[X86] getFauxShuffleMask - don't allow undefs in constant for AND/ANDNP shuffle masks

Early out from getTargetConstantBitsFromNode call instead of just returning if an undef was found.

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -5719,12 +5719,13 @@ static bool getFauxShuffleMask(SDValue N, const APInt &DemandedElts,
     SDValue N1 = N.getOperand(1);
     bool IsAndN = (X86ISD::ANDNP == Opcode);
     uint64_t ZeroMask = IsAndN ? 255 : 0;
-    if (!getTargetConstantBitsFromNode(IsAndN ? N0 : N1, 8, UndefElts, EltBits))
+    if (!getTargetConstantBitsFromNode(IsAndN ? N0 : N1, 8, UndefElts, EltBits,
+                                       /*AllowWholeUndefs*/ false,
+                                       /*AllowPartialUndefs*/ false))
       return false;
     // We can't assume an undef src element gives an undef dst - the other src
     // might be zero.
-    if (!UndefElts.isZero())
-      return false;
+    assert(UndefElts.isZero() && "Expected UNDEF element in AND/ANDNP mask");
     for (int i = 0, e = (int)EltBits.size(); i != e; ++i) {
       const APInt &ByteBits = EltBits[i];
       if (ByteBits != 0 && ByteBits != 255)