[PATCH v6 02/15] RISC-V: Add support for the Zvbc extension

[Christoph Müllner]

+Ken Dockser
+Nicolas Brunie

I've added Ken and Nicolas (spec authors) to give an authoritative answer, and
because this looks like a valid public-review comment for the specification.

The spec indeed mentions "the 64-bit value from integer register rs1
(vector-scalar)",
which is unclear for RV32.

BR
Christoph

On Mon, Jul 17, 2023 at 9:02 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 01.07.2023 07:20, Christoph Muellner wrote:
> > --- a/opcodes/riscv-opc.c
> > +++ b/opcodes/riscv-opc.c
> > @@ -1902,6 +1902,12 @@ const struct riscv_opcode riscv_opcodes[] =
> >  {"vwsll.vx",    0, INSN_CLASS_ZVBB, "Vd,Vt,sVm", MATCH_VWSLL_VX, MASK_VWSLL_VX, match_opcode, 0},
> >  {"vwsll.vi",    0, INSN_CLASS_ZVBB, "Vd,Vt,VjVm", MATCH_VWSLL_VI, MASK_VWSLL_VI, match_opcode, 0},
> >
> > +/* Zvbc instructions.  */
> > +{"vclmul.vv",   0, INSN_CLASS_ZVBC, "Vd,Vt,VsVm", MATCH_VCLMUL_VV, MASK_VCLMUL_VV, match_opcode, 0},
> > +{"vclmul.vx",   0, INSN_CLASS_ZVBC, "Vd,Vt,sVm", MATCH_VCLMUL_VX, MASK_VCLMUL_VX, match_opcode, 0},
>
> I realize this is more a spec question than an implementation one, but
> implementation might be affected by the answer to the question: What
> exactly are this and ...
>
> > +{"vclmulh.vv",   0, INSN_CLASS_ZVBC, "Vd,Vt,VsVm", MATCH_VCLMULH_VV, MASK_VCLMULH_VV, match_opcode, 0},
> > +{"vclmulh.vx",   0, INSN_CLASS_ZVBC, "Vd,Vt,sVm", MATCH_VCLMULH_VX, MASK_VCLMULH_VX, match_opcode, 0},
>
> ... this insn doing in RV32 mode? There are no 64 bits to take from
> the GPR, yet that's what the doc presently says. Is the value coming
> from a pair of GPRs, or is it sign- or zero-extended? Or is this an
> RV64-only insn? (Note how the doc explicitly describes the behavior
> for vandn's scalar-source form; the only thing left to be implied
> there is that truncation / sign-extension are to - I assume - element
> size, but maybe that's said somewhere in more general terms.)
>
> As a nit: The two vclmulh lines have one too many blanks, resulting
> in columns to not be aligned.
>
> Jan