[llvm] [InstCombine] Lower flag check pattern to use a bitmask-shift (PR #169557)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> I also pulled out the logic for `createBitMapSeq()` and moved that into `ConstantComparesGatherer` (I think this is the wrong place since this logic is for generating a new IR sequence, not Analysis so might not belong in `Analysis/ValueTracking.cpp`, so if someone knows a better spot please let me know!).

Yeah it is a bit weird. We usually put the common transform logic in `llvm/lib/Transforms/Utils/Local.cpp`. But I don't have a strong objection as we also have BuildSubAggregate in ValueTracking.



https://github.com/llvm/llvm-project/pull/169557