Backport r6579 (code generation bug on ARM).

src/arm/jump-target-arm.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 125 matching lines @@
   ASSERT(!cgen()->has_valid_frame() || cgen()->HasValidEntryRegisters());
 
   if (cgen()->has_valid_frame()) {
     if (direction_ != FORWARD_ONLY) cgen()->frame()->ForgetTypeInfo();
     // If there is a current frame we can use it on the fall through.
     if (!entry_frame_set_) {
       entry_frame_ = *cgen()->frame();
       entry_frame_set_ = true;
     } else {
       cgen()->frame()->MergeTo(&entry_frame_);
+      // On fall through we may have to merge both ways.
+      if (direction_ != FORWARD_ONLY) {
+        // This will not need to adjust the virtual frame entries that are
+        // register allocated since that was done above and they now match.
+        // But it does need to adjust the entry_frame_ of this jump target
+        // to make it potentially less optimistic.  Later code can branch back
+        // to this jump target and we need to assert that that code does not
+        // have weaker assumptions about types.
+        entry_frame_.MergeTo(cgen()->frame());
+      }
     }
   } else {
     // If there is no current frame we must have an entry frame which we can
     // copy.
     ASSERT(entry_frame_set_);
     RegisterFile empty;
     cgen()->SetFrame(new VirtualFrame(&entry_frame_), &empty);
   }
 
   __ bind(&entry_label_);
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM