Correctly handle multiple DBG_VALUE instructions at the same SlotIndex.

It is possible to have multiple DBG_VALUEs for the same variable:

32L TEST32rr %vreg0<kill>, %vreg0, %EFLAGS<imp-def>; GR32:%vreg0
    DBG_VALUE 2, 0, !"i"
    DBG_VALUE %noreg, %0, !"i"

When that happens, keep the last one instead of the first.

llvm-svn: 136842

llvm/lib/CodeGen/LiveDebugVariables.cpp

@@ -179,6 +179,9 @@ public:
     LocMap::iterator I = locInts.find(Idx);
     if (!I.valid() || I.start() != Idx)
       I.insert(Idx, Idx.getNextSlot(), getLocationNo(LocMO));
+    else
+      // A later DBG_VALUE at the same SlotIndex overrides the old location.
+      I.setValue(getLocationNo(LocMO));
   }
 
   /// extendDef - Extend the current definition as far as possible down the