diff --git a/llvm/lib/Support/StringRef.cpp b/llvm/lib/Support/StringRef.cpp
--- a/llvm/lib/Support/StringRef.cpp
+++ b/llvm/lib/Support/StringRef.cpp
@@ -148,6 +148,23 @@
 
   const char *Stop = Start + (Size - N + 1);
 
+  if (N == 2) {
+    // Provide a fast path for newline finding (CRLF case) in InclusionRewriter.
+    // This is basically a naive search with a little bit twiddling.
+
+    // In theory we could use uint16_t, but some architectures don't support
+    // 16-bit arithmetic and will require a (& 65535) after the bit operations.
+    // Using 32-bit arithmetic with a shift of 16 would be more efficient for
+    // those cases.
+    uint32_t NeedleWord =
+        (uint32_t)(uint8_t)Needle[0] << 16 | (uint8_t)Needle[1];
+    uint32_t HaystackWord =
+        (uint32_t)(uint8_t)Start[0] << 16 | (uint8_t)Start[1];
+    for (Start++; Start < Stop && NeedleWord != HaystackWord;)
+      HaystackWord = HaystackWord << 16 | (uint8_t) * ++Start;
+    return NeedleWord == HaystackWord ? Start - Data - 1 : npos;
+  }
+
   // For short haystacks or unsupported needles fall back to the naive algorithm
   if (Size < 16 || N > 255) {
     do {