diff --git a/llvm/include/llvm/Analysis/TargetTransformInfo.h b/llvm/include/llvm/Analysis/TargetTransformInfo.h
index f55f21c94a85a..934012b2e53f5 100644
--- a/llvm/include/llvm/Analysis/TargetTransformInfo.h
+++ b/llvm/include/llvm/Analysis/TargetTransformInfo.h
@@ -1534,6 +1534,14 @@ class TargetTransformInfo {
       Function *F, Type *RetTy, ArrayRef<Type *> Tys,
       TTI::TargetCostKind CostKind = TTI::TCK_SizeAndLatency) const;
 
+  /// \returns The cost of propagating Type \p DataType through Basic Block /
+  /// function boundaries. If \p IsCallingConv is specified, then \p DataType is
+  /// associated with either a function argument or return. Otherwise, \p
+  /// DataType is used in either a GEP instruction, or spans across BasicBlocks
+  /// (this is relevant because SelectionDAG builder may, for example, scalarize
+  /// illegal vectors across blocks, which introduces extract/insert code).
+  InstructionCost getDataFlowCost(Type *DataType, bool IsCallingConv) const;
+
   /// \returns The number of pieces into which the provided type must be
   /// split during legalization. Zero is returned when the answer is unknown.
   unsigned getNumberOfParts(Type *Tp) const;
@@ -2096,6 +2104,8 @@ class TargetTransformInfo::Concept {
   virtual InstructionCost getCallInstrCost(Function *F, Type *RetTy,
                                            ArrayRef<Type *> Tys,
                                            TTI::TargetCostKind CostKind) = 0;
+  virtual InstructionCost getDataFlowCost(Type *DataType,
+                                          bool IsCallingConv) = 0;
   virtual unsigned getNumberOfParts(Type *Tp) = 0;
   virtual InstructionCost
   getAddressComputationCost(Type *Ty, ScalarEvolution *SE, const SCEV *Ptr) = 0;
@@ -2781,6 +2791,9 @@ class TargetTransformInfo::Model final : public TargetTransformInfo::Concept {
                                    TTI::TargetCostKind CostKind) override {
     return Impl.getCallInstrCost(F, RetTy, Tys, CostKind);
   }
+  InstructionCost getDataFlowCost(Type *DataType, bool IsCallingConv) override {
+    return Impl.getDataFlowCost(DataType, IsCallingConv);
+  }
   unsigned getNumberOfParts(Type *Tp) override {
     return Impl.getNumberOfParts(Tp);
   }
diff --git a/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h b/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
index 7828bdc1f1f43..5a25a88c3eb46 100644
--- a/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
+++ b/llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
@@ -772,6 +772,10 @@ class TargetTransformInfoImplBase {
     return 1;
   }
 
+  InstructionCost getDataFlowCost(Type *DataType, bool IsCallingConv) const {
+    return 0;
+  }
+
   // Assume that we have a register of the right size for the type.
   unsigned getNumberOfParts(Type *Tp) const { return 1; }
 
diff --git a/llvm/include/llvm/CodeGen/BasicTTIImpl.h b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
index 9f8d3ded9b3c1..c6a5c38a1b3fd 100644
--- a/llvm/include/llvm/CodeGen/BasicTTIImpl.h
+++ b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
@@ -2410,6 +2410,10 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
     return 10;
   }
 
+  InstructionCost getDataFlowCost(Type *DataType, bool IsCallingConv) {
+    return 0;
+  }
+
   unsigned getNumberOfParts(Type *Tp) {
     std::pair<InstructionCost, MVT> LT = getTypeLegalizationCost(Tp);
     return LT.first.isValid() ? *LT.first.getValue() : 0;
diff --git a/llvm/lib/Analysis/TargetTransformInfo.cpp b/llvm/lib/Analysis/TargetTransformInfo.cpp
index 7e721cbc87f3f..edef9afa747d6 100644
--- a/llvm/lib/Analysis/TargetTransformInfo.cpp
+++ b/llvm/lib/Analysis/TargetTransformInfo.cpp
@@ -1116,6 +1116,13 @@ TargetTransformInfo::getCallInstrCost(Function *F, Type *RetTy,
   return Cost;
 }
 
+InstructionCost TargetTransformInfo::getDataFlowCost(Type *DataType,
+                                                     bool IsCallingConv) const {
+  InstructionCost Cost = TTIImpl->getDataFlowCost(DataType, IsCallingConv);
+  assert(Cost >= 0 && "TTI should not produce negative costs!");
+  return Cost;
+}
+
 unsigned TargetTransformInfo::getNumberOfParts(Type *Tp) const {
   return TTIImpl->getNumberOfParts(Tp);
 }
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
index 437e01c37c6b6..52e6d02772914 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp
@@ -306,6 +306,14 @@ bool GCNTTIImpl::hasBranchDivergence(const Function *F) const {
   return !F || !ST->isSingleLaneExecution(*F);
 }
 
+InstructionCost GCNTTIImpl::getDataFlowCost(Type *DataType,
+                                            bool IsCallingConv) {
+  if (IsCallingConv  || isTypeLegal(DataType))
+    return BaseT::getDataFlowCost(DataType, IsCallingConv);
+
+  return getNumberOfParts(DataType);
+}
+
 unsigned GCNTTIImpl::getNumberOfRegisters(unsigned RCID) const {
   // NB: RCID is not an RCID. In fact it is 0 or 1 for scalar or vector
   // registers. See getRegisterClassForType for the implementation.
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.h b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.h
index b423df17302ca..c195c860075eb 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.h
@@ -161,6 +161,8 @@ class GCNTTIImpl final : public BasicTTIImplBase<GCNTTIImpl> {
   InstructionCost getCFInstrCost(unsigned Opcode, TTI::TargetCostKind CostKind,
                                  const Instruction *I = nullptr);
 
