http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46096
Summary: Code produces two different outputs when optimized
respectively with -O2 and without it.
Product: gcc
Version: 4.3.4
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: zwei...@gmail.com
Created attachment 22093
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22093
Minimal testcase
The code attached is a very simple application of threads using SDL_threads
library.
In the code just one thread is created and it should enter in a loop waiting
for a class variable to become 4 and exit printing "END" on the screen. Since
the variable is modified to 4 in the main program, the thread should exit and
print "END" on the screen always. However, this does not happen all the time in
the -O2 compiled version.
The compiled version WITHOUT -O2 gives the expected output "END" (Reproducible:
always).
On the other hand, the -O2 version of the code produces an executable which
sometimes print and sometimes do not print "END" on the screen (Occasionally
one may need to run the program 20 times to spot 1 error).
I attached the very simple test.cpp file.
And here is the output from g++ without optimization:
g++ -v -save-temps -o sdl_thread -Wall test.cpp -lSDL
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-4.3.4/work/gcc-4.3.4/configure
--prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/4.3.4
--includedir=/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/4.3.4
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/4.3.4/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/4.3.4/info
--with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4
--host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --disable-altivec
--disable-fixed-point --enable-nls --without-included-gettext
--with-system-zlib --disable-checking --disable-werror --enable-secureplt
--disable-multilib --enable-libmudflap --disable-libssp --enable-libgomp
--disable-libgcj --with-arch=i686 --enable-languages=c,c++,treelang,fortran
--enable-shared --enable-threads=posix --enable-__cxa_atexit
--enable-clocale=gnu --with-bugurl=http://bugs.gentoo.org/
--with-pkgversion='Gentoo 4.3.4 p1.1, pie-10.1.5'
Thread model: posix
gcc version 4.3.4 (Gentoo 4.3.4 p1.1, pie-10.1.5)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'sdl_thread' '-Wall'
'-shared-libgcc' '-mtune=generic' '-march=i686'
/usr/libexec/gcc/i686-pc-linux-gnu/4.3.4/cc1plus -E -quiet -v -D_GNU_SOURCE
test.cpp -D_FORTIFY_SOURCE=2 -mtune=generic -march=i686 -Wall -fpch-preprocess
-o test.ii
ignoring nonexistent directory
"/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../../i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/i686-pc-linux-gnu
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include/g++-v4/backward
/usr/local/include
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'sdl_thread' '-Wall'
'-shared-libgcc' '-mtune=generic' '-march=i686'
/usr/libexec/gcc/i686-pc-linux-gnu/4.3.4/cc1plus -fpreprocessed test.ii -quiet
-dumpbase test.cpp -mtune=generic -march=i686 -auxbase test -Wall -version -o
test.s
GNU C++ (Gentoo 4.3.4 p1.1, pie-10.1.5) version 4.3.4 (i686-pc-linux-gnu)
compiled by GNU C version 4.3.4, GMP version 4.3.2, MPFR version 2.4.1-p5.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: a9af7e955b36498814b0c0d47ad1b377
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'sdl_thread' '-Wall'
'-shared-libgcc' '-mtune=generic' '-march=i686'
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../../i686-pc-linux-gnu/bin/as -V
-Qy -o test.o test.s
GNU assembler version 2.18 (i686-pc-linux-gnu) using BFD version (GNU Binutils)
2.18
COMPILER_PATH=/usr/libexec/gcc/i686-pc-linux-gnu/4.3.4/:/usr/libexec/gcc/i686-pc-linux-gnu/4.3.4/:/usr/libexec/gcc/i686-pc-linux-gnu/:/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/:/usr/lib/gcc/i686-pc-linux-gnu/:/usr/libexec/gcc/i686-pc-linux-gnu/4.3.4/:/usr/libexec/gcc/i686-pc-linux-gnu/:/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/:/usr/lib/gcc/i686-pc-linux-gnu/:/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../../i686-pc-linux-gnu/bin/
LIBRARY_PATH=/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/:/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/:/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../../i686-pc-linux-gnu/lib/:/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'sdl_thread' '-Wall'
'-shared-libgcc' '-mtune=generic' '-march=i686'
/usr/libexec/gcc/i686-pc-linux-gnu/4.3.4/collect2 --eh-frame-hdr -m elf_i386
-dynamic-linker /lib/ld-linux.so.2 -o sdl_thread
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../crt1.o
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../crti.o
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/crtbegin.o
-L/usr/lib/gcc/i686-pc-linux-gnu/4.3.4 -L/usr/lib/gcc/i686-pc-linux-gnu/4.3.4
-L/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../../i686-pc-linux-gnu/lib
-L/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../.. test.o -lSDL -lstdc++ -lm
-lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/i686-pc-linux-gnu/4.3.4/crtend.o
/usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../crtn.o
