[SetVector] Add erase() method

This is a recommit of r264414 after fixing the buildbot failure caused by
incompatible use of std::vector.erase().

The original message:

Add erase() which returns an iterator pointing to the next element after the
erased one. This makes it possible to erase selected elements while iterating
over the SetVector :
  while (I != E)
    if (test(*I))
      I = SetVector.erase(I);
    else
      ++I;

Reviewers: qcolombet, mcrosier, MatzeB, dblaikie

Subscribers: dberlin, dblaikie, mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D18281

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264450 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/SetVector.h

@@ -151,6 +151,24 @@ public:
     return false;
   }
 
+  /// Erase a single element from the set vector.
+  /// \returns an iterator pointing to the next element that followed the
+  /// element erased. This is the end of the SetVector if the last element is
+  /// erased.
+  iterator erase(iterator I) {
+    const key_type &V = *I;
+    assert(set_.count(V) && "Corrupted SetVector instances!");
+    set_.erase(V);
+
+    // FIXME: No need to use the non-const iterator when built with
+    // std:vector.erase(const_iterator) as defined in C++11. This is for
+    // compatibility with non-standard libstdc++ up to 4.8 (fixed in 4.9).
+    auto NI = vector_.begin();
+    std::advance(NI, std::distance<iterator>(NI, I));
+
+    return vector_.erase(NI);
+  }
+
   /// \brief Remove items from the set vector based on a predicate function.
   ///
   /// This is intended to be equivalent to the following code, if we could

unittests/ADT/CMakeLists.txt

@@ -32,6 +32,7 @@ set(ADTSources
   PostOrderIteratorTest.cpp
   RangeAdapterTest.cpp
   SCCIteratorTest.cpp
+  SetVectorTest.cpp
   SmallPtrSetTest.cpp
   SmallStringTest.cpp
   SmallVectorTest.cpp

unittests/ADT/SetVectorTest.cpp

@@ -0,0 +1,34 @@
+//===- llvm/unittest/ADT/SetVector.cpp ------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// SetVector unit tests.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SetVector.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+TEST(SetVector, EraseTest) {
+  SetVector<int> S;
+  S.insert(0);
+  S.insert(1);
+  S.insert(2);
+
+  auto I = S.erase(std::next(S.begin()));
+
+  // Test that the returned iterator is the expected one-after-erase
+  // and the size/contents is the expected sequence {0, 2}.
+  EXPECT_EQ(std::next(S.begin()), I);
+  EXPECT_EQ(2u, S.size());
+  EXPECT_EQ(0, *S.begin());
+  EXPECT_EQ(2, *std::next(S.begin()));
+}
+