[New-bugs-announce] [issue45115] Windows: enable compiler optimizations when building Python in debug mode

STINNER Victor report at bugs.python.org
Mon Sep 6 11:21:42 EDT 2021

New submission from STINNER Victor <vstinner at python.org>:

The Visual Studio project of Python, PCBuild\ directory, disables compiler optimizations when Python is built in debug mode. It seems to be the default in Visual Studio.

Disabling compiler optimizations cause two kinds of issues:

* It increases the stack memory: tests using a deep call stack are more likely to crash (test_pickle, test_marshal, test_exceptions).

* Running the Python test suite take 19 min 41 sec instead of 12 min 19 sec on Windows x64: 1.6x slower. Because of that, we cannot use a debug build in the GitHub Action pre-commit CI, and we miss bugs which are catched "too late", in Windows buildbots. See my latest attempt to use a debug build in GitHub Actions: https://github.com/python/cpython/pull/24914

Example of test_marshal:

        # The max stack depth should match the value in Python/marshal.c.
        # BUG: https://bugs.python.org/issue33720
        # Windows always limits the maximum depth on release and debug builds
        #if os.name == 'nt' and hasattr(sys, 'gettotalrefcount'):
        if os.name == 'nt':
            MAX_MARSHAL_STACK_DEPTH = 1000
            MAX_MARSHAL_STACK_DEPTH = 2000

I propose to only change the compiler options for the pythoncore project which builds most important files for the Python "core". See attached PR.

components: Windows
messages: 401141
nosy: paul.moore, steve.dower, tim.golden, vstinner, zach.ware
priority: normal
severity: normal
status: open
title: Windows: enable compiler optimizations when building Python in debug mode
versions: Python 3.11

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