diff --git a/include/llvm/Target/TargetRegisterInfo.h b/include/llvm/Target/TargetRegisterInfo.h
index b792889db80..a5bd7c9f6f5 100644
--- a/include/llvm/Target/TargetRegisterInfo.h
+++ b/include/llvm/Target/TargetRegisterInfo.h
@@ -850,6 +850,29 @@ static inline raw_ostream &operator<<(raw_ostream &OS, const PrintReg &PR) {
   return OS;
 }
 
+/// PrintRegUnit - Helper class for printing register units on a raw_ostream.
+///
+/// Register units are named after their root registers:
+///
+///   AL      - Single root.
+///   FP0~ST7 - Dual roots.
+///
+/// Usage: OS << PrintRegUnit(Unit, TRI) << '\n';
+///
+class PrintRegUnit {
+  const TargetRegisterInfo *TRI;
+  unsigned Unit;
+public:
+  PrintRegUnit(unsigned unit, const TargetRegisterInfo *tri)
+    : TRI(tri), Unit(unit) {}
+  void print(raw_ostream&) const;
+};
+
+static inline raw_ostream &operator<<(raw_ostream &OS, const PrintRegUnit &PR) {
+  PR.print(OS);
+  return OS;
+}
+
 } // End llvm namespace
 
 #endif
diff --git a/lib/Target/TargetRegisterInfo.cpp b/lib/Target/TargetRegisterInfo.cpp
index a989cf4a7af..2395f2ba12a 100644
--- a/lib/Target/TargetRegisterInfo.cpp
+++ b/lib/Target/TargetRegisterInfo.cpp
@@ -46,6 +46,27 @@ void PrintReg::print(raw_ostream &OS) const {
   }
 }
 
+void PrintRegUnit::print(raw_ostream &OS) const {
+  // Generic printout when TRI is missing.
+  if (!TRI) {
+    OS << "Unit~" << Unit;
+    return;
+  }
+
+  // Check for invalid register units.
+  if (Unit >= TRI->getNumRegUnits()) {
+    OS << "BadUnit~" << Unit;
+    return;
+  }
+
+  // Normal units have at least one root.
+  MCRegUnitRootIterator Roots(Unit, TRI);
+  assert(Roots.isValid() && "Unit has no roots.");
+  OS << TRI->getName(*Roots);
+  for (++Roots; Roots.isValid(); ++Roots)
+    OS << '~' << TRI->getName(*Roots);
+}
+
 /// getAllocatableClass - Return the maximal subclass of the given register
 /// class that is alloctable, or NULL.
 const TargetRegisterClass *