[llvm] [RISCV][GISel][WIP] Support s64 G_PHI on RV32 when D extension is enabled. (PR #119026)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > Make s64 unconditionally legal and split and remap the phi in regbankselect
> 
> Is there prior art for that?


> 
> Would I create G_UNMERGEs to split the s64 PHI inputs or do I need to peek through the existing G_MERGEs to find their inputs?



https://github.com/llvm/llvm-project/pull/119026