[ADT] Add initializer_list constructor to SmallDenseMap

[kuhar]

Summary

Make it easier to initialize small maps inline. Note that DenseMap already has an initializer_list constructor.

[dblaikie]

Sounds good

llvm/unittests/ADT/DenseMapTest.cpp

551

I'd probably test this with = rather than () style syntax - to demonstrate that it's intentional/verify that implicit construction works

[kuhar]

Use the assignment syntax in the test, per David's suggestion.

llvm/include/llvm/ADT/DenseMap.h

public:
   }
 
   template<typename InputIt>
   SmallDenseMap(const InputIt &I, const InputIt &E) {
     init(NextPowerOf2(std::distance(I, E)));
     this->insert(I, E);
   }
 
+  SmallDenseMap(std::initializer_list<typename BaseT::value_type> Vals)
+      : SmallDenseMap(Vals.begin(), Vals.end()) {}
+
   ~SmallDenseMap() {
     this->destroyAll();
     deallocateBuckets();
   }
 
   void swap(SmallDenseMap& RHS) {
     unsigned TmpNumEntries = RHS.NumEntries;
     RHS.NumEntries = NumEntries;

llvm/unittests/ADT/DenseMapTest.cpp

TEST(DenseMapCustomTest, FindAsTest) {
 
   // find_as() tests
   EXPECT_EQ(1u, map.find_as("a")->second);
   EXPECT_EQ(2u, map.find_as("b")->second);
   EXPECT_EQ(3u, map.find_as("c")->second);
   EXPECT_TRUE(map.find_as("d") == map.end());
 }
 
+TEST(DenseMapCustomTest, SmallDenseMapInitializerList) {
+  SmallDenseMap<int, int> M = {{0, 0}, {0, 1}, {1, 2}};
+  EXPECT_EQ(2u, M.size());
+  EXPECT_EQ(1u, M.count(0));
+  EXPECT_EQ(0, M[0]);
+  EXPECT_EQ(1u, M.count(1));
+  EXPECT_EQ(2, M[1]);
+}
+
 struct ContiguousDenseMapInfo {
   static inline unsigned getEmptyKey() { return ~0; }
   static inline unsigned getTombstoneKey() { return ~0U - 1; }
   static unsigned getHashValue(const unsigned& Val) { return Val; }
   static bool isEqual(const unsigned& LHS, const unsigned& RHS) {
     return LHS == RHS;
   }
 };