For target descriptions with very large and very dense register files, TableGen
can take an extremely long time to run. This change makes a dent in that (~15%
in my measurements) by accelerating the single hottest operation with better data
structures.
I believe there's still a lot of room to make this even faster with more global
changes that require replacing some of the existing datastructures in this area
with bit vectors, but that's a more involved change and I wanted to get this
simpler improvement in first.
llvm-svn: 227562
157d3f8255