The following code demonstrates that when optimization is turned on, the memory
reference is being moved out of the loop. Thus, the volatile attribute is not
being honored.
As a workaround (and perhaps better solution), the user could use a module
instead of a common block. Gfortran works ok in the case of module variables.
The below example is from x86 cygwin. But the same thing happens with x86_64
Linux on the current trunk.
$ cat vol.f
subroutine wait4it ()
implicit none
logical event
volatile event
common /xyzzy/ event
do
if (event) exit
end do
end subroutine
$ gfortran -O -S vol.f
$ cat vol.s
.file "vol.f"
.text
.globl _wait4it_
.def _wait4it_; .scl 2; .type 32; .endef
_wait4it_:
pushl %ebp
movl %esp, %ebp
cmpl $0, _xyzzy_
jne L4
L5:
jmp L5
L4:
popl %ebp
ret
.comm _xyzzy_, 16 # 4
$
$ gfortran --version
GNU Fortran (GCC) 4.3.0 20071222 (experimental) [trunk revision 127783]
Copyright (C) 2007 Free Software Foundation, Inc.
GNU Fortran comes with NO WARRANTY, to the extent permitted by law.
You may redistribute copies of GNU Fortran
under the terms of the GNU General Public License.
For more information about these matters, see the file named COPYING
$
--
Summary: VOLATILE attribute not being honored with common block
variable
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: w6ws at earthlink dot net
GCC build triplet: i686-pc-cygwin
GCC host triplet: i686-pc-cygwin
GCC target triplet: i686-pc-cygwin
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35037
