From: "Joseph S. Myers" <jsm@polyomino.org.uk>
To: Richard Kenner <kenner@vlsi1.ultra.nyu.edu>
Cc: gcc@gcc.gnu.org
Subject: Re: SRA problem with uninitialzed fields
Date: Fri, 24 Sep 2004 18:50:00 -0000 [thread overview]
Message-ID: <Pine.LNX.4.61.0409241607300.10667@digraph.polyomino.org.uk> (raw)
In-Reply-To: <10409241604.AA01618@vlsi1.ultra.nyu.edu>
On Fri, 24 Sep 2004, Richard Kenner wrote:
> But what about the C test case I sent? Isn't that valid C++ also and
> wouldn't it have the problem I mentioned if that hook is false?
C++ bit-fields have a restricted width representation but their type is
the underlying type rather than a special restricted width type. (Thus
e.g. with 64-bit long, 32-bit int, unsigned long:40 + unsigned long:40 has
type unsigned long:40 in C but type unsigned long in C++.) A proper
implementation that keeps the types those that accord with the language
semantics would be for the GIMPLE generated to include explicit mask
operations for assignments to bit-fields. If it doesn't represent that
assignment to a bit-field from the same type may change the value, then
there are likely to be problems. At one point there were, but I don't see
such problems at present in some quick tests.
--
Joseph S. Myers http://www.srcf.ucam.org/~jsm28/gcc/
http://www.srcf.ucam.org/~jsm28/gcc/#c90status - status of C90 for GCC 4.0
jsm@polyomino.org.uk (personal mail)
jsm28@gcc.gnu.org (Bugzilla assignments and CCs)
next prev parent reply other threads:[~2004-09-24 16:16 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-24 18:43 Richard Kenner
2004-09-24 18:50 ` Joseph S. Myers [this message]
-- strict thread matches above, loose matches on Subject: below --
2004-09-24 18:53 Richard Kenner
2004-09-24 19:02 ` Joseph S. Myers
2004-09-25 2:38 ` Robert Dewar
2004-09-25 2:59 ` Joseph S. Myers
2004-09-24 16:55 Richard Kenner
2004-09-24 18:23 ` Joseph S. Myers
2004-09-24 16:01 Richard Kenner
2004-09-24 16:16 ` Andrew Pinski
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