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

src/mips64/macro-assembler-mips64.cc

Index: src/mips64/macro-assembler-mips64.cc
diff --git a/src/mips64/macro-assembler-mips64.cc b/src/mips64/macro-assembler-mips64.cc
index 64b3d552e3167def47cb2772a4e1cf03041bd8e7..bc935326cfe1aac1e816742154a45e0bcc0aeca6 100644
--- a/src/mips64/macro-assembler-mips64.cc
+++ b/src/mips64/macro-assembler-mips64.cc
@@ -4243,6 +4243,20 @@ void MacroAssembler::IsObjectNameType(Register object,
 // Support functions.
 
 
+void MacroAssembler::GetMapConstructor(Register result, Register map,
+                                       Register temp, Register temp2) {
+  Label done, loop;
+  ld(result, FieldMemOperand(map, Map::kConstructorOrBackPointerOffset));
+  bind(&loop);
+  JumpIfSmi(result, &done);
+  GetObjectType(result, temp, temp2);
+  Branch(&done, ne, temp2, Operand(MAP_TYPE));
+  ld(result, FieldMemOperand(result, Map::kConstructorOrBackPointerOffset));
+  Branch(&loop);
+  bind(&done);
+}
+
+
 void MacroAssembler::TryGetFunctionPrototype(Register function,
                                              Register result,
                                              Register scratch,
@@ -4295,7 +4309,7 @@ void MacroAssembler::TryGetFunctionPrototype(Register function,
     // Non-instance prototype: Fetch prototype from constructor field
     // in initial map.
     bind(&non_instance);
-    ld(result, FieldMemOperand(result, Map::kConstructorOffset));
+    GetMapConstructor(result, result, scratch, at);
   }
 
   // All done.