http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47732
Summary: counter decremented to zero not detected when other
counter overflows
Product: gcc
Version: 4.3.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: j.k.annot.at.in...@gmail.com
Created attachment 23336
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23336
preprocessor output
gcc version 4.3.3 [gcc-4_3-branch revision 147732] (SUSE Linux)
Target: x86_64-suse-linux
Configured with: ../configure --prefix=/usr --infodir=/usr/share/info
--mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64
--enable-languages=c,c++,objc,fortran,obj-c++,java,ada
--enable-checking=release --with-gxx-include-dir=/usr/include/c++/4.3
--enable-ssp --disable-libssp --with-bugurl=http://bugs.opensuse.org/
--with-pkgversion='SUSE Linux' --disable-libgcj --disable-libmudflap
--with-slibdir=/lib64 --with-system-zlib --enable-__cxa_atexit
--enable-libstdcxx-allocator=new --disable-libstdcxx-pch
--enable-version-specific-runtime-libs --program-suffix=-4.3
--enable-linux-futex --without-system-libunwind --with-cpu=generic
--build=x86_64-suse-linux
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O2' '-mtune=generic'
/usr/lib64/gcc/x86_64-suse-linux/4.3/cc1 -E -quiet -v verify_counter_nonzero.c
-mtune=generic -O2 -fpch-preprocess -o verify_counter_nonzero.i
A local counter (named lCounter) is decremented in a while-loop, and the loop
must stop when the counter reaches zero.
In the same loop, a second local counter (lVeryHighCounter) is incremented and
overflows in the same cycle where the first counter reaches zero.
The overflow of the second counter seems to trigger that it is not detected
that the first counter reaches zero: (lCounter != 0) remains false.
A static counter (named sCounter) is used to observe what happens and to stop
the program as soon as the bug is observed.
The used -O2 option is needed to reproduce the bug.
Using -O1 or -O3 does not reproduce the bug.
extern int printf(const char *, ...);
extern void exit(int);
static intsCounter= 3;
voidverify_counter_nonzero(
intaDummy
)
{
printf("sCounter value: %d\n", sCounter);
if (sCounter == 0) {
printf("Compiler bug detected! This function should not be called when
counter reached 0.\n");
exit(0);
}
}
intmain()
{
intlCounter= 3;
intlVeryHighCounter= 0x8000 - 3;
while (lCounter != 0) {
verify_counter_nonzero(lVeryHighCounter);
sCounter-= 1;
lCounter-= 1;
lVeryHighCounter+= 1;
/* In the same cycle where lCounter is decremented to 0,
lVeryHighCounter is incremented (and overflows) from 0x7FFF to
0x8000.
This seems to trigger the bug: the loop condition (lCounter != 0)
should become false,
but remains true.
*/
}
printf("Compiler bug not detected! Loop terminated correctly.\n");
}
