had gotten out of sync: isCastable didn't think it was possible to
cast the x86_mmx type to anything, while it did think it possible
to cast an i64 to x86_mmx.
llvm-svn: 128705
adjusted unittest
I have added some doxygen to OptionalOperandTraits,
so hopefully there will be no confusion in the future.
Incidentally OptionalOperandTraits is not used any more (IIUC),
but the obvious client would be BranchInstr, and I plan
to rearrange it that way.
llvm-svn: 98624