BasicAA will already call getModRefBehavior() on the Function of
the CallBase if there are no operand bundles. This happens through
getBestAAResults(), i.e. it is a recursive call that will query
other AA providers, not just the BasicAA implementation.
As such, there is no need to reimplement the same functionality
in GlobalsModRef, a combination of BasicAA and GlobalsModRef already
handles it. This does mean that this no longer works under
-disable-basic-aa, but that's a testing only option.
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