diff --git a/llvm/lib/Analysis/TargetLibraryInfo.cpp b/llvm/lib/Analysis/TargetLibraryInfo.cpp
--- a/llvm/lib/Analysis/TargetLibraryInfo.cpp
+++ b/llvm/lib/Analysis/TargetLibraryInfo.cpp
@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Support/CommandLine.h"
@@ -945,11 +946,18 @@
   if (funcName.empty())
     return false;
 
-  const auto *Start = std::begin(StandardNames);
-  const auto *End = std::end(StandardNames);
-  const auto *I = std::lower_bound(Start, End, funcName);
-  if (I != End && *I == funcName) {
-    F = (LibFunc)(I - Start);
+  static bool IsInitialized = false;
+  static DenseMap<StringRef, unsigned> Indices;
+  if (!IsInitialized) {
+    unsigned Idx = 0;
+    Indices.reserve(LibFunc::NumLibFuncs);
+    for (const auto &Func : StandardNames)
+      Indices[Func] = Idx++;
+    IsInitialized = true;
+  }
+
+  if (auto Loc = Indices.find(funcName); Loc != Indices.end()) {
+    F = (LibFunc)Loc->second;
     return true;
   }
   return false;