Use getZExtOrTrunc helper instead of manually doing zext/trunc check.  NFC.

The code here was doing exactly what is already in getZExtOrTrunc().
Just use that method instead.

llvm-svn: 242260
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 21ab072..51057a0 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -599,8 +599,7 @@
                             false, false, 0);
 
   // Truncate or zero extend offset to target pointer type.
-  unsigned CastOpc = IdxVT.bitsGT(PtrVT) ? ISD::TRUNCATE : ISD::ZERO_EXTEND;
-  Tmp3 = DAG.getNode(CastOpc, dl, PtrVT, Tmp3);
+  Tmp3 = DAG.getZExtOrTrunc(Tmp3, dl, PtrVT);
   // Add the offset to the index.
   unsigned EltSize = EltVT.getSizeInBits()/8;
   Tmp3 = DAG.getNode(ISD::MUL, dl, IdxVT, Tmp3,