From: Zack Weinberg <zack@codesourcery.com>
To: Chris Lattner <sabre@nondot.org>
Cc: Tim Hollebeek <tim@hollebeek.com>, gcc@gcc.gnu.org
Subject: Re: pure and const functions
Date: Fri, 30 Aug 2002 23:02:00 -0000 [thread overview]
Message-ID: <20020831060218.GG321@codesourcery.com> (raw)
In-Reply-To: <Pine.LNX.4.30.0204261254150.3330-100000@nondot.org>
On Fri, Apr 26, 2002 at 12:55:51PM -0500, Chris Lattner wrote:
> On Fri, 26 Apr 2002, Zack Weinberg wrote:
> > > Sure, but are there any good examples of a function that would be _useful_
> > > to be marked as pure or const, but which might not return?
> >
> > The examples being kicked around earlier were of routines that were
> > pure except for assertions to enforce data structure integrity. We
> > would like the compiler to optimize on the basis that the data
> > structure is correct and therefore the pure function will always
> > return.
>
> Ok, now I'm more confused than before. :) When optimizing, do you
> consider it ok for the compiler to drop the assertions in a pure function,
> if it decides to elide the call to the function?
Yes. Generally this comes up in code of the form
if (pure_function_which_contains_assertions (structure)
&& expression_which_would_be_provably_false_if_it_had_been_written_first)
{
huge block of code which does something with structure
}
where 'predicate' contains some assertions. We want GCC to realize
that the entire block is dead code. Losing the assertions is a minor
price to pay.
zw
next prev parent reply other threads:[~2002-08-30 23:02 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-04-26 10:17 Chris Lattner
2002-04-26 10:21 ` Kris Warkentin
2002-04-26 10:30 ` Chris Lattner
2002-04-26 10:34 ` Magnus Fromreide
2002-04-26 10:35 ` Chris Lattner
2002-04-26 10:59 ` Magnus Fromreide
2002-04-26 11:03 ` Chris Lattner
2002-04-26 11:27 ` Magnus Fromreide
2002-04-26 12:49 ` Russ Allbery
2002-04-26 10:36 ` Kris Warkentin
2002-04-26 10:46 ` Chris Lattner
2002-04-26 10:26 ` Tim Hollebeek
2002-04-26 10:30 ` Chris Lattner
2002-04-26 10:56 ` Zack Weinberg
2002-04-26 11:01 ` Chris Lattner
2002-08-30 23:02 ` Zack Weinberg [this message]
2002-04-26 10:56 ` Tony Finch
2002-04-26 12:11 ` Mark Mitchell
-- strict thread matches above, loose matches on Subject: below --
2002-04-29 17:25 John Wehle
2002-04-29 9:29 Robert Dewar
2002-04-29 9:34 ` Chris Lattner
2002-04-29 8:30 Robert Dewar
2002-04-29 8:57 ` Chris Lattner
2002-04-29 8:30 Chris Lattner
2002-04-29 9:23 ` Daniel Berlin
2002-04-29 9:52 ` Chris Lattner
2002-04-29 9:58 ` Mark Dettinger
2002-04-29 5:18 Robert Dewar
2002-04-29 5:44 ` Mark Dettinger
2002-04-29 3:59 Mark Dettinger
2002-04-26 5:16 Mark Dettinger
2002-04-26 11:20 ` Joseph S. Myers
2002-04-26 12:59 ` Jakub Jelinek
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