[builtins] Migrate String.prototype.charCodeAt and String.prototype.charAt to TurboFan.

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index 5456cd5b4f3b277811ac5de80078def8b745d47a..be780bf92802a8f4828eac591f4af1d2d020f74b 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -4187,6 +4187,199 @@ BUILTIN(ObjectProtoToString) {
   return *result;
 }
 
+// -----------------------------------------------------------------------------
+// ES6 section 21.1 String Objects
+
+// ES6 section 21.1.3.1 String.prototype.charAt ( pos )
+void Builtins::Generate_StringPrototypeCharAt(
+    compiler::CodeStubAssembler* assembler) {
+  typedef compiler::CodeStubAssembler::Label Label;
+  typedef compiler::Node Node;
+  typedef compiler::CodeStubAssembler::Variable Variable;
+
+  Node* receiver = assembler->Parameter(0);
+  Node* position = assembler->Parameter(1);
+  Node* context = assembler->Parameter(4);
+
+  // Check that {receiver} is coercible to Object and convert it to a String.
+  receiver =
+      assembler->ToThisString(context, receiver, "String.prototype.charAt");
+
+  // Convert the {position} to a Smi and check that it's in bounds of the
+  // {receiver}.
+  // TODO(bmeurer): Find an abstraction for this!
+  {
+    // Check if the {position} is already a Smi.
+    Variable var_position(assembler, MachineRepresentation::kTagged);
+    var_position.Bind(position);
+    Label if_positionissmi(assembler),
+        if_positionisnotsmi(assembler, Label::kDeferred);
+    assembler->Branch(assembler->WordIsSmi(position), &if_positionissmi,
+                      &if_positionisnotsmi);
+    assembler->Bind(&if_positionisnotsmi);
+    {
+      // Convert the {position} to an Integer via the ToIntegerStub.
+      Callable callable = CodeFactory::ToInteger(assembler->isolate());
+      Node* index = assembler->CallStub(callable, context, position);
+
+      // Check if the resulting {index} is now a Smi.
+      Label if_indexissmi(assembler, Label::kDeferred),
+          if_indexisnotsmi(assembler, Label::kDeferred);
+      assembler->Branch(assembler->WordIsSmi(index), &if_indexissmi,
+                        &if_indexisnotsmi);
+
+      assembler->Bind(&if_indexissmi);
+      {
+        var_position.Bind(index);
+        assembler->Goto(&if_positionissmi);
+      }
+
+      assembler->Bind(&if_indexisnotsmi);
+      {
+        // The ToIntegerStub canonicalizes everything in Smi range to Smi
+        // representation, so any HeapNumber returned is not in Smi range.
+        // The only exception here is -0.0, which we treat as 0.
+        Node* index_value = assembler->LoadHeapNumberValue(index);
+        Label if_indexiszero(assembler, Label::kDeferred),
+            if_indexisnotzero(assembler, Label::kDeferred);
+        assembler->Branch(assembler->Float64Equal(
+                              index_value, assembler->Float64Constant(0.0)),
+                          &if_indexiszero, &if_indexisnotzero);
+
+        assembler->Bind(&if_indexiszero);
+        {
+          var_position.Bind(assembler->SmiConstant(Smi::FromInt(0)));
+          assembler->Goto(&if_positionissmi);
+        }
+
+        assembler->Bind(&if_indexisnotzero);
+        {
+          // The {index} is some other integral Number, that is definitely
+          // neither -0.0 nor in Smi range.
+          assembler->Return(assembler->EmptyStringConstant());
+        }
+      }
+    }
+    assembler->Bind(&if_positionissmi);
+    position = var_position.value();
+
+    // Determine the actual length of the {receiver} String.
+    Node* receiver_length =
+        assembler->LoadObjectField(receiver, String::kLengthOffset);
+
+    // Return "" if the Smi {position} is outside the bounds of the {receiver}.
+    Label if_positioninbounds(assembler),
+        if_positionnotinbounds(assembler, Label::kDeferred);
+    assembler->Branch(assembler->SmiAboveOrEqual(position, receiver_length),
+                      &if_positionnotinbounds, &if_positioninbounds);
+    assembler->Bind(&if_positionnotinbounds);
+    assembler->Return(assembler->EmptyStringConstant());
+    assembler->Bind(&if_positioninbounds);
+  }
+
+  // Load the character code at the {position} from the {receiver}.
+  Node* code = assembler->StringCharCodeAt(receiver, position);
