diff --git a/src/coreclr/jit/assertionprop.cpp b/src/coreclr/jit/assertionprop.cpp
index b3d52ce9773e48..427ca469d3cd94 100644
--- a/src/coreclr/jit/assertionprop.cpp
+++ b/src/coreclr/jit/assertionprop.cpp
@@ -2769,7 +2769,50 @@ GenTree* Compiler::optVNBasedFoldExpr(BasicBlock* block, GenTree* parent, GenTre
         case GT_CALL:
             return optVNBasedFoldExpr_Call(block, parent, tree->AsCall());
 
-            // We can add more VN-based foldings here.
+        case GT_STORE_BLK:
+        {
+            if (!opts.IsReadyToRun())
+            {
+                // TODO: Implement CORINFO_HELP_ASSIGN_STRUCT for R2R/ILC
+                break;
+            }
+
+            // Replace STORE_BLK (struct copy) with CORINFO_HELP_ASSIGN_STRUCT which performs
+            // bulk copy for byrefs.
+            GenTreeBlk* blk = tree->AsBlk();
+            if (!blk->OperIsInitBlkOp() && blk->IsReverseOp() && (blk->GetLayout()->GetGCPtrCount() > 3))
+            {
+                GenTree* addr = blk->Addr();
+                GenTree* data = blk->Data();
+                if (data->OperIs(GT_BLK))
+                {
+                    data = data->AsBlk()->Addr();
+                }
+                else
+                {
+                    assert(data->OperIs(GT_LCL_VAR, GT_LCL_FLD));
+                }
+
+                // For now, we use it only for newly created objects where we know we don't have to
+                // be precise (from GC's point of view) and update card tables.
+                // For that, we expect addr to be "JIT_New + offset"
+                VNFuncApp funcApp;
+                if (vnStore->GetVNFunc(vnStore->VNLiberalNormalValue(addr->gtVNPair), &funcApp) &&
+                    (funcApp.m_func == VNFunc(GT_ADD)) && vnStore->GetVNFunc(funcApp.m_args[0], &funcApp) &&
+                    (funcApp.m_func == VNF_JitNew))
+                {
+                    const unsigned gcPtrs = blk->GetLayout()->GetGCPtrCount();
+                    if (!CheckedOps::MulOverflows((int)gcPtrs, TARGET_POINTER_SIZE, true))
+                    {
+                        GenTree* slots = gtNewIconNode((ssize_t)gcPtrs * TARGET_POINTER_SIZE, TYP_I_IMPL);
+                        GenTreeCall* call = gtNewHelperCallNode(CORINFO_HELP_ASSIGN_STRUCT, TYP_VOID, data, addr, slots);
+                        fgMorphArgs(call);
+                        return call;
+                    }
+                }
+            }
+            break;
+        }
 
         default:
             break;
@@ -6469,6 +6512,10 @@ Compiler::fgWalkResult Compiler::optVNBasedFoldCurStmt(BasicBlock* block,
     // This can occur for HFA return values (see hfa_sf3E_r.exe)
     if (tree->TypeGet() == TYP_STRUCT)
     {
+        if (tree->OperIs(GT_STORE_BLK) && tree->AsBlk()->GetLayout()->HasGCPtr())
+        {
+            goto PERFORM_FOLD;
+        }
         return WALK_CONTINUE;
     }
 
@@ -6545,6 +6592,7 @@ Compiler::fgWalkResult Compiler::optVNBasedFoldCurStmt(BasicBlock* block,
             // Unknown node, continue to walk.
             return WALK_CONTINUE;
     }
+PERFORM_FOLD:
 
     // Perform the VN-based folding:
     GenTree* newTree = optVNBasedFoldExpr(block, parent, tree);
diff --git a/src/coreclr/vm/jithelpers.cpp b/src/coreclr/vm/jithelpers.cpp
index 98d6780258a6c6..a93c399b946e77 100644
--- a/src/coreclr/vm/jithelpers.cpp
+++ b/src/coreclr/vm/jithelpers.cpp
@@ -4780,15 +4780,15 @@ HCIMPLEND
 //========================================================================
 
 /*************************************************************/
-HCIMPL3(VOID, JIT_StructWriteBarrier, void *dest, void* src, CORINFO_CLASS_HANDLE typeHnd_)
+HCIMPL3(VOID, JIT_StructWriteBarrier, void* src, void* dest, size_t byteSize)
 {
     FCALL_CONTRACT;
 
-    TypeHandle typeHnd(typeHnd_);
-    MethodTable *pMT = typeHnd.AsMethodTable();
+    _ASSERT(byteSize > 0);
+    _ASSERT((byteSize % TARGET_POINTER_SIZE) == 0);
 
     HELPER_METHOD_FRAME_BEGIN_NOPOLL();    // Set up a frame
-    CopyValueClass(dest, src, pMT);
+    memmoveGCRefs(dest, src, byteSize);
     HELPER_METHOD_FRAME_END_POLL();
 
 }