Index: include/llvm/Support/Format.h
===================================================================
--- include/llvm/Support/Format.h
+++ include/llvm/Support/Format.h
@@ -259,21 +259,26 @@
   unsigned Width;
   bool Hex;
   bool Upper;
+  bool HexPrefix;
   friend class raw_ostream;
 public:
-    FormattedNumber(uint64_t HV, int64_t DV, unsigned W, bool H, bool U)
-      : HexValue(HV), DecValue(DV), Width(W), Hex(H), Upper(U) { }
+  FormattedNumber(uint64_t HV, int64_t DV, unsigned W, bool H, bool U,
+                  bool Prefix)
+      : HexValue(HV), DecValue(DV), Width(W), Hex(H), Upper(U),
+        HexPrefix(Prefix) {}
 };
 
 /// format_hex - Output \p N as a fixed width hexadecimal. If number will not
 /// fit in width, full number is still printed.  Examples:
-///   OS << format_hex(255, 4)        => 0xff
-///   OS << format_hex(255, 4, true)  => 0xFF
-///   OS << format_hex(255, 6)        => 0x00ff
-///   OS << format_hex(255, 2)        => 0xff
-inline FormattedNumber format_hex(uint64_t N, unsigned Width, bool Upper=false) {
+///   OS << format_hex(255, 4)              => 0xff
+///   OS << format_hex(255, 4, true)        => 0xFF
+///   OS << format_hex(255, 6)              => 0x00ff
+///   OS << format_hex(255, 2)              => 0xff
+///   OS << format_hex(255, 2, true, false) => FF
+inline FormattedNumber format_hex(uint64_t N, unsigned Width,
+                                  bool Upper = false, bool HexPrefix = true) {
   assert(Width <= 18 && "hex width must be <= 18");
-  return FormattedNumber(N, 0, Width, true, Upper);
+  return FormattedNumber(N, 0, Width, true, Upper, HexPrefix);
 }
 
 /// format_decimal - Output \p N as a right justified, fixed-width decimal. If 
@@ -283,7 +288,7 @@
 ///   OS << format_decimal(-1, 3)    => " -1"
 ///   OS << format_decimal(12345, 3) => "12345"
 inline FormattedNumber format_decimal(int64_t N, unsigned Width) {
-  return FormattedNumber(0, N, Width, false, false);
+  return FormattedNumber(0, N, Width, false, false, false);
 }
 
 
Index: lib/Support/raw_ostream.cpp
===================================================================
--- lib/Support/raw_ostream.cpp
+++ lib/Support/raw_ostream.cpp
@@ -410,9 +410,12 @@
 raw_ostream &raw_ostream::operator<<(const FormattedNumber &FN) {
   if (FN.Hex) {
     unsigned Nibbles = (64 - countLeadingZeros(FN.HexValue)+3)/4;
-    unsigned Width = (FN.Width > Nibbles+2) ? FN.Width : Nibbles+2;
-        
+    unsigned PrefixChars = FN.HexPrefix ? 2 : 0;
+    unsigned Width = std::max(FN.Width, Nibbles + PrefixChars);
+
     char NumberBuffer[20] = "0x0000000000000000";
+    if (!FN.HexPrefix)
+      NumberBuffer[1] = '0';
     char *EndPtr = NumberBuffer+Width;
     char *CurPtr = EndPtr;
     const char A = FN.Upper ? 'A' : 'a';