• Austin Seipp's avatar
    Refactor GCTDecl.h, and mitigate #7602 a bit · 28b031c5
    Austin Seipp authored
    
    
    This basically cleans a lot of GCTDecl up - I found it quite hard to
    read and a bit confusing. The changes are mostly cosmetic: better
    delineation between the alternative cases and light touchups, and tries
    to make every branch as consistent as possible.
    
    However, this patch does have one significant effect: it will ensure
    that any LLVM-based compilers will use __thread if they support it.
    Before, they would simply always use pthread_getspecific and
    pthread_setspecific, which are almost surely even *more* inefficient.
    
    The details are a bit too long and boring to go into here; see #7602.
    After talking with Simon, we decided to play it safe - __thread can at
    least be optimized by future clang releases even further on OS X if they
    choose, and it's safer until we can investigate the pthread
    implementation further on Mavericks.
    
    For Linux, the story isn't so bleak if you use Clang (for whatever
    reason) - Linux directly writes to `%fs` for __thread slots (while OS X
    will perform a load followed by an indirect call.) So it should still be
    fairly competitive, speed-wise.
    Signed-off-by: default avatarAustin Seipp <austin@well-typed.com>
    28b031c5
GCTDecl.h 5.14 KB