Re: [avr-chat] Missed Optimisation ?

[Michael Hennebry]

On Sat, 5 Mar 2011, Graham Davies wrote:

> Michael Hennebry wrote:
>
> > > [this bit is me writing] ...  When debugging a program, I like to be
> > > able to follow along the logic I expressed in the source code, so
> > > I would not be happy if it had changed beyond all recognition ...
>
> > This is an argument against optimization generally,
> > not specifically the kind under discussion.
>
> No, it isn't.  It's an argument only against optimization that prevents me 
> from "... follow[ing] along the logic I expressed in the source code" and 
> that "change[s the program flow] beyond all recognition".  I think in your 
> eagerness to disagree with me you are ignoring what I actually write.

Your complaint is precisely that of the -O0 crowd on AVR-freaks.
It applies to neither of the optimizations under discussion.

> > ... the as-if rule applies even to volatiles when the
> > compiler has enough information to use it.
>
> No, it doesn't, for reasons that have been adequately explained, mainly 
> conformance to the standard.
>
> > Except for atomicity, the semantics are the same ...
>
> The C language is unaware of atomicity.  The semantics are different in the 
> presence of read side-effects.

Which are absent both in this case and
the one that started the discussion.

--
Michael   address@hidden
"Pessimist: The glass is half empty.
Optimist:   The glass is half full.
Engineer:   The glass is twice as big as it needs to be."