[libre-riscv-dev] VBLOCK - rerun the VL section

[Luke Kenneth Casson Leighton]

I have an idea, based on looking at the strncpy example:
https://libre-riscv.org/simple_v_extension/appendix/#strncpy

VBLOCK effectively has its own Program Counter. It has to, because there is
no way in hell it is ok to let PC advance through the VBLOCK.

So in the example, the bne goes to the start of the instruction
(fortunately).

Every example that I have seen, SETVL is called right at the top of the
loop.

A potential "trick" therefore is to set the VBLOCK PC CSR insteard of use
branch. This keeps execution *inside* the VBLOCK.

I'm wondering therefore if, when that trick is deployed, if it would be
worthwhile re-running the SETVL portion of the VBLOCK header.

Thoughts appreciated.

L.



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