[Distutils] special compiler options for only one file

[Andrew Dalke]

Hi all,

  I have a Python extension which uses CPU-specific features,
if available. This is done through a run-time check. If the
hardware supports the POPCNT instruction then it selects one
implementation of my inner loop, if SSSE3 is available then
it selects another, otherwise it falls back to generic versions
of my performance critical kernel. (Some 95%+ of the time is
spent in this kernel.)

Unfortunately, there's a failure mode I didn't expect. I
use -mssse3 and -O3 to compile all of the C code, even though
only one file needs that -mssse3 option.

As a result, the other files are compiled with the expectation
that SSSE3 will exist. This causes a segfault for the line

     start_target_popcount = (int)(query_popcount * threshold);

because the compiler used fisttpl, which is an SSSE-3 instruction.
After all, I told it to assume that ssse3 exists.

The Debian packager for my package recently ran into this problem,
because the test machine has a gcc which understands -mssse3 but
the machine itself has an older CPU without those instructions.

I'm trying to come up with a solution that can be automated for
the Debian distribution. I want a solution where the same binary
can work on older machines and on newer ones

Ideally I would like to say that only one file is compiled
with the -mssse3 option. Since my selector code isn't part of this
file, SSSE-3 code will never be executed unless the CPU supports is.

However, I can't figure out any way to tell distutils that
a set of compiler options are specific to a single file.

Is that even possible?

Cheers,

				Andrew
				dalke at dalkescientific.com