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Re: forcing the compiler to reload from memory with c++0x

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Dmitriy Vyukov wrote:
> 
> On 2 фев, 16:45, Alexander Terekhov <terek...@web.de> wrote:
> > Dmitriy Vyukov wrote:
> >
> > [...]
> >
> > > Alexander, you are inconsistent here.
> > > Why can't printf() output go to nowhere on its own in the first place?
> > > Abstract output is basically the same as abstract memory accesses on
> > > abstract machine, no? And what is that abstract "standard output"
> > > device or file? If we go down to that formal hair-splitting level,
> > > then I believe we won't conclude anything useful. For example, is
> > > there dynamic memory? Well, I'm not sure. Is zero bytes of dynamic
> > > memory still dynamic memory? I guess it's nothing.
> > > If you want, there is always an implementation. And it's possible to
> > > loosely define such group of implementations as "sane industrial
> > > implementations". And in that context volatile access indeed means the
> > > most natural memory access instruction in generated code (MOV, LD or
> > > whatever). And that is observable. And that is what Anthony meant, I
> > > think.
> >
> > Stop abstracting into absurdity. "MOV, LD or whatever" are not
> > externally observable in the case of
> >
> > int main() {
> > Â  volatile int i;
> > Â  // volatile write = has no observable effect
> > Â  i = 1;
> > Â  // volatile read = has no observable effect
> > Â  int n = i;
> >
> > }
> >
> > because the above program is the same as
> >
> > int main() {
> >
> > }
> >
> > for any reasonable observer of the outcome.
> 
> I can observe it in disassembler or by timing the program. A compiler
> can't do any assumptions on how I'm going to observe it.

Can you really point out a chapter and verse guaranteeing that int
main() {} is faster than int main() { volatile int i = 1; int n = i; }?
As I told: disassembler is irrelevant.

regards,
alexander.

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Re: forcing the compiler to reload from memory with c++0x Alexander Terekhov <terekhov@web.de> - 2011-02-01 14:17 +0100
  Re: forcing the compiler to reload from memory with c++0x Alexander Terekhov <terekhov@web.de> - 2011-02-02 14:45 +0100
    Re: forcing the compiler to reload from memory with c++0x Dmitriy Vyukov <dvyukov@gmail.com> - 2011-02-02 07:02 -0800
      Re: forcing the compiler to reload from memory with c++0x Alexander Terekhov <terekhov@web.de> - 2011-02-02 16:33 +0100
  Re: forcing the compiler to reload from memory with c++0x Alexander Terekhov <terekhov@web.de> - 2011-02-01 16:32 +0100
    Re: forcing the compiler to reload from memory with c++0x Alexander Terekhov <terekhov@web.de> - 2011-02-02 12:13 +0100
      Re: forcing the compiler to reload from memory with c++0x Dmitriy Vyukov <dvyukov@gmail.com> - 2011-02-02 04:54 -0800
    Re: forcing the compiler to reload from memory with c++0x Dmitriy Vyukov <dvyukov@gmail.com> - 2011-02-01 21:02 -0800
    Re: forcing the compiler to reload from memory with c++0x Joshua Maurice <joshuamaurice@gmail.com> - 2011-02-01 15:19 -0800
  Re: forcing the compiler to reload from memory with c++0x Anthony Williams <anthony.ajw@gmail.com> - 2011-02-01 13:51 +0000

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