use a SUB instruction instead of an ADD, because -128 can be
encoded in an 8-bit signed immediate field, while +128 can't be.
This avoids the need for a 32-bit immediate field in this case.
A similar optimization applies to 64-bit adds with 0x80000000,
with the 32-bit signed immediate field.
To support this, teach tablegen how to handle 64-bit constants.
llvm-svn: 57663
This makes the parser much easier to understand, eliminates a ton of global variables,
and gives tblgen nice caret diagnostics. It is also faster, but tblgen probably doesn't
care about performance.
There are a couple of FIXMEs which I will take care of next.
llvm-svn: 44274
