[llvm] [GlobalISel] Remove GI known bits cache (PR #157352)

[David Green via llvm-commits]

davemgreen wrote:

> I thought the point of this cache was to make this work through phis

It was added from https://github.com/llvm/llvm-project/commit/618dec2aeffd9d7778b581176e0897b10731e273, which mentions compile-time. There was an adjustment to the comment that talks about phis in https://github.com/llvm/llvm-project/commit/5bf0023b0d706bb8817f1e58145996cccc2f2c58.

https://github.com/llvm/llvm-project/pull/157352