Experimental: add a pre-merge step to perform some frame moves that do...

src/jump-target-ia32.cc

 // 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 127 matching lines @@
   // block.
   ASSERT(!cgen_->has_valid_frame() || cgen_->HasValidEntryRegisters());
 
   // Compute the frame to use for entry to the block.
   ComputeEntryFrame(mergable_elements);
 
   if (is_linked()) {
     // There were forward jumps.  Handle merging the reaching frames
     // and possible fall through to the entry frame.
 
+    // Some moves required to merge to an expected frame require
+    // purely frame state changes, and do not require any code
+    // generation.  Perform those first to increase the possibility of
+    // finding equal frames below.
+    if (cgen_->has_valid_frame()) {
+      cgen_->frame()->PrepareMergeTo(entry_frame_);
+    }
+    for (int i = 0; i < reaching_frames_.length(); i++) {
+      reaching_frames_[i]->PrepareMergeTo(entry_frame_);
+    }
+
     // If there is a fall through to the jump target and it needs
     // merge code, process it first.
     if (cgen_->has_valid_frame() && !cgen_->frame()->Equals(entry_frame_)) {
       // Loop over all the reaching frames, looking for any that can
       // share merge code with this one.
       for (int i = 0; i < reaching_frames_.length(); i++) {
         if (cgen_->frame()->Equals(reaching_frames_[i])) {
           // Set the reaching frames element to null to avoid
           // processing it later, and then bind its entry label.
           delete reaching_frames_[i];
@@ skipping 80 matching lines @@
   }
 
   is_linked_ = false;
   is_bound_ = true;
 }
 
 #undef __
 
 
 } }  // namespace v8::internal