[ADT] Teach DenseMap to support StringRef keys.

While often you want to use something specialized like StringMap, when
the strings already have persistent storage a normal densemap over them
can be more efficient.

This can't go into StringRef.h because of really obnoxious header chains
from the hashing code to the endian detection code to CPU feature
detection code to StringMap.

llvm-svn: 240528

1 files changed, 25 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/DenseMapTest.cpp b/llvm/unittests/ADT/DenseMapTest.cpp
index 97807771725..2c6fe358832 100644
--- a/llvm/unittests/ADT/DenseMapTest.cpp
+++ b/llvm/unittests/ADT/DenseMapTest.cpp
@@ -323,6 +323,31 @@ TYPED_TEST(DenseMapTest, ConstIteratorTest) {
   EXPECT_TRUE(cit == cit2);
 }
 
+// Make sure DenseMap works with StringRef keys.
+TEST(DenseMapCustomTest, StringRefTest) {
+  DenseMap<StringRef, int> M;
+
+  M["a"] = 1;
+  M["b"] = 2;
+  M["c"] = 3;
+
+  EXPECT_EQ(3u, M.size());
+  EXPECT_EQ(1, M.lookup("a"));
+  EXPECT_EQ(2, M.lookup("b"));
+  EXPECT_EQ(3, M.lookup("c"));
+
+  EXPECT_EQ(0, M.lookup("q"));
+
+  // Test the empty string, spelled various ways.
+  EXPECT_EQ(0, M.lookup(""));
+  EXPECT_EQ(0, M.lookup(StringRef()));
+  EXPECT_EQ(0, M.lookup(StringRef("a", 0)));
+  M[""] = 42;
+  EXPECT_EQ(42, M.lookup(""));
+  EXPECT_EQ(42, M.lookup(StringRef()));
+  EXPECT_EQ(42, M.lookup(StringRef("a", 0)));
+}
+
 // Key traits that allows lookup with either an unsigned or char* key;
 // In the latter case, "a" == 0, "b" == 1 and so on.
 struct TestDenseMapInfo {