https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114657
Bug ID: 114657 Summary: Invalid type conversion from some _BitInt bit-fields Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: juuso.alasuutari at gmail dot com Target Milestone: --- Created attachment 57911 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57911&action=edit Preprocessed test program source Summary ------- GCC's type conversion from some bit-precise integer-typed bit-fields does not match the description in the C23 standard. Expected vs. observed behavior ------------------------------ Based on footnote on page 47 of ISO/IEC 9899/2024 6.3.1.1 (n3320.pdf), the converted type of a _BitInt bit-field should match the original bit-precise integer: "E.g. unsigned _BitInt(7): 2 is a bit-field that can hold the values 0, 1, 2, 3, and converts to unsigned _BitInt(7)." My expectation would then be to see the following output, which does in fact happen when compiling with clang-19: $ ./test unsigned _BitInt(7) This is what GCC does: $ ./test unsigned _BitInt(2) Output of gcc-14 -v ------------------- Using built-in specs. COLLECT_GCC=gcc-14 COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/14/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Debian 14-20240330-1' --with-bugurl=file:///usr/share/doc/gcc-14/README.Bugs --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2,rust --prefix=/usr --with-gcc-major-version-only --program-suffix=-14 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/libexec --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-libstdcxx-backtrace --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none=/build/reproducible-path/gcc-14-14-20240330/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/reproducible-path/gcc-14-14-20240330/debian/tmp-gcn/usr --enable-offload-defaulted --without-cuda-driver --enable-checking=yes,extra,rtl --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 14.0.1 20240330 (experimental) [master r14-9728-g6fc84f680d0] (Debian 14-20240330-1) Compilation command ------------------- gcc-14 -std=gnu23 -Wall -Wextra -Wpedantic -save-temps -o test test.c