[ADT] Use SmallPtrSet or SmallSet flexibly (NFC)

I'm trying to remove the redirection in SmallSet.h:

template <typename PointeeType, unsigned N>
class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N>
{};

to make it clear that we are using SmallPtrSet.  There are only
handful places that rely on this redirection.

Now, this unit test is unique in that supply multiple key types via
TYPED_TESTS.

This patch adds UniversalSmallSet to work around the problem.

Author: kazutakahirata

llvm/unittests/ADT/DenseMapTest.cpp

@@ -387,9 +387,13 @@ TYPED_TEST(DenseMapTest, ConstIteratorTest) {
   EXPECT_TRUE(cit == cit2);
 }
 
+template <typename T, unsigned N>
+using UniversalSmallSet =
+    std::conditional_t<std::is_pointer_v<T>, SmallPtrSet<T, N>, SmallSet<T, N>>;
+
 TYPED_TEST(DenseMapTest, KeysValuesIterator) {
-  SmallSet<typename TypeParam::key_type, 10> Keys;
-  SmallSet<typename TypeParam::mapped_type, 10> Values;
+  UniversalSmallSet<typename TypeParam::key_type, 10> Keys;
+  UniversalSmallSet<typename TypeParam::mapped_type, 10> Values;
   for (int I = 0; I < 10; ++I) {
     auto K = this->getKey(I);
     auto V = this->getValue(I);
@@ -398,8 +402,8 @@ TYPED_TEST(DenseMapTest, KeysValuesIterator) {
     this->Map[K] = V;
   }
 
-  SmallSet<typename TypeParam::key_type, 10> ActualKeys;
-  SmallSet<typename TypeParam::mapped_type, 10> ActualValues;
+  UniversalSmallSet<typename TypeParam::key_type, 10> ActualKeys;
+  UniversalSmallSet<typename TypeParam::mapped_type, 10> ActualValues;
   for (auto K : this->Map.keys())
     ActualKeys.insert(K);
   for (auto V : this->Map.values())
@@ -410,8 +414,8 @@ TYPED_TEST(DenseMapTest, KeysValuesIterator) {
 }
 
 TYPED_TEST(DenseMapTest, ConstKeysValuesIterator) {
-  SmallSet<typename TypeParam::key_type, 10> Keys;
-  SmallSet<typename TypeParam::mapped_type, 10> Values;
+  UniversalSmallSet<typename TypeParam::key_type, 10> Keys;
+  UniversalSmallSet<typename TypeParam::mapped_type, 10> Values;
   for (int I = 0; I < 10; ++I) {
     auto K = this->getKey(I);
     auto V = this->getValue(I);
@@ -421,8 +425,8 @@ TYPED_TEST(DenseMapTest, ConstKeysValuesIterator) {
   }
 
   const TypeParam &ConstMap = this->Map;
-  SmallSet<typename TypeParam::key_type, 10> ActualKeys;
-  SmallSet<typename TypeParam::mapped_type, 10> ActualValues;
+  UniversalSmallSet<typename TypeParam::key_type, 10> ActualKeys;
+  UniversalSmallSet<typename TypeParam::mapped_type, 10> ActualValues;
   for (auto K : ConstMap.keys())
     ActualKeys.insert(K);
   for (auto V : ConstMap.values())