Index: lib/CodeGen/MachineInstr.cpp
===================================================================
--- lib/CodeGen/MachineInstr.cpp
+++ lib/CodeGen/MachineInstr.cpp
@@ -408,7 +408,14 @@
     OS << '>';
     break;
   case MachineOperand::MO_RegisterMask:
-    OS << "<regmask>";
+    OS << "<regmask";
+    for (unsigned i = 0; i < TRI->getNumRegs(); ++i) {
+      unsigned MaskWord = i / 32;
+      unsigned MaskBit = i % 32;
+      if (getRegMask()[MaskWord] & (1 << MaskBit))
+        OS << " " << PrintReg(i, TRI);
+    }
+    OS << ">";
     break;
   case MachineOperand::MO_RegisterLiveOut:
     OS << "<regliveout>";