On 3/6/20 6:22 PM, Krste Asanovic wrote:

EXTERNAL MAIL



Date: 2020/3/6
Task Group: Vector Extension
Chair: Krste Asanovic
Number of Attendees: ~21
Current issues on github: https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_riscv_riscv-2Dv-2Dspec&d=DwIBAg&c=aUq983L2pue2FqKFoP6PGHMJQyoJ7kl3s3GZ-_haXqY&r=AYJ4kbebphYpRw2lYDUDCk5w5Qa3-DR3bQnFjLVmM80&m=7iUw4AQUNARUmLrctcmUnaVeTQFEsr3iPkKAmbvN7TQ&s=SnwnLsCrm8ukZcK2uhKQB4CLhuFujbyBzFx1vgL4iQA&e=

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#367 Tail Agnostic

The discussion reviewed the proposal that long temporal vector
registers with renaming could be handled using vector length trimming.

The proposal was then added that masking should also be given option
of being agnostic giving three options:
1) tail-undisturbed + masking-undisturbed
2) tail-agnostic + masking-undisturbed
3) tail-agnostic + masking-agnostic

We've discussed before, but allowing the *-agnostic options means code
can be written and tested on an implementation that supports them and
then fail on an implementation that maps them to #1. And vice-versa.

Bill

All implementations would have to support all options.

Simple implementations can ignore setting and treat all as 1).

Option 2) could be implemented as option 1) even if option 3) was
supported.

The recommendation was that agnostic destination elements had to only
be either zero or undisturbed.

Discussion to continue with this suggestion.