Allow IfBuilder's to join existing (captured) continuations.

src/hydrogen.h

 // Copyright 2012 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 923 matching lines @@
 
   HArgumentsObject* arguments_object_;
   HArgumentsElements* arguments_elements_;
 
   FunctionState* outer_;
 };
 
 
 class HIfContinuation V8_FINAL {
  public:
-  HIfContinuation() { continuation_captured_ = false; }
+  HIfContinuation() : continuation_captured_(false) {}
+  HIfContinuation(HBasicBlock* true_branch,
+                  HBasicBlock* false_branch,
+                  int position = RelocInfo::kNoPosition)
+      : continuation_captured_(true), true_branch_(true_branch),
+        false_branch_(false_branch), position_(position) {}
   ~HIfContinuation() { ASSERT(!continuation_captured_); }
 
   void Capture(HBasicBlock* true_branch,
                HBasicBlock* false_branch,
                int position) {
     ASSERT(!continuation_captured_);
     true_branch_ = true_branch;
     false_branch_ = false_branch;
     position_ = position;
     continuation_captured_ = true;
   }
 
   void Continue(HBasicBlock** true_branch,
                 HBasicBlock** false_branch,
                 int* position) {
     ASSERT(continuation_captured_);
     *true_branch = true_branch_;
     *false_branch = false_branch_;
     if (position != NULL) *position = position_;
     continuation_captured_ = false;
   }
 
   bool IsTrueReachable() { return true_branch_ != NULL; }
   bool IsFalseReachable() { return false_branch_ != NULL; }
   bool TrueAndFalseReachable() {
     return IsTrueReachable() || IsFalseReachable();
   }
 
+  HBasicBlock* true_branch() const { return true_branch_; }
+  HBasicBlock* false_branch() const { return false_branch_; }
+
+ private:
   bool continuation_captured_;
   HBasicBlock* true_branch_;
   HBasicBlock* false_branch_;
   int position_;
 };
 
 
 class HGraphBuilder {
  public:
   explicit HGraphBuilder(CompilationInfo* info)
@@ skipping 384 matching lines @@
 
     template<class Condition, class P2, class P3>
     Condition* AndIf(HValue* p1, P2 p2, P3 p3) {
       And();
       return If<Condition>(p1, p2, p3);
     }
 
     void Or();
     void And();
 
+    // Captures the current state of this IfBuilder in the specified
+    // continuation and ends this IfBuilder.
     void CaptureContinuation(HIfContinuation* continuation);
 
+    // Joins the specified continuation from this IfBuilder and ends this
+    // IfBuilder. This appends a Goto instruction from the true branch of
+    // this IfBuilder to the true branch of the continuation unless the
+    // true branch of this IfBuilder is already finished. And vice versa
+    // for the false branch.
+    //
+    // The basic idea is as follows: You have several nested IfBuilder's
+    // that you want to join based on two possible outcomes (i.e. success
+    // and failure, or whatever). You can do this easily using this method
+    // now, for example:
+    //
+    //   HIfContinuation cont(graph()->CreateBasicBlock(),
+    //                        graph()->CreateBasicBlock());
+    //   ...
+    //     IfBuilder if_whatever(this);
+    //     if_whatever.If<Condition>(arg);
+    //     if_whatever.Then();
+    //     ...
+    //     if_whatever.Else();
+    //     ...
+    //     if_whatever.JoinContinuation(&cont);
+    //   ...
+    //     IfBuilder if_something(this);
+    //     if_something.If<Condition>(arg1, arg2);
+    //     if_something.Then();
+    //     ...
+    //     if_something.Else();
+    //     ...
+    //     if_something.JoinContinuation(&cont);
+    //   ...
+    //   IfBuilder if_finally(this, &cont);
+    //   if_finally.Then();
+    //   // continues after then code of if_whatever or if_something.
+    //   ...
+    //   if_finally.Else();
+    //   // continues after else code of if_whatever or if_something.
+    //   ...
+    //   if_finally.End();
+    void JoinContinuation(HIfContinuation* continuation);
+
     void Then();
     void Else();
     void End();
 
     void Deopt(const char* reason);
     void ElseDeopt(const char* reason) {
       Else();
       Deopt(reason);
     }
 
@@ skipping 989 matching lines @@
   }
 
  private:
   HGraphBuilder* builder_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_