[issue21122] CPython fails to build modules with LLVM LTO on Mac OS X

[Ned Deily]

Ned Deily added the comment:

Just as an experiment (using the 3.4 branch and the Xcode 5.1 clang), the list of unique symbols not found during the test dlopen in setup.py when using -flto:

 _PyArg_ParseTuple
 _PyArg_ParseTupleAndKeywords
 _PyBaseObject_Type
 _PyBool_Type
 _PyByteArray_Type
 _PyBytes_Type
 _PyCFunction_Type
 _PyExc_AssertionError
 _PyExc_BufferError
 _PyExc_EOFError
 _PyExc_IndexError
 _PyExc_IOError
 _PyExc_KeyError
 _PyExc_LookupError
 _PyExc_MemoryError
 _PyExc_NotImplementedError
 _PyExc_OSError
 _PyExc_OverflowError
 _PyExc_RuntimeError
 _PyExc_TypeError
 _PyExc_ValueError
 _PyModule_Create2
 __Py_NoneStruct

Anyone see a pattern there? 

Do we know if anyone has tried to use LTO with a Python build previously?  I've never tried it myself and there certainly could be ld and/or dyld differences on OS X.  Also, some thought would need to go into and tests developed to see what the performance trade-offs are.  For example, I could imagine that LTO might be have more impact if the standard library extension modules were statically linked, e.g. via Modules/Setup*.  And there are at least three separate current build configurations to consider on OS X: unshared, --enable-shared, --enable-framework.  One would need to look at things like what effect these all have on memory and shared memory footprints as well as cpu resources and real time, with and without LTO and/or other optimizations.  It certainly would be an interesting project for someone with the interest and time.

Potentially supporting LTO seems to me to be more of a feature than a bug so I think should be considered a 3.5 issue, at least initially.

----------
components: +Build -Extension Modules
nosy: +brett.cannon, ned.deily, ronaldoussoren
title: CPython fails to build modules with LLVM LTO on Mac OS -> CPython fails to build modules with LLVM LTO on Mac OS X
type: compile error -> 
versions: +Python 3.5 -Python 3.4

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<http://bugs.python.org/issue21122>
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