[llvm] Add a threshold to RegStackify to avoid register spills at runtime (PR #97283)

[Derek Schuff via llvm-commits]

dschuff wrote:

The job of RegStackify is to convert wasm locals into stack values.
My understanding of how optimizing codegen in wasm engines work is that they generally first convert all wasm locals and all stack values into SSA values, do their optimizations, and then run regular register allocation against the SSA values. Thus, it shouldn't really matter whether the original values were in wasm locals or on the wasm stack, the amount of register pressure and spilling should be the same.
Are you observing a difference in the register spilling on some engine? Can you say more about why it's happening?

+cc some potentially-interested people  (@jakobkummerow @eqrion @sunfishcode)

https://github.com/llvm/llvm-project/pull/97283