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bpo-43693: Eliminate unused "fast locals". (gh-26587)

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Currently, if an arg value escapes (into the closure for an inner function) we end up allocating two indices in the fast locals even though only one gets used.  Additionally, using the lower index would be better in some cases, such as with no-arg `super()`.  To address this, we update the compiler to fix the offsets so each variable only gets one "fast local".  As a consequence, now some cell offsets are interspersed with the locals (only when an arg escapes to an inner function).

https://bugs.python.org/issue43693
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Eric Snow 2021-06-15 16:35:25 -06:00 • committed by GitHub
parent 1d10bf0bb9
commit ac38a9f2df
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12 changed files with 4189 additions and 4214 deletions
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Lib/importlib/_bootstrap_external.py
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@ -358,6 +358,7 @@ _code_type = type(_write_atomic.__code__)
# Python 3.11a1 3453 (add co_fastlocalnames and co_fastlocalkinds)
# Python 3.11a1 3454 (compute cell offsets relative to locals bpo-43693)
# Python 3.11a1 3455 (add MAKE_CELL bpo-43693)
# Python 3.11a1 3456 (interleave cell args bpo-43693)
#
# MAGIC must change whenever the bytecode emitted by the compiler may no
@ -367,7 +368,7 @@ _code_type = type(_write_atomic.__code__)
# Whenever MAGIC_NUMBER is changed, the ranges in the magic_values array
# in PC/launcher.c must also be updated.
MAGIC_NUMBER = (3455).to_bytes(2, 'little') + b'\r\n'
MAGIC_NUMBER = (3456).to_bytes(2, 'little') + b'\r\n'
_RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little') # For import.c
_PYCACHE = '__pycache__'