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gcc/expmed.c: Ensure vector modes are tieable before extraction 

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.

gcc/ChangeLog:

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

	* expmed.c (extract_bit_field_1): Ensure modes are tieable.
This commit is contained in:
Jonathan Wright 2021-10-11 23:02:16 +01:00
parent 2fc2026061
commit 4e5929e457
1 changed files with 2 additions and 1 deletions
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gcc/expmed.c
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@ -1735,7 +1735,8 @@ 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);