From: "Paulo J. Matos" <paulo@matos-sorge.com>
To: gcc@gcc.gnu.org
Subject: Volatile qualification on pointer and data
Date: Tue, 20 Sep 2011 16:08:00 -0000 [thread overview]
Message-ID: <j5adnq$bb4$1@dough.gmane.org> (raw)
Hi,
I am noticing a very concerning change of behaviour from GCC45 to GCC46
on our applications.
The following code:
static const unsigned int foo = 1;
unsigned int test( void )
{
const volatile unsigned int *bar = &foo;
return ( *bar );
}
in GCC45 works as expected:
$test:
ld AL,#foo ;; AL is return register
bra 0,X ;; end function
in GCC46:
$test:
ld AL,0
bra 0,X
This is worrying because qualifying the data as volatile should be
enough to prevent these sort of optimizations. It did until GCC46.
I noticed that this seems to be implementation dependent according to
C99 6.7.3.6, however, this change of implementation is unexpected and I
don't see a reason for it. Is there any reason for this change?
The correct code is generated is both the pointer and data are qualified
as volatile even it is not straightforward code since it has some moves
to and from the stack pointer.
This is easily reproducible in i386 so, it's definitely not backend
specific.
Cheers,
--
PMatos
next reply other threads:[~2011-09-20 16:08 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-20 16:08 Paulo J. Matos [this message]
2011-09-20 16:36 ` Ian Lance Taylor
2011-09-21 7:07 ` David Brown
2011-09-21 8:22 ` Paulo J. Matos
2011-09-21 10:20 ` David Brown
2011-09-21 13:57 ` Ian Lance Taylor
2011-09-21 14:25 ` David Brown
2011-09-21 14:57 ` Paulo J. Matos
2011-09-22 8:39 ` David Brown
2011-09-22 21:15 ` Richard Guenther
2011-09-23 11:33 ` Paulo J. Matos
2011-09-23 11:51 ` Paulo J. Matos
2011-09-23 13:17 ` Paulo J. Matos
2011-09-21 18:51 ` Georg-Johann Lay
2011-09-22 8:53 ` David Brown
2011-09-24 15:10 ` John Regehr
2011-09-24 15:49 ` David Brown
2011-09-24 16:26 ` David Brown
2011-09-24 19:38 ` John Regehr
2011-09-25 13:03 ` David Brown
2011-09-25 15:15 ` Andreas Schwab
2011-09-25 16:33 ` David Brown
2011-09-25 16:36 ` David Brown
2011-09-25 16:06 ` Dave Korn
2011-09-25 22:05 ` David Brown
2011-09-25 22:05 ` David Brown
2011-09-26 7:14 ` Miles Bader
2011-09-26 8:53 ` David Brown
2011-09-26 8:58 ` David Brown
2011-09-21 8:14 ` Paulo J. Matos
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