[PATCH] D30853: Improve the genericity of `llvm::enumerate()`.

[Zachary Turner via Phabricator via llvm-commits]

zturner created this revision.

This all started when I tried to store the results of an `enumerate` range into a vector and then sort according to the value.  In doing so, I found out that `enumerate` was insufficiently generic, as it did not support `iterator_facade_base` and so you couldn't even call `std::distance()` on two of its iterators.

Ideally, one should not have to write this code:

  std::vector<std::pair<size_t, std::string>> Items;
  for (auto X : enumerate(Range))
    Items.push_back(std::make_pair(X.Index, X.Value));

just to get something they can sort.  It would be nice if you could write one line like `std::vector<std::pair<size_t, std::string>>(enumerate(X).begin(), enumerate(X).end());`

But the value type of an `enumerate` isn't even a pair, so you don't know how to specify it (if that was what you wanted).  We'd like to make use of type deduction.

To make all this work I re-wrote `enumerate` to support `iterator_facade_base`, and I add an additional helper function called `to_vector` which you can now call as `auto Results = to_vector<N>(enumerate(Range));` (replacing `enumerate` with whatever adapter you want), and it will return you a `SmallVector<T, N>` where `T` is the value type of the original range.


https://reviews.llvm.org/D30853

Files:
  llvm/include/llvm/ADT/STLExtras.h
  llvm/unittests/ADT/STLExtrasTest.cpp
  llvm/utils/TableGen/GlobalISelEmitter.cpp

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