[Atomics] code stubs for atomic operations

src/code-stubs.h

Index: src/code-stubs.h
diff --git a/src/code-stubs.h b/src/code-stubs.h
index 1a80a5b7bc764d581a7dbd8f2a23915a6e45ecdb..a382a910d81fd85018c735f3cdd747c53f74591e 100644
--- a/src/code-stubs.h
+++ b/src/code-stubs.h
@@ -22,6 +22,7 @@ namespace internal {
 #define CODE_STUB_LIST_ALL_PLATFORMS(V)     \
   /* PlatformCodeStubs */                   \
   V(ArrayConstructor)                       \
+  V(AtomicsLoad)                            \
   V(BinaryOpICWithAllocationSite)           \
   V(CallApiCallback)                        \
   V(CallApiGetter)                          \
@@ -2512,7 +2513,7 @@ class ScriptContextFieldStub : public HandlerStub {
 
  private:
   static const int kContextIndexBits = 9;
-  static const int kSlotIndexBits = 13;
+  static const int kSlotIndexBits = 12;
   class ContextIndexBits : public BitField<int, 0, kContextIndexBits> {};
   class SlotIndexBits
       : public BitField<int, kContextIndexBits, kSlotIndexBits> {};
@@ -3121,6 +3122,14 @@ class ToObjectStub final : public HydrogenCodeStub {
   DEFINE_HYDROGEN_CODE_STUB(ToObject, HydrogenCodeStub);
 };
 
+class AtomicsLoadStub : public PlatformCodeStub {
+ public:
+  explicit AtomicsLoadStub(Isolate* isolate) : PlatformCodeStub(isolate) {}
+
+  DEFINE_CALL_INTERFACE_DESCRIPTOR(AtomicsLoad);
+  DEFINE_PLATFORM_CODE_STUB(AtomicsLoad, PlatformCodeStub);
+};
+
 #undef DEFINE_CALL_INTERFACE_DESCRIPTOR
 #undef DEFINE_PLATFORM_CODE_STUB
 #undef DEFINE_HANDLER_CODE_STUB