[ADT] Make filter_iterator support bidirectional iteration
This makes it possible to reverse a filtered range. For example, here's
a way to visit memory accesses in a BasicBlock in reverse order:
auto MemInsts = reverse(make_filter_range(BB, [](Instruction &I) {
return isa<StoreInst>(&I) || isa<LoadInst>(&I);
}));
for (auto &MI : MemInsts)
...
To implement this functionality, I factored out forward iteration
functionality into filter_iterator_base, and added a specialization of
filter_iterator_impl which supports bidirectional iteration. Thanks to
Tim Shen, Zachary Turner, and others for suggesting this design and
providing feedback! This version of the patch supersedes the original
(https://reviews.llvm.org/D45792).
This was motivated by a problem we encountered in D45657: we'd like to
visit the non-debug-info instructions in a BasicBlock in reverse order.
Testing: check-llvm, check-clang
Differential Revision: https://reviews.llvm.org/D45853
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330875
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