Build fails with LTO

[eli-schwartz]

I tried to build with the following *FLAGS to optimize the build: -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing

Note the -Werror=* flags are used to help detect cases where the compiler tries to optimize by assuming UB cannot exist in the source code -- if it does exist, ordinarily the code would be miscompiled, and this says to make the miscompilation a fatal error.

I got this error:

FAILED: fortran/libnetcdff.so.7.1.0 
: && /usr/bin/x86_64-pc-linux-gnu-gfortran -fPIC -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -fallow-argument-mismatch  -Wl,-O1 -Wl,--as-needed -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Wl,--defsym=__gentoo_check_ldflags__=0 -shared -Wl,-soname,libnetcdff.so.7 -o fortran/libnetcdff.so.7.1.0 fortran/CMakeFiles/netcdff_c.dir/nf_lib.c.o fortran/CMakeFiles/netcdff_c.dir/nf_v2compat.c.o fortran/CMakeFiles/netcdff.dir/typeSizes.F90.o fortran/CMakeFiles/netcdff.dir/module_netcdf_nc_data.F90.o fortran/CMakeFiles/netcdff.dir/module_netcdf_nc_interfaces.F90.o fortran/CMakeFiles/netcdff.dir/module_netcdf_nf_data.F90.o fortran/CMakeFiles/netcdff.dir/module_netcdf_nf_interfaces.F90.o fortran/CMakeFiles/netcdff.dir/module_netcdf_f03.F90.o fortran/CMakeFiles/netcdff.dir/nf_attio.F90.o fortran/CMakeFiles/netcdff.dir/nf_control.F90.o fortran/CMakeFiles/netcdff.dir/nf_dim.F90.o fortran/CMakeFiles/netcdff.dir/nf_misc.F90.o fortran/CMakeFiles/netcdff.dir/nf_genatt.F90.o fortran/CMakeFiles/netcdff.dir/nf_geninq.F90.o fortran/CMakeFiles/netcdff.dir/nf_genvar.F90.o fortran/CMakeFiles/netcdff.dir/nf_vario.F90.o fortran/CMakeFiles/netcdff.dir/nf_var1io.F90.o fortran/CMakeFiles/netcdff.dir/nf_varaio.F90.o fortran/CMakeFiles/netcdff.dir/nf_varmio.F90.o fortran/CMakeFiles/netcdff.dir/nf_varsio.F90.o fortran/CMakeFiles/netcdff.dir/nf_nc_noparallel.F90.o fortran/CMakeFiles/netcdff.dir/module_netcdf4_nc_interfaces.F90.o fortran/CMakeFiles/netcdff.dir/module_netcdf4_nf_interfaces.F90.o fortran/CMakeFiles/netcdff.dir/module_netcdf4_f03.F90.o fortran/CMakeFiles/netcdff.dir/nf_nc4.F90.o fortran/CMakeFiles/netcdff.dir/nf_logging.F90.o fortran/CMakeFiles/netcdff.dir/netcdf4.F90.o fortran/CMakeFiles/netcdff.dir/module_netcdf_fortv2_c_interfaces.F90.o fortran/CMakeFiles/netcdff.dir/nf_fortv2.F90.o  -Wl,-rpath,::::::::::  /usr/lib64/libnetcdf.so.19  -ldl  /usr/lib64/libhdf5_hl.so  /usr/lib64/libhdf5.so  /usr/lib64/libz.so  /usr/lib64/libdl.a  -lm  /usr/lib64/libzstd.so  /usr/lib64/libbz2.so  /usr/lib64/libcurl.so  /usr/lib64/libxml2.so && :
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/netcdf4_func.F90:807:81: error: type of ‘nf_inq_var_fill’ does not match original declaration [-Werror=lto-type-mismatch]
  807 |     nf90_inq_var_fill_EightByteReal = nf_inq_var_fill(ncid, varid, no_fill, fill)
      |                                                                                 ^
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1761:1: note: type mismatch in parameter 5
 1761 |  Function nf_inq_var_fill( ncid, varid, no_fill, fill_value) RESULT(status)
      | ^
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1761:1: note: type ‘long int’ should match type ‘void’
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1761:1: note: ‘nf_inq_var_fill’ was previously declared here
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1761:1: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/netcdf4_func.F90:747:81: error: type of ‘nf_def_var_fill’ does not match original declaration [-Werror=lto-type-mismatch]
  747 |     nf90_def_var_fill_EightByteReal = nf_def_var_fill(ncid, varid, no_fill, fill)
      |                                                                                 ^
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1733:1: note: type mismatch in parameter 5
 1733 |  Function nf_def_var_fill( ncid, varid, no_fill, fill_value) RESULT(status)
      | ^
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1733:1: note: type ‘long int’ should match type ‘void’
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1733:1: note: ‘nf_def_var_fill’ was previously declared here
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1733:1: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/netcdf4_func.F90:470:76: error: type of ‘nf_inq_enum_member’ does not match original declaration [-Werror=lto-type-mismatch]
  470 |     nf90_inq_enum_member = nf_inq_enum_member(ncid, xtype, idx, name, value)
      |                                                                            ^
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1220:1: note: type mismatch in parameter 7
 1220 |  Function nf_inq_enum_member( ncid, xtype, idx, name, value) RESULT (status)
      | ^
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1220:1: note: type ‘long int’ should match type ‘void’
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1220:1: note: ‘nf_inq_enum_member’ was previously declared here
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1220:1: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/netcdf4_func.F90:447:63: error: type of ‘nf_insert_enum’ does not match original declaration [-Werror=lto-type-mismatch]
  447 |     nf90_insert_enum = nf_insert_enum(ncid, xtype, name, value)
      |                                                               ^
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1144:1: note: type mismatch in parameter 6
 1144 |  Function nf_insert_enum( ncid, xtype, name, value) RESULT (status)
      | ^
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1144:1: note: type ‘long int’ should match type ‘void’
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1144:1: note: ‘nf_insert_enum’ was previously declared here
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1144:1: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
/var/tmp/portage/sci-libs/netcdf-fortran-9999/work/netcdf-fortran-9999/fortran/nf_nc4.F90:1899:73: error: type of ‘nc_inq_var_filter’ does not match original declaration [-Werror=lto-type-mismatch]
 1899 |  cstatus = nc_inq_var_filter(cncid, cvarid, cfilterid, cnparams, cparams)
      |                                                                         ^
/usr/include/netcdf.h:978:1: note: ‘nc_inq_var_filter’ was previously declared here
  978 | nc_inq_var_filter(int ncid, int varid, unsigned int* idp, size_t* nparams, unsigned int* params);
      | ^
/usr/include/netcdf.h:978:1: note: code may be misoptimized unless ‘-fno-strict-aliasing’ is used
lto1: some warnings being treated as errors
lto-wrapper: fatal error: /usr/bin/x86_64-pc-linux-gnu-gfortran returned 1 exit status
compilation terminated.
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: error: lto-wrapper failed
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

Downstream report: https://bugs.gentoo.org/927588
Full build log: build.log

Note: the downstream report was for the latest stable release but my local reproducer used a git checkout and it is still reproducible there.