
> /* We can operate directly on the encoding if:
>       a3 - a2 == a2 - a1 && b3 - b2 == b2 - b1
> 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)