diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index e41d459f39d2..15baf14f2d90 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1496,6 +1496,11 @@ SDValue SelectionDAG::getVectorShuffle(EVT VT, SDLoc dl, SDValue N1,
     N1 = getUNDEF(VT);
     commuteShuffle(N1, N2, MaskVec);
   }
+  // Reset our undef status after accounting for the mask.
+  N2Undef = N2.getOpcode() == ISD::UNDEF;
+  // Re-check whether both sides ended up undef.
+  if (N1.getOpcode() == ISD::UNDEF && N2Undef)
+    return getUNDEF(VT);
 
   // If Identity shuffle return that node.
   bool Identity = true;
@@ -1506,11 +1511,36 @@ SDValue SelectionDAG::getVectorShuffle(EVT VT, SDLoc dl, SDValue N1,
     return N1;
 
   // Shuffling a constant splat doesn't change the result.
-  bool SplatHasUndefs;
-  if (N2Undef && N1.getOpcode() == ISD::BUILD_VECTOR)
-    if (cast<BuildVectorSDNode>(N1)->getConstantSplatNode(SplatHasUndefs) &&
-        !SplatHasUndefs)
-      return N1;
+  if (N2Undef) {
+    SDValue V = N1;
+
+    // Look through any bitcasts. We check that these don't change the number
+    // (and size) of elements and just changes their types.
+    while (V.getOpcode() == ISD::BITCAST)
+      V = V->getOperand(0);
+
+    // A splat should always show up as a build vector node.
+    if (auto *BV = dyn_cast<BuildVectorSDNode>(V)) {
+      bool SplatHasUndefs;
+      SDValue Splat = BV->getSplatValue(SplatHasUndefs);
+      // If this is a splat of an undef, shuffling it is also undef.
+      if (Splat && Splat.getOpcode() == ISD::UNDEF)
+        return getUNDEF(VT);
+
+      // We only have a splat which can skip shuffles if there is a splatted
+      // value and no undef lanes rearranged by the shuffle.
+      if (Splat && !SplatHasUndefs) {
+        // Splat of <x, x, ..., x>, return <x, x, ..., x>, provided that the
+        // number of elements match or the value splatted is a zero constant.
+        if (V.getValueType().getVectorNumElements() ==
+            VT.getVectorNumElements())
+          return N1;
+        if (auto *C = dyn_cast<ConstantSDNode>(Splat))
+          if (C->isNullValue())
+            return N1;
+      }
+    }
+  }
 
   FoldingSetNodeID ID;
   SDValue Ops[2] = { N1, N2 };
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 39537e358b9f..306a659c9831 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -7924,47 +7924,6 @@ static SDValue lowerVectorShuffle(SDValue Op, const X86Subtarget *Subtarget,
         return DAG.getVectorShuffle(VT, dl, V1, V2, NewMask);
       }
 
-  // Check for a shuffle of a splat, and return just the splat. While DAG
-  // combining will do a similar transformation, this shows up with the
-  // internally created shuffles and so we handle it specially here as we won't
-  // have another chance to DAG-combine the generic shuffle instructions.
-  if (V2IsUndef) {
-    SDValue V = V1;
-
-    // Look through any bitcasts. These can't change the size, just the number
-    // of elements which we check later.
-    while (V.getOpcode() == ISD::BITCAST)
-      V = V->getOperand(0);
-
-    // A splat should always show up as a build vector node.
-    if (V.getOpcode() == ISD::BUILD_VECTOR) {
-      SDValue Base;
-      bool AllSame = true;
-      for (unsigned i = 0; i != V->getNumOperands(); ++i)
-        if (V->getOperand(i).getOpcode() != ISD::UNDEF) {
-          Base = V->getOperand(i);
-          break;
-        }
-      // Splat of <u, u, ..., u>, return <u, u, ..., u>
-      if (!Base)
-        return V1;
-      for (unsigned i = 0; i != V->getNumOperands(); ++i)
-        if (V->getOperand(i) != Base) {
-          AllSame = false;
-          break;
-        }
-      // Splat of <x, x, ..., x>, return <x, x, ..., x>, provided that the
-      // number of elements match or the value splatted is a zero constant.
-      if (AllSame) {
-        if (V.getValueType().getVectorNumElements() == (unsigned)NumElements)
-          return V1;
-        if (auto *C = dyn_cast<ConstantSDNode>(Base))
-          if (C->isNullValue())
-            return V1;
-      }
-    }
-  }
-
   // For integer vector shuffles, try to collapse them into a shuffle of fewer
   // lanes but wider integers. We cap this to not form integers larger than i64
   // but it might be interesting to form i128 integers to handle flipping the
diff --git a/llvm/test/CodeGen/X86/widen_cast-6.ll b/llvm/test/CodeGen/X86/widen_cast-6.ll
index 7c06ad8ca664..46d8dd787a3b 100644
--- a/llvm/test/CodeGen/X86/widen_cast-6.ll
+++ b/llvm/test/CodeGen/X86/widen_cast-6.ll
@@ -1,9 +1,13 @@
 ; RUN: llc < %s -march=x86 -mattr=+sse4.1 | FileCheck %s
-; CHECK: movd
 
 ; Test bit convert that requires widening in the operand.
 
 define i32 @return_v2hi() nounwind {
+; CHECK-LABEL: @return_v2hi
+; CHECK:      pushl
+; CHECK-NEXT: xorl %eax, %eax
+; CHECK-NEXT: popl
+; CHECK-NEXT: ret
 entry:
 	%retval12 = bitcast <2 x i16> zeroinitializer to i32		; <i32> [#uses=1]
 	ret i32 %retval12