Ned Deily <n...@python.org> added the comment:
A followup - Ronald asked:
> w.r.t. detection of the clang/llvm version on Apple's system compiler: Is it
> worthwhile to do so?
Now that Xcode 9.3 (for macOS 10.13+) is officially released, I ran a quick
series of test on it and on the most recent Xcode versions for the last several
macOS OS families: 10.12, 10.11, and 10.9 (I didn't have a 10.10 system
available at the moment). Only looking at the most recent supported
Xcode/compiler version for each major release is reasonable since I think most
people follow Apple's strong encouragement to keep software updated and only
use the most recent releases. And I think most people follow Apple's lead in
using their build tools, via Xcode or the command line utilities, rather than a
third-party compiler.
By that measure, it seems clear that (1) there is only one current version that
exhibits the performance degradation, that is the Xcode 9.2 version labeled
Apple LLVM 9.0.0 (clang-900.0.39.2) and (2) that is now only an issue for macOS
10.12 (Sierra) where Xcode 9.2 is (and will likely remain) the most recent
version. For macOS 10.13 (High Sierra), the compiler in the newly released
Xcode 9.3 does not exhibit the problem. And the most recent versions of Xcode
for the tested earlier macOS releases do not either.
BTW, the MacPorts project maintains a handy webpage listing Xcode releases and
compiler versions by macOS release:
https://trac.macports.org/wiki/XcodeVersionInfo
Here are the results. The methodology was to download and build the just
released Python 2.7.15rc1 from source using the default configure options, i.e.
just ./configure, and then run the test program 3 times with it and then three
times with the Apple-provided system /usr/bin/python2.7 as a baseline.
ProductName: Mac OS X
ProductVersion: 10.13.4
BuildVersion: 17E199
2.7.15rc1 (default, Apr 15 2018, 00:22:29)
[GCC 4.2.1 Compatible Apple LLVM 9.1.0 (clang-902.0.39.1)]
1.181971
1.180467
1.173380
2.7.10 (default, Oct 6 2017, 22:29:07)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)]
1.567072
1.587779
1.570056
ProductName: Mac OS X
ProductVersion: 10.12.6
BuildVersion: 16G1314
2.7.15rc1 (default, Apr 15 2018, 00:31:39)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)]
6.290989
6.356802
6.295680
2.7.10 (default, Feb 7 2017, 00:08:15)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.34)]
1.306507
1.312231
1.302826
ProductName: Mac OS X
ProductVersion: 10.11.6
BuildVersion: 15G20015
2.7.15rc1 (default, Apr 15 2018, 00:38:12)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)]
1.846332
1.855483
1.896600
2.7.10 (default, Oct 23 2015, 19:19:21)
[GCC 4.2.1 Compatible Apple LLVM 7.0.0 (clang-700.0.59.5)]
1.453702
1.426298
1.440348
ProductName: Mac OS X
ProductVersion: 10.9.5
BuildVersion: 13F1911
2.7.15rc1 (default, Apr 15 2018, 00:42:08)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.57)]
1.720303
1.712045
1.710216
2.7.5 (default, Mar 9 2014, 22:15:05)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)]
1.681696
1.685704
1.686414
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