diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 0eaba12330e74..6eaac2c93fb1a 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -35301,6 +35301,20 @@ static SDValue combineX86ShuffleChain(ArrayRef<SDValue> Inputs, SDValue Root,
     return CanonicalizeShuffleInput(RootVT, V1);
   }
 
+  // See if the shuffle is a hidden identity shuffle - repeated args in HOPs
+  // etc. can be simplified.
+  if (VT1 == VT2 && VT1.getSizeInBits() == RootSizeInBits) {
+    SmallVector<int> ScaledMask, IdentityMask;
+    unsigned NumElts = VT1.getVectorNumElements();
+    if (BaseMask.size() <= NumElts &&
+        scaleShuffleElements(BaseMask, NumElts, ScaledMask)) {
+      for (unsigned i = 0; i != NumElts; ++i)
+        IdentityMask.push_back(i);
+      if (isTargetShuffleEquivalent(RootVT, ScaledMask, IdentityMask, V1, V2))
+        return CanonicalizeShuffleInput(RootVT, V1);
+    }
+  }
+
   // Handle 128/256-bit lane shuffles of 512-bit vectors.
   if (RootVT.is512BitVector() &&
       (NumBaseMaskElts == 2 || NumBaseMaskElts == 4)) {
diff --git a/llvm/test/CodeGen/X86/horizontal-sum.ll b/llvm/test/CodeGen/X86/horizontal-sum.ll
index f9ed90e348729..6f3c7828c4e67 100644
--- a/llvm/test/CodeGen/X86/horizontal-sum.ll
+++ b/llvm/test/CodeGen/X86/horizontal-sum.ll
@@ -26,13 +26,12 @@ define <4 x float> @pair_sum_v4f32_v4f32(<4 x float> %0, <4 x float> %1, <4 x fl
 ; SSSE3-SLOW-NEXT:    addps %xmm1, %xmm0
 ; SSSE3-SLOW-NEXT:    haddps %xmm2, %xmm2
 ; SSSE3-SLOW-NEXT:    movshdup {{.*#+}} xmm1 = xmm2[1,1,3,3]
-; SSSE3-SLOW-NEXT:    movddup {{.*#+}} xmm2 = xmm2[0,0]
-; SSSE3-SLOW-NEXT:    addps %xmm1, %xmm2
+; SSSE3-SLOW-NEXT:    addps %xmm2, %xmm1
 ; SSSE3-SLOW-NEXT:    haddps %xmm3, %xmm3
-; SSSE3-SLOW-NEXT:    movshdup {{.*#+}} xmm1 = xmm3[1,1,3,3]
-; SSSE3-SLOW-NEXT:    addps %xmm3, %xmm1
-; SSSE3-SLOW-NEXT:    shufps {{.*#+}} xmm1 = xmm1[0,1],xmm2[2,3]
-; SSSE3-SLOW-NEXT:    shufps {{.*#+}} xmm0 = xmm0[0,1],xmm1[2,0]
+; SSSE3-SLOW-NEXT:    movshdup {{.*#+}} xmm2 = xmm3[1,1,3,3]
+; SSSE3-SLOW-NEXT:    addps %xmm3, %xmm2
+; SSSE3-SLOW-NEXT:    shufps {{.*#+}} xmm2 = xmm2[0,1],xmm1[2,3]
+; SSSE3-SLOW-NEXT:    shufps {{.*#+}} xmm0 = xmm0[0,1],xmm2[2,0]
 ; SSSE3-SLOW-NEXT:    retq
 ;
 ; SSSE3-FAST-LABEL: pair_sum_v4f32_v4f32:
@@ -109,13 +108,12 @@ define <4 x i32> @pair_sum_v4i32_v4i32(<4 x i32> %0, <4 x i32> %1, <4 x i32> %2,
 ; SSSE3-SLOW-NEXT:    paddd %xmm1, %xmm0
 ; SSSE3-SLOW-NEXT:    phaddd %xmm2, %xmm2
 ; SSSE3-SLOW-NEXT:    pshufd {{.*#+}} xmm1 = xmm2[1,1,1,1]
-; SSSE3-SLOW-NEXT:    pshufd {{.*#+}} xmm2 = xmm2[0,1,0,1]
-; SSSE3-SLOW-NEXT:    paddd %xmm1, %xmm2
+; SSSE3-SLOW-NEXT:    paddd %xmm2, %xmm1
 ; SSSE3-SLOW-NEXT:    phaddd %xmm3, %xmm3
-; SSSE3-SLOW-NEXT:    pshufd {{.*#+}} xmm1 = xmm3[1,1,1,1]
-; SSSE3-SLOW-NEXT:    paddd %xmm3, %xmm1
-; SSSE3-SLOW-NEXT:    shufps {{.*#+}} xmm1 = xmm1[0,1],xmm2[2,3]
-; SSSE3-SLOW-NEXT:    shufps {{.*#+}} xmm0 = xmm0[0,1],xmm1[2,0]
