[Atomics] Make Atomics.exchange a builtin using TF

src/builtins/builtins-sharedarraybuffer.cc

Index: src/builtins/builtins-sharedarraybuffer.cc
diff --git a/src/builtins/builtins-sharedarraybuffer.cc b/src/builtins/builtins-sharedarraybuffer.cc
index 53caf1fe21640ef1afb948c0f94c0bf8d2a1ee93..0a0e4064967e1f123e2bcc90aea82f629993bb5c 100644
--- a/src/builtins/builtins-sharedarraybuffer.cc
+++ b/src/builtins/builtins-sharedarraybuffer.cc
@@ -266,5 +266,71 @@ void Builtins::Generate_AtomicsStore(compiler::CodeAssemblerState* state) {
   a.Return(a.SmiConstant(0));
 }
 
+void Builtins::Generate_AtomicsExchange(compiler::CodeAssemblerState* state) {
+  using compiler::Node;
+  CodeStubAssembler a(state);
+  Node* array = a.Parameter(1);
+  Node* index = a.Parameter(2);
+  Node* value = a.Parameter(3);
+  Node* context = a.Parameter(4 + 2);
+
+  Node* instance_type;
+  Node* backing_store;
+  ValidateSharedTypedArray(&a, array, context, &instance_type, &backing_store);
+
+  Node* index_word32 = ConvertTaggedAtomicIndexToWord32(&a, index, context);
+  Node* array_length_word32 = a.TruncateTaggedToWord32(
+      context, a.LoadObjectField(array, JSTypedArray::kLengthOffset));
+  ValidateAtomicIndex(&a, index_word32, array_length_word32, context);
+  Node* index_word = a.ChangeUint32ToWord(index_word32);
+
+  Node* value_integer = a.ToInteger(context, value);
+  Node* value_word32 = a.TruncateTaggedToWord32(context, value_integer);
+
+  CodeStubAssembler::Label i8(&a), u8(&a), i16(&a), u16(&a), i32(&a), u32(&a),
+      other(&a);
+  int32_t case_values[] = {
+      FIXED_INT8_ARRAY_TYPE,   FIXED_UINT8_ARRAY_TYPE, FIXED_INT16_ARRAY_TYPE,
+      FIXED_UINT16_ARRAY_TYPE, FIXED_INT32_ARRAY_TYPE, FIXED_UINT32_ARRAY_TYPE,
+  };
+  CodeStubAssembler::Label* case_labels[] = {
+      &i8, &u8, &i16, &u16, &i32, &u32,
+  };
+  a.Switch(instance_type, &other, case_values, case_labels,
+           arraysize(case_labels));
+
+  a.Bind(&u8);

[binji, 2017/01/13 00:08:50]

nit: I'd prefer matching the order of the case labels: i8, u8, i16, u16, i32,
u32

[aseemgarg, 2017/01/14 01:48:19]

Done.

+  a.Return(a.SmiFromWord32(a.AtomicExchange(MachineType::Uint8(), backing_store,
+                                            index_word, value_word32)));
+
+  a.Bind(&i8);
+  a.Return(a.SmiFromWord32(a.AtomicExchange(MachineType::Int8(), backing_store,
+                                            index_word, value_word32)));
+
+  a.Bind(&u16);
+  a.Return(a.SmiFromWord32(
+      a.AtomicExchange(MachineType::Uint16(), backing_store,
+                       a.WordShl(index_word, 1), value_word32)));
+
+  a.Bind(&i16);
+  a.Return(a.SmiFromWord32(a.AtomicExchange(MachineType::Int16(), backing_store,
+                                            a.WordShl(index_word, 1),
+                                            value_word32)));
+
+  a.Bind(&u32);
+  a.Return(a.ChangeUint32ToTagged(
+      a.AtomicExchange(MachineType::Uint32(), backing_store,
+                       a.WordShl(index_word, 2), value_word32)));
+
+  a.Bind(&i32);
+  a.Return(a.ChangeInt32ToTagged(
+      a.AtomicExchange(MachineType::Int32(), backing_store,
+                       a.WordShl(index_word, 2), value_word32)));
+
+  // This shouldn't happen, we've already validated the type.
+  a.Bind(&other);
+  a.Return(a.SmiConstant(0));
+}
+
 }  // namespace internal
 }  // namespace v8