https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65311
Bug ID: 65311 Summary: Segmentation fault when doing unaligned assignment in a loop Product: gcc Version: 4.9.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: emil.styrke at gmail dot com Created attachment 34948 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34948&action=edit Demonstration of bug (no includes) The attached code segfaults when compiled with -O3. I realize the code is dodgy (and breaks strict aliasing rules according to my understanding), but even with -fno-strict-aliasing it breaks. It works fine on -O2. $ g++-4.9 -o test test.cpp -Wall -Wextra -O3 -fno-strict-aliasing -fwrapv -fno-aggressive-loop-optimizations $ ./test Segmenteringsfel (minnesutskrift skapad) $ g++-4.9 -v Using built-in specs. COLLECT_GCC=g++-4.9 COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.9/lto-wrapper Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.9.1-16ubuntu6' --with-bugurl=file:///usr/share/doc/gcc-4.9/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.9 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.9 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.9-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.9.1 (Ubuntu 4.9.1-16ubuntu6)