Add reverse(ContainerTy) range adapter.

For cases where we needed a foreach loop in reverse over a container,
we had to do something like

  for (const GlobalValue *GV : make_range(TypeInfos.rbegin(),
                                          TypeInfos.rend())) {

This provides a convenience method which shortens this to

  for (const GlobalValue *GV : reverse(TypeInfos)) {

There are 2 versions of this, with a preference to the rbegin() version.

The first uses rbegin() and rend() to construct an iterator_range.

The second constructs an iterator_range from the begin() and end() methods
wrapped in std::reverse_iterator's.

Reviewed by David Blaikie.

llvm-svn: 243563

1 files changed, 77 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/RangeAdapterTest.cpp b/llvm/unittests/ADT/RangeAdapterTest.cpp
new file mode 100644
index 00000000000..7547f84ce49
--- /dev/null
+++ b/llvm/unittests/ADT/RangeAdapterTest.cpp
@@ -0,0 +1,77 @@
+//===- RangeAdapterTest.cpp - Unit tests for range adapters  --------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/ADT/STLExtras.h"
+#include "gtest/gtest.h"
+
+#include <iterator>
+#include <list>
+#include <vector>
+
+using namespace llvm;
+
+namespace {
+
+// A wrapper around vector which exposes rbegin(), rend().
+class ReverseOnlyVector {
+  std::vector<int> Vec;
+public:
+  ReverseOnlyVector(std::initializer_list<int> list) : Vec(list) { }
+
+  typedef std::vector<int>::reverse_iterator reverse_iterator;
+  reverse_iterator rbegin() { return Vec.rbegin(); }
+  reverse_iterator rend() { return Vec.rend(); }
+};
+
+// A wrapper around vector which exposes begin(), end(), rbegin() and rend().
+// begin() and end() don't have implementations as this ensures that we will
+// get a linker error if reverse() chooses begin()/end() over rbegin(), rend().
+class BidirectionalVector {
+  std::vector<int> Vec;
+
+public:
+  BidirectionalVector(std::initializer_list<int> list) : Vec(list) { }
+
+  typedef std::vector<int>::iterator iterator;
+  iterator begin();
+  iterator end();
+
+  typedef std::vector<int>::reverse_iterator reverse_iterator;
+  reverse_iterator rbegin() { return Vec.rbegin(); }
+  reverse_iterator rend() { return Vec.rend(); }
+};
+
+// Test fixture
+template <typename T>
+class RangeAdapterTest : public ::testing::Test { };
+
+typedef ::testing::Types<std::vector<int>,
+                         std::list<int>,
+                         int[4],
+                         ReverseOnlyVector,
+                         BidirectionalVector,
+                         const std::vector<int>,
+                         const std::list<int>,
+                         const int[4]> RangeAdapterTestTypes;
+TYPED_TEST_CASE(RangeAdapterTest, RangeAdapterTestTypes);
+
+TYPED_TEST(RangeAdapterTest, TrivialOperation) {
+  TypeParam v = { 0, 1, 2, 3 };
+
+  int counter = 3;
+  for (int i : reverse(v))
+    EXPECT_EQ(i, counter--);
+
+  counter = 0;
+  for (int i : reverse(reverse(v)))
+    EXPECT_EQ(i, counter++);
+}
+
+} // anonymous namespace