Before emitting code to merge frames, forget the sync flag (telling...

src/virtual-frame.cc

 // Copyright 2009 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 212 matching lines @@
 
 // Make the type of all elements be MEMORY.
 void VirtualFrame::SpillAll() {
   for (int i = 0; i < elements_.length(); i++) {
     SpillElementAt(i);
   }
 }
 
 
 void VirtualFrame::PrepareMergeTo(VirtualFrame* expected) {
-  // No code needs to be generated to invalidate valid elements.  No
-  // code needs to be generated to move values to memory if they are
-  // already synced.
+  // Perform state changes on this frame that will make merge to the
+  // expected frame simpler or else increase the likelihood that his
+  // frame will match another.
   for (int i = 0; i < elements_.length(); i++) {
     FrameElement source = elements_[i];
     FrameElement target = expected->elements_[i];
+
     if (!target.is_valid() ||
         (target.is_memory() && !source.is_memory() && source.is_synced())) {
+      // No code needs to be generated to invalidate valid elements.
+      // No code needs to be generated to move values to memory if
+      // they are already synced.  We perform those moves here, before
+      // merging.
       if (source.is_register()) {
         // If the frame is the code generator's current frame, we have
         // to decrement both the frame-internal and global register
         // counts.
         if (cgen_->frame() == this) {
           Unuse(source.reg());
         } else {
           frame_registers_.Unuse(source.reg());
         }
       }
       elements_[i] = target;
+    } else if (target.is_register() && !source.is_memory()) {
+      // If an element's target is a register, and the element is not
+      // in memory, then the sync state of the element is irrelevant.
+      // We clear the sync bit.
+      ASSERT(source.is_valid());
+      elements_[i].clear_sync();
     }
   }
 }
 
 
 void VirtualFrame::PrepareForCall(int spilled_args, int dropped_args) {
   ASSERT(height() >= dropped_args);
   ASSERT(height() >= spilled_args);
   ASSERT(dropped_args <= spilled_args);
 
@@ skipping 271 matching lines @@
   for (int i = 0; i < kNumRegisters; i++) {
     if (frame_registers_.count(i) != other->frame_registers_.count(i)) {
       return false;
     }
   }
 
   return true;
 }
 
 } }  // namespace v8::internal