I have here a testcase where -fstrict-aliasing seems to miscompiles the code.
$ gcc-4.4 tc.c -o tc && ./tc $ gcc-4.4 tc.c -o tc -O1 && ./tc $ gcc-4.4 tc.c -o tc -O1 -fstrict-aliasing && ./tc Segmentation fault $ gcc-4.4 tc.c -o tc -O1 -fstrict-aliasing -DOK && ./tc 0xaf8bea20 This also happens with the gcc-4.5 snapshot. > gcc-4.4 -v Using built-in specs. Target: i586-suse-linux Configured with: ../configure --prefix=/usr --infodir=/usr/share/info --mandir=/usr/share/man --libdir=/usr/lib --libexecdir=/usr/lib --enable-languages=c,c++,objc,fortran,obj-c++,java,ada --enable-checking=release --with-gxx-include-dir=/usr/include/c++/4.4 --enable-ssp --disable-libssp --with-bugurl=http://bugs.opensuse.org/ --with-pkgversion='SUSE Linux' --disable-libgcj --disable-libmudflap --with-slibdir=/lib --with-system-zlib --enable-__cxa_atexit --enable-libstdcxx-allocator=new --disable-libstdcxx-pch --enable-version-specific-runtime-libs --program-suffix=-4.4 --enable-linux-futex --without-system-libunwind --with-arch-32=i586 --with-tune=generic --build=i586-suse-linux Thread model: posix gcc version 4.4.1 [gcc-4_4-branch revision 150839] (SUSE Linux) > gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/i586-suse-linux/4.5/lto-wrapper Target: i586-suse-linux Configured with: ../configure --prefix=/usr --infodir=/usr/share/info --mandir=/usr/share/man --libdir=/usr/lib --libexecdir=/usr/lib --enable-languages=c,c++,objc,fortran,obj-c++,java,ada --enable-checking=release --with-gxx-include-dir=/usr/include/c++/4.5 --enable-ssp --disable-libssp --disable-plugin --with-bugurl=http://bugs.opensuse.org/ --with-pkgversion='SUSE Linux' --disable-libgcj --disable-libmudflap --with-slibdir=/lib --with-system-zlib --enable-__cxa_atexit --enable-libstdcxx-allocator=new --disable-libstdcxx-pch --enable-version-specific-runtime-libs --program-suffix=-4.5 --enable-linux-futex --without-system-libunwind --enable-gold --with-plugin-ld=/usr/bin/gold --with-arch-32=i586 --with-tune=generic --build=i586-suse-linux Thread model: posix gcc version 4.5.0 20100331 (experimental) [trunk revision 157870] (SUSE Linux) -- Summary: [4.4/4.5 regression] miscompilation in strict-aliasing optimization Product: gcc Version: 4.5.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: jengelh at medozas dot de GCC build triplet: i586-suse-linux-gnu GCC host triplet: i586-suse-linux-gnu GCC target triplet: i586-suse-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43637
