[llvm] [ISel] Replace expensive move from wzr by two moves via floating point immediate (PR #146538)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

I think in theory this shouldn't be much of an improvement, if the existing operation is already split and one of the mops is essentially the new instruction. In practice it is probably a good idea though.

There are certain cpus where it will not be helpful. Do you mind adding a tuning feature that keeps the old patterns for cortex-a53, a55, a510, a520 and a310. Those are all in-order and this will just be extra instructions.

https://github.com/llvm/llvm-project/pull/146538