[llvm] Reland "[LICM] Sink unused l-invariant loads in preheader #157559" (PR #170204)

[Brendon Cahoon via llvm-commits]

bcahoon wrote:

> I will wait for this #219025 PR. Once the batching gets enabled, I will do the batched forget values here as well, which will resolve the compile time.

Perhaps another option is to use SE->forgetLoop(L) afterwards instead of calling forgetValue for each instruction?

https://github.com/llvm/llvm-project/pull/170204