Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -16310,18 +16310,42 @@
   return SDValue();
 }
 
-static SDValue combineConcatVectorOfScalars(SDNode *N, SelectionDAG &DAG) {
+static SDValue combineConcatVectorOfScalars(SDNode *N, SelectionDAG &DAG,
+                                            unsigned LegalOperations) {
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   EVT OpVT = N->getOperand(0).getValueType();
 
+  SDLoc DL(N);
+  EVT VT = N->getValueType(0);
+
+  // concat_vectors( bitcast (scalar_to_vector %A), UNDEF) -->
+  //     bitcast (scalar_to_vector %A)
+  if (!LegalOperations && N->getNumOperands() > 1) {
+    SDValue Op0 = N->getOperand(0);
+    if (Op0.hasOneUse() && Op0.getOpcode() == ISD::BITCAST &&
+        Op0.getOperand(0).hasOneUse() &&
+        Op0.getOperand(0).getOpcode() == ISD::SCALAR_TO_VECTOR) {
+      bool AllUndefs =
+          std::all_of(N->op_begin() + 1, N->op_end(),
+                      [](const SDValue &U) { return U.isUndef(); });
+
+      if (AllUndefs) {
+        SDValue Scalar = Op0.getOperand(0).getOperand(0);
+        EVT SVT = Scalar.getValueType();
+
+        EVT NewVT = EVT::getVectorVT(*DAG.getContext(), SVT,
+                                     VT.getSizeInBits() / SVT.getSizeInBits());
+        SDValue STV = DAG.getNode(ISD::SCALAR_TO_VECTOR, DL, NewVT, Scalar);
+        return DAG.getBitcast(VT, STV);
+      }
+    }
+  }
+
   // If the operands are legal vectors, leave them alone.
   if (TLI.isTypeLegal(OpVT))
     return SDValue();
 
-  SDLoc DL(N);
-  EVT VT = N->getValueType(0);
   SmallVector<SDValue, 8> Ops;
-
   EVT SVT = EVT::getIntegerVT(*DAG.getContext(), OpVT.getSizeInBits());
   SDValue ScalarUndef = DAG.getNode(ISD::UNDEF, DL, SVT);
 
@@ -16551,7 +16575,7 @@
   }
 
   // Fold CONCAT_VECTORS of only bitcast scalars (or undef) to BUILD_VECTOR.
-  if (SDValue V = combineConcatVectorOfScalars(N, DAG))
+  if (SDValue V = combineConcatVectorOfScalars(N, DAG, LegalOperations))
     return V;
 
   // Fold CONCAT_VECTORS of EXTRACT_SUBVECTOR (or undef) to VECTOR_SHUFFLE.
Index: test/CodeGen/X86/simplify_concat_vectors.ll
===================================================================
--- test/CodeGen/X86/simplify_concat_vectors.ll
+++ test/CodeGen/X86/simplify_concat_vectors.ll
@@ -0,0 +1,18 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=x86_64-unknown-unknown -mattr=+avx < %s | FileCheck %s
+
+define void @PR32957(<2 x float>* %in, <8 x float>* %out) {
+; CHECK-LABEL: PR32957:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
+; CHECK-NEXT:    vmovaps %ymm0, (%rsi)
+; CHECK-NEXT:    vzeroupper
+; CHECK-NEXT:    retq
+  %ld = load <2 x float>, <2 x float>* %in, align 8
+  %ext = extractelement <2 x float> %ld, i64 0
+  %ext2 = extractelement <2 x float> %ld, i64 1
+  %ins = insertelement <8 x float> <float undef, float undef, float 0.0, float 0.0, float 0.0, float 0.0, float 0.0, float 0.0>, float %ext, i64 0
+  %ins2 = insertelement <8 x float> %ins, float %ext2, i64 1
+  store <8 x float> %ins2, <8 x float>* %out, align 32
+  ret void
+}