[llvm] r198914 - ARM IAS: support implicit immediate 0s for {LD, ST}R{B, }T

[Tim Northover]

> If you have a way to implement it with InstAlias, be my guest. I
> couldn't find one and I spend some time with gdb trying to fit the
> patterns to match.

Did you investigate the loop I pointed out in TableGen for bugs?
There's nothing absolutely horrific that should prevent this being
written as an alias: all of the MCOperands are determined from the
assembly syntax and associated Operand sub-classes.

Cheers.

Tim.