Add support for near labels....

src/assembler.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 74 matching lines @@
 
   friend class Assembler;
   friend class RegexpAssembler;
   friend class Displacement;
   friend class ShadowTarget;
   friend class RegExpMacroAssemblerIrregexp;
 };
 
 
 // -----------------------------------------------------------------------------
+// NearLabels are labels used for short jumps (in Intel jargon).
+// NearLabels should be used if it can be guaranteed that the jump range is
+// within -128 to +127. We already use short jumps when jumping backwards,
+// so using a NearLabel will only have performance impact if used for forward
+// jumps.
+class NearLabel BASE_EMBEDDED {

[Søren Thygesen Gjesse, 2010/09/15 10:38:20]

How about adding a type to the Label class

class Label ...

  enum LabelType {
    kTypeFar = ;
    kTypeNear = ;
    ...
  }


  Label(LabelType type = kTypeFar)

  ...

  LabelType type_;
}

the NearLabel class could then inherit from Label and construct a Label with
type kTypeNear. Then the following two lines would achieve the same:

Label label(Label::kTypeNear)
NearLabel label

+ public:
+  NearLabel() { Unuse(); }
+  ~NearLabel() { ASSERT(!is_linked()); }
+
+  void Unuse() {
+    pos_ = -1;
+    unresolved_branches_ = 0;
+#ifdef DEBUG
+    for (int i = 0; i < kMaxUnresolvedBranches; i++) {
+      unresolved_positions_[i] = -1;
+    }
+#endif
+  }
+
+  int pos() {
+    ASSERT(is_bound());
+    return pos_;
+  }
+
+  bool is_bound() { return pos_ >= 0; }
+  bool is_linked() { return !is_bound() && unresolved_branches_ > 0; }
+  bool is_unused() { return !is_bound() && unresolved_branches_ == 0; }
+
+  void bind_to(int position) {
+    ASSERT(!is_bound());
+    pos_ = position;
+  }
+
+  void link_to(int position) {
+    ASSERT(!is_bound());
+    ASSERT(unresolved_branches_ < kMaxUnresolvedBranches);
+    unresolved_positions_[unresolved_branches_++] = position;
+  }
+
+ private:
+  static const int kMaxUnresolvedBranches = 8;
+  int pos_;
+  int unresolved_branches_;
+  int unresolved_positions_[kMaxUnresolvedBranches];
+
+  friend class Assembler;
+};
+
+
+// -----------------------------------------------------------------------------
 // Relocation information
 
 
 // Relocation information consists of the address (pc) of the datum
 // to which the relocation information applies, the relocation mode
 // (rmode), and an optional data field. The relocation mode may be
 // "descriptive" and not indicate a need for relocation, but simply
 // describe a property of the datum. Such rmodes are useful for GC
 // and nice disassembly output.
 
@@ skipping 460 matching lines @@
   unsigned int num_bits_set;
   for (num_bits_set = 0; x; x >>= 1) {
     num_bits_set += x & 1;
   }
   return num_bits_set;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_ASSEMBLER_H_