Ned Deily <[email protected]> added the comment:
> Clang 6.0 doesn't support LTO and PGO?
No, it appears not. And it's not an oversight that we don't use the these
options.
As Łukasz points out, for the current macOS installer variants we supply are
designed to run on all Mac systems from macOS 10.9 on. To accomplish that
safely, we build the Python binaries on macOS 10.9 system to ensure they will
be compatible, in other words, we build on the oldest system support and rely
on upward compatibility when running on newer systems. The other approach is to
build on the newest systems available after adding runtime checks throughout
the C code to test for the presence of newer features (i.e. runtime calls that
have been added in an operating system release newer than the oldest one
support). While this ("weaklinking") can be a viable option, it's a lot more
work to implement initially and then keep updated over each o/s release to
avoid segfaults and other failures when users on older systems try to use newer
features. Eventually we would like to fully support weaklinking so that we
could provide one installer variant for all supported o/s versions that has all
features available at each o/s version, it's not a high priority item at the
moment (for example, supporting the upcoming 11.0 Big Sur with Apple Silicon
is) and the current practices have worked well for many years.
Keep in mind that the main goal of the python.org macOS installers is to
provide a single installable binary that works correctly on a wide-range of
macOS releases and hardware. What we provide today works on all Macs capable
of running macOS 10.9 or later. In particular, it is *not* a goal to provide
the most optimized configuration for a particular system. In general, consider
the range of hardware and operating system releases, that's not easy to do. I
believe that the intended users for the python.org macOS pythons are (1)
beginners (like in a teaching environment where ease of deployment and
uniformity is key) and (2) third-party Mac applications developers who want an
embeddable Python that will allow their applications to work on multiple levels
of macOS. If you are looking for the highest performance for a particular use,
like benchmarking, you should look elsewhere - like one of the third-party
distributors who specialize in numeric Pythons - or build it yourself on your
own system.
So, thanks for the suggestion but we won't be using it now. Sometime in the
future, if and when we support weaklinking and/or use newer toolchains across
the board we will look at adding and other optimizations.
----------
resolution: -> not a bug
stage: patch review -> resolved
status: open -> closed
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<https://bugs.python.org/issue41181>
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