Experimental: statically distinguish between named basic block entries...

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 34 matching lines @@
 // frame.  For backward jumps, the merge code is generated at the edge
 // leaving the predecessor block.
 //
 // A jump target must have been reached via control flow (either by
 // jumping, branching, or falling through) at the time it is bound.
 // In particular, this means that at least one of the control-flow
 // graph edges reaching the target must be a forward edge.
 
 class JumpTarget : public ZoneObject {  // Shadows are dynamically allocated.
  public:
+  // Forward-only jump targets can only be reached by forward CFG edges.
+  enum Directionality { FORWARD_ONLY, BIDIRECTIONAL };
+
   // Construct a jump target with a given code generator used to generate
   // code and to provide access to a current frame.
-  explicit JumpTarget(CodeGenerator* cgen);
+  explicit JumpTarget(CodeGenerator* cgen,
+                      Directionality direction = FORWARD_ONLY);
 
   // Construct a jump target without a code generator.  A code generator
   // must be supplied before using the jump target as a label.  This is
   // useful, eg, when jump targets are embedded in AST nodes.
   JumpTarget();
 
   virtual ~JumpTarget() { Unuse(); }
 
-  // Supply a code generator.  This function expects to be given a non-null
-  // code generator, and to be called only when the code generator is not
-  // yet set.
-  void set_code_generator(CodeGenerator* cgen);
+  // Supply a code generator and directionality to an already
+  // constructed jump target.  This function expects to be given a
+  // non-null code generator, and to be called only when the code
+  // generator is not yet set.
+  void Initialize(CodeGenerator* cgen,
+                  Directionality direction = FORWARD_ONLY);
 
   // Accessors.
   CodeGenerator* code_generator() const { return cgen_; }
 
   Label* entry_label() { return &entry_label_; }
 
   VirtualFrame* expected_frame() const { return expected_frame_; }
   void set_expected_frame(VirtualFrame* frame) {
     expected_frame_ = frame;
   }
@@ skipping 58 matching lines @@
   void Call();
 
  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_;
+
   // A list of frames reaching this block via forward jumps.
   List<VirtualFrame*> reaching_frames_;
 
   // A parallel list of labels for merge code.
   List<Label> merge_labels_;
 
   // The (mergable) frame expected at backward jumps to the block.
   VirtualFrame* expected_frame_;
 
   // The actual entry label of the block.
@@ skipping 47 matching lines @@
   bool is_shadowing_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(ShadowTarget);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_JUMP_TARGET_H_