+  InstructionCost getDataFlowCost(Type *DataType, bool IsCallingConv);
+
   bool isInlineAsmSourceOfDivergence(const CallInst *CI,
                                      ArrayRef<unsigned> Indices = {}) const;
 
diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index ae0819c964bef..3a66dad1d10e6 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -9075,15 +9075,16 @@ BoUpSLP::getEntryCost(const TreeEntry *E, ArrayRef<Value *> VectorizedVals,
   auto *FinalVecTy = FixedVectorType::get(ScalarTy, EntryVF);
 
   bool NeedToShuffleReuses = !E->ReuseShuffleIndices.empty();
+  InstructionCost CommonCost = 0;
   if (E->State == TreeEntry::NeedToGather) {
     if (allConstant(VL))
-      return 0;
+      return CommonCost;
     if (isa<InsertElementInst>(VL[0]))
       return InstructionCost::getInvalid();
-    return processBuildVector<ShuffleCostEstimator, InstructionCost>(
-        E, ScalarTy, *TTI, VectorizedVals, *this, CheckedExtracts);
+    return CommonCost +
+           processBuildVector<ShuffleCostEstimator, InstructionCost>(
+               E, ScalarTy, *TTI, VectorizedVals, *this, CheckedExtracts);
   }
-  InstructionCost CommonCost = 0;
   SmallVector<int> Mask;
   bool IsReverseOrder = isReverseOrder(E->ReorderIndices);
   if (!E->ReorderIndices.empty() &&
@@ -9222,6 +9223,18 @@ BoUpSLP::getEntryCost(const TreeEntry *E, ArrayRef<Value *> VectorizedVals,
                                             OpTE->Scalars.size());
     }
 
+    // Calculate the cost difference of propagating a vector vs series of
+    // scalars across blocks. This may be nonzero in the case of illegal
+    // vectors.
+    Type *ScalarTy = VL0->getType()->getScalarType();
+    if (ScalarTy && isValidElementType(ScalarTy)) {
+      ScalarCost += TTI->getDataFlowCost(ScalarTy,
+                                         /*IsCallingConv=*/false) *
+                    EntryVF;
+      CommonCost += TTI->getDataFlowCost(
+          FixedVectorType::get(ScalarTy, EntryVF), /*IsCallingConv=*/false);
+    }
+
     return CommonCost - ScalarCost;
   }
   case Instruction::ExtractValue:
@@ -10241,6 +10254,27 @@ InstructionCost BoUpSLP::getTreeCost(ArrayRef<Value *> VectorizedVals) {
 
     InstructionCost C = getEntryCost(&TE, VectorizedVals, CheckedExtracts);
     Cost += C;
+
+    // Calculate the cost difference of propagating a vector vs series of scalars
+    // across blocks. This may be nonzero in the case of illegal vectors.
+    Instruction *VL0 = TE.getMainOp();
+    if (VL0 && ((I + 1) < VectorizableTree.size())) {
+      Instruction *VL1 = VectorizableTree[I + 1]->getMainOp();
+      if (VL1 && (VL0->getParent() != VL1->getParent())) {
+        Type *ScalarTy = VL0->getType()->getScalarType();
+        if (ScalarTy && isValidElementType(ScalarTy)) {
+          InstructionCost ScalarDFlow =
+              TTI->getDataFlowCost(ScalarTy,
+                                 /*IsCallingConv=*/false) *
+              TE.getVectorFactor();
+          InstructionCost VectorDFlow = TTI->getDataFlowCost(
+              FixedVectorType::get(ScalarTy, TE.getVectorFactor()),
+              /*IsCallingConv=*/false);
+          Cost += (VectorDFlow - ScalarDFlow);
+        }
+      }
+    }
+
     LLVM_DEBUG(dbgs() << "SLP: Adding cost " << C << " for bundle "
                       << shortBundleName(TE.Scalars) << ".\n"
                       << "SLP: Current total cost = " << Cost << "\n");
@@ -10257,8 +10291,9 @@ InstructionCost BoUpSLP::getTreeCost(ArrayRef<Value *> VectorizedVals) {
   for (ExternalUser &EU : ExternalUses) {
     // We only add extract cost once for the same scalar.
     if (!isa_and_nonnull<InsertElementInst>(EU.User) &&
-        !ExtractCostCalculated.insert(EU.Scalar).second)
+        !ExtractCostCalculated.insert(EU.Scalar).second) {
       continue;
+    }
 
     // Uses by ephemeral values are free (because the ephemeral value will be
     // removed prior to code generation, and so the extraction will be
@@ -10267,8 +10302,14 @@ InstructionCost BoUpSLP::getTreeCost(ArrayRef<Value *> VectorizedVals) {
       continue;
 
     // No extract cost for vector "scalar"
-    if (isa<FixedVectorType>(EU.Scalar->getType()))
+    if (isa<FixedVectorType>(EU.Scalar->getType())) {
+      // Account for any additional costs required by CallingConvention for the
+      // type.
+      if (isa_and_nonnull<ReturnInst>(EU.User))
+        Cost +=
+            TTI->getDataFlowCost(EU.Scalar->getType(), /*IsCallingConv=*/true);
       continue;
+    }
 
     // If found user is an insertelement, do not calculate extract cost but try
     // to detect it as a final shuffled/identity match.