Use existing isLE variable

Author: ostannard

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -15495,8 +15495,7 @@ SDValue DAGCombiner::visitTRUNCATE(SDNode *N) {
       unsigned BuildVecNumElts =  BuildVect.getNumOperands();
       unsigned TruncVecNumElts = VT.getVectorNumElements();
       unsigned TruncEltOffset = BuildVecNumElts / TruncVecNumElts;
-      unsigned FirstElt =
-          DAG.getDataLayout().isBigEndian() ? (TruncEltOffset - 1) : 0;
+      unsigned FirstElt = isLE ? 0 : (TruncEltOffset - 1);
 
       assert((BuildVecNumElts % TruncVecNumElts) == 0 &&
              "Invalid number of elements");