[llvm] [RISC-V] Use an optional offset operand instead of zero-offset InstAliases (PR #210901)

[Alexander Richardson via llvm-commits]

arichardson wrote:

> lw a0, -2049(f0)

Looks like this one also doesn't change. I added your test in https://github.com/llvm/llvm-project/pull/214070, but it does not change.

https://github.com/llvm/llvm-project/pull/210901