tree fe92fd78316a77b12726b0b2709a86eb779b0811
parent cbe384f933eba31939fc62f4585a829bf42be308
author Rupert Swarbrick <rswarbrick@lowrisc.org> 1611233711 +0000
committer Rupert Swarbrick <rswarbrick@gmail.com> 1611523177 +0000

[otbn] Add support for "const values" to RIG

This is going to be important for generating loop bodies. The trick is
that we want to say something like "don't touch x3, x4 or x10 in the
loop body" to make sure that they still have the same values each
iteration. This way, they can be used as base addresses for memory
accesses or jumps, without having to worry that they'll get trashed on
the following iteration.

This also adds support for "forgetting values" in the model. We'll
generate a loop body by iterating over all known registers and either
marking them const or forgetting their exact values. This guarantees
that we don't use a trashable register as a base address.

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>