[llvm] [FnSpecialization] Enable function specialization of call chains (PR #163891)

[Alexandros Lamprineas via llvm-commits]

labrinea wrote:

I briefly looked at the patch series and I am not convinced it's the right approach. Perhaps it's best to handle non constant foldable calls in the instruction cost visitor separately, similarly to branches and switches which are not folded to a constant. I mean to compute the profitability of specializing that call instead of folding it. But then all this adds compile time complexity which I am not sure it is worth it.

https://github.com/llvm/llvm-project/pull/163891