Re: [PATCH v11 3/7] target/riscv/vector_helpers: do early exit when vstart >= vl

[Richard Henderson <richard.henderson@linaro.org>]

On 3/11/24 03:58, Daniel Henrique Barboza wrote:
> We're going to make changes that will required each helper to be
> responsible for the 'vstart' management, i.e. we will relieve the
> 'vstart < vl' assumption that helpers have today.
> 
> Helpers are usually able to deal with vstart >= vl, i.e. doing nothing
> aside from setting vstart = 0 at the end, but the tail update functions
> will update the tail regardless of vstart being valid or not.
> 
> Unifying the tail update process in a single function that would handle
> the vstart >= vl case isn't trivial. We have 2 functions that are used
> to update tail: vext_set_tail_elems_1s() and vext_set_elems_1s(). The
> latter is a more generic function that is also used to mask elements.
> There's no easy way of making all callers using vext_set_tail_elems_1s()
> because we're not encoding NF properly in all cases [1].
> 
> This patch takes a blunt approach: do an early exit in every single
> vector helper if vstart >= vl. We can worry about unifying the tail
> update process later.
> 
> [1]https://lore.kernel.org/qemu-riscv/1590234b-0291-432a-a0fa-c5a6876097bc@linux.alibaba.com/
> 
> Signed-off-by: Daniel Henrique Barboza<dbarboza@ventanamicro.com>
> ---
>   target/riscv/vcrypto_helper.c   | 32 ++++++++++++
>   target/riscv/vector_helper.c    | 90 +++++++++++++++++++++++++++++++++
>   target/riscv/vector_internals.c |  4 ++
>   target/riscv/vector_internals.h |  9 ++++
>   4 files changed, 135 insertions(+)

This does seem like the only viable short-term solution.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~