Teach TableGen to automatically generate missing SubRegIndex instances.

The RegisterInfo.td file should only specify the indexes that sources need to
refer to. The rest is inferred.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131058 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed