diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -37897,6 +37897,48 @@
           Ops, Mask, RootSizeInBits, SDLoc(Root), DAG, Subtarget))
     return DAG.getBitcast(Root.getValueType(), HOp);
 
+  // Try to refine our inputs given our knowledge of target shuffle mask.
+  for (auto I : enumerate(Ops)) {
+    int OpIdx = I.index();
+    SDValue &Op = I.value();
+
+    // What range of shuffle mask element values results in picking from Op?
+    int lo = OpIdx * Mask.size();
+    int hi = lo + Mask.size();
+
+    // Which elements of Op do we demand, given the mask's granularity?
+    APInt OpDemandedElts(Mask.size(), 0);
+    for (int MaskElt : Mask) {
+      if (isInRange(MaskElt, lo, hi)) { // Picks from Op?
+        int OpEltIdx = MaskElt - lo;
+        OpDemandedElts.setBit(OpEltIdx);
+      }
+    }
+
+    // Is the shuffle result smaller than the root?
+    if (Op.getValueSizeInBits() < RootSizeInBits) {
+      // We padded the mask with undefs. But we now need to undo that.
+      unsigned NumExpectedVectorElts = Mask.size();
+      unsigned EltSizeInBits = RootSizeInBits / NumExpectedVectorElts;
+      unsigned NumOpVectorElts = Op.getValueSizeInBits() / EltSizeInBits;
+      assert(!OpDemandedElts.extractBits(
+                 NumExpectedVectorElts - NumOpVectorElts, NumOpVectorElts) &&
+             "Demanding the virtual undef widening padding?");
+      OpDemandedElts = OpDemandedElts.trunc(NumOpVectorElts); // NUW
+    }
+
+    // The Op itself may be of different VT, so we need to scale the mask.
+    unsigned NumOpElts = Op.getValueType().getVectorNumElements();
+    APInt OpScaledDemandedElts = APIntOps::ScaleBitMask(OpDemandedElts, NumOpElts);
+
+    // Can this operand be simplified any further, given it's demanded elements?
+    if (SDValue NewOp =
+            DAG.getTargetLoweringInfo().SimplifyMultipleUseDemandedVectorElts(
+                Op, OpScaledDemandedElts, DAG))
+      Op = NewOp;
+  }
+  // FIXME: should we rerun resolveTargetShuffleInputsAndMask() now?
+
   // Widen any subvector shuffle inputs we've collected.
   if (any_of(Ops, [RootSizeInBits](SDValue Op) {
         return Op.getValueSizeInBits() < RootSizeInBits;
diff --git a/llvm/test/CodeGen/X86/insertelement-ones.ll b/llvm/test/CodeGen/X86/insertelement-ones.ll
--- a/llvm/test/CodeGen/X86/insertelement-ones.ll
+++ b/llvm/test/CodeGen/X86/insertelement-ones.ll
@@ -312,6 +312,7 @@
 ; SSE2-LABEL: insert_v16i8_x123456789ABCDEx:
 ; SSE2:       # %bb.0:
 ; SSE2-NEXT:    movdqa {{.*#+}} xmm1 = [0,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255]
+; SSE2-NEXT:    pand %xmm1, %xmm0
 ; SSE2-NEXT:    movl $255, %eax
 ; SSE2-NEXT:    movd %eax, %xmm2
 ; SSE2-NEXT:    pandn %xmm2, %xmm1
@@ -323,6 +324,7 @@
 ; SSE3-LABEL: insert_v16i8_x123456789ABCDEx:
 ; SSE3:       # %bb.0:
 ; SSE3-NEXT:    movdqa {{.*#+}} xmm1 = [0,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255]
+; SSE3-NEXT:    pand %xmm1, %xmm0
 ; SSE3-NEXT:    movl $255, %eax
 ; SSE3-NEXT:    movd %eax, %xmm2
 ; SSE3-NEXT:    pandn %xmm2, %xmm1
@@ -365,6 +367,7 @@
 ; SSE2-LABEL: insert_v32i8_x123456789ABCDEzGHIJKLMNOPQRSTxx:
 ; SSE2:       # %bb.0:
 ; SSE2-NEXT:    movdqa {{.*#+}} xmm2 = [0,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255]
+; SSE2-NEXT:    pand %xmm2, %xmm0
 ; SSE2-NEXT:    movl $255, %eax
 ; SSE2-NEXT:    movd %eax, %xmm3
 ; SSE2-NEXT:    pandn %xmm3, %xmm2
@@ -380,6 +383,7 @@
 ; SSE3-LABEL: insert_v32i8_x123456789ABCDEzGHIJKLMNOPQRSTxx:
 ; SSE3:       # %bb.0:
 ; SSE3-NEXT:    movdqa {{.*#+}} xmm2 = [0,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255]
+; SSE3-NEXT:    pand %xmm2, %xmm0
 ; SSE3-NEXT:    movl $255, %eax
 ; SSE3-NEXT:    movd %eax, %xmm3
 ; SSE3-NEXT:    pandn %xmm3, %xmm2
diff --git a/llvm/test/CodeGen/X86/oddshuffles.ll b/llvm/test/CodeGen/X86/oddshuffles.ll
--- a/llvm/test/CodeGen/X86/oddshuffles.ll
+++ b/llvm/test/CodeGen/X86/oddshuffles.ll
@@ -2261,12 +2261,13 @@
 ;
 ; AVX1-LABEL: splat_v3i32:
 ; AVX1:       # %bb.0:
-; AVX1-NEXT:    vmovq {{.*#+}} xmm0 = mem[0],zero
-; AVX1-NEXT:    vpinsrd $2, 8(%rdi), %xmm0, %xmm1
-; AVX1-NEXT:    vxorps %xmm2, %xmm2, %xmm2
-; AVX1-NEXT:    vblendps {{.*#+}} ymm0 = ymm2[0],ymm0[1],ymm2[2,3,4,5,6,7]
-; AVX1-NEXT:    vpshufd {{.*#+}} xmm1 = xmm1[0,1,0,1]
-; AVX1-NEXT:    vblendps {{.*#+}} ymm1 = ymm2[0,1],ymm1[2],ymm2[3,4,5,6,7]
+; AVX1-NEXT:    movq (%rdi), %rax
+; AVX1-NEXT:    vmovq %rax, %xmm0
+; AVX1-NEXT:    vxorps %xmm1, %xmm1, %xmm1
+; AVX1-NEXT:    vblendps {{.*#+}} ymm0 = ymm1[0],ymm0[1],ymm1[2,3,4,5,6,7]
+; AVX1-NEXT:    vmovd %eax, %xmm2
+; AVX1-NEXT:    vpshufd {{.*#+}} xmm2 = xmm2[0,0,0,0]
+; AVX1-NEXT:    vblendps {{.*#+}} ymm1 = ymm1[0,1],ymm2[2],ymm1[3,4,5,6,7]
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-SLOW-LABEL: splat_v3i32:
@@ -2288,12 +2289,13 @@
 ;
 ; XOP-LABEL: splat_v3i32:
 ; XOP:       # %bb.0:
-; XOP-NEXT:    vmovq {{.*#+}} xmm0 = mem[0],zero
-; XOP-NEXT:    vpinsrd $2, 8(%rdi), %xmm0, %xmm1
-; XOP-NEXT:    vxorps %xmm2, %xmm2, %xmm2
-; XOP-NEXT:    vblendps {{.*#+}} ymm0 = ymm2[0],ymm0[1],ymm2[2,3,4,5,6,7]
-; XOP-NEXT:    vpshufd {{.*#+}} xmm1 = xmm1[0,1,0,1]
-; XOP-NEXT:    vblendps {{.*#+}} ymm1 = ymm2[0,1],ymm1[2],ymm2[3,4,5,6,7]
+; XOP-NEXT:    movq (%rdi), %rax
+; XOP-NEXT:    vmovq %rax, %xmm0
+; XOP-NEXT:    vxorps %xmm1, %xmm1, %xmm1
+; XOP-NEXT:    vblendps {{.*#+}} ymm0 = ymm1[0],ymm0[1],ymm1[2,3,4,5,6,7]
+; XOP-NEXT:    vmovd %eax, %xmm2
+; XOP-NEXT:    vpshufd {{.*#+}} xmm2 = xmm2[0,0,0,0]
+; XOP-NEXT:    vblendps {{.*#+}} ymm1 = ymm1[0,1],ymm2[2],ymm1[3,4,5,6,7]
 ; XOP-NEXT:    retq
   %1 = load <3 x i32>, <3 x i32>* %ptr, align 1
   %2 = shufflevector <3 x i32> %1, <3 x i32> undef, <16 x i32> <i32 0, i32 1, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
diff --git a/llvm/test/CodeGen/X86/vselect.ll b/llvm/test/CodeGen/X86/vselect.ll
--- a/llvm/test/CodeGen/X86/vselect.ll
+++ b/llvm/test/CodeGen/X86/vselect.ll
@@ -568,12 +568,13 @@
 ; SSE2-NEXT:    psrad $31, %xmm0
 ; SSE2-NEXT:    movd %edi, %xmm1
 ; SSE2-NEXT:    pshufd {{.*#+}} xmm2 = xmm1[1,0,1,1]
-; SSE2-NEXT:    por %xmm1, %xmm2
+; SSE2-NEXT:    movdqa %xmm2, %xmm3
+; SSE2-NEXT:    por %xmm1, %xmm3
 ; SSE2-NEXT:    shufps {{.*#+}} xmm1 = xmm1[0,1],xmm2[1,3]
 ; SSE2-NEXT:    shufps {{.*#+}} xmm1 = xmm1[2,0],xmm2[1,1]
-; SSE2-NEXT:    pand %xmm0, %xmm2
+; SSE2-NEXT:    pand %xmm0, %xmm3
 ; SSE2-NEXT:    pandn %xmm1, %xmm0
-; SSE2-NEXT:    por %xmm2, %xmm0
+; SSE2-NEXT:    por %xmm3, %xmm0
 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: simplify_select: