bpo-36851: Clean the frame stack if the execution ends with a return and the stack is not empty #13191
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pablogsal changed the title pablogsal force-pushed the clean_stack branch 2 times, most recently from 9cda466 to 2d0a4e8 Compare 
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https://bugs.python.org/issue36851
When evaluating a frame object, it is possible to exit the execution with some variables in the stack. The frame deallocator (frame_dealloc) only cleans the stack if f_stacktop is not NULL, but this only happens for generators and when trace functions are set. The eval loop does this cleanup already if an exception is being raised, but not if a RETURN_VALUE is set.
In the PyconUS sprints, @DinoV and I have been working on this and we have decided that the cleanest approach is shared the same goto label with the path for exception handling, effectively cleaning up