Custom call IC-s for String.prototype.{charAt,charCodeAt}.

src/codegen.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 92 matching lines @@
   F(IsNonNegativeSmi, 1, 1)                                                  \
   F(IsArray, 1, 1)                                                           \
   F(IsRegExp, 1, 1)                                                          \
   F(CallFunction, -1 /* receiver + n args + function */, 1)                  \
   F(IsConstructCall, 0, 1)                                                   \
   F(ArgumentsLength, 0, 1)                                                   \
   F(Arguments, 1, 1)                                                         \
   F(ClassOf, 1, 1)                                                           \
   F(ValueOf, 1, 1)                                                           \
   F(SetValueOf, 2, 1)                                                        \
-  F(FastCharCodeAt, 2, 1)                                                    \
-  F(CharFromCode, 1, 1)                                                      \
+  F(StringCharCodeAt, 2, 1)                                                  \
+  F(StringCharFromCode, 1, 1)                                                \
+  F(StringCharAt, 2, 1)                                                      \
   F(ObjectEquals, 2, 1)                                                      \
   F(Log, 3, 1)                                                               \
   F(RandomHeapNumber, 0, 1)                                                  \
   F(IsObject, 1, 1)                                                          \
   F(IsFunction, 1, 1)                                                        \
   F(IsUndetectableObject, 1, 1)                                              \
   F(StringAdd, 2, 1)                                                         \
   F(SubString, 3, 1)                                                         \
   F(StringCompare, 2, 1)                                                     \
   F(RegExpExec, 4, 1)                                                        \
@@ skipping 47 matching lines @@
     ASSERT(top_ != NULL);
     return top_;
   }
 
  private:
   static CodeGenerator* top_;
   CodeGenerator* previous_;
 };
 
 
+// State of used registers in a virtual frame.
+class FrameRegisterState {
+ public:
+  // Captures the current state of the given frame.
+  explicit FrameRegisterState(VirtualFrame* frame);
+
+  // Saves the state in the stack.
+  void Save(MacroAssembler* masm) const;
+
+  // Restores the state from the stack.
+  void Restore(MacroAssembler* masm) const;
+
+ private:
+  // Constants indicating special actions.  They should not be multiples
+  // of kPointerSize so they will not collide with valid offsets from
+  // the frame pointer.
+  static const int kIgnore = -1;
+  static const int kPush = 1;
+
+  // This flag is ored with a valid offset from the frame pointer, so
+  // it should fit in the low zero bits of a valid offset.
+  static const int kSyncedFlag = 2;
+
+  // C++ doesn't allow zero length arrays, so we make the array length 1 even
+  // if we don't need it.
+  static const int kRegistersArrayLength =
+      (RegisterAllocator::kNumRegisters == 0) ?
+          1 : RegisterAllocator::kNumRegisters;
+  int registers_[kRegistersArrayLength];
+};
+
+
+// Helper interface to prepare to/restore after making runtime calls.
+class RuntimeCallHelper {
+ public:
+  virtual ~RuntimeCallHelper() {}
+
+  virtual void BeforeCall(MacroAssembler* masm) const = 0;
+
+  virtual void AfterCall(MacroAssembler* masm) const = 0;
+
+ protected:
+  RuntimeCallHelper() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(RuntimeCallHelper);
+};
+
+
+// RuntimeCallHelper implementation that saves/restores state of a
+// virtual frame.
+class VirtualFrameRuntimeCallHelper : public RuntimeCallHelper {
+ public:
+  // Does not take ownership of |frame_state|.
+  explicit VirtualFrameRuntimeCallHelper(const FrameRegisterState* frame_state)
+      : frame_state_(frame_state) {}
+
+  virtual void BeforeCall(MacroAssembler* masm) const;
+
+  virtual void AfterCall(MacroAssembler* masm) const;
+
+ private:
+  const FrameRegisterState* frame_state_;
+};
+
+
+// RuntimeCallHelper implementation used in IC stubs: enters/leaves a
+// newly created internal frame before/after the runtime call.
+class ICRuntimeCallHelper : public RuntimeCallHelper {
+ public:
+  ICRuntimeCallHelper() {}
+
+  virtual void BeforeCall(MacroAssembler* masm) const;
+
+  virtual void AfterCall(MacroAssembler* masm) const;
+};
+
+
+// Trivial RuntimeCallHelper implementation.
+class NopRuntimeCallHelper : public RuntimeCallHelper {
+ public:
+  NopRuntimeCallHelper() {}
+
+  virtual void BeforeCall(MacroAssembler* masm) const {}
+
+  virtual void AfterCall(MacroAssembler* masm) const {}
+};
+
+
 // Deferred code objects are small pieces of code that are compiled
 // out of line. They are used to defer the compilation of uncommon
 // paths thereby avoiding expensive jumps around uncommon code parts.
 class DeferredCode: public ZoneObject {
  public:
   DeferredCode();
   virtual ~DeferredCode() { }
 
   virtual void Generate() = 0;
 
@@ skipping 10 matching lines @@
   const char* comment() const { return comment_; }
 #else
   void set_comment(const char* comment) { }
   const char* comment() const { return ""; }
 #endif
 
   inline void Jump();
   inline void Branch(Condition cc);
   void BindExit() { masm_->bind(&exit_label_); }
 
+  const FrameRegisterState* frame_state() const { return &frame_state_; }
+
   void SaveRegisters();
   void RestoreRegisters();
 
  protected:
   MacroAssembler* masm_;
 
  private:
-  // Constants indicating special actions.  They should not be multiples
-  // of kPointerSize so they will not collide with valid offsets from
-  // the frame pointer.
-  static const int kIgnore = -1;
-  static const int kPush = 1;
-
-  // This flag is ored with a valid offset from the frame pointer, so
-  // it should fit in the low zero bits of a valid offset.
-  static const int kSyncedFlag = 2;
-
   int statement_position_;
   int position_;
 
   Label entry_label_;
   Label exit_label_;
 
-  // C++ doesn't allow zero length arrays, so we make the array length 1 even
-  // if we don't need it.
-  static const int kRegistersArrayLength =
-      (RegisterAllocator::kNumRegisters == 0) ?
-          1 : RegisterAllocator::kNumRegisters;
-  int registers_[kRegistersArrayLength];
+  FrameRegisterState frame_state_;
 
 #ifdef DEBUG
   const char* comment_;
 #endif
   DISALLOW_COPY_AND_ASSIGN(DeferredCode);
 };
 
 class StackCheckStub : public CodeStub {
  public:
   StackCheckStub() { }
@@ skipping 353 matching lines @@
   ToBooleanStub() { }
 
   void Generate(MacroAssembler* masm);
 
  private:
   Major MajorKey() { return ToBoolean; }
   int MinorKey() { return 0; }
 };
 
 
+enum StringIndexFlags {

[Mads Ager (chromium), 2010/05/26 09:17:07]

How about renaming these to something like:

INDEX_IS_NUMBER
INDEX_IS_ARRAY_INDEX

I think that makes it easier to read at the call site. 

I would also like the comments on the generators to say how the code generated
depends on these flags.

