Index: include/llvm/CodeGen/SelectionDAGNodes.h
===================================================================
--- include/llvm/CodeGen/SelectionDAGNodes.h
+++ include/llvm/CodeGen/SelectionDAGNodes.h
@@ -85,7 +85,8 @@
 
   /// If N is a BUILD_VECTOR node whose elements are all the same constant or
   /// undefined, return true and return the constant value in \p SplatValue.
-  bool isConstantSplatVector(const SDNode *N, APInt &SplatValue);
+  bool isConstantSplatVector(const SDNode *N, APInt &SplatValue,
+                             bool AllowShrink = true);
 
   /// Return true if the specified node is a BUILD_VECTOR where all of the
   /// elements are ~0 or undef.
Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -116,7 +116,8 @@
 //                              ISD Namespace
 //===----------------------------------------------------------------------===//
 
-bool ISD::isConstantSplatVector(const SDNode *N, APInt &SplatVal) {
+bool ISD::isConstantSplatVector(const SDNode *N, APInt &SplatVal,
+                                bool AllowShrink) {
   auto *BV = dyn_cast<BuildVectorSDNode>(N);
   if (!BV)
     return false;
@@ -124,9 +125,11 @@
   APInt SplatUndef;
   unsigned SplatBitSize;
   bool HasUndefs;
-  EVT EltVT = N->getValueType(0).getVectorElementType();
-  return BV->isConstantSplat(SplatVal, SplatUndef, SplatBitSize, HasUndefs) &&
-         EltVT.getSizeInBits() >= SplatBitSize;
+  unsigned EltSize = N->getValueType(0).getVectorElementType().getSizeInBits();
+  unsigned MinSplatBits = AllowShrink ? 0 : EltSize;
+  return BV->isConstantSplat(SplatVal, SplatUndef, SplatBitSize, HasUndefs,
+                             MinSplatBits) &&
+         EltSize >= SplatBitSize;
 }
 
 // FIXME: AllOnes and AllZeros duplicate a lot of code. Could these be
Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -29567,8 +29567,8 @@
   // In SetLT case, The second operand of the comparison can be either 1 or 0.
   APInt SplatVal;
   if ((CC == ISD::SETLT) &&
-      !((ISD::isConstantSplatVector(SetCC.getOperand(1).getNode(), SplatVal) &&
-         SplatVal == 1) ||
+      !((ISD::isConstantSplatVector(SetCC.getOperand(1).getNode(), SplatVal,
+                                    false) && SplatVal.isOneValue()) ||
         (ISD::isBuildVectorAllZeros(SetCC.getOperand(1).getNode()))))
     return false;
 
@@ -32083,7 +32083,7 @@
     return SDValue();
 
   APInt SplatVal;
-  if (!ISD::isConstantSplatVector(Op1.getNode(), SplatVal) ||
+  if (!ISD::isConstantSplatVector(Op1.getNode(), SplatVal, false) ||
       !SplatVal.isMask())
     return SDValue();
 
@@ -32667,7 +32667,7 @@
     "Unexpected types for truncate operation");
 
   APInt C;
-  if (ISD::isConstantSplatVector(In.getOperand(1).getNode(), C)) {
+  if (ISD::isConstantSplatVector(In.getOperand(1).getNode(), C, false)) {
     // C should be equal to UINT32_MAX / UINT16_MAX / UINT8_MAX according
     // the element size of the destination type.
     return C.isMask(VT.getScalarSizeInBits()) ? In.getOperand(0) :
@@ -35374,7 +35374,8 @@
 
   SDNode *N1 = N->getOperand(1).getNode();
   APInt SplatVal;
-  if (!ISD::isConstantSplatVector(N1, SplatVal) || !SplatVal.isOneValue())
+  if (!ISD::isConstantSplatVector(N1, SplatVal, false) ||
+      !SplatVal.isOneValue())
     return SDValue();
 
   SDValue AllOnesVec = getOnesVector(VT, DAG, SDLoc(N));