graphlab hits LLVM bug on older 64-bit Mac about powergraph HOT 7 CLOSED

Following up:

• I uninstalled Xcode (4.6.3 btw) and reinstalled it, to no avail. Same for the command-line tools.
• I downloaded MacCPUID from Intel and found that my processor is specifically an Intel Core2 Duo P8800, which (as the llvm link would suggest) indeed does not have SSE 4.2 support.

from powergraph.

Hi Daniel,
Would you mind trying to configure using the following flag:
./configure -D HAS_CRC32:BOOL=false
And then recompile.
Let us know if this works for you.

from powergraph.

It worked! (For the graph-analytics package.)

Thanks!

from powergraph.

Is it possible to prevent this error on MAC by adding a default -D HAS_CRC32:BOOL=false to any MAC compilation?

from powergraph.

Hmm... It is not exactly a Mac bug, but is more of an LLVM issue in certain versions of LLVM. Alternatively, I am happy to completely disable the CRC32 check. I am only using it one place as a hash function where it provides a small speedup. But it is most definitely not necessary.

Also, I am not sure why this line in CMakeLists should succeed.

check_cxx_source_compiles("int main(int argc, char** argv) { __builtin_ia32_crc32di(0,0);}" HAS_CRC32)

while when that fails when it is actually used. (perhaps it got optimized away?)

from powergraph.

@ylow / @dbickson: the reason why CMake is succeeding when it shouldn't be is because clang is optimizing away __builtin_ia32_crc32di before it gets to the Cannot select: intrinsic %llvm.x86.sse42.crc32.64.64 error. A simple way to make sure it gets compiled is to change the check to:

check_cxx_source_compiles("int main(int argc, char** argv) { return __builtin_ia32_crc32di(0,0); }" HAS_CRC32)

According to the llvm bug report about this, the proper way to do this is to not use the intrinsic, but use a wrapper function defined in smmintrin.h, as in:

#include <smmintrin.h>

int main(int argc, char** argv) { return _mm_crc32_u64(0,0); }

Finally, it appears that at least on my mac that support sse4.2, setting clang -mtune=native doesn't actually appear to enable sse 4.2. In order to get that snippet above to compile, I need to do clang -msse4.2 crc.cc. @ylow: it seems you removed setting this flag in 627d587, would it be alright to re-enable it?

from powergraph.

Aha. cool. Thanks for looking this up. I will reenable the flag.

from powergraph.