> -----Original Message-----
> From: Robin Dapp <[email protected]>
> Sent: 08 September 2026 21:30
> To: gcc-patches <[email protected]>
> Cc: Robin Dapp <[email protected]>; Tamar Christina
> <[email protected]>; Richard Sandiford
> <[email protected]>
> Subject: [PATCH] aarch64: Set REGMODE_NATURAL_SIZE for advsimd vectors.
>
> Hi,
>
> Here now the split-out version after the middle-end and riscv changes
> have already been installed:
>
> Similar to the riscv changes, this patch adjusts aarch64's
> REGMODE_NATURAL_SIZE so it returns the size of one vector.
> Subsequently, subregs of vectors smaller than a vector are invalid.
>
> Bootstrapped and regtested on aarch64.
OK.
Thank you!
Tamar
>
> Regards
> Robin
>
> ---
> gcc/config/aarch64/aarch64.cc | 15 +++++++--------
> 1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
> index 5544d5f8c7a..71d8ab438b7 100644
> --- a/gcc/config/aarch64/aarch64.cc
> +++ b/gcc/config/aarch64/aarch64.cc
> @@ -2996,20 +2996,19 @@ aarch64_regmode_natural_size (machine_mode
> mode)
> /* The natural size for SVE data modes is one SVE data vector,
> and similarly for predicates. We can't independently modify
> anything smaller than that. */
> - /* ??? For now, only do this for variable-width SVE registers.
> - Doing it for constant-sized registers breaks lower-subreg.cc. */
> - /* ??? And once that's fixed, we should probably have similar
> - code for Advanced SIMD. */
> - if (!aarch64_sve_vg.is_constant ())
> - {
> - /* REGMODE_NATURAL_SIZE influences general subreg validity rules,
> - so we need to handle memory-only modes as well. */
> + if (VECTOR_MODE_P (mode))
> + {
> unsigned int vec_flags = aarch64_classify_vector_memory_mode (mode);
> if (vec_flags & VEC_SVE_PRED)
> return BYTES_PER_SVE_PRED;
> if (vec_flags & VEC_SVE_DATA)
> return BYTES_PER_SVE_VECTOR;
> + if (vec_flags & VEC_ADVSIMD)
> + return MAX (exact_div (GET_MODE_SIZE (mode),
> + aarch64_ldn_stn_vectors (mode)).to_constant (),
> + UNITS_PER_WORD);
> }
> +
> return UNITS_PER_WORD;
> }
>
> --
> 2.55.0
