This change is mostly motivated by exposing information about the original query instruction to the actual scanning work in getPointerDependencyFrom when used by GVN PRE. In a follow up change, I will use this to be more precise with regards to the semantics of volatile instructions encountered in the scan of a basic block.
Worth noting, is that this change (despite appearing quite simple) is not semantically preserving. By providing more information to the helper routine, we allow some optimizations to kick in that weren't previously able to (when called from this code path.) In particular, we see that treatment of !invariant.load becomes more precise. In theory, we might see a difference with an ordered/atomic instruction as well, but I'm having a hard time actually finding a test case which shows that.
Test wise, I've included new tests for !invariant.load which illustrate this difference.
I've also included some updated TBAA tests which highlight that this change isn't needed for that optimization to kick in - it's handled inside alias analysis itself. Arguably, these might call for being submitted separately. I don't have a strong preference either way and will defer to the reviewers.
Eventually, it would be nice to factor the !invariant.load handling inside alias analysis as well.