Prevent looping when DenseSet is abused.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@70572 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/DenseMap.h

@@ -346,12 +346,12 @@ private:
     // probe almost the entire table until it found the empty bucket.  If the
     // table completely filled with tombstones, no lookup would ever succeed,
     // causing infinite loops in lookup.
+    ++NumEntries;
     if (NumEntries*4 >= NumBuckets*3 ||
         NumBuckets-(NumEntries+NumTombstones) < NumBuckets/8) {
       this->grow(NumBuckets * 2);
       LookupBucketFor(Key, TheBucket);
     }
-    ++NumEntries;
 
     // If we are writing over a tombstone, remember this.
     if (!KeyInfoT::isEqual(TheBucket->first, getEmptyKey()))

unittests/ADT/DenseSetTest.cpp

@@ -0,0 +1,30 @@
+//===- llvm/unittest/ADT/DenseSetTest.cpp - DenseSet 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 "gtest/gtest.h"
+#include <llvm/ADT/DenseSet.h>
+
+using namespace llvm;
+
+namespace {
+
+// Test fixture
+class DenseSetTest : public testing::Test {
+};
+
+// Test hashing with a set of only two entries.
+TEST_F(DenseSetTest, DoubleEntrySetTest) {
+  llvm::DenseSet<unsigned> set(2);
+  set.insert(0);
+  set.insert(1);
+  // Original failure was an infinite loop in this call:
+  EXPECT_EQ(0, set.count(2));
+}
+
+}