David Daney wrote:
> Maciej W. Rozycki wrote:
>> 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
>>> 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
>>>> 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
>>> 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
>>> 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.
> This seems to be the most sensible option.
> I will try to work up the GCC patch tonight.
This means generic MIPS code (MIPS I) wil have broken atomic
intrinsics when run on modern MIPS machines.