[llvm] [MIR] Allow overriding isSSA, noPhis, noVRegs in MIR input (PR #108546)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Passes that insert phis should be clearing the no phis property

> If FinalizeISel pass is (potentially) creating PHI instructions, then it should probably set the noPhis property to false

That sounds like an unnecessary burden on passes that create instructions. Surely the only supported use case is that functions start off with noPhis=false _even if they happen to contain zero phi instructions_, and after phi elimination they have noPhis=true. Any pass that might create phis simply should not be run after that point.

https://github.com/llvm/llvm-project/pull/108546