Work around a GCC behavior with hardware transactional memory built-ins.
GCC doesn't treat the PowerPC transactional built-ins as compiler
barriers, moving instructions past the transaction boundaries and
altering their atomicity.
__lll_trylock_elision sets the adapt_count variable too
aggressively, and incorrectly on persistent aborts. Taking
a cue from s390, adapt_count is only updated if the lock
is locked, or a persistent failure occurs.
In addition, the abort codes have been renumbered and
refactored for clarity. As it stands, glibc only cares
if the abort is persistent or not.
All aborts are now persistent, excepting a busy lock. This
includes changing _ABORT_NESTED_TRYLOCK into a persistent
abort.
* sysdeps/unix/sysv/linux/powerpc/elision-trylock.c
(__lll_trylock_elision): Fix setting of adapt_count.
* sysdeps/unix/sysv/linux/powerpc/htm.h
(_ABORT_PERSISTENT): Define to clarify persistent aborts.
(_ABORT_NESTED_TRYLOCK): Renumber, and make persistent.
(_ABORT_SYSCALL): Renumber, and clarify definition.
(_ABORT_LOCK_BUSY): Renumber, make non-persistent.
This patch adds support for lock elision using ISA 2.07 hardware
transactional memory instructions for pthread_mutex primitives.
Similar to s390 version, the for elision logic defined in
'force-elision.h' is only enabled if ENABLE_LOCK_ELISION is defined.
Also, the lock elision code should be able to be built even with
a compiler that does not provide HTM support with builtins.
However I have noted the performance is sub-optimal due scheduling
pressures.
