[llvm] [RISCV] Generate MIPS load/store pair instructions (PR #124717)

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

> > A thought: The lowering path can be:
> > 
> > 1. Merge two consecutive load/stores into **pseudo** load/store pair instructions no matter what the offsets are.
> > 2. Expand these pseudos in `RISCVExpandPseudo` by checking if their offsets are valid.
> > 
> > In this way, other vendor pair extensions like THead's can also benefit from this pass.
> 
> Why couldn't we check the offsets in this pass?

Yes we could. I was thinking that we may make use of PseudoInstExpansion.

https://github.com/llvm/llvm-project/pull/124717