First steps towards better code generation for LBranch:

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
===================================================================
--- src/x64/full-codegen-x64.cc	(revision 8272)
+++ src/x64/full-codegen-x64.cc	(working copy)
@@ -377,7 +377,7 @@
 void FullCodeGenerator::TestContext::Plug(Slot* slot) const {
   codegen()->Move(result_register(), slot);
   codegen()->PrepareForBailoutBeforeSplit(TOS_REG, false, NULL, NULL);
-  codegen()->DoTest(true_label_, false_label_, fall_through_);
+  codegen()->DoTest(this);
 }
 
 
@@ -410,7 +410,7 @@
     if (true_label_ != fall_through_) __ jmp(true_label_);
   } else {
     __ LoadRoot(result_register(), index);
-    codegen()->DoTest(true_label_, false_label_, fall_through_);
+    codegen()->DoTest(this);
   }
 }
 
@@ -455,7 +455,7 @@
   } else {
     // For simplicity we always test the accumulator register.
     __ Move(result_register(), lit);
-    codegen()->DoTest(true_label_, false_label_, fall_through_);
+    codegen()->DoTest(this);
   }
 }
 
@@ -491,7 +491,7 @@
   __ Drop(count);
   __ Move(result_register(), reg);
   codegen()->PrepareForBailoutBeforeSplit(TOS_REG, false, NULL, NULL);
-  codegen()->DoTest(true_label_, false_label_, fall_through_);
+  codegen()->DoTest(this);
 }
 
 
@@ -566,7 +566,8 @@
 }
 
 
-void FullCodeGenerator::DoTest(Label* if_true,
+void FullCodeGenerator::DoTest(Expression* condition,
+                               Label* if_true,
                                Label* if_false,
                                Label* fall_through) {
   ToBooleanStub stub;