Set the iterator category for graph iterators to input_iterator_tag when
the visited set is stored externally. In that case we can't provide
multi-pass guarantee, so we should not claim to be a forward iterator.

Fixes: #116400

C++s iterator concept requires operator* to return the same type as is specified by the iterators reference type. This functionality is especially important for older generic code that did not yet make use of auto.
An example from within LLVM is iterator_adaptor_base which uses the reference type of the iterator it is wrapping as its return type for operator* (this class is used as base for a lot of other functionality like filter iterators and so on).
Using any of the graph traversal iterators listed above with it would previously fail to compile due to reference being non-const while operator* returned a const reference.

This patch fixes that by correctly specifying reference and using it as the return type of operator* explicitly to prevent further issues in the future.

Differential Revision: https://reviews.llvm.org/D151198

At the moment, ReversePostOrderTraversal performs a post-order walk on
the entry node of the passed in graph, rather than the graph type
itself.

If GT::NodeRef is the same as GraphT, everything works as expected and
this is the case for the current uses in-tree. But it does not work as
expected if GraphT != GT::NodeRef. In that case, we either fail to build
(if there is no GraphTrait specialization for GT:NodeRef) or we pick the
GraphTrait specialization for GT::NodeRef, instead of the specialization
of GraphT.

Both the depth-first and post-order iterators pick the expected
specalization and this patch updates ReversePostOrderTraversal to
delegate to po_begin & po_end to pick the right specialization, rather
than forcing using GraphTraits<GT::NodeRef>, by first getting the entry
node.

This makes `ReversePostOrderTraversal<Graph<6>> RPOT(G);` build and
work as expected in the test.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D100169

to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636

clang-format (https://reviews.llvm.org/D33932) to keep primary headers
at the top and handle new utility headers like 'gmock' consistently with
other utility headers.

No other change was made. I did no manual edits, all of this is
clang-format.

This should allow other changes to have more clear and focused diffs,
and is especially motivated by moving some headers into more focused
libraries.

llvm-svn: 304786

Reviewers: dblaikie

Subscribers: mzolotukhin, llvm-commits

Differential Revision: https://reviews.llvm.org/D23522

llvm-svn: 278752

If the template specialization for externally managed sets in
PostOrderIterator call too far out of sync with each other, this unit
test will fail to build. This is especially useful for developers who
may not build Clang (the only in-tree user) every time.

llvm-svn: 222447