See https://github.com/riscv/riscv-v-spec/pull/317

https://github.com/riscv/riscv-v-spec/pull/295

Closes #33

* (Partially) fix #30

With this change (and a renamed parse-opcodes) it's possible to as a
Python module without having to patch the repo.  Example:

  from parse_opcodes import parse_inputs

  if __name__ == "__main__":
      (namelist, pseudos, mask, match, arguments) = parse_inputs(["opcodes", "opcodes-rvc"])

* Fix #30: Rename parse-opcode to parse_opcode to enable module use

See https://github.com/riscv/riscv-v-spec/pull/247

See https://github.com/riscv/riscv-v-spec/pull/227

* rvv: fault-first also support segement

  based on 7.8.1, add missing segment supoort for fault first load

Signed-off-by: Chih-Min Chao <chihmin.chao@sifive.com>

* rvv: comparision instructions has 'm' prefix

  add 'm' prefix since the destination is mask register

  ref:
    https://github.com/riscv/riscv-v-spec/pull/181



Signed-off-by: Chih-Min Chao <chihmin.chao@sifive.com>

* rvv: reserved vid.v operand

  follow v0.7.1 change
  ref:
    https://github.com/riscv/riscv-v-spec/issues/160



Signed-off-by: Chih-Min Chao <chihmin.chao@sifive.com>

* rvv: add vfrsub.vf

  follow v-spec 0.7.1

  ref:
    https://github.com/riscv/riscv-v-spec/commit/65d2e233d4f5a95d27edf3fcd8b590b6b3deffbc



Signed-off-by: Chih-Min Chao <chihmin.chao@sifive.com>

* rvv: add amo encoding table

Signed-off-by: Chih-Min Chao <chihmin.chao@sifive.com>

Note that vmiota is being renamed to viota:
https://github.com/riscv/riscv-v-spec/pull/180

This is not currently stated in the spec, but there is a pull request to
make this explicit: https://github.com/riscv/riscv-v-spec/pull/179

 add most of vector instruction encoding described in v-spec 0.7.
 except for 'Zvamo' extension

Signed-off-by: Chih-Min Chao <chihmin.chao@sifive.com>

Signed-off-by: Chih-Min Chao <chihmin.chao@sifive.com>

Current generation flow assumes that opcodes are provided
in a `cat ./opcodes | ./parse_opcodes -c' manner. However,
Windows CMD has no `cat' command, and it uses `type' instead,
so implementation of cross-platform script is complicated.

In this patch, we allow parsing opcode files directly by Python,
if their names are provided as a command line arguments, not depending
on the host shell. If no arguments are passed, script behaves as usual,
reading opcodes from the stdin.

Go has a convention for generated code comments
(https://golang.org/s/generatedcode), i.e. they must match the regex
^// Code generated .* DO NOT EDIT\.$

Adjust the generated header to follow this convention.