diff --git a/lib/CodeGen/MachineCopyPropagation.cpp b/lib/CodeGen/MachineCopyPropagation.cpp
index ed3f349..56be93a 100644
--- a/lib/CodeGen/MachineCopyPropagation.cpp
+++ b/lib/CodeGen/MachineCopyPropagation.cpp
@@ -191,8 +191,11 @@
 
     // Not a copy.
     SmallVector<unsigned, 2> Defs;
+    bool HasRegMask = false;
     for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
       MachineOperand &MO = MI->getOperand(i);
+      if (MO.isRegMask())
+        HasRegMask = true;
       if (!MO.isReg())
         continue;
       unsigned Reg = MO.getReg();
@@ -220,6 +223,20 @@
       }
     }
 
+    // The instruction has a register mask operand which means that it clobbers
+    // a large set of registers.  It is possible to use the register mask to
+    // prune the available copies, but treat it like a basic block boundary for
+    // now.
+    if (HasRegMask) {
+      // FIXME: We could possibly erase some MaybeDeadCopies if their registers
+      // are clobbered by the mask.
+      MaybeDeadCopies.clear();
+      AvailCopyMap.clear();
+      CopyMap.clear();
+      SrcMap.clear();
+      continue;
+    }
+
     for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
       unsigned Reg = Defs[i];