Reland parts of 'Use weak cells in map checks in polymorphic ICs'

src/x64/macro-assembler-x64.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_X64_MACRO_ASSEMBLER_X64_H_
 #define V8_X64_MACRO_ASSEMBLER_X64_H_
 
 #include "src/assembler.h"
 #include "src/bailout-reason.h"
 #include "src/frames.h"
@@ skipping 829 matching lines @@
   void Cmp(const Operand& dst, Smi* src);
   void Push(Handle<Object> source);
 
   // Load a heap object and handle the case of new-space objects by
   // indirecting via a global cell.
   void MoveHeapObject(Register result, Handle<Object> object);
 
   // Load a global cell into a register.
   void LoadGlobalCell(Register dst, Handle<Cell> cell);
 
+  // Compare the given value and the value of weak cell.
+  void CmpWeakValue(Register value, Handle<WeakCell> cell, Register scratch);
+
+  // Load the value of the weak cell in the value register. Branch to the given
+  // miss label if the weak cell was cleared.
+  void LoadWeakValue(Register value, Handle<WeakCell> cell, Label* miss);
+
   // Emit code to discard a non-negative number of pointer-sized elements
   // from the stack, clobbering only the rsp register.
   void Drop(int stack_elements);
   // Emit code to discard a positive number of pointer-sized elements
   // from the stack under the return address which remains on the top,
   // clobbering the rsp register.
   void DropUnderReturnAddress(int stack_elements,
                               Register scratch = kScratchRegister);
 
   void Call(Label* target) { call(target); }
@@ skipping 785 matching lines @@
     masm->popfq();                                                           \
   }                                                                          \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_