[string] Refactor direct string conversions

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"
@@ skipping 674 matching lines @@
                                char const* method_name);
 
   // Type checks.
   // Check whether the map is for an object with special properties, such as a
   // JSProxy or an object with interceptors.
   Node* InstanceTypeEqual(Node* instance_type, int type);
   Node* IsSpecialReceiverMap(Node* map);
   Node* IsSpecialReceiverInstanceType(Node* instance_type);
   Node* IsStringInstanceType(Node* instance_type);
   Node* IsOneByteStringInstanceType(Node* instance_type);
+  Node* IsExternalStringInstanceType(Node* instance_type);
+  Node* IsShortExternalStringInstanceType(Node* instance_type);
   Node* IsSequentialStringInstanceType(Node* instance_type);
   Node* IsString(Node* object);
   Node* IsJSObject(Node* object);
   Node* IsJSGlobalProxy(Node* object);
   Node* IsJSReceiverInstanceType(Node* instance_type);
   Node* IsJSReceiver(Node* object);
   Node* IsJSReceiverMap(Node* map);
   Node* IsMap(Node* object);
   Node* IsCallableMap(Node* map);
   Node* IsDeprecatedMap(Node* map);
@@ skipping 26 matching lines @@
   // Return the single character string with only {code}.
   Node* StringFromCharCode(Node* code);
   // Return a new string object which holds a substring containing the range
   // [from,to[ of string.  |from| and |to| are expected to be tagged.
   Node* SubString(Node* context, Node* string, Node* from, Node* to);
 
   // Return a new string object produced by concatenating |first| with |second|.
   Node* StringAdd(Node* context, Node* first, Node* second,
                   AllocationFlags flags = kNone);
 
-  // Tries to unpack |string| into a pseudo-sequential string. For instance,
-  // In addition to the work done by TryDerefExternalString and
-  // MaybeDerefIndirectString, this method can also unpack sliced strings into
-  // a (string, offset) pair. The same GC restrictions on the returned string
-  // value apply as for TryDerefExternalString.
-  void TryUnpackString(Variable* var_string, Variable* var_offset,
-                       Variable* var_instance_type, Label* if_bailout);
-
   // Unpack the external string, returning a pointer that (offset-wise) looks
   // like a sequential string.
   // Note that this pointer is not tagged and does not point to a real
   // sequential string instance, and may only be used to access the string
   // data. The pointer is GC-safe as long as a reference to the container
   // ExternalString is live.
   // |string| must be an external string. Bailout for short external strings.
   Node* TryDerefExternalString(Node* const string, Node* const instance_type,
                                Label* if_bailout);
 
@@ skipping 633 matching lines @@
  private:
   Node* GetArguments();
 
   CodeStubAssembler* assembler_;
   CodeStubAssembler::ParameterMode argc_mode_;
   Node* argc_;
   Node* arguments_;
   Node* fp_;
 };
 
+class ToDirectStringAssembler : public CodeStubAssembler {
+ private:
+  enum StringPointerKind { PTR_TO_DATA, PTR_TO_STRING };
+
+ public:
+  explicit ToDirectStringAssembler(compiler::CodeAssemblerState* state,
+                                   Node* string);
+
+  // Converts flat cons, thin, and sliced strings and returns the direct
+  // string. The result can be either a sequential or external string.
+  Node* TryToDirect(Label* if_bailout);
+
+  // Returns a pointer to the beginning of the string data.
+  Node* PointerToData(Label* if_bailout) {
+    return TryToSequential(PTR_TO_DATA, if_bailout);
+  }
+
+  // Returns a pointer that, offset-wise, looks like a String.
+  Node* PointerToString(Label* if_bailout) {
+    return TryToSequential(PTR_TO_STRING, if_bailout);
+  }
+
+  Node* string() { return var_string_.value(); }
+  Node* instance_type() { return var_instance_type_.value(); }
+  Node* offset() { return var_offset_.value(); }
+  Node* is_external() { return var_is_external_.value(); }
+
+ private:
+  Node* TryToSequential(StringPointerKind ptr_kind, Label* if_bailout);
+
+  Variable var_string_;
+  Variable var_instance_type_;
+  Variable var_offset_;
+  Variable var_is_external_;
+};
+
 #ifdef DEBUG
 #define CSA_ASSERT(csa, x) \
   (csa)->Assert([&] { return (x); }, #x, __FILE__, __LINE__)
 #define CSA_ASSERT_JS_ARGC_OP(csa, Op, op, expected)               \
   (csa)->Assert(                                                   \
       [&] {                                                        \
         const CodeAssemblerState* state = (csa)->state();          \
         /* See Linkage::GetJSCallDescriptor(). */                  \
         int argc_index = state->parameter_count() - 2;             \
         compiler::Node* const argc = (csa)->Parameter(argc_index); \
@@ skipping 16 matching lines @@
   }
 #else
 #define CSA_SLOW_ASSERT(csa, x) ((void)0)
 #endif
 
 DEFINE_OPERATORS_FOR_FLAGS(CodeStubAssembler::AllocationFlags);
 
 }  // namespace internal
 }  // namespace v8
 #endif  // V8_CODE_STUB_ASSEMBLER_H_