This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: type based aliasing again - meaning of "undefined"
- To: Ross Morgan-Linial <rmorgan at jetcity dot com>
- Subject: Re: type based aliasing again - meaning of "undefined"
- From: David Edelsohn <dje at watson dot ibm dot com>
- Date: Wed, 15 Sep 1999 18:16:13 -0400
- Cc: gcc at gcc dot gnu dot org
I, personally, have been using "undefined" in the colloquial
sense, not as in the C standard. We are arguing that behavior which is
implementation-dependent allows the compiler as much lattitude as it cares
to use.
One line of reasoning is that if the compiler can behave the way
we have implemented and by doing that it produces better optimized code,
then that should be the default behavior. Only non-conforming code which
depends upon implementation-dependent behavior is broken, so users should
be required to tell the compiler that the source code is non-conforming
explicitly.
The further argument is that if we bend on the default behavior
for this implementation-defined case, then we will be forced to treat any
change in compiler behavior this way and never add any additional default
optimizations. This latter argument is based on conjecture, not fact.
David