[llvm] [ValueTracking] Compute known bits of or/and/xor recurrences from start and step (PR #222334)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> isKnownNonZero also learns that an or recurrence with a non-zero start value is never zero. LoopIdiomRecognize needs this to convert the clz loop in ffmpeg's sbc_calc_scalefactors after InstCombine removes the zero check

Please add a PhaseOrdering test.


https://github.com/llvm/llvm-project/pull/222334