https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87043
Bug ID: 87043 Summary: maybe-uninitialized warning for initialized variable Product: gcc Version: 8.1.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: fortran Assignee: unassigned at gcc dot gnu.org Reporter: pvitt at posteo dot de Target Milestone: --- We have a MWE that provokes a "may be uninitialized" warning despite the value being initialized in all cases. Additionally, this warning is only created with -O[1,2,3,s,fast}, but not with -O{g}. The gcc is from Arch Linux. $ gfortran -v -save-temps -O3 -Wmaybe-uninitialized uninitialized.f90 Driving: gfortran -v -save-temps -O3 -Wmaybe-uninitialized uninitialized.f90 -l gfortran -l m -shared-libgcc Using built-in specs. COLLECT_GCC=gfortran COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/8.1.1/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared --enable-threads=posix --enable-libmpx --with-system-zlib --with-isl --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object --enable-linker-build-id --enable-lto --enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu --enable-gnu-indirect-function --enable-multilib --disable-werror --enable-checking=release --enable-default-pie --enable-default-ssp Thread model: posix gcc version 8.1.1 20180531 (GCC) COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O3' '-Wmaybe-uninitialized' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-pc-linux-gnu/8.1.1/f951 uninitialized.f90 -quiet -dumpbase uninitialized.f90 -mtune=generic -march=x86-64 -auxbase uninitialized -O3 -Wmaybe-uninitialized -version -fintrinsic-modules-path /usr/lib/gcc/x86_64-pc-linux-gnu/8.1.1/finclude -o uninitialized.s GNU Fortran (GCC) version 8.1.1 20180531 (x86_64-pc-linux-gnu) compiled by GNU C version 8.1.1 20180531, GMP version 6.1.2, MPFR version 4.0.1, MPC version 1.1.0, isl version isl-0.19-GMP GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 GNU Fortran2008 (GCC) version 8.1.1 20180531 (x86_64-pc-linux-gnu) compiled by GNU C version 8.1.1 20180531, GMP version 6.1.2, MPFR version 4.0.1, MPC version 1.1.0, isl version isl-0.19-GMP GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 uninitialized.f90:20:0: max_err_len = maxval(len_trim(error_messages)) Warning: ‘error_messages.dim[0].ubound’ may be used uninitialized in this function [-Wmaybe-uninitialized] [stripped assembler output...] $ cat uninitialized.f90 module m implicit none integer, parameter :: error_buflen = 80 integer :: world_rank, world_size contains subroutine test() character(len=error_buflen), allocatable :: error_messages(:) integer :: allocstat, max_err_len max_err_len = 0 if (world_rank == 0 ) then allocate(error_messages(world_size), stat=allocstat) else allocate(error_messages(0)) end if if (world_rank == 0) then max_err_len = maxval(len_trim(error_messages)) end if if (max_err_len > error_buflen-10) then write(*,'(a)') 'Note...' end if end subroutine test end module program uninitialized use m implicit none read(*,*) world_rank world_size = 2 call test() end program