On Fri, 20 Jan 2006 19:53:14 EST, Chuck Ebbert said: > /* > * setbit.c -- test the Linux set_bit() function > * > * Compare the output of this program with and without the > * -finline-functions option to GCC. > * > * If they are not the same, set_bit is broken. > * > * Result on i386 with gcc 3.3.2 (Fedora Core 2): > * > * [me@d2 t]$ gcc -O2 -o setbit.ex setbit.c ; ./setbit.ex > * 00010001 > * [me@d2 t]$ gcc -O2 -o setbit.ex -finline-functions setbit.c ; ./setbit.ex > * 00000001 It certainly seems to be gcc version dependent (and I'd not be surprised if the exact combo of -O2, -Os, and -mfoo and -fwhatever flags as well). Trond is probably right that a memory clobber will force gcc to DTIT (Do The Intended Thing, which may be different from a DTRT) regardless of what gcc's code generator decides to do.... % gcc -v Using built-in specs. Target: i386-redhat-linux Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-libgcj-multifile --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --with-java-home=/usr/lib/jvm/java-1.4.2-gcj-1.4.2.0/jre --host=i386-redhat-linux Thread model: posix gcc version 4.1.0 20060117 (Red Hat 4.1.0-0.15) % gcc -O2 -o setbit.ex setbit.c ; ./setbit.ex 00000001 % gcc -O2 -o setbit.ex -finline-functions setbit.c ; ./setbit.ex 00000001 Fedora Core -devel tree as of this morning (so sort-of FC5 test2).
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