diff --git a/unittests/ADT/IntEqClassesTest.cpp b/unittests/ADT/IntEqClassesTest.cpp
new file mode 100644
index 0000000..fc908c1
--- /dev/null
+++ b/unittests/ADT/IntEqClassesTest.cpp
@@ -0,0 +1,107 @@
+//===---- ADT/IntEqClassesTest.cpp - IntEqClasses unit tests ----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/IntEqClasses.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(IntEqClasses, Simple) {
+  IntEqClasses ec(10);
+
+  ec.join(0, 1);
+  ec.join(3, 2);
+  ec.join(4, 5);
+  ec.join(7, 6);
+
+  EXPECT_EQ(0u, ec.findLeader(0));
+  EXPECT_EQ(0u, ec.findLeader(1));
+  EXPECT_EQ(2u, ec.findLeader(2));
+  EXPECT_EQ(2u, ec.findLeader(3));
+  EXPECT_EQ(4u, ec.findLeader(4));
+  EXPECT_EQ(4u, ec.findLeader(5));
+  EXPECT_EQ(6u, ec.findLeader(6));
+  EXPECT_EQ(6u, ec.findLeader(7));
+  EXPECT_EQ(8u, ec.findLeader(8));
+  EXPECT_EQ(9u, ec.findLeader(9));
+
+  // join two non-leaders.
+  ec.join(1, 3);
+
+  EXPECT_EQ(0u, ec.findLeader(0));
+  EXPECT_EQ(0u, ec.findLeader(1));
+  EXPECT_EQ(0u, ec.findLeader(2));
+  EXPECT_EQ(0u, ec.findLeader(3));
+  EXPECT_EQ(4u, ec.findLeader(4));
+  EXPECT_EQ(4u, ec.findLeader(5));
+  EXPECT_EQ(6u, ec.findLeader(6));
+  EXPECT_EQ(6u, ec.findLeader(7));
+  EXPECT_EQ(8u, ec.findLeader(8));
+  EXPECT_EQ(9u, ec.findLeader(9));
+
+  // join two leaders.
+  ec.join(4, 8);
+
+  EXPECT_EQ(0u, ec.findLeader(0));
+  EXPECT_EQ(0u, ec.findLeader(1));
+  EXPECT_EQ(0u, ec.findLeader(2));
+  EXPECT_EQ(0u, ec.findLeader(3));
+  EXPECT_EQ(4u, ec.findLeader(4));
+  EXPECT_EQ(4u, ec.findLeader(5));
+  EXPECT_EQ(6u, ec.findLeader(6));
+  EXPECT_EQ(6u, ec.findLeader(7));
+  EXPECT_EQ(4u, ec.findLeader(8));
+  EXPECT_EQ(9u, ec.findLeader(9));
+
+  // join mixed.
+  ec.join(9, 1);
+
+  EXPECT_EQ(0u, ec.findLeader(0));
+  EXPECT_EQ(0u, ec.findLeader(1));
+  EXPECT_EQ(0u, ec.findLeader(2));
+  EXPECT_EQ(0u, ec.findLeader(3));
+  EXPECT_EQ(4u, ec.findLeader(4));
+  EXPECT_EQ(4u, ec.findLeader(5));
+  EXPECT_EQ(6u, ec.findLeader(6));
+  EXPECT_EQ(6u, ec.findLeader(7));
+  EXPECT_EQ(4u, ec.findLeader(8));
+  EXPECT_EQ(0u, ec.findLeader(9));
+
+  // compressed map.
+  ec.compress();
+  EXPECT_EQ(3u, ec.getNumClasses());
+
+  EXPECT_EQ(0u, ec[0]);
+  EXPECT_EQ(0u, ec[1]);
+  EXPECT_EQ(0u, ec[2]);
+  EXPECT_EQ(0u, ec[3]);
+  EXPECT_EQ(1u, ec[4]);
+  EXPECT_EQ(1u, ec[5]);
+  EXPECT_EQ(2u, ec[6]);
+  EXPECT_EQ(2u, ec[7]);
+  EXPECT_EQ(1u, ec[8]);
+  EXPECT_EQ(0u, ec[9]);
+
+  // uncompressed map.
+  ec.uncompress();
+  EXPECT_EQ(0u, ec.findLeader(0));
+  EXPECT_EQ(0u, ec.findLeader(1));
+  EXPECT_EQ(0u, ec.findLeader(2));
+  EXPECT_EQ(0u, ec.findLeader(3));
+  EXPECT_EQ(4u, ec.findLeader(4));
+  EXPECT_EQ(4u, ec.findLeader(5));
+  EXPECT_EQ(6u, ec.findLeader(6));
+  EXPECT_EQ(6u, ec.findLeader(7));
+  EXPECT_EQ(4u, ec.findLeader(8));
+  EXPECT_EQ(0u, ec.findLeader(9));
+}
+
+} // end anonymous namespace