Experimental: introduce a simple mechanism to allow jump targets with...

src/jump-target.h

 // Copyright 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 113 matching lines @@
               Hint hint = no_hint);
   void Branch(Condition cc,
               Result* arg0,
               Result* arg1,
               Result* arg2,
               Result* arg3,
               Hint hint = no_hint);
 
   // Bind a jump target.  If there is no current frame at the binding
   // site, there must be at least one frame reaching via a forward
-  // jump.  This frame will be used to establish an expected frame for
-  // the block, which will be the current frame after the bind.
-  void Bind();
-  void Bind(Result* arg);
-  void Bind(Result* arg0, Result* arg1);
-  void Bind(Result* arg0, Result* arg1, Result* arg2);
-  void Bind(Result* arg0, Result* arg1, Result* arg2, Result* arg3);
+  // jump.
+  //
+  // The number of mergable elements is a number of frame elements
+  // counting from the top down which must be "mergable" (not
+  // constants or copies) in the entry frame at the jump target.
+  // Backward jumps to the target must contain the same constants and
+  // sharing as the entry frame, except for the mergable elements.
+  //
+  // A mergable elements argument of kAllElements indicates that all
+  // frame elements must be mergable.  Mergable elements are ignored
+  // completely for forward-only jump targets.
+  void Bind(int mergable_elements = kAllElements);
+  void Bind(Result* arg, int mergable_elements = kAllElements);
+  void Bind(Result* arg0, Result* arg1, int mergable_elements = kAllElements);
+  void Bind(Result* arg0,
+            Result* arg1,
+            Result* arg2,
+            int mergable_elements = kAllElements);
+  void Bind(Result* arg0,
+            Result* arg1,
+            Result* arg2,
+            Result* arg3,
+            int mergable_elements = kAllElements);
 
   // Emit a call to a jump target.  There must be a current frame at
   // the call.  The frame at the target is the same as the current
   // frame except for an extra return address on top of it.  The frame
   // after the call is the same as the frame before the call.
   void Call();
 
+  static const int kAllElements = -1;  // Not a valid number of elements.
+
  protected:
   // The code generator gives access to its current frame.
   CodeGenerator* cgen_;
 
   // Used to emit code.
   MacroAssembler* masm_;
 
  private:
   // Directionality flag set at initialization time.
   Directionality direction_;
@@ skipping 19 matching lines @@
   bool is_linked_;
 
   // Add a virtual frame reaching this labeled block via a forward
   // jump, and a fresh label for its merge code.
   void AddReachingFrame(VirtualFrame* frame);
 
   // Choose an element from a pair of frame elements to be in the
   // expected frame.  Return null if they are incompatible.
   FrameElement* Combine(FrameElement* left, FrameElement* right);
 
-  // Compute a frame to use for entry to this block.
-  void ComputeEntryFrame();
+  // Compute a frame to use for entry to this block.  Mergable
+  // elements is as described for the Bind function.
+  void ComputeEntryFrame(int mergable_elements);
 
   DISALLOW_COPY_AND_ASSIGN(JumpTarget);
 };
 
 
 // -------------------------------------------------------------------------
 // Shadow jump targets
 //
 // Shadow jump targets represent a jump target that is temporarily shadowed
 // by another one (represented by the original during shadowing).  They are
@@ skipping 32 matching lines @@
   bool is_shadowing_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(ShadowTarget);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_JUMP_TARGET_H_