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Date: Tue, 3 Mar 2009 10:17:30 -0300 From: Thiago Galesi <thiagogalesi@...il.com> To: Will Newton <will.newton@...il.com> Cc: Pekka Enberg <penberg@...helsinki.fi>, akpm@...ux-foundation.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] crc32: remove useless __pure modifier from functions > > Did you see any change in size of your kernel with this annotation? It > didn't seem to have any effect as far as I could tell. No, because I didn't test it with the kernel. Anyway, probably size won't change a lot. What the compiler does is: if (you're saying) it's a pure function, and it has been called previously with the same parameters, the return value is identical, hence, the compiler doesn't need to call the function again. Here's the test I did http://duskblue.org/pure_test.tar.gz Pretty straighforward, but you have to 'make CFLAGS=-O1' to make the optimization work. > > There are a number of functions in lib/ code that could be marked > __pure or __attribute_const__ but I'm not sure if it's worth the > effort, for my compiler (gcc 4.2) at least. > What const does is similar: it indicates that the function will not change parameters marked with __const, so it will not need to reload them after the function is called. -- - Thiago Galesi -- 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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