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Re: Disable optimizations on one function (was: 'pragma optimize' ...)
- From: Andrew Haley <aph at redhat dot com>
- To: noloader at gmail dot com
- Cc: "gcc-help at gcc dot gnu dot org" <gcc-help at gcc dot gnu dot org>
- Date: Thu, 16 Jul 2015 10:59:04 +0100
- Subject: Re: Disable optimizations on one function (was: 'pragma optimize' ...)
- Authentication-results: sourceware.org; auth=none
- References: <CAH8yC8kU9JXSyFHrW9neztA4btnjXuxv+m3KyPWp84F=Y1Rv7A at mail dot gmail dot com> <55A7729F dot 2090604 at redhat dot com> <CAH8yC8nh0KreX37vExaXY-dNTM0_FZGHCno8oL+DU+7P-cwXwA at mail dot gmail dot com>
On 16/07/15 10:40, Jeffrey Walton wrote:
>>> Many folks try and cast ptr to volatile, but that's an abuse because
>>> GCC considers volatile something for memory mapped hardware. Volatile
>>> should not be used in an attempt to tame the optimizer.
>>
>> GCC does not consider volatile to be something for memory mapped
>> hardware.
>
> OK, this appears to be creating a moving definition (or the definition
> has changed since I took note of it). I took the last definition from
> Ian Lance Taylor. See http://www.airs.com/blog/archives/154 and, for
> example, https://gcc.gnu.org/ml/gcc-help/2012-03/msg00257.html.
Well, reluctant as I am to argue with Ian, the definition of volatile
I used is a direct quote from the standard. There are problems with
volatile as defined, it's true: for example, nowhere is it specified
exactly what constitutes a memory access. And Ian is quite right to
say that the standard doesn't guarantee that a pointer-to-volatile
should be handled as though it pointed to a volatile object. But in
this case, with GCC, I think it's fine.
Andrew.