[llvm] [ARMISelDAGToDAG] use MO_FrameIndex to represent FrameIndex rather than MO_Register (PR #69654)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

I suspect this will trigger assembler errors in some cases.  ARM has a variety of addressing modes, and most of them aren't compatible with SelectAddrModeImm12.  Particularly for the constraints that are not "m"; "Uv" is explicitly documented to be an operand for a "vldr", which only has a 10 bit offset.

And it looks like the handling for the case where the the stack frame is actually larger than 4096 bytes is missing?

https://github.com/llvm/llvm-project/pull/69654