https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96105
Bug ID: 96105 Summary: GCC not consistent on whether no_unique_address array is an empty data member Product: gcc Version: 11.0 Status: UNCONFIRMED Keywords: accepts-invalid, rejects-valid, wrong-code Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: hstong at ca dot ibm.com Target Milestone: --- GCC treats an array marked `no_unique_address` and whose base element type is an empty class as not an empty data member in `C` but does treat such an array as an empty data member in `A` for the purposes of `B`. It appears that GCC's handling of `B` is erroneous. Compiler Explorer link: https://godbolt.org/z/XX5W3v ### SOURCE (<stdin>): struct Empty {}; struct A { Empty emp [[no_unique_address]][3]; }; struct B : A { float f; }; struct C { Empty emp [[no_unique_address]][3]; float f; }; extern char szc[sizeof(C)]; extern char szc[sizeof(float) * 2]; // GCC likes this extern char szb[sizeof(B)]; extern char szb[sizeof(float) * 2]; // GCC does not like this ### COMPILER INVOCATION: g++ -fsyntax-only -std=c++2a -Wall -Wextra -pedantic-errors -xc++ - ### ACTUAL OUTPUT: <stdin>:19:13: error: conflicting declaration 'char szb [8]' <stdin>:18:13: note: previous declaration as 'char szb [4]' ### EXPECTED OUTPUT: (clean compile) ### COMPILER VERSION INFO (g++ -v): Using built-in specs. COLLECT_GCC=/opt/wandbox/gcc-head/bin/g++ COLLECT_LTO_WRAPPER=/opt/wandbox/gcc-head/libexec/gcc/x86_64-pc-linux-gnu/11.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../source/configure --prefix=/opt/wandbox/gcc-head --enable-languages=c,c++ --disable-multilib --without-ppl --without-cloog-ppl --enable-checking=release --disable-nls --enable-lto LDFLAGS=-Wl,-rpath,/opt/wandbox/gcc-head/lib,-rpath,/opt/wandbox/gcc-head/lib64,-rpath,/opt/wandbox/gcc-head/lib32 Thread model: posix Supported LTO compression algorithms: zlib gcc version 11.0.0 20200706 (experimental) (GCC)