[PATCH 3/6] gcc/expmed.c: Ensure vector modes are tieable before extraction

[PATCH 3/6] gcc/expmed.c: Ensure vector modes are tieable before extraction

[Jonathan Wright]

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Hi,

Extracting a bitfield from a vector can be achieved by casting the
vector to a new type whose elements are the same size as the desired
bitfield, before generating a subreg. However, this is only an
optimization if the original vector can be accessed in the new
machine mode without first being copied - a condition denoted by the
TARGET_MODES_TIEABLE_P hook.

This patch adds a check to make sure that the vector modes are
tieable before attempting to generate a subreg. This is a necessary
prerequisite for a subsequent patch that will introduce new machine
modes for Arm Neon vector-tuple types.

Bootstrapped and regression tested on aarch64-none-linux-gnu and
x86_64-pc-linux-gnu - no issues.

Ok for master?

Thanks,
Jonathan

---

gcc/ChangeLog:

2021-10-11  Jonathan Wright  <jonathan.wright@arm.com>

	* expmed.c (extract_bit_field_1): Ensure modes are tieable.

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diff --git a/gcc/expmed.c b/gcc/expmed.c
index 59734d4841cbd2056a7d5bda9134af79c8024c87..f58fb9d877d66809b39253ccdc803f0ecb009326 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -1734,7 +1734,8 @@ extract_bit_field_1 (rtx str_rtx, poly_uint64 bitsize, poly_uint64 bitnum,
       FOR_EACH_MODE_FROM (new_mode, new_mode)
 	if (known_eq (GET_MODE_SIZE (new_mode), GET_MODE_SIZE (GET_MODE (op0)))
 	    && known_eq (GET_MODE_UNIT_SIZE (new_mode), GET_MODE_SIZE (tmode))
-	    && targetm.vector_mode_supported_p (new_mode))
+	    && targetm.vector_mode_supported_p (new_mode)
+	    && targetm.modes_tieable_p (GET_MODE (op0), new_mode))
 	  break;
       if (new_mode != VOIDmode)
 	op0 = gen_lowpart (new_mode, op0);

Re: [PATCH 3/6] gcc/expmed.c: Ensure vector modes are tieable before extraction

[Richard Sandiford]

Jonathan Wright <Jonathan.Wright@arm.com> writes:
> Hi,
>
> Extracting a bitfield from a vector can be achieved by casting the
> vector to a new type whose elements are the same size as the desired
> bitfield, before generating a subreg. However, this is only an
> optimization if the original vector can be accessed in the new
> machine mode without first being copied - a condition denoted by the
> TARGET_MODES_TIEABLE_P hook.
>
> This patch adds a check to make sure that the vector modes are
> tieable before attempting to generate a subreg. This is a necessary
> prerequisite for a subsequent patch that will introduce new machine
> modes for Arm Neon vector-tuple types.
>
> Bootstrapped and regression tested on aarch64-none-linux-gnu and
> x86_64-pc-linux-gnu - no issues.
>
> Ok for master?
>
> Thanks,
> Jonathan
>
> ---
>
> gcc/ChangeLog:
>
> 2021-10-11  Jonathan Wright  <jonathan.wright@arm.com>
>
>         * expmed.c (extract_bit_field_1): Ensure modes are tieable.

OK, thanks.

Richard

> diff --git a/gcc/expmed.c b/gcc/expmed.c
> index 59734d4841cbd2056a7d5bda9134af79c8024c87..f58fb9d877d66809b39253ccdc803f0ecb009326 100644
> --- a/gcc/expmed.c
> +++ b/gcc/expmed.c
> @@ -1734,7 +1734,8 @@ extract_bit_field_1 (rtx str_rtx, poly_uint64 bitsize, poly_uint64 bitnum,
>        FOR_EACH_MODE_FROM (new_mode, new_mode)
>  	if (known_eq (GET_MODE_SIZE (new_mode), GET_MODE_SIZE (GET_MODE (op0)))
>  	    && known_eq (GET_MODE_UNIT_SIZE (new_mode), GET_MODE_SIZE (tmode))
> -	    && targetm.vector_mode_supported_p (new_mode))
> +	    && targetm.vector_mode_supported_p (new_mode)
> +	    && targetm.modes_tieable_p (GET_MODE (op0), new_mode))
>  	  break;
>        if (new_mode != VOIDmode)
>  	op0 = gen_lowpart (new_mode, op0);