[PATCH] D45853: (WIP) Alternate approach to reversing filtered iterators

[Tim Shen via Phabricator via llvm-commits]

timshen added inline comments.


================
Comment at: include/llvm/ADT/STLExtras.h:324
+    assert(Payload && "Payload should be engaged when findPrevValid is called");
+    while (this->I != Payload->Begin && !Payload->Pred(*this->I))
+      BaseT::operator--();
----------------
I think it's better to have:
  while (!Payload->Pred(*this->I))

Notice that as it is described in http://en.cppreference.com/w/cpp/concept/BidirectionalIterator, the precondition is "a is decrementable (there exists such b that a == ++b)". Therefore, there must be an iterator value that satisfies `Payload->Pred(*this->I)`. If users wrote a bug by decrementing on begin, I'd rather keep looping and let sanitizers catch it.


https://reviews.llvm.org/D45853