in this simple function
bug.c:
void restore() {
register long reg_ebx asm ("ebx");
reg_ebx = saved_ebx;
}
$ gcc -v
Utilisation des specs internes.
Target: i386-redhat-linux
Configuré avec: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk
--disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-cpu=generic --build=i386-redhat-linux
Modèle de thread: posix
gcc version 4.3.2 20080905 (Red Hat 4.3.2-3) (GCC)
$ uname -a
Linux lima.univ-paris1.fr 2.6.24-0.83.rc5.fc9 #1 SMP Tue Dec 11 12:04:08 EST
2007 i686 i686 i386 GNU/Linux
$ gcc -O -S -ffixed-ebx -fomit-frame-pointer bug.c
$ cat bug.c
restore:
rep
ret
.size restore, .-restore
.comm saved_ebx,4,4
the function is empty: the assignment to reg_ebx has been discarded (because
considered as a local variable). In the presence of asm it should be kept.
It is OK if -O is not given.
Maybe there is a way do it differently (btw I cannot declare the var as global
nor static in my application).
--
Summary: probelm with optmization and local variable stored in an
asm register
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: daniel dot diaz at univ-paris1 dot fr
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37613
