This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: Loop unrolling
- To: Martin von Loewis <martin at mira dot isdn dot cs dot tu-berlin dot de>
- Subject: Re: Loop unrolling
- From: Kaz Kylheku <kaz at espresso dot cafe dot net>
- Date: Thu, 4 Jun 1998 04:42:49 -0700 (PDT)
- cc: amylaar at cygnus dot co dot uk, egcs at cygnus dot com
On Wed, 3 Jun 1998, Martin von Loewis wrote:
> > i has automatic storage, and its address is never taken, so the compiler
> > might decide to allocate this object to some 'write-only-memory'.
>
> No, it may not. Modification of i is 'observable behaviour' as per
> [intro.execution]/6. So I want to observe this on the machine in front
> of me. If the compiler optimizes the loop away, I cannot observe it.
> If it would leave the loop, I could observe it, eg. by means of a
> debugger.
What document is this from? I don't recognize it as being part of the
current C standard. Clause 6 of ISO C describes the elements of
the language.
Is that from the C++ DWP? How does it define observable behavior?
Who is the observer?