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From: "Hartmut Schirmer" <hartmut.schirmer@arcor.de>
To: <tim@hollebeek.com>, "Kevin Lawton" <kevinlawton2001@yahoo.com>
Cc: "Zack Weinberg" <zack@codesourcery.com>,
	"Michael Matz" <matz@suse.de>,
	"Jamie Lokier" <egcs@tantalophile.demon.co.uk>, <gcc@gcc.gnu.org>
References: <20021016004929.GO15067@codesourcery.com> <20021016013810.22926.qmail@web80304.mail.yahoo.com> <20021015191724.A21405@hollebeek.com>
Subject: Re: Request of new __attribute__ for switch statements (elimination of the bounds check)
Date: Wed, 16 Oct 2002 13:27:00 -0000
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> "Tim Hollebeek"  wrote:
> On Tue, Oct 15, 2002 at 06:38:10PM -0700, Kevin Lawton wrote:
> >
> > --- Zack Weinberg <zack@codesourcery.com> wrote:
> >
> > > Sure.  The question is how _soon_ you will be screwed to the point
> > > that the program crashes.  Ideally this happens as soon after the
> > > actual data corruption event as possible.
> >
> [snip]
> >
> > If we wanted to stop people from shooting theirselves
> > in the feet, we wouldn't allow them to use C.  At
> > any rate, sometimes it's even possible to prove the
> > case targets are populated:
> >
> >   switch (a & 0x3) {
>
> then ask for the compiler to understand and DTRT with this syntax,
> instead of some funky attribute.
>
> Sure, recognizing "switch ((expr) & (integral constant 2^n-1))" only
> works for tables that are powers of two, but I suspect that would
> already go quite a ways towards what many people need.

Other nice things to have:
- warn about unreachable case values
- removed unreachable code

gcc need not be perfect on this. Just checking easy available
properties of  the switch value would be a great help.

Hartmut