[X86] Simplify the AVX512 code in LowerTruncate a little.

We don't need to create an ISD::TRUNCATE node to return, we started with one and can return it. Also remove the call to getExtendInVec, the result is just going to be a getNode of that value passed in.

llvm-svn: 327914

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -16976,10 +16976,9 @@ SDValue X86TargetLowering::LowerTRUNCATE(SDValue Op, SelectionDAG &DAG) const {
       // Make sure we're allowed to promote 512-bits.
       if (Subtarget.canExtendTo512DQ())
         return DAG.getNode(ISD::TRUNCATE, DL, VT,
-                           getExtendInVec(X86ISD::VSEXT, DL, MVT::v16i32, In,
-                                          DAG));
+                           DAG.getNode(X86ISD::VSEXT, DL, MVT::v16i32, In));
     } else {
-      return DAG.getNode(ISD::TRUNCATE, DL, VT, In);
+      return Op;
     }
   }