Index: lib/MC/MCRegisterInfo.cpp
===================================================================
--- lib/MC/MCRegisterInfo.cpp
+++ lib/MC/MCRegisterInfo.cpp
@@ -75,7 +75,8 @@
 
   DwarfLLVMRegPair Key = { RegNum, 0 };
   const DwarfLLVMRegPair *I = std::lower_bound(M, M+Size, Key);
-  assert(I != M+Size && I->FromReg == RegNum && "Invalid RegNum");
+  if (I == M+Size || I->FromReg != RegNum)
+    return -1;
   return I->ToReg;
 }