For the I tried to use profile guided optimizations and after about an hour of compiling (it's a big project), this is what I got:
0 0x10da73b51 __assert_rtn + 144 1 0x10dad99fb ld::tool::OutputFile::addressOf(ld::Internal const&, ld::Fixup const*, ld::Atom const**) + 155 2 0x10dadafaf ld::tool::OutputFile::applyFixUps(ld::Internal&, unsigned long long, ld::Atom const*, unsigned char*) + 1663 3 0x10dae03a5 ld::tool::OutputFile::writeAtoms(ld::Internal&, unsigned char*) + 495 4 0x10dad8e4f ld::tool::OutputFile::writeOutputFile(ld::Internal&) + 779 5 0x10dad3551 ld::tool::OutputFile::write(ld::Internal&) + 149 6 0x10da7481a main + 1028 A linker snapshot was created at: /tmp/libMeldaProductionAudioPluginKernel.dylib-2015-03-15-174847.ld-snapshot ld: Assertion failed: (_mode == modeFinalAddress), function finalAddress, file /SourceCache/ld64/ld64-241.9/src/ld/ld.hpp, line 731.
For the record, on Windows it works, but the build for generating profile guided database doesn't work 100%, but in most cases it does...