Memory barriers for PPC

[Andrew Haley]

Gary Benson wrote:
> Andrew Haley wrote:
>> +#ifdef __PPC
> 
> Can you make this "#ifdef PPC"?
> 
>> +#define READ_MEM_BARRIER __asm __volatile ("":::"memory")
>> +#define WRITE_MEM_BARRIER __asm __volatile ("":::"memory")
> 
> What's the difference between this and __sync_synchronize()?

This one is just a compiler memory barrier: it stops the compiler from
re-ordering reads or writes.  It doesn't generate any actual code.
__sync_synchronize() is much more heavyweight: it generates a full
memory barrier across all processors in an SMP system.

Andrew.