[PATCH] D68916: [ARM] Accept ldrb.w mnemonic for certain addressing modes (PR43382)

[Momchil Velikov via Phabricator via llvm-commits]

chill added a comment.

In D68916#1708356 <https://reviews.llvm.org/D68916#1708356>, @efriedma wrote:

> Adding aliases seems like the right approach; we have aliases for a bunch of other instructions.
>
> I'm not sure why you need the AsmMatchConverter, though; needs a comment to explain.
>
> Why is Rt listed twice here?


For both aliases we need something to match the writeback out operand of `t2LDRB_PRE` and `t2LDRB_POST`. 
For `t2LDR_PRE` the writeback is well hidden in `$addr` operand and something like `$addr.base` does not seem to work.
For `t2LDR_POST` the `$Rn` operand is not a GPR, it's a memory operand and likewise does not match.

`$Rt` is just a placeholder in both cases.

And that's why we need the `AsmMatchConverter`s - to replace *that* `Rt` with the correct writeback register from the memory operands.


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https://reviews.llvm.org/D68916