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RE: criteria.html open issues
- To: "Joern Rennecke" <amylaar at redhat dot com>,"Zack Weinberg" <zackw at Stanford dot EDU>
- Subject: RE: criteria.html open issues
- From: <bobbymcn2002 at yahoo dot com>
- Date: Fri, 15 Jun 2001 09:45:43 -0500
- Cc: <dewar at gnat dot com>,<acahalan at cs dot uml dot edu>,<gcc at gcc dot gnu dot org>
What do you think about -O3?
-----Original Message-----
From: gcc-owner@gcc.gnu.org [mailto:gcc-owner@gcc.gnu.org]On Behalf Of
Joern Rennecke
Sent: Friday, June 15, 2001 9:23 AM
To: Zack Weinberg
Cc: dewar@gnat.com; acahalan@cs.uml.edu; gcc@gcc.gnu.org
Subject: Re: criteria.html open issues
> I didn't mean to imply that there shouldn't be defaults, only that
> categorizing optimizations by _levels_ isn't useful. Keep -O and/or
> -O2 by all means, but let's not have -O3, -O4, ... -O9 the way some
> vendor compilers do. I might even suggest eliminating -O1 (make -O
> synonymous with -O2). It's never been clear what the difference is in
> terms of the tradeoffs I mentioned.
That is because -O1 has also another, even more important goal.
It provides reasonably fast compilation with optimization while
still generating code that is fairly easy to debug.
-O2 enables a number of more agressive optimizations that can
leave you completely lost, as instructions are out of order, or
split and / or combined with instructions from other statements, and
operate on different data with different lifetimes as in the source.
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