Fix PR1187.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43692 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 7819640..92c2634 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -466,7 +466,7 @@
           continue;
         if (MRegisterInfo::isVirtualRegister(PhysReg))
           PhysReg = vrm.getPhys(PhysReg);
-        if (mri_->regsOverlap(PhysReg, reg))
+        if (PhysReg && mri_->regsOverlap(PhysReg, reg))
           return true;
       }
     }