[llvm] [DAG] isGuaranteedNotToBeUndefOrPoison - ISD::LOAD nodes are not poison if the LoadSDNode is known to be dereferenceable (PR #160884)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> If we are talking about the result of a load (as it seems, but I'm not an expert in SDAG), then it can be poison or undef. The patch doesn't look right.

I must be missing something - why is ValueTracking's isGuaranteedNotToBeUndefOrPoison allowed to do this?
https://github.com/llvm/llvm-project/blob/f7aa472800a26e3bed11e49834f446fd43385df7/llvm/lib/Analysis/ValueTracking.cpp#L7675-L7679

https://github.com/llvm/llvm-project/pull/160884