tree 6262730f3fcf6e79990b417518db4531bd369800
parent 6302a55d979f296314309561dc490c56b961f529
author Rupert Swarbrick <rswarbrick@lowrisc.org> 1594717024 +0100
committer Rupert Swarbrick <rswarbrick@gmail.com> 1594911930 +0100

[otbn] Add OTBN encoding information to insns.yml

This patch defines a way to write "encoding schemes" in the YAML. This
is slightly inspired by the LLVM approach [1] but massively
simplified. I initially had something even simpler, without allowing
any hierarchy in the encoding schemes, but it was quite ugly to fill
in the instruction encodings and I was worried that it would make it
very difficult to change the encodings if we needed to later.

Instructions now have encodings defined, and we have code in the
Python parser that resolves the (hierarchical) scheme used by an
instruction into a flat one, then matches up the named operands with
the fields in the encoding scheme.

We finally check that the encoding is not ambiguous: that no bit
pattern matches more than one instruction.

Once this is all done, the documentation generator now spits out an
encoding table next to each instruction.

Final encoding work by Stefan.

[1] See e.g. llvm/lib/Target/RISCV/RISCVInstrFormatsC.td in the LLVM
    source tree.

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
Co-authored-by: Stefan Wallentowitz <stefan.wallentowitz@gi-de.com>