On Fri, Nov 27, 2015 at 11:04 AM, yalin wang <yalin.wang2010@xxxxxxxxx> wrote: >> On Nov 27, 2015, at 16:53, Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> wrote: >> It seems that gcc happily compiles >> >> for (i = 0; i < 1000000000; ++i) ; >> >> into simply >> >> i = 1000000000; >> >> (which is then usually eliminated as a dead store). At least at -O2, and >> when i is not declared volatile. So it would seem that the loops at >> >> arch/mips/pci/pci-rt2880.c:235 >> arch/mips/pmcs-msp71xx/msp_setup.c:80 >> arch/mips/sni/reset.c:35 >> >> actually don't do anything. (In the middle one, i is 'register', but >> that doesn't change anything.) Is mips compiled with some special flags >> that would make gcc actually emit code for the above? >> > you can try to declare i as volatile int i; > may gcc will not optimize it . Might be, but Rasmus as I can see asked about *existing* code. -- With Best Regards, Andy Shevchenko
