On Mon, 2013-09-16 at 13:38 +0930, Rusty Russell wrote: > Predates git, does anyone remember the rationale? > > ie: > int test_bit(int nr, const volatile unsigned long *addr) > > I noticed because gcc failed to elimiate some code in a patch I was > playing with. > > I'm nervous about subtle bugs involved in ripping it out, even if noone > knows why. Should I add __test_bit()?
It seems to me that if you do b = *ptr & 0xf; c = b << 2; if (test_bit(1, ptr)) the compiler could optimize away the memory access on ptr without the volatile. We'd have to add a lot of mb(). Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/