!fixup add assert when VectorTripCount is already set

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -953,6 +953,9 @@ void VPlan::prepareToExecute(Value *TripCountV, Value *VectorTripCountV,
 
   if (!VectorTripCount.getUnderlyingValue())
     VectorTripCount.setUnderlyingValue(VectorTripCountV);
+  else
+    assert(VectorTripCount.getUnderlyingValue() == VectorTripCountV &&
+           "VectorTripCount set earlier must much VectorTripCountV");
 
   IRBuilder<> Builder(State.CFG.PrevBB->getTerminator());
   // FIXME: Model VF * UF computation completely in VPlan.