Index: clang/lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- clang/lib/CodeGen/CGDebugInfo.cpp
+++ clang/lib/CodeGen/CGDebugInfo.cpp
@@ -354,13 +354,9 @@
   if (!MemBuffer)
     return None;
 
-  llvm::MD5 Hash;
-  llvm::MD5::MD5Result Result;
-
-  Hash.update(MemBuffer->getBuffer());
-  Hash.final(Result);
-
-  Hash.stringifyResult(Result, Checksum);
+  llvm::toHex(
+      llvm::MD5::hash(llvm::arrayRefFromStringRef(MemBuffer->getBuffer())),
+      /*LowerCase*/ true, Checksum);
   return llvm::DIFile::CSK_MD5;
 }
 
Index: llvm/include/llvm/ADT/StringExtras.h
===================================================================
--- llvm/include/llvm/ADT/StringExtras.h
+++ llvm/include/llvm/ADT/StringExtras.h
@@ -29,14 +29,15 @@
 
 namespace llvm {
 
-template<typename T> class SmallVectorImpl;
 class raw_ostream;
 
 /// hexdigit - Return the hexadecimal character for the
 /// given number \p X (which should be less than 16).
 inline char hexdigit(unsigned X, bool LowerCase = false) {
-  const char HexChar = LowerCase ? 'a' : 'A';
-  return X < 10 ? '0' + X : HexChar + X - 10;
+  assert(X <= 16);
+  static const char *const LUT = "0123456789ABCDEF";
+  const uint8_t Offset = LowerCase ? 32 : 0;
+  return LUT[X] | Offset;
 }
 
 /// Given an array of c-style strings terminated by a null pointer, construct
@@ -164,23 +165,26 @@
 
 /// Convert buffer \p Input to its hexadecimal representation.
 /// The returned string is double the size of \p Input.
-inline std::string toHex(StringRef Input, bool LowerCase = false) {
-  static const char *const LUT = "0123456789ABCDEF";
-  const uint8_t Offset = LowerCase ? 32 : 0;
-  size_t Length = Input.size();
-
-  std::string Output;
-  Output.reserve(2 * Length);
-  for (size_t i = 0; i < Length; ++i) {
-    const unsigned char c = Input[i];
-    Output.push_back(LUT[c >> 4] | Offset);
-    Output.push_back(LUT[c & 15] | Offset);
+inline void toHex(ArrayRef<uint8_t> Input, bool LowerCase,
+                  SmallVectorImpl<char> &Output) {
+  const size_t Length = Input.size();
+  Output.resize_for_overwrite(Length * 2);
+
+  for (size_t i = 0; i < Length; i++) {
+    const uint8_t c = Input[i];
+    Output[i * 2    ] = hexdigit(c >> 4, LowerCase);
+    Output[i * 2 + 1] = hexdigit(c & 15, LowerCase);
   }
-  return Output;
 }
 
 inline std::string toHex(ArrayRef<uint8_t> Input, bool LowerCase = false) {
-  return toHex(toStringRef(Input), LowerCase);
+  SmallString<16> Output;
+  toHex(Input, LowerCase, Output);
+  return std::string(Output);
+}
+
+inline std::string toHex(StringRef Input, bool LowerCase = false) {
+  return toHex(arrayRefFromStringRef(Input), LowerCase);
 }
 
 /// Store the binary representation of the two provided values, \p MSB and
Index: llvm/include/llvm/Support/MD5.h
===================================================================
--- llvm/include/llvm/Support/MD5.h
+++ llvm/include/llvm/Support/MD5.h
@@ -88,7 +88,7 @@
 
   /// Translates the bytes in \p Res to a hex string that is
   /// deposited into \p Str. The result will be of length 32.
-  static void stringifyResult(MD5Result &Result, SmallString<32> &Str);
+  static void stringifyResult(MD5Result &Result, SmallVectorImpl<char> &Str);
 
   /// Computes the hash for a given bytes.
   static std::array<uint8_t, 16> hash(ArrayRef<uint8_t> Data);
Index: llvm/lib/Support/MD5.cpp
===================================================================
--- llvm/lib/Support/MD5.cpp
+++ llvm/lib/Support/MD5.cpp
@@ -40,10 +40,9 @@
 #include "llvm/Support/MD5.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Endian.h"
-#include "llvm/Support/Format.h"
-#include "llvm/Support/raw_ostream.h"
 #include <array>
 #include <cstdint>
 #include <cstring>
@@ -281,14 +280,12 @@
 
 SmallString<32> MD5::MD5Result::digest() const {
   SmallString<32> Str;
-  raw_svector_ostream Res(Str);
-  for (int i = 0; i < 16; ++i)
-    Res << format("%.2x", Bytes[i]);
+  toHex(Bytes, /*LowerCase*/ true, Str);
   return Str;
 }
 
-void MD5::stringifyResult(MD5Result &Result, SmallString<32> &Str) {
-  Str = Result.digest();
+void MD5::stringifyResult(MD5Result &Result, SmallVectorImpl<char> &Str) {
+  toHex(Result.Bytes, /*LowerCase*/ true, Str);
 }
 
 std::array<uint8_t, 16> MD5::hash(ArrayRef<uint8_t> Data) {