[Python-Dev] Compiler for the Mac OS X version of Python 3.4

Ned Deily nad at acm.org
Sat Sep 14 22:32:04 CEST 2013

In article <70C99F87-E9A5-4838-A1E9-4739FBF2E6A5 at gmail.com>,
 Raymond Hettinger <raymond.hettinger at gmail.com> wrote:
> I was exercising the alpha two release of 3.4 and noticed that
> it is still being built under GCC 4.2.1.  
> Is there any reason we have to use an old compiler?

Yes, kinda.  It's because the 64-bit/32-bit installer we supply is 
designed to run on multiple versions of OS X: 10.6 (Snow Leopard), 10.7, 
10.8, and the upcoming 10.9.  The safest way to ensure that the bits 
produced (executables, shared libs, and .so bundles) are linked with 
compatible versions of system shared libraries and frameworks is to 
build on the lowest supported system, 10.6, or - carefully - with a 10.6 
SDK on a newer system.  The standard compiler in the Apple Developer 
Tools for 10.6 is gcc 4.2.  Clang was very immature at that point.  The 
most recent Developer Tools for 10.8 and 10.7 systems, Xcode 4.6.x, have 
a mature clang but do not provide a 10.6 SDK.  Even with using an SDK, 
it's still possible to end up inadvertently linking with the wrong 
versions of system libraries.  We have been burned by that in the past.

> I would like to see it built under the latest version of Clang
> (like the other tools on the Mac) or under GCC 4.8.1.
> I've better using the latter for many months.  It works great
> and produces *much* better code (in terms of readability
> for those of us who look at assembly output and in terms
> of speed (approx 20-25% better for cpu bound code)).
> I'm wondering whether is some issue that forces us to use
> GCC 4.2.1 or whether that is just an artifact of continuing
> to do what we've always been doing.

I'd like to move to Apple's latest clang, as well.  (Apple is dropping 
gcc totally from the next release of Xcode.)  There are a couple of 
approaches that may work and still reliably support multiple versions of 
OS X.  Investigating this is on my list of things to do prior to the 
next alpha.  I've opened a bug tracker issue for this (Issue19019).

 Ned Deily,
 nad at acm.org

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