Re: __sync_lock_test_and_set on ARM

["Phil Endecott" <spam_from_gcc_help_2 at chezphil dot org>]

David Daney wrote:
> Andrew Haley wrote:
> > Phil Endecott writes:
> >  > Andrew Haley wrote:
> >  > > this stuff really should be done by the compiler. 
> >  > 
> >  > Yes.  I've filed a bug asking for a __sync_lock_test_and_set builtin:
> >  > 
> >  > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33413
> >
> > Surer, but the problem is that for most of the things we want to do
> > (lightweight locks, for example) __sync_lock_test_and_set() doesn't
> > really do what we need: we need compare_and_swap().  That's why the
> > kernel helper is so useful, because it's robust even if we are on
> > pre-ARMv6 hardware.
>
> Probably the enhancement request should be expanded to include *all* the 
> __sync_* atomic memory primitives  which includes compare_and_swap.

No, because none of the others can be implemented without kernel 
support or other magic.

Gcc should implement those __sync primitives that the hardware 
provides, and perhaps those that cane be synthesized directly from 
them, but it shouldn't try to provide more.


Phil.