Handle more edge cases in intrinsic name binary search

I tried to make the AMDGPU intrinsic info table use this instead of
another StringMatcher, and some issues arose.

llvm-svn: 258871
diff --git a/llvm/unittests/IR/IntrinsicsTest.cpp b/llvm/unittests/IR/IntrinsicsTest.cpp
new file mode 100644
index 0000000..0d12126
--- /dev/null
+++ b/llvm/unittests/IR/IntrinsicsTest.cpp
@@ -0,0 +1,40 @@
+//===- llvm/unittest/IR/IntrinsicsTest.cpp - ------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/IntrinsicInst.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+static const char *const NameTable1[] = {
+  "llvm.foo",
+  "llvm.foo.a",
+  "llvm.foo.b",
+  "llvm.foo.b.a",
+  "llvm.foo.c",
+};
+
+TEST(IntrinNameLookup, Basic) {
+  int I = Intrinsic::lookupLLVMIntrinsicByName(NameTable1, "llvm.foo");
+  EXPECT_EQ(0, I);
+  I = Intrinsic::lookupLLVMIntrinsicByName(NameTable1, "llvm.foo.f64");
+  EXPECT_EQ(0, I);
+  I = Intrinsic::lookupLLVMIntrinsicByName(NameTable1, "llvm.foo.b");
+  EXPECT_EQ(2, I);
+  I = Intrinsic::lookupLLVMIntrinsicByName(NameTable1, "llvm.foo.b.a");
+  EXPECT_EQ(3, I);
+  I = Intrinsic::lookupLLVMIntrinsicByName(NameTable1, "llvm.foo.c");
+  EXPECT_EQ(4, I);
+  I = Intrinsic::lookupLLVMIntrinsicByName(NameTable1, "llvm.foo.c.f64");
+  EXPECT_EQ(4, I);
+}
+
+} // end namespace