This patch introduces -gen-automata, a backend for generating deterministic finite-state automata.

DFAs are already generated by the -gen-dfa-packetizer backend. This backend is more generic and will

hopefully be used to implement the DFA generation (and determinization) for the packetizer in the

future.

This backend allows not only generation of a DFA from an NFA (nondeterministic finite-state

automaton), it also emits sidetables that allow a path through the DFA under a sequence of inputs to

be analyzed, and the equivalent set of all possible NFA transitions extracted.

This allows a user to not just answer "can my problem be solved?" but also "what is the

solution?". Clearly this analysis is more expensive than just playing a DFA forwards so is

opt-in. The DFAPacketizer has this behaviour already but this is a more compact and generic

representation.

Examples are bundled in unittests/TableGen/Automata.td. Some are trivial, but the BinPacking example

is a stripped-down version of the original target problem I set out to solve, where we pack values

(actually immediates) into bins (an immediate pool in a VLIW bundle) subject to a set of esoteric

constraints.