From: kenner@vlsi1.ultra.nyu.edu (Richard Kenner)
To: iant@google.com
Cc: ebotcazou@adacore.com, gcc-patches@gcc.gnu.org, matz@suse.de,
richard.guenther@gmail.com
Subject: Re: [PATCH] Fix optimization regression in constant folder
Date: Mon, 01 Oct 2007 19:32:00 -0000 [thread overview]
Message-ID: <10710011934.AA24578@vlsi1.ultra.nyu.edu> (raw)
In-Reply-To: <m3ve9q207p.fsf@localhost.localdomain>
> The rest of don't us really understand what the semantics of sizetypes
> are. The only documentation is in tree.h, and it only says what
> sizetypes are, it doesn't say what semantics they should have.
Right, because nobody was thinking about these issues back when they
were created.
> In particular I don't understand why sizetypes are sign extended. Why
> do we have negative sizetype values?
Think about virtual origins for arrays or similar such. There are a
few cases that come up in Ada where DECL_FIELD_OFFSET (which must be
of sizetype) is a small negative value.
> And TYPE_OVERFLOW_WRAPS is not quite sufficient, since it does not
> permit canonicalizations.
>
> TYPE_OVERFLOW_WRAPS seems clearly correct for sizetypes (if not, why
> not, and give us an example).
For the reason you just gave: it suppresses some optimizations.
> So it seems that we should do is separate TYPE_OVERFLOW_UNDEFINED into
> two different meanings:
>
> 1) We can assume that computations in this type will never overflow,
> but we should be careful not to introduce overflow where it was not
> present. (TYPE_OVERFLOW_UNDEFINED)
>
> 2) We can assume that computations in this type will never overflow,
> no matter what we do. (TYPE_IGNORE_OVERFLOWS)
>
> Then a few places which currently check TYPE_OVERFLOW_WRAPS can check
> TYPE_IGNORE_OVERFLOWS instead.
That would probably work.
> I really want to move toward a semantics for sizetypes which does not
> involve mysterious checks for TYPE_IS_SIZETYPE. If we can't do that,
> we are going to keep breaking the way you want it to work.
I see it exactly the opposite way around: sizetype means "handle this
computations in the most efficient way possible" (like my EXACT_DIV_EXPR).
So any optimization conditionalized on an attribute of the type can simply
can "|| TYPE_IS_SIZETYPE". But if we go the approach of defining flags in
a special way to deal with case and then get rid of TYPE_IS_SIZETYPE, we
have to go through exactly the same problem as now if some other
attributes are added to types that suppress only some optimizations.
next prev parent reply other threads:[~2007-10-01 19:32 UTC|newest]
Thread overview: 140+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-17 14:35 Eric Botcazou
2007-09-17 14:45 ` Richard Guenther
2007-09-17 14:56 ` Eric Botcazou
2007-09-17 15:13 ` Richard Guenther
2007-09-18 11:12 ` Eric Botcazou
2007-09-18 11:22 ` Richard Guenther
2007-09-18 13:17 ` Richard Kenner
2007-09-19 11:33 ` Eric Botcazou
2007-09-19 14:40 ` Richard Guenther
2007-09-19 14:50 ` Richard Kenner
2007-09-19 15:50 ` Eric Botcazou
2007-09-29 10:27 ` Eric Botcazou
2007-09-29 14:59 ` Richard Guenther
2007-09-29 15:12 ` Eric Botcazou
2007-09-29 15:38 ` Richard Guenther
2007-09-29 17:46 ` Richard Guenther
2007-09-29 18:43 ` Eric Botcazou
2007-09-29 20:52 ` Richard Guenther
2007-09-30 14:38 ` Eric Botcazou
2007-09-30 16:01 ` Eric Botcazou
2007-09-30 16:03 ` Richard Guenther
2007-09-30 16:36 ` Eric Botcazou
2007-09-30 17:37 ` Richard Guenther
2007-09-30 18:53 ` Eric Botcazou
2007-09-30 17:59 ` Richard Kenner
2007-09-30 18:38 ` Richard Guenther
2007-09-30 21:16 ` Richard Kenner
2007-09-30 22:10 ` Eric Botcazou
[not found] ` <m3r6kf3gyx.fsf@localhost.localdomain>
[not found] ` <200710010127.59677.ebotcazou@adacore.com>
2007-10-01 0:10 ` Ian Lance Taylor
2007-10-01 0:51 ` Richard Kenner
2007-10-01 1:54 ` Michael Matz
2007-10-01 2:53 ` Richard Kenner
2007-10-01 3:25 ` Michael Matz
2007-10-01 3:40 ` Richard Kenner
2007-10-01 9:12 ` Richard Guenther
2007-10-01 12:29 ` Richard Kenner
