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bpo-42282: Fold constants inside named expressions #23190

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ncoghlan
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@ncoghlan ncoghlan commented Nov 7, 2020

  • The AST optimiser wasn't descending into named expressions, so
    any constant subexpressions weren't being folded at compile time
  • Remove "default:" clauses inside the AST optimiser code to reduce the
    risk of similar bugs passing unnoticed in future compiler changes

https://bugs.python.org/issue42282

* The AST optimiser wasn't descending into named expressions, so
  any constant subexpressions weren't being folded at compile time
* Remove "default:" clauses inside the AST optimiser code to reduce the
  risk of similar bugs passing unnoticed in future compiler changes
@ncoghlan
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ncoghlan commented Nov 7, 2020

@brandtbucher I noticed this omission while working on PEP 642.

@ncoghlan ncoghlan requested a review from methane November 7, 2020 11:11
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LGTM

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ncoghlan commented Nov 7, 2020

The CI failures were due to one of the switch statements using an int rather than an AST enum type, so the compiler didn't know there were unhandled cases after I dropped the default: clause. I switched it to using cmpop_ty and added the missing cases.

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ncoghlan commented Nov 7, 2020

There was a second set of CI failures due to a regression in binary operator folding (it wasn't clearing divide-by-zero errors), but the failure after that was just a GitHub Actions glitch (I have the tests passing locally now - I hadn't checked that before the first push).

@ncoghlan ncoghlan merged commit 8805a4d into python:master Nov 7, 2020
shihai1991 added a commit to shihai1991/cpython that referenced this pull request Nov 7, 2020
…lots1

* origin/master: (80 commits)
  bpo-42282: Fold constants inside named expressions (pythonGH-23190)
  bpo-41028: Doc: Move switchers to docsbuild-scripts. (pythonGH-20969)
  bpo-42133: update parts of the stdlib to fall back to `__spec__.loader` when `__loader__` is missing (python#22929)
  Remove outdated reference to pywin32 from platform module (pythonGH-22005)
  bpo-41832: PyType_FromModuleAndSpec() now accepts NULL tp_doc (pythonGH-23123)
  Minor grammar edits for the descriptor howto guide (GH-python#23175)
  bpo-42179: Doc/tutorial: Remove mention of __cause__ (pythonGH-23162)
  bpo-26389: Allow passing an exception object in the traceback module (pythonGH-22610)
  bpo-42260: PyConfig_Read() only parses argv once (pythonGH-23168)
  bpo-42260: Add _PyConfig_FromDict() (pythonGH-23167)
  bpo-41877 Check for asert, aseert, assrt in mocks (pythonGH-23165)
  [docs] fix wrongly named AsyncContextDecorator (pythonGH-23164)
  bpo-42262: Add Py_NewRef() and Py_XNewRef() (pythonGH-23152)
  bpo-42266: Handle monkey-patching descriptors in LOAD_ATTR cache (pythonGH-23157)
  bpo-40816 Add AsyncContextDecorator class (pythonGH-20516)
  bpo-42260: Add _PyInterpreterState_SetConfig() (pythonGH-23158)
  Disable peg generator tests when building with PGO (pythonGH-23141)
  bpo-1635741: _sqlite3 uses PyModule_AddObjectRef() (pythonGH-23148)
  bpo-1635741: Fix PyInit_pyexpat() error handling (pythonGH-22489)
  bpo-42260: Main init modify sys.flags in-place (pythonGH-23150)
  ...
adorilson pushed a commit to adorilson/cpython that referenced this pull request Mar 13, 2021
* The AST optimiser wasn't descending into named expressions, so
  any constant subexpressions weren't being folded at compile time
* Remove "default:" clauses inside the AST optimiser code to reduce the
  risk of similar bugs passing unnoticed in future compiler changes
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4 participants