From 2962e3e6b2f5ce87c28631353dfecd564531c5f8 Mon Sep 17 00:00:00 2001
From: Tim Shen <timshen91@gmail.com>
Date: Tue, 9 Aug 2016 20:23:13 +0000
Subject: [PATCH] [ADT] Change iterator_adaptor_base's default template
 arguments to forward more underlying typedefs

Reviewers: chandlerc

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D23217

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278157 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/ADT/iterator.h        |  9 ++++++++-
 unittests/Support/IteratorTest.cpp | 18 ++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/include/llvm/ADT/iterator.h b/include/llvm/ADT/iterator.h
index 2898a677db3..14830d06c2a 100644
--- a/include/llvm/ADT/iterator.h
+++ b/include/llvm/ADT/iterator.h
@@ -155,7 +155,14 @@ template <
     typename T = typename std::iterator_traits<WrappedIteratorT>::value_type,
     typename DifferenceTypeT =
         typename std::iterator_traits<WrappedIteratorT>::difference_type,
-    typename PointerT = T *, typename ReferenceT = T &,
+    typename PointerT = typename std::conditional<
+        std::is_same<T, typename std::iterator_traits<
+                            WrappedIteratorT>::value_type>::value,
+        typename std::iterator_traits<WrappedIteratorT>::pointer, T *>::type,
+    typename ReferenceT = typename std::conditional<
+        std::is_same<T, typename std::iterator_traits<
+                            WrappedIteratorT>::value_type>::value,
+        typename std::iterator_traits<WrappedIteratorT>::reference, T &>::type,
     // Don't provide these, they are mostly to act as aliases below.
     typename WrappedTraitsT = std::iterator_traits<WrappedIteratorT>>
 class iterator_adaptor_base
diff --git a/unittests/Support/IteratorTest.cpp b/unittests/Support/IteratorTest.cpp
index 83848328c0c..853d16cef46 100644
--- a/unittests/Support/IteratorTest.cpp
+++ b/unittests/Support/IteratorTest.cpp
@@ -16,6 +16,24 @@ using namespace llvm;
 
 namespace {
 
+template <int> struct Shadow;
+
+struct WeirdIter : std::iterator<std::input_iterator_tag, Shadow<0>, Shadow<1>,
+                                 Shadow<2>, Shadow<3>> {};
+
+struct AdaptedIter : iterator_adaptor_base<AdaptedIter, WeirdIter> {};
+
+// Test that iterator_adaptor_base forwards typedefs, if value_type is
+// unchanged.
+static_assert(std::is_same<typename AdaptedIter::value_type, Shadow<0>>::value,
+              "");
+static_assert(
+    std::is_same<typename AdaptedIter::difference_type, Shadow<1>>::value, "");
+static_assert(std::is_same<typename AdaptedIter::pointer, Shadow<2>>::value,
+              "");
+static_assert(std::is_same<typename AdaptedIter::reference, Shadow<3>>::value,
+              "");
+
 TEST(PointeeIteratorTest, Basic) {
   int arr[4] = { 1, 2, 3, 4 };
   SmallVector<int *, 4> V;