From: Ralph Loader <suckfish@ihug.co.nz>
To: Kevin Lawton <kevinlawton2001@yahoo.com>
Cc: gcc@gcc.gnu.org
Subject: Re: Request of new __attribute__ for switch statements (elimination of the bounds check)
Date: Sat, 12 Oct 2002 04:18:00 -0000 [thread overview]
Message-ID: <1034388936.18375.6.camel@suckfish> (raw)
In-Reply-To: <20021011190521.57024.qmail@web80309.mail.yahoo.com>
A more general feature would be a __builtin_not_reached() that informs
the compiler that a particular code path will never be executed and can
be removed at compile time.
Then the example below could be achieved by adding
default: __builtin_not_reached();
to the switch statement.
Ralph.
On Sat, 2002-10-12 at 08:05, Kevin Lawton wrote:
> All,
>
> For implementation of machine simulators, it's quite common
> to have completely populated switch statements on byte values:
>
> unsigned char byte;
>
> switch (byte) {
> case 0:
> case 1:
> ...
> case 255:
> }
>
> But I don't know of any way to tell the compiler to _not_ generate
> a bounds check on the switch variable 'byte'. All of the target
> space is covered.
>
> To solve this, could we add an attribute to switch?
>
> switch (byte) __attribute (( no-bounds-check )) {
> ...
> }
>
> This would also be useful for cases, where it is known that
> all possible targets are covered with case statements, yet
> they don't appear to be fully populated to the compiler
> (it's known only to the programmer that the logic prevents
> certain values).
>
> Thanks,
> -Kevin
>
> __________________________________________________
> Do you Yahoo!?
> New DSL Internet Access from SBC & Yahoo!
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next prev parent reply other threads:[~2002-10-12 2:15 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-10-11 13:20 Kevin Lawton
2002-10-12 4:18 ` Ralph Loader [this message]
2002-10-14 8:31 ` Richard Zidlicky
2002-10-14 10:09 ` Dale Johannesen
2002-10-14 21:11 ` Jamie Lokier
2002-10-14 22:01 ` Zack Weinberg
2002-10-15 8:12 ` Michael Matz
2002-10-15 19:15 ` Zack Weinberg
2002-10-15 19:18 ` Dale Johannesen
2002-10-16 14:07 ` Richard Henderson
2002-10-15 21:16 ` Kevin Lawton
2002-10-15 23:40 ` Tim Hollebeek
2002-10-16 3:40 ` Michael Matz
2002-10-16 13:38 ` Tim Hollebeek
2002-10-16 14:23 ` Michael Matz
2002-10-16 13:27 ` Hartmut Schirmer
2002-10-16 3:25 ` Joseph S. Myers
2002-10-16 7:57 ` Fergus Henderson
2002-10-16 11:19 ` Daniel Jacobowitz
2002-10-15 7:54 ` Michael Matz
2002-10-15 13:29 ` Jamie Lokier
2002-10-15 14:06 ` Kevin Lawton
2002-10-15 15:32 ` Jamie Lokier
2002-10-15 14:28 ` Michael Matz
2002-10-15 15:19 ` Jamie Lokier
2002-10-11 13:22 Robert Dewar
2002-10-11 15:12 ` Kevin Lawton
2002-10-12 10:43 ` Alexandre Oliva
2002-10-15 6:43 Mattias Engdegård
2002-10-15 22:40 Robert Dewar
2002-10-15 23:57 ` Zack Weinberg
2002-10-16 9:19 Robert Dewar
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