https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104983
Bug ID: 104983 Summary: gcc ignore side effect inside CommaExpr and failed to update value variable's value Product: gcc Version: 8.4.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: 141242068 at smail dot nju.edu.cn Target Milestone: --- The code: ``` int main() { int a = 0; unsigned long long one = 1; unsigned long long crf1 = 0; unsigned long long crf2 = 0; unsigned long long crf3 = 0; unsigned long long *cty1[] = {&crf1}; unsigned long long *cty2[] = {&crf2}; unsigned long long *cty3[] = {&crf3}; ((-1ULL / (0xffffffffffffffffull + (*cty1[0]))) < a++, ((unsigned long long)((*cty2[0]) * (*cty3[0])))); if (a != 1) __builtin_abort(); return 0; } ``` Note that, a is updated only once in the above expression, and -1ull is unsigned type, it should not trigger integer overflow. But when compile the above code with -fopen-simd, the generated executable will abort. ``` $ gcc -fopenmp-simd a.c -o a.out && ./a.out [1] 2409988 abort (core dumped) ./a.out ``` My gcc version is: ``` $ gcc -v Using built-in specs. COLLECT_GCC=gcc-8 COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 8.4.0-3ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-8 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 8.4.0 (Ubuntu 8.4.0-3ubuntu2) ```