Re: [PATCH] aarch64: allow usage of zero reg for CRC32 instructions

Hi Shreesh.

> On 13 Aug 2026, at 11:51, Shreesh Adiga <[email protected]> wrote:
> 
> This avoids unnecessary moves when either the initial CRC
> value or the data operand is a constant zero. For example:
> __crc32w(0, x) previously generated "mov w1, 0; crc32w w0, w1, w0"
> whereas now it generates "crc32w w0, wzr, w0".
> 

The patch looks good to me, but it would be nice to have some simple tests in the test suite for this.
Thanks,
Kyrill

> gcc/ChangeLog:
> 
> * config/aarch64/aarch64.md: allow usage of zero reg for CRC32
> instructions
> 
> Signed-off-by: Shreesh Adiga <[email protected]>
> ---
> gcc/config/aarch64/aarch64.md | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
> index 9cb55602c36..9f26e558e48 100644
> --- a/gcc/config/aarch64/aarch64.md
> +++ b/gcc/config/aarch64/aarch64.md
> @@ -4959,8 +4959,8 @@ (define_expand "<neg_not_op><mode>cc"
> ;; CRC32 instructions.
> (define_insn "aarch64_<crc_variant>"
>   [(set (match_operand:SI 0 "register_operand" "=r")
> -        (unspec:SI [(match_operand:SI 1 "register_operand" "r")
> -                    (match_operand:<crc_mode> 2 "register_operand" "r")]
> + (unspec:SI [(match_operand:SI 1 "aarch64_reg_or_zero" "rZ")
> +    (match_operand:<crc_mode> 2 "aarch64_reg_or_zero" "rZ")]
>          CRC))]
>   "TARGET_CRC32"
>   {
> -- 
> 2.54.0
>