Re: [PATCH 2/2] Simplify subreg of vec_merge of vec_duplicate

[Richard Sandiford]

"H.J. Lu" <hjl.to...@gmail.com> writes:
> We may simplify
>
>   (subreg (vec_merge (vec_duplicate X) (vector) (const_int 1)) 0)
>
> to X when mode of X is the same as of mode of subreg.
>
> gcc/
>
>       PR target/87537
>       * simplify-rtx.c (simplify_subreg): Simplify subreg of vec_merge
>       of vec_duplicate.
>
> gcc/testsuite/
>
>       PR target/87537
>       * gcc.target/i386/pr87537-1.c: New test.
> ---
>  gcc/simplify-rtx.c                        | 11 +++++++++++
>  gcc/testsuite/gcc.target/i386/pr87537-1.c | 12 ++++++++++++
>  2 files changed, 23 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr87537-1.c
>
> diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
> index 9bc53866b9f..e2a0533b23d 100644
> --- a/gcc/simplify-rtx.c
> +++ b/gcc/simplify-rtx.c
> @@ -6601,6 +6601,17 @@ simplify_subreg (machine_mode outermode, rtx op,
>        return NULL_RTX;
>      }
>  
> +  /* Return X for
> +     (subreg (vec_merge (vec_duplicate X) (vector) (const_int 1)) 0)
> +   */
> +  if (known_eq (byte, 0U)
> +      && GET_CODE (op) == VEC_MERGE
> +      && GET_CODE (XEXP (op, 0)) == VEC_DUPLICATE
> +      && GET_MODE (XEXP (XEXP (op, 0), 0)) == outermode
> +      && CONST_INT_P (XEXP (op, 2))
> +      && INTVAL (XEXP (op, 2)) == 1)
> +    return XEXP (XEXP (op, 0), 0);

Would be good to handle the more general case of:

  unsigned int idx;
  if (constant_multiple_p (byte, GET_MODE_SIZE (outermode), &idx)
      ...
      && (INTVAL (XEXP (op, 2)) & (HOST_WIDE_INT_1U << idx)) != 0)

(untested!)  Please also add some selftests to test_vector_ops.

Thanks,
Richard