From: Paolo Bonzini <bonzini@gnu.org>
To: Jeff Law <law@redhat.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: RFA: New pass to delete unexecutable paths in the CFG
Date: Tue, 08 Nov 2011 20:38:00 -0000 [thread overview]
Message-ID: <4EB98DE2.1050009@gnu.org> (raw)
In-Reply-To: <4EB98316.2080803@redhat.com>
On 11/08/2011 08:29 PM, Jeff Law wrote:
>> Just to understand, what does this do with your optimization?
>>
>> void f(void *p) {
>> if (p) {
>> puts("sell_soul_to_devil"); puts("post_reload_rewrite"); }
>>
>> *p = 2; }
>>
>> ... f(NULL);
>>
>> Does the program sell its soul to the devil before crashing?
>
> If "f" is not inlined into its caller, then there's nothing for the
> new pass to do. There's no explicit NULL dereference and there's no
> assignments to "p", so there's no PHI at the merge point for P.
But is that just a limitation of the representation? With assertions as
in VRP you'd have
if (p_1) goto BB1 else goto BB2
BB1: ... goto BB3;
BB2: p_2 = assert(p_1, p_1 == 0); goto BB3;
p_3 = phi (p_1<BB1>, p_2<BB2>);
*p_3 = 2;
What would happen then?
Paolo
next prev parent reply other threads:[~2011-11-08 20:15 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-07 9:58 Jeff Law
2011-11-07 10:19 ` Jakub Jelinek
2011-11-07 10:21 ` Richard Guenther
2011-11-07 10:30 ` Richard Guenther
2011-11-07 19:20 ` Jeff Law
2011-11-07 16:14 ` Jeff Law
2011-11-07 16:30 ` Richard Guenther
2011-11-07 16:57 ` Kai Tietz
2011-11-07 19:03 ` Jeff Law
2011-11-08 11:50 ` Paolo Bonzini
2011-11-08 19:48 ` Jeff Law
2011-11-08 20:38 ` Paolo Bonzini [this message]
2011-11-08 20:59 ` Jeff Law
2011-11-09 8:37 ` Paolo Bonzini
2011-11-09 18:11 ` Jeff Law
2011-11-09 18:12 ` Jakub Jelinek
2011-11-09 22:45 ` Paolo Bonzini
2011-11-10 19:27 ` Jeff Law
2011-11-07 19:14 ` Jeff Law
2011-11-07 14:16 ` Tom Tromey
2011-11-07 15:54 ` Jeff Law
2011-11-07 15:54 ` Richard Guenther
2011-11-07 19:09 ` Jeff Law
2011-11-07 22:34 ` Richard Guenther
2011-11-08 20:02 ` Jeff Law
2011-11-09 9:50 ` Richard Guenther
2011-11-09 17:43 ` Jeff Law
2011-11-07 15:55 ` Tom Tromey
2011-11-07 17:01 ` Paolo Bonzini
2011-11-15 7:52 ` RFA: disable -fdelete-null-pointer-checks for Java Jeff Law
2011-11-07 19:05 ` RFA: New pass to delete unexecutable paths in the CFG Jeff Law
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