[builtins] migrate C++ String Iterator builtins to baseline TurboFan

src/code-stub-assembler.h

 // Copyright 2016 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_CODE_STUB_ASSEMBLER_H_
 #define V8_CODE_STUB_ASSEMBLER_H_
 
 #include <functional>
 
 #include "src/compiler/code-assembler.h"
 #include "src/objects.h"
 
 namespace v8 {
 namespace internal {
 
 class CallInterfaceDescriptor;
 class StatsCounter;
 class StubCache;
 
 enum class PrimitiveType { kBoolean, kNumber, kString, kSymbol };
 
+enum class UnicodeEncoding {
+  // Different unicode encodings in a |word32|:
+  UTF16,  // hi 16bits -> trailing surrogate or 0, low 16bits -> lead surrogate
+  UTF32,  // full UTF32 code unit / Unicode codepoint
+};
+
 // Provides JavaScript-specific "macro-assembler" functionality on top of the
 // CodeAssembler. By factoring the JavaScript-isms out of the CodeAssembler,
 // it's possible to add JavaScript-specific useful CodeAssembler "macros"
 // without modifying files in the compiler directory (and requiring a review
 // from a compiler directory OWNER).
 class CodeStubAssembler : public compiler::CodeAssembler {
  public:
   // Create with CallStub linkage.
   // |result_size| specifies the number of results returned by the stub.
   // TODO(rmcilroy): move result_size to the CallInterfaceDescriptor.
@@ skipping 405 matching lines @@
                               PrimitiveType primitive_type,
                               char const* method_name);
 
   // String helpers.
   // Load a character from a String (might flatten a ConsString).
   compiler::Node* StringCharCodeAt(compiler::Node* string,
                                    compiler::Node* smi_index);
   // Return the single character string with only {code}.
   compiler::Node* StringFromCharCode(compiler::Node* code);
 
+  compiler::Node* StringFromCodePoint(compiler::Node* codepoint,
+                                      UnicodeEncoding encoding);
+
   // Type conversion helpers.
   // Convert a String to a Number.
   compiler::Node* StringToNumber(compiler::Node* context,
                                  compiler::Node* input);
   // Convert an object to a name.
   compiler::Node* ToName(compiler::Node* context, compiler::Node* input);
   // Convert a Non-Number object to a Number.
   compiler::Node* NonNumberToNumber(compiler::Node* context,
                                     compiler::Node* input);
   // Convert any object to a Number.
@@ skipping 340 matching lines @@
                                            Label* bailout);
 
   static const int kElementLoopUnrollThreshold = 8;
 };
 
 DEFINE_OPERATORS_FOR_FLAGS(CodeStubAssembler::AllocationFlags);
 
 }  // namespace internal
 }  // namespace v8
 #endif  // V8_CODE_STUB_ASSEMBLER_H_