First steps towards better code generation for LBranch:

src/full-codegen.h

Index: src/full-codegen.h
===================================================================
--- src/full-codegen.h	(revision 8228)
+++ src/full-codegen.h	(working copy)
@@ -298,7 +298,10 @@
   // Helper function to convert a pure value into a test context.  The value
   // is expected on the stack or the accumulator, depending on the platform.
   // See the platform-specific implementation for details.
-  void DoTest(Label* if_true, Label* if_false, Label* fall_through);
+  void DoTest(Expression* condition,
+              Label* if_true,
+              Label* if_false,
+              Label* fall_through);
 
   // Helper function to split control flow and avoid a branch to the
   // fall-through label if it is set up.
@@ -347,7 +350,7 @@
                        Label* if_true,
                        Label* if_false,
                        Label* fall_through) {
-    TestContext context(this, if_true, if_false, fall_through);
+    TestContext context(this, expr, if_true, if_false, fall_through);
     VisitInCurrentContext(expr);
   }
 
@@ -670,11 +673,13 @@
 
   class TestContext : public ExpressionContext {
    public:
-    explicit TestContext(FullCodeGenerator* codegen,
-                         Label* true_label,
-                         Label* false_label,
-                         Label* fall_through)
+    TestContext(FullCodeGenerator* codegen,
+                Expression* condition,
+                Label* true_label,
+                Label* false_label,
+                Label* fall_through)
         : ExpressionContext(codegen),
+          condition_(condition),
           true_label_(true_label),
           false_label_(false_label),
           fall_through_(fall_through) { }
@@ -704,6 +709,7 @@
     virtual bool IsTest() const { return true; }
 
    private:
+    Expression* condition_;
     Label* true_label_;
     Label* false_label_;
     Label* fall_through_;