On Wed, 19 Sep 2007, David Daney wrote:
> Currently, I (and thus GCC 4.3) am assuming that Linux emulates 'll', 'sc' and
> 'sync', If sync is not emulated, we would need to adjust the code generation
> so that it is not emitted on ISAs that don't support it.
While adding "sync" is trivial enough I may have a patch ready by
tomorrow, that will not change the existing userbase and I am not entirely
sure forcing such a hasty upgrade on people would be reasonable; likely
> > A workaround for a CPU erratum fits within the "-mfix-*" option family quite
> > well though.
> Do we know which CPUs require branch-likely?
The R10000; there is a note about it in <asm-mips/war.h> at
> I would be inclined to agree with adding a "-mfix-??" option.
> The only place where GCC's __sync_* primitives are generated without
> explicitly writing them into your program is in GCJ compiled java code that
> uses volatile fields.
> If we expect the use of the __sync_* primitives on CPUs that require
> branch-likely to be rare, we shouldn't penalize those trying to rid themselves
> of the beasts.
Another option is to depend on the setting of -mbranch-likely. By
default it is on only for the processors which implement it and do not
discourage it, i.e. these of the MIPS II, MIPS III and MIPS IV ISAs.