[X86][NFC]Remove dead code in X86ISelLowering.cpp

[XinWang10]

Summary

Look at the code in X86ISelLowering.cpp line 15579, when NumV2Elements == 0,
it has been handled in that scope, and will not move to the line 15612.

[RKSimon]

LGTM - was this by manual inspection or did an analyzer spot it?

[XinWang10]

Thanks for your review. This is detected by our inner analyzer.

llvm/lib/Target/X86/X86ISelLowering.cpp

if (Subtarget.hasAVX2())
     if (SDValue Extract = lowerShuffleOfExtractsAsVperm(DL, V1, V2, Mask, DAG))
       return Extract;
 
   // Try to use shift instructions.
   if (SDValue Shift =
           lowerShuffleAsShift(DL, MVT::v4i32, V1, V2, Mask, Zeroable, Subtarget,
                               DAG, /*BitwiseOnly*/ false))
     return Shift;
-  if (!Subtarget.preferLowerShuffleAsShift() && NumV2Elements == 0)
-    if (SDValue Rotate =
-            lowerShuffleAsBitRotate(DL, MVT::v4i32, V1, Mask, Subtarget, DAG))
-      return Rotate;
 
   // There are special ways we can lower some single-element blends.
   if (NumV2Elements == 1)
     if (SDValue V = lowerShuffleAsElementInsertion(
             DL, MVT::v4i32, V1, V2, Mask, Zeroable, Subtarget, DAG))
       return V;
 
   // We have different paths for blend lowering, but they all must use the