[libre-riscv-dev] [Bug 139] Add LD.X and ST.X? Strided

[bugzilla-daemon at libre-riscv.org]

http://bugs.libre-riscv.org/show_bug.cgi?id=139

--- Comment #26 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #24)
> (In reply to Jacob Lifshay from comment #23)
> 
> > > more in a mo - twin-SUBVL doesn't sound right.  SUBVL is intended to
> > > be applied globally.  the CSRs would need a total redesign to cope.
> > 
> > I had always intended SUBVL to vary from value to value, even faster than VL
> > would vary.
> 
> Varying is not a problem at all. Having *two* SUBVLs (or even worse three),
> one for src1, one for src2 and another for rd, we're into major redesign
> territory.

not really, swizzles would be the only ops with different SUBVL values.

note that in the suggested encoding, rs2's subvl is always 1, and we can assume
that rs1 and rs3 have matching SUBVLs (can use an additional swizzle when they
don't match), so we only need to encode the new (dest) SUBVL (which would be
written to the csr) and can use the old (src) subvl from the csr.

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