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| From | yalin wang <yalin.wang2010@gmail.com> |
| Newsgroups | linux.kernel |
| Subject | Re: no-op delay loops |
| Date | Fri, 27 Nov 2015 10:10:03 +0100 |
| Message-ID | <qzncv-Rf-15@gated-at.bofh.it> (permalink) |
| References | <qzn2P-yf-23@gated-at.bofh.it> |
| X-Original-To | Rasmus Villemoes <linux@rasmusvillemoes.dk> |
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| X-Original-Cc | Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org, linux-kernel@vger.kernel.org |
| X-Original-Date | Fri, 27 Nov 2015 17:04:43 +0800 |
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> On Nov 27, 2015, at 16:53, Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote: > > Hi, > > 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 . Thanks -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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no-op delay loops Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2015-11-27 10:00 +0100
Re: no-op delay loops yalin wang <yalin.wang2010@gmail.com> - 2015-11-27 10:10 +0100
Re: no-op delay loops Andy Shevchenko <andy.shevchenko@gmail.com> - 2015-11-27 10:30 +0100
Re: no-op delay loops Arnd Bergmann <arnd@arndb.de> - 2015-11-27 12:20 +0100
Re: no-op delay loops Ralf Baechle <ralf@linux-mips.org> - 2015-11-27 12:50 +0100
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