https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84494
Bug ID: 84494 Summary: Invalid constexpr with default assignment operator Product: gcc Version: 7.3.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: pigman46 at gmail dot com Target Milestone: --- $ cat test.cpp #include <iostream> struct X { constexpr X() = default; constexpr X(int x) : m_value(x) {} constexpr X& operator=(const X &o) = default; int m_value {}; }; int main () { constexpr int x = (X() = X(10)).m_value; std::cout << x << std::endl; std::cout << (X() = X(10)).m_value << std::endl; } g++ -v -save-temps -o test test.cpp -Wall -Wextra Using built-in specs. COLLECT_GCC=/usr/bin/g++ COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-redhat-linux Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,objc,obj-c++,fortran,ada,go,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl --enable-libmpx --enable-offload-targets=nvptx-none --without-cuda-driver --enable-gnu-indirect-function --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux Thread model: posix gcc version 7.3.1 20180130 (Red Hat 7.3.1-2) (GCC) COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'test' '-Wall' '-Wextra' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/libexec/gcc/x86_64-redhat-linux/7/cc1plus -E -quiet -v -D_GNU_SOURCE test.cpp -mtune=generic -march=x86-64 -Wall -Wextra -fpch-preprocess -o test.ii ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/7/include-fixed" ignoring nonexistent directory "/usr/lib/gcc/x86_64-redhat-linux/7/../../../../x86_64-redhat-linux/include" #include "..." search starts here: #include <...> search starts here: /usr/lib/gcc/x86_64-redhat-linux/7/../../../../include/c++/7 /usr/lib/gcc/x86_64-redhat-linux/7/../../../../include/c++/7/x86_64-redhat-linux /usr/lib/gcc/x86_64-redhat-linux/7/../../../../include/c++/7/backward /usr/lib/gcc/x86_64-redhat-linux/7/include /usr/local/include /usr/include End of search list. COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'test' '-Wall' '-Wextra' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/libexec/gcc/x86_64-redhat-linux/7/cc1plus -fpreprocessed test.ii -quiet -dumpbase test.cpp -mtune=generic -march=x86-64 -auxbase test -Wall -Wextra -version -o test.s GNU C++14 (GCC) version 7.3.1 20180130 (Red Hat 7.3.1-2) (x86_64-redhat-linux) compiled by GNU C version 7.3.1 20180130 (Red Hat 7.3.1-2), GMP version 6.1.2, MPFR version 3.1.5, MPC version 1.0.2, isl version isl-0.16.1-GMP GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 GNU C++14 (GCC) version 7.3.1 20180130 (Red Hat 7.3.1-2) (x86_64-redhat-linux) compiled by GNU C version 7.3.1 20180130 (Red Hat 7.3.1-2), GMP version 6.1.2, MPFR version 3.1.5, MPC version 1.0.2, isl version isl-0.16.1-GMP GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 41dde25dbc62f10f0477c356c02ccf33 COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'test' '-Wall' '-Wextra' '-shared-libgcc' '-mtune=generic' '-march=x86-64' as -v --64 -o test.o test.s GNU assembler version 2.29 (x86_64-redhat-linux) using BFD version version 2.29-6.fc27 COMPILER_PATH=/usr/libexec/gcc/x86_64-redhat-linux/7/:/usr/libexec/gcc/x86_64-redhat-linux/7/:/usr/libexec/gcc/x86_64-redhat-linux/:/usr/lib/gcc/x86_64-redhat-linux/7/:/usr/lib/gcc/x86_64-redhat-linux/ LIBRARY_PATH=/usr/lib/gcc/x86_64-redhat-linux/7/:/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-redhat-linux/7/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'test' '-Wall' '-Wextra' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/libexec/gcc/x86_64-redhat-linux/7/collect2 -plugin /usr/libexec/gcc/x86_64-redhat-linux/7/liblto_plugin.so -plugin-opt=/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper -plugin-opt=-fresolution=test.res -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --build-id --no-add-needed --eh-frame-hdr --hash-style=gnu -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o test /usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crt1.o /usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crti.o /usr/lib/gcc/x86_64-redhat-linux/7/crtbegin.o -L/usr/lib/gcc/x86_64-redhat-linux/7 -L/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-redhat-linux/7/../../.. test.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-redhat-linux/7/crtend.o /usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crtn.o COLLECT_GCC_OPTIONS='-v' '-save-temps' '-o' 'test' '-Wall' '-Wextra' '-shared-libgcc' '-mtune=generic' '-march=x86-64' $ ./test 0 10 If using "= default" on a constexpr copy/move assignment operator, an constexpr evaluation involving this operator produces an invalid result. In this case, m_value contains 0 instead of 10. Its usage in a non-constexpr context yields the expected value.