Frame stack is not cleaned after execution is finished with return

[pablogsal]

BPO	36851
Nosy	@vstinner, @DinoV, @pablogsal
PRs	bpo-36851: Clean the frame stack if the execution ends with a return and the stack is not empty #13191

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-05-09.15:52:19.181>
created_at = <Date 2019-05-08.15:40:55.125>
labels = ['interpreter-core', '3.8']
title = 'Frame stack is not cleaned after execution is finished with return'
updated_at = <Date 2019-05-13.15:31:20.580>
user = 'https://github.com/pablogsal'

bugs.python.org fields:

activity = <Date 2019-05-13.15:31:20.580>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-05-09.15:52:19.181>
closer = 'pablogsal'
components = ['Interpreter Core']
creation = <Date 2019-05-08.15:40:55.125>
creator = 'pablogsal'
dependencies = []
files = []
hgrepos = []
issue_num = 36851
keywords = ['patch']
message_count = 3.0
messages = ['341891', '341986', '342341']
nosy_count = 3.0
nosy_names = ['vstinner', 'dino.viehland', 'pablogsal']
pr_nums = ['13191']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue36851'
versions = ['Python 3.8']

[pablogsal]

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, Dino 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

[pablogsal]

New changeset f00828a by Pablo Galindo in branch 'master':
bpo-36851: Clean the frame stack if the execution ends with a return and the stack is not empty (GH-13191)
f00828a

[vstinner]

I marked bpo-36725 as a duplicate of this issue.