[llvm] [RISCV][SelectionDAG] Sign extend splats of i32 in getConstant on RV64 (PR #67027)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Yes but that's already something that function does for other instructions. For example the pointer operand of the scalar store SW demands all bits but the data operand only demands the lower 32 bits.

Trying this out locally, this seems to catch more cases. Will work on a PR for it

https://github.com/llvm/llvm-project/pull/67027