[libre-riscv-dev] SV auto-width

[Luke Kenneth Casson Leighton]

talking on comp.arch has been extremely useful.  the guy who developed
the mill architecture pointed out that dynamic auto-width is
problematic in several ways.

given that it will:

(a) require adjustment to the compilers
(b) need to be at the maximum bitwidth of src and dest
(c) not be well understood (resulting in bugs)
(d) need a special (micro-code-like) pipeline stage to do the conversion
(e) mean that the architectural design has to be adjusted

i'm inclined to *not* support dynamic auto-width in the Libre RISCV
SoC, and to even remove it from the SV specification entirely.

thoughts?

l.