2007-10-01 12:40 ` Richard Guenther
2007-10-01 13:07 ` Eric Botcazou
2007-10-01 13:15 ` Richard Kenner
2007-10-01 14:15 ` Richard Guenther
2007-10-01 14:23 ` Richard Kenner
2007-10-01 14:29 ` Richard Guenther
2007-10-01 14:35 ` Richard Kenner
2007-10-01 17:51 ` Ian Lance Taylor
2007-10-01 19:32 ` Richard Kenner [this message]
2007-10-01 19:51 ` Ian Lance Taylor
2007-10-01 20:28 ` Richard Kenner
2007-10-02 13:58 ` Michael Matz
2007-10-03 6:41 ` Eric Botcazou
2007-10-03 7:00 ` Ian Lance Taylor
2007-10-03 7:10 ` Eric Botcazou
2007-10-03 14:18 ` Ian Lance Taylor
2007-10-03 15:53 ` Eric Botcazou
2007-10-04 5:20 ` Michael Matz
2007-10-10 17:31 ` Mark Mitchell
2007-10-10 22:43 ` Richard Kenner
2007-10-11 0:40 ` Mark Mitchell
2007-10-11 1:02 ` Richard Kenner
2007-10-11 15:06 ` Michael Matz
2007-10-11 15:10 ` Richard Guenther
2007-10-11 15:55 ` Michael Matz
2007-10-11 15:57 ` Richard Guenther
2007-10-11 16:02 ` Richard Kenner
2007-10-11 15:59 ` Richard Kenner
2007-10-11 16:02 ` Richard Guenther
2007-10-11 16:08 ` Richard Kenner
2007-10-11 16:14 ` Richard Guenther
2007-10-11 16:37 ` Richard Kenner
2007-10-11 16:44 ` Richard Guenther
2007-10-11 16:50 ` Richard Kenner
2007-10-11 15:32 ` Richard Kenner
2007-10-11 16:03 ` Michael Matz
2007-10-11 16:06 ` Richard Guenther
2007-10-11 16:19 ` Richard Kenner
2007-10-11 16:25 ` Michael Matz
2007-10-11 16:12 ` Richard Kenner
2007-10-11 16:38 ` Michael Matz
2007-10-11 16:47 ` Richard Kenner
2007-10-11 17:04 ` Michael Matz
2007-10-11 17:17 ` Ian Lance Taylor
2007-10-11 18:41 ` Michael Matz
[not found] ` <10710111850.AA27 912@vlsi1.ultra.nyu.edu>
[not found] ` <10710111850.AA27 912@vlsi1.ultra.nyu.edu>
[not found] ` <10710111850.AA27 912@vlsi1.ultra.nyu.edu>
[not found] ` <10710111850.AA27 912@vlsi1.ultra.nyu.edu>
[not found] ` <10710111850.AA27 912@vlsi1.ultra.nyu.edu>
[not found] ` <10710111850.AA27 912@vlsi1.ultra.nyu.edu>
2007-10-11 18:45 ` Richard Kenner
2007-10-11 19:10 ` Michael Matz
2007-10-11 19:17 ` Richard Kenner
2007-10-11 19:30 ` Michael Matz
2007-10-11 20:06 ` Richard Kenner
2007-10-11 21:24 ` Ian Lance Taylor
2007-10-12 2:36 ` Richard Kenner
2007-10-12 4:40 ` Ian Lance Taylor
2007-10-12 4:56 ` Mark Mitchell
2007-10-12 12:30 ` Richard Kenner
2007-10-12 17:48 ` Mark Mitchell
2007-10-12 18:08 ` Richard Kenner
2007-10-12 18:37 ` Mark Mitchell
2007-10-12 18:51 ` Richard Kenner
2007-10-12 20:13 ` Richard Guenther
2007-10-14 11:09 ` Eric Botcazou
2007-10-12 11:42 ` Richard Kenner
2007-10-14 10:31 ` Eric Botcazou
2007-10-14 11:24 ` Richard Guenther
2007-10-14 11:58 ` Eric Botcazou
2007-10-14 12:16 ` Richard Kenner
2007-10-14 13:29 ` Richard Guenther
2007-10-15 2:12 ` Richard Kenner
2007-10-15 7:33 ` Michael Matz
2007-10-15 11:36 ` Richard Kenner
2007-10-15 13:27 ` Richard Guenther
2007-10-15 13:28 ` Richard Kenner
2007-10-14 16:07 ` Ian Lance Taylor
2007-10-14 16:27 ` Richard Guenther
2007-10-15 3:26 ` Richard Kenner
2007-10-15 9:12 ` Richard Guenther
2007-10-15 11:41 ` Richard Kenner
2007-10-15 13:15 ` Richard Guenther
2007-10-15 13:17 ` Richard Kenner
2007-10-15 3:29 ` Richard Kenner
2007-10-15 2:17 ` Richard Kenner
2007-10-15 5:21 ` Ian Lance Taylor
2007-10-15 11:01 ` Richard Kenner
2007-10-11 17:21 ` Richard Kenner
2007-10-11 16:16 ` Richard Kenner
2007-10-11 16:51 ` Michael Matz
2007-10-11 16:57 ` Richard Kenner
2007-10-11 17:06 ` Richard Guenther
2007-10-11 17:24 ` Richard Kenner
2007-10-11 17:31 ` Michael Matz
2007-10-11 17:54 ` Richard Kenner
2007-10-12 8:20 ` Richard Guenther
2007-10-12 11:47 ` Paolo Bonzini
2007-10-12 12:44 ` Richard Kenner
2007-10-12 12:49 ` Richard Guenther
2007-10-11 15:57 ` Mark Mitchell
2007-10-11 16:01 ` Richard Kenner
2007-10-11 16:03 ` Richard Guenther
2007-10-11 16:16 ` Richard Kenner
2007-10-11 16:11 ` Mark Mitchell
2007-10-11 16:29 ` Richard Kenner
2007-10-01 6:07 ` Eric Botcazou
2007-10-01 6:07 ` Eric Botcazou
2007-10-01 8:58 ` Richard Guenther
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