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Date: Fri, 27 Nov 2015 11:25:02 +0200 From: Andy Shevchenko <andy.shevchenko@...il.com> To: yalin wang <yalin.wang2010@...il.com> Cc: Rasmus Villemoes <linux@...musvillemoes.dk>, Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: no-op delay loops On Fri, Nov 27, 2015 at 11:04 AM, yalin wang <yalin.wang2010@...il.com> wrote: >> On Nov 27, 2015, at 16:53, Rasmus Villemoes <linux@...musvillemoes.dk> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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