------- Comment #1 from pinskia at gmail dot com 2009-06-07 07:23 -------
Subject: Re: New: Array + XOR swap fails
Both of these are undefined. Look up about sequence point rules.
Sent from my iPhone
On Jun 7, 2009, at 12:15 AM, "ashutosh dot sharma dot 0204 at gmail
dot com" <gcc-bugzi...@gcc.gnu.org> wrote:
> Compiler Version:
> gcc (GCC) 4.2.4 (Ubuntu 4.2.4-1ubuntu3)
> Copyright (C) 2007 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions. There
> is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
> PURPOSE.
>
>
> Sample code:
>
> #include <stdio.h>
>
> int main() {
> int a[2];
> a[0]=10;
> a[1]=20;
> printf("a[0] = %d a[1] = %d\n", a[0], a[1]);
> a[0]^=a[1]^=a[0]^=a[1];
> printf("a[0] = %d a[1] = %d\n", a[0], a[1]);
> return 0;
> }
>
> gcc test.c -o test -O2
>
> a[0] = 10 a[1] = 20
> a[0] = 20 a[1] = 10
>
> gcc test.c -o test -O0
>
> a[0] = 10 a[1] = 20
> a[0] = 0 a[1] = 10
>
> Bug: When compiled with -O0 swap fails.
> Swap only fails in case of array. Following code works fine with -O0:
>
> #include <stdio.h>
>
> int main() {
> int a, b;
> a=10;
> b=20;
> printf("a = %d b = %d\n", a, b);
> a^=b^=a^=b;
> printf("a = %d b = %d\n", a, b);
> return 0;
> }
>
>
> --
> Summary: Array + XOR swap fails
> Product: gcc
> Version: unknown
> Status: UNCONFIRMED
> Severity: major
> Priority: P3
> Component: c
> AssignedTo: unassigned at gcc dot gnu dot org
> ReportedBy: ashutosh dot sharma dot 0204 at gmail dot com
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40366
>
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40366
