Only handle widening of lowest subvector

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -42620,8 +42620,8 @@ static SDValue combineTargetShuffle(SDValue N, const SDLoc &DL,
       assert((SubOps.size() == 2 || SubOps.size() == 4) &&
              "Unexpected split ops");
       // Bail if we were permuting a widened vector.
-      if ((SubOps.size() == 2 && SubOps[1].isUndef()) ||
-          (SubOps.size() == 4 && SubOps[2].isUndef() && SubOps[3].isUndef()))
+      if (SubOps[1].isUndef() &&
+          (SubOps.size() == 2 || (SubOps[2].isUndef() && SubOps[3].isUndef())))
         return SDValue();
       // Bail if any subops would have folded into the concat.
       if (any_of(SubOps, [](SDValue Op) { return isShuffleFoldableLoad(Op); }))