From: Martin Uecker <muecker@gwdg.de>
To: Paul Floyd <paulf@free.fr>, "gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Subject: Re: Safe transposition of logical and operands
Date: Mon, 18 Sep 2023 22:52:16 +0200 [thread overview]
Message-ID: <36ac57c1e19b68fd588208a9ac03b58fe29fab32.camel@gwdg.de> (raw)
In-Reply-To: <1dbda88a-60dd-bb00-1217-244d111598fb@free.fr>
Am Montag, dem 18.09.2023 um 22:15 +0200 schrieb Paul Floyd via Gcc:
>
> On 18-09-23 21:09, Martin Uecker wrote:
>
> > I do not understand why memcheck cares about the potential trap when
> > deciding to do the backwards transformation that combines the two
> > comparisons? Can't you just remove this condition? I assume it
> > is meant as a filter to only transform cases which really come
> > from an '&&' condition in the source, but as this example show, this
> > is too strict. Or am I missing something?
>
> My understanding is that this is a generic transformation of
>
> if (a && b) [which might have been transposed from if (b && a)]
>
> into
>
> if (a & b) [with appropriate extension to the right size].
>
> That means both get evaluated and we can't take that risk that one of
> them traps.
Is the problem that valgrind transforms the code before it then
emulates it and the problem is that during emulation the code
could trap?
Martin
next prev parent reply other threads:[~2023-09-18 20:52 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-17 19:33 Paul Floyd
2023-09-17 20:51 ` Jonathan Wakely
2023-09-18 7:03 ` Paul Floyd
2023-09-18 7:23 ` Jonathan Wakely
2023-09-18 8:00 ` Richard Biener
2023-09-18 14:46 ` Floyd, Paul
2023-09-18 14:55 ` Richard Biener
2023-09-18 17:56 ` Paul Floyd
2023-09-18 19:09 ` Martin Uecker
2023-09-18 20:15 ` Paul Floyd
2023-09-18 20:52 ` Martin Uecker [this message]
2023-09-19 5:03 ` Paul Floyd
2023-09-18 9:36 ` Jonathan Wakely
2023-09-18 10:30 ` Andreas Schwab
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