+
+  // And return the single character string with only that {code}.
+  Node* result = assembler->StringFromCharCode(code);
+  assembler->Return(result);
+}
+
+// ES6 section 21.1.3.2 String.prototype.charCodeAt ( pos )
+void Builtins::Generate_StringPrototypeCharCodeAt(
+    compiler::CodeStubAssembler* assembler) {
+  typedef compiler::CodeStubAssembler::Label Label;
+  typedef compiler::Node Node;
+  typedef compiler::CodeStubAssembler::Variable Variable;
+
+  Node* receiver = assembler->Parameter(0);
+  Node* position = assembler->Parameter(1);
+  Node* context = assembler->Parameter(4);
+
+  // Check that {receiver} is coercible to Object and convert it to a String.
+  receiver =
+      assembler->ToThisString(context, receiver, "String.prototype.charCodeAt");
+
+  // Convert the {position} to a Smi and check that it's in bounds of the
+  // {receiver}.
+  // TODO(bmeurer): Find an abstraction for this!
+  {
+    // Check if the {position} is already a Smi.
+    Variable var_position(assembler, MachineRepresentation::kTagged);
+    var_position.Bind(position);
+    Label if_positionissmi(assembler),
+        if_positionisnotsmi(assembler, Label::kDeferred);
+    assembler->Branch(assembler->WordIsSmi(position), &if_positionissmi,
+                      &if_positionisnotsmi);
+    assembler->Bind(&if_positionisnotsmi);
+    {
+      // Convert the {position} to an Integer via the ToIntegerStub.
+      Callable callable = CodeFactory::ToInteger(assembler->isolate());
+      Node* index = assembler->CallStub(callable, context, position);
+
+      // Check if the resulting {index} is now a Smi.
+      Label if_indexissmi(assembler, Label::kDeferred),
+          if_indexisnotsmi(assembler, Label::kDeferred);
+      assembler->Branch(assembler->WordIsSmi(index), &if_indexissmi,
+                        &if_indexisnotsmi);
+
+      assembler->Bind(&if_indexissmi);
+      {
+        var_position.Bind(index);
+        assembler->Goto(&if_positionissmi);
+      }
+
+      assembler->Bind(&if_indexisnotsmi);
+      {
+        // The ToIntegerStub canonicalizes everything in Smi range to Smi
+        // representation, so any HeapNumber returned is not in Smi range.
+        // The only exception here is -0.0, which we treat as 0.
+        Node* index_value = assembler->LoadHeapNumberValue(index);
+        Label if_indexiszero(assembler, Label::kDeferred),
+            if_indexisnotzero(assembler, Label::kDeferred);
+        assembler->Branch(assembler->Float64Equal(
+                              index_value, assembler->Float64Constant(0.0)),
+                          &if_indexiszero, &if_indexisnotzero);
+
+        assembler->Bind(&if_indexiszero);
+        {
+          var_position.Bind(assembler->SmiConstant(Smi::FromInt(0)));
+          assembler->Goto(&if_positionissmi);
+        }
+
+        assembler->Bind(&if_indexisnotzero);
+        {
+          // The {index} is some other integral Number, that is definitely
+          // neither -0.0 nor in Smi range.
+          assembler->Return(assembler->NaNConstant());
+        }
+      }
+    }
+    assembler->Bind(&if_positionissmi);
+    position = var_position.value();
+
+    // Determine the actual length of the {receiver} String.
+    Node* receiver_length =
+        assembler->LoadObjectField(receiver, String::kLengthOffset);
+
+    // Return NaN if the Smi {position} is outside the bounds of the {receiver}.
+    Label if_positioninbounds(assembler),
+        if_positionnotinbounds(assembler, Label::kDeferred);
+    assembler->Branch(assembler->SmiAboveOrEqual(position, receiver_length),
+                      &if_positionnotinbounds, &if_positioninbounds);
+    assembler->Bind(&if_positionnotinbounds);
+    assembler->Return(assembler->NaNConstant());
+    assembler->Bind(&if_positioninbounds);
+  }
+
+  // Load the character at the {position} from the {receiver}.
+  Node* value = assembler->StringCharCodeAt(receiver, position);
+  Node* result = assembler->SmiFromWord32(value);
+  assembler->Return(result);
+}
+
+// -----------------------------------------------------------------------------
+// ES6 section 21.1 ArrayBuffer Objects
 
 // ES6 section 24.1.2.1 ArrayBuffer ( length ) for the [[Call]] case.
 BUILTIN(ArrayBufferConstructor) {