Index: lib/CodeGen/MachineOperand.cpp
===================================================================
--- lib/CodeGen/MachineOperand.cpp
+++ lib/CodeGen/MachineOperand.cpp
@@ -764,7 +764,7 @@
     // Print the sub register.
     if (unsigned SubReg = getSubReg()) {
       if (TRI)
-        OS << '.' << TRI->getSubRegIndexName(SubReg);
+        OS << '.' << StringRef(TRI->getSubRegIndexName(SubReg)).lower();
       else
         OS << ".subreg" << SubReg;
     }