+; SSSE3-SLOW-NEXT:    pshufd {{.*#+}} xmm2 = xmm3[1,1,1,1]
+; SSSE3-SLOW-NEXT:    paddd %xmm3, %xmm2
+; SSSE3-SLOW-NEXT:    shufps {{.*#+}} xmm2 = xmm2[0,1],xmm1[2,3]
+; SSSE3-SLOW-NEXT:    shufps {{.*#+}} xmm0 = xmm0[0,1],xmm2[2,0]
 ; SSSE3-SLOW-NEXT:    retq
 ;
 ; SSSE3-FAST-LABEL: pair_sum_v4i32_v4i32:
@@ -136,9 +134,8 @@ define <4 x i32> @pair_sum_v4i32_v4i32(<4 x i32> %0, <4 x i32> %1, <4 x i32> %2,
 ; AVX1-SLOW-NEXT:    vpaddd %xmm2, %xmm1, %xmm1
 ; AVX1-SLOW-NEXT:    vpunpcklqdq {{.*#+}} xmm0 = xmm0[0],xmm1[0]
 ; AVX1-SLOW-NEXT:    vphaddd %xmm3, %xmm3, %xmm1
-; AVX1-SLOW-NEXT:    vpshufd {{.*#+}} xmm2 = xmm1[1,1,1,1]
-; AVX1-SLOW-NEXT:    vpshufd {{.*#+}} xmm1 = xmm1[0,0,0,0]
-; AVX1-SLOW-NEXT:    vpaddd %xmm2, %xmm1, %xmm1
+; AVX1-SLOW-NEXT:    vpshufd {{.*#+}} xmm2 = xmm1[0,0,0,0]
+; AVX1-SLOW-NEXT:    vpaddd %xmm1, %xmm2, %xmm1
 ; AVX1-SLOW-NEXT:    vpblendw {{.*#+}} xmm0 = xmm0[0,1,2,3,4,5],xmm1[6,7]
 ; AVX1-SLOW-NEXT:    retq
 ;
@@ -161,9 +158,8 @@ define <4 x i32> @pair_sum_v4i32_v4i32(<4 x i32> %0, <4 x i32> %1, <4 x i32> %2,
 ; AVX2-SLOW-NEXT:    vpaddd %xmm2, %xmm1, %xmm1
 ; AVX2-SLOW-NEXT:    vshufps {{.*#+}} xmm0 = xmm0[0,2],xmm1[0,3]
 ; AVX2-SLOW-NEXT:    vphaddd %xmm3, %xmm3, %xmm1
-; AVX2-SLOW-NEXT:    vpbroadcastq %xmm1, %xmm2
-; AVX2-SLOW-NEXT:    vpbroadcastd %xmm1, %xmm1
-; AVX2-SLOW-NEXT:    vpaddd %xmm2, %xmm1, %xmm1
+; AVX2-SLOW-NEXT:    vpbroadcastd %xmm1, %xmm2
+; AVX2-SLOW-NEXT:    vpaddd %xmm1, %xmm2, %xmm1
 ; AVX2-SLOW-NEXT:    vblendps {{.*#+}} xmm0 = xmm0[0,1,2],xmm1[3]
 ; AVX2-SLOW-NEXT:    retq
   %5 = shufflevector <4 x i32> %0, <4 x i32> poison, <2 x i32> <i32 0, i32 2>
@@ -441,7 +437,7 @@ define <8 x i32> @pair_sum_v8i32_v4i32(<4 x i32> %0, <4 x i32> %1, <4 x i32> %2,
 ; AVX1-SLOW-NEXT:    vpblendw {{.*#+}} xmm2 = xmm2[0,1,2,3,4,5],xmm5[6,7]
 ; AVX1-SLOW-NEXT:    vpshufd {{.*#+}} xmm1 = xmm1[1,3,1,1]
 ; AVX1-SLOW-NEXT:    vinsertps {{.*#+}} xmm1 = xmm1[0,1],xmm3[1],zero
-; AVX1-SLOW-NEXT:    vinsertps {{.*#+}} xmm1 = xmm1[0,1,2],xmm4[1]
+; AVX1-SLOW-NEXT:    vblendps {{.*#+}} xmm1 = xmm1[0,1,2],xmm4[3]
 ; AVX1-SLOW-NEXT:    vpaddd %xmm1, %xmm2, %xmm1
 ; AVX1-SLOW-NEXT:    vpunpcklqdq {{.*#+}} xmm0 = xmm0[0],xmm1[0]
 ; AVX1-SLOW-NEXT:    vpshufd {{.*#+}} xmm1 = xmm1[2,3,2,3]
@@ -493,7 +489,7 @@ define <8 x i32> @pair_sum_v8i32_v4i32(<4 x i32> %0, <4 x i32> %1, <4 x i32> %2,
 ; AVX2-SLOW-NEXT:    vshufps {{.*#+}} xmm3 = xmm2[0,2],xmm1[0,3]
 ; AVX2-SLOW-NEXT:    vinsertps {{.*#+}} xmm3 = xmm3[0,1,2],xmm4[0]
 ; AVX2-SLOW-NEXT:    vshufps {{.*#+}} xmm1 = xmm2[1,3],xmm1[1,3]
-; AVX2-SLOW-NEXT:    vinsertps {{.*#+}} xmm1 = xmm1[0,1,2],xmm4[1]
+; AVX2-SLOW-NEXT:    vblendps {{.*#+}} xmm1 = xmm1[0,1,2],xmm4[3]
 ; AVX2-SLOW-NEXT:    vpaddd %xmm1, %xmm3, %xmm1
 ; AVX2-SLOW-NEXT:    vpunpcklqdq {{.*#+}} xmm0 = xmm0[0],xmm1[0]
 ; AVX2-SLOW-NEXT:    vpshufd {{.*#+}} xmm1 = xmm1[2,3,2,3]