[llvm] [SCEV] Speed up forgetLoop by avoiding def-use walk for loop-header PHIs (PR #201572)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

IR diff: https://github.com/dtcxzyw/llvm-opt-benchmark-nightly/pull/456
@Enna1 @nikic IIUC this patch was intended to be a non-functional change (i.e., just a compile-time improvement), right?


https://github.com/llvm/llvm-project/pull/201572