RISC-V Vector TG meeting minutes, April 17, 2020

Krste Asanovic

Also a reminder that the next meeting will be a half hour earlier.
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Date: 2020/4/17
Task Group: Vector Extension
Chair: Krste Asanovic
Number of Attendees: ~15
Current issues on github: https://github.com/riscv/riscv-v-spec

Issues discussed: new "effective element width", location of agnostic bits

The following issues were discussed.

New "effective element width" proposal

We discussed the proposal sent on mailing list to reuse the width
field to encode an effective element width, as a way to improve
efficiency on mixed-width floating-point code and to reduce impact of
dropping fixed width loads and stores on integer code. Consensus was
to explore the options for encoding effective element width on mailing
list and discuss next time.

Location of tail/mask-agnostic bits

Discussion reached consensus on placing these in the vtype register,
noting that later extensions could redefine vtype CSR written by
vsetvl as a "window" into a larger group of vector configuration CSRs.
It was noted that there is no space to add more configuration
instructions in existing footprint, and that the exisitng instructions
fit the base immediate format.

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