Hi,

This series makes changes in vext_set_tail_elements_1s() to be a little
nicer to the emulation.

First patch makes the function a no-op when vta == 0. Aside from the
logic simplification we also have a little performance boost.

Second patch makes the function debug only. The logic is explained in
the commit message, but long story short: we don't have to implement any
tail-agnostic policy at all to be spec compliant, but this function has
its uses for debug purposes, so keeping it as a debug option allow users
to disable it on demand.

Patches are based on top of Alistair's riscv-to-apply.next.
 
Daniel Henrique Barboza (2):
  target/riscv/vector_helper.c: skip set tail when vta is zero
  target/riscv/vector_helper.c: make vext_set_tail_elems_1s() debug only

 target/riscv/vector_helper.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

-- 
2.40.0

On Thu, Apr 27, 2023 at 17:57:06 -0300, Daniel Henrique Barboza wrote:

: Second patch makes the function debug only. The logic is explained in
: the commit message, but long story short: we don't have to implement any
: tail-agnostic policy at all to be spec compliant, but this function has
: its uses for debug purposes, so keeping it as a debug option allow users
: to disable it on demand.

Yes, please don't remove this functionality completely -- our internal
stress test tool for the vector crypto patches relies on it.

-- 
Dickon Hood                                    Senior Software Engineer
                                                         Codethink Ltd.
                                 3rd Floor, Dale House, 35 Dale Street,
https://www.codethink.co.uk/        Manchester, M1 2HF, United Kingdom.

On Thu, 27 Apr 2023 13:57:06 PDT (-0700), dbarboza@ventanamicro.com wrote:
> Hi,
>
> This series makes changes in vext_set_tail_elements_1s() to be a little
> nicer to the emulation.
>
> First patch makes the function a no-op when vta == 0. Aside from the
> logic simplification we also have a little performance boost.
>
> Second patch makes the function debug only. The logic is explained in
> the commit message, but long story short: we don't have to implement any
> tail-agnostic policy at all to be spec compliant, but this function has
> its uses for debug purposes, so keeping it as a debug option allow users
> to disable it on demand.
>
> Patches are based on top of Alistair's riscv-to-apply.next.
>
> Daniel Henrique Barboza (2):
>   target/riscv/vector_helper.c: skip set tail when vta is zero
>   target/riscv/vector_helper.c: make vext_set_tail_elems_1s() debug only
>
>  target/riscv/vector_helper.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)

Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>

Though this made me think: it'd be nice to have some sort of 
"aggressively do odd things for VTA/VMA" mode in QEMU, as that could 
help shake out bugs in software.