b9337b108e
As we've seen in https://github.com/llvm/llvm-project/issues/58285 throwing away MemorySSA when only debug instructions are removed can lead to different code when debug info is present or not present. This is the second attempt at fixing the problem. The first one was https://reviews.llvm.org/D145051 which was reverted due to a 15% compile time regression for tramp3d-v4 in NewPM-ReleaseLTO-g. Differential Revision: https://reviews.llvm.org/D145478