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 not. > > 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 R10000_LLSC_WAR. > 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. Maciej
