CheckPrototypes uses weak cells to embed maps.

src/ic/arm/handler-compiler-arm.cc

Index: src/ic/arm/handler-compiler-arm.cc
diff --git a/src/ic/arm/handler-compiler-arm.cc b/src/ic/arm/handler-compiler-arm.cc
index 3a0756a77b24d9fe1542c2ca9912b56a1fa58634..8827d36bf26fa50d13601de6b2c212b80fd081c4 100644
--- a/src/ic/arm/handler-compiler-arm.cc
+++ b/src/ic/arm/handler-compiler-arm.cc
@@ -416,11 +416,11 @@ Register PropertyHandlerCompiler::CheckPrototypes(
       __ ldr(reg, FieldMemOperand(scratch1, Map::kPrototypeOffset));
     } else {
       Register map_reg = scratch1;
+      __ ldr(map_reg, FieldMemOperand(reg, HeapObject::kMapOffset));
       if (depth != 1 || check == CHECK_ALL_MAPS) {
-        // CheckMap implicitly loads the map of |reg| into |map_reg|.
-        __ CheckMap(reg, map_reg, current_map, miss, DONT_DO_SMI_CHECK);
-      } else {
-        __ ldr(map_reg, FieldMemOperand(reg, HeapObject::kMapOffset));
+        Handle<WeakCell> cell = Map::WeakCellForMap(current_map);
+        __ CmpWeakValue(map_reg, cell, scratch2);
+        __ b(ne, miss);
       }
 
       // Check access rights to the global object.  This has to happen after
@@ -451,7 +451,10 @@ Register PropertyHandlerCompiler::CheckPrototypes(
 
   if (depth != 0 || check == CHECK_ALL_MAPS) {
     // Check the holder map.
-    __ CheckMap(reg, scratch1, current_map, miss, DONT_DO_SMI_CHECK);
+    __ ldr(scratch1, FieldMemOperand(reg, HeapObject::kMapOffset));
+    Handle<WeakCell> cell = Map::WeakCellForMap(current_map);
+    __ CmpWeakValue(scratch1, cell, scratch2);
+    __ b(ne, miss);
   }
 
   // Perform security check for access to the global object.