[SafepointIRVerifier] Allow non-dereferencing uses of unrelocated or poisoned PHI nodes
PHI that has at least one unrelocated input cannot cause any issues by itself,
though its uses should be carefully verified. With this patch PHIs are allowed
to have any inputs but when all inputs are unrelocated the PHI is marked as
unrelocated and if not all inputs are unrelocated then the PHI is marked as
poisoned. Poisoned pointers can be used only in three ways: to derive new
pointers, in PHIs or in comparisons against constants that are exclusively
derived from null.
Patch by Daniil Suchkov!
Differential Revision: https://reviews.llvm.org/D41006
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321438
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