[Llvm-bgq-discuss] bgclang r192411-20131010 on vesta/mira (with LTO)

[Hal Finkel]

Hello again,

I've updated our bgclang install on vesta and mira to r192411-20131010.

The primary motivation behind this release is to let you all play with a new feature: link-time optimization (LTO). I consider LTO here to be alpha quality, and I already know of at least one bug (building HACC with LTO and debugging symbols (-g) will crash the link-time optimizer). Nevertheless, the potential performance benefit is significant, and so please feel free to try it and provide feedback. Here's how:

 1. Pass the command-line argument -flto to bgclang when both compiling and linking (you'll also want -O2 or -O3).

 2. If you build using static archives (.a files), you need to construct them using bundled 'ar' utility. bgclang-ar (and equivalently powerpc64-bgq-linux-clang-ar) are provided in the wbin directory for this purpose. If you'd like to view the symbols in these archives, the system 'nm' utility will not help you. Use bgclang-nm (or powerpc64-bgq-linux-clang-nm) from the wbin directory instead.

    If you fail to use the bundled 'ar' utility, and instead use the system 'ar', when you link you'll likely receive an error message like this:
      error adding symbols: Archive has no index; run ranlib to add one

For those maintaining their own installs, RPMs (and SRPMs) are available on the trac page: https://trac.alcf.anl.gov/projects/llvm-bgq

Thanks again,
Hal

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory