Move Maps' back pointers from "transitions" to "constructor" field

src/ia32/macro-assembler-ia32.cc

Index: src/ia32/macro-assembler-ia32.cc
diff --git a/src/ia32/macro-assembler-ia32.cc b/src/ia32/macro-assembler-ia32.cc
index 53ffa39357c97a47aa53df3f934a712fb30e9380..db9ef767743939affc3187f00a19957ea4330dd7 100644
--- a/src/ia32/macro-assembler-ia32.cc
+++ b/src/ia32/macro-assembler-ia32.cc
@@ -1919,6 +1919,20 @@ void MacroAssembler::NegativeZeroTest(Register result,
 }
 
 
+void MacroAssembler::GetMapConstructor(Register result, Register map,
+                                       Register temp) {
+  Label done, loop;
+  mov(result, FieldOperand(map, Map::kConstructorOrBackPointerOffset));
+  bind(&loop);
+  JumpIfSmi(result, &done);
+  CmpObjectType(result, MAP_TYPE, temp);
+  j(not_equal, &done);
+  mov(result, FieldOperand(result, Map::kConstructorOrBackPointerOffset));
+  jmp(&loop);
+  bind(&done);
+}
+
+
 void MacroAssembler::TryGetFunctionPrototype(Register function,
                                              Register result,
                                              Register scratch,
@@ -1970,7 +1984,7 @@ void MacroAssembler::TryGetFunctionPrototype(Register function,
     // Non-instance prototype: Fetch prototype from constructor field
     // in initial map.
     bind(&non_instance);
-    mov(result, FieldOperand(result, Map::kConstructorOffset));
+    GetMapConstructor(result, result, scratch);
   }
 
   // All done.