+  // Accepts smis or heap numbers.
+  STRING_ANY_NUMBER_INDEX,
+
+  // Accepts smis or heap numbers that are valid array indices
+  // (ECMA-262 15.4). Invalid indices are reported as being out of
+  // range.
+  STRING_REQUIRE_ARRAY_INDEX
+};
+
+
+// Generates code implementing String.prototype.charCodeAt.
+//
+// Only supports the case when the receiver is a string and the index
+// is a number (smi or heap number) that is a valid index into the
+// string. Otherwise, bails out to the provided labels.
+//
+// Register usage: |object| may be changed to another string in a way
+// that doesn't affect charCodeAt/charAt semantics, |index| is
+// preserved, |scratch| and |result| are clobbered.
+class StringCharCodeAtGenerator {
+ public:
+  StringCharCodeAtGenerator(Register object,
+                            Register index,
+                            Register scratch,
+                            Register result,
+                            Label* receiver_not_string,
+                            Label* index_not_number,
+                            Label* index_out_of_range,
+                            StringIndexFlags index_flags)
+      : object_(object),
+        index_(index),
+        scratch_(scratch),
+        result_(result),
+        receiver_not_string_(receiver_not_string),
+        index_not_number_(index_not_number),
+        index_out_of_range_(index_out_of_range),
+        index_flags_(index_flags) {
+    ASSERT(!scratch_.is(object_));
+    ASSERT(!scratch_.is(index_));
+    ASSERT(!scratch_.is(result_));
+    ASSERT(!result_.is(object_));
+    ASSERT(!result_.is(index_));
+  }
+
+  // Generates the fast case code. On the fallthrough path |result|
+  // register contains the result.
+  void GenerateFast(MacroAssembler* masm);
+
+  // Generates the slow case code. Must not be naturally
+  // reachable. Expected to be put after a ret instruction (e.g., in
+  // deferred code). Always jumps back to the fast case.
+  void GenerateSlow(MacroAssembler* masm,
+                    const RuntimeCallHelper& call_helper);
+
+ private:
+  Register object_;
+  Register index_;
+  Register scratch_;
+  Register result_;
+
+  Label* receiver_not_string_;
+  Label* index_not_number_;
+  Label* index_out_of_range_;
+
+  StringIndexFlags index_flags_;
+
+  Label call_runtime_;
+  Label index_not_smi_;
+  Label got_smi_index_;
+  Label exit_;
+
+  DISALLOW_COPY_AND_ASSIGN(StringCharCodeAtGenerator);
+};
+
+
+// Generates code for creating a one-char string from a char code.
+class StringCharFromCodeGenerator {
+ public:
+  StringCharFromCodeGenerator(Register code,
+                              Register result)
+      : code_(code),
+        result_(result) {
+    ASSERT(!code_.is(result_));
+  }
+
+  // Generates the fast case code. On the fallthrough path |result|
+  // register contains the result.
+  void GenerateFast(MacroAssembler* masm);
+
+  // Generates the slow case code. Must not be naturally
+  // reachable. Expected to be put after a ret instruction (e.g., in
+  // deferred code). Always jumps back to the fast case.
+  void GenerateSlow(MacroAssembler* masm,
+                    const RuntimeCallHelper& call_helper);
+
+ private:
+  Register code_;
+  Register result_;
+
+  Label slow_case_;
+  Label exit_;
+
+  DISALLOW_COPY_AND_ASSIGN(StringCharFromCodeGenerator);
+};
+
+
+// Generates code implementing String.prototype.charAt.
+//
+// Only supports the case when the receiver is a string and the index
+// is a number (smi or heap number) that is a valid index into the
+// string. Otherwise, bails out to the provided labels.
+//
+// Register usage: |object| may be changed to another string in a way
+// that doesn't affect charCodeAt/charAt semantics, |index| is
+// preserved, |scratch1|, |scratch2|, and |result| are clobbered.
+class StringCharAtGenerator {
+ public:
+  StringCharAtGenerator(Register object,
+                        Register index,
+                        Register scratch1,
+                        Register scratch2,
+                        Register result,
+                        Label* receiver_not_string,
+                        Label* index_not_number,
+                        Label* index_out_of_range,
+                        StringIndexFlags index_flags)
+      : char_code_at_generator_(object,
+                                index,
+                                scratch1,
+                                scratch2,
+                                receiver_not_string,
+                                index_not_number,
+                                index_out_of_range,
+                                index_flags),
+        char_from_code_generator_(scratch2, result) {}
+
+  // Generates the fast case code. On the fallthrough path |result|
+  // register contains the result.
+  void GenerateFast(MacroAssembler* masm);
+
+  // Generates the slow case code. Must not be naturally
+  // reachable. Expected to be put after a ret instruction (e.g., in
+  // deferred code). Always jumps back to the fast case.
+  void GenerateSlow(MacroAssembler* masm,
+                    const RuntimeCallHelper& call_helper);
+
+ private:
+  StringCharCodeAtGenerator char_code_at_generator_;
+  StringCharFromCodeGenerator char_from_code_generator_;
+
+  DISALLOW_COPY_AND_ASSIGN(StringCharAtGenerator);
+};
+
+
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CODEGEN_H_