On Fri, 13 Jun 2025, Gábor Németh wrote: > > > A new option is added to warn if floating point literals have non-standard > > > suffices (currently Q and W) in pedantic mode. The option is ON by > > > default. > > > > I don't think we should turn this off when building GCC itself (as opposed > > to target libraries). Host floating-point should only be used for limited > > purposes such as reporting timing statistics, not for anything that could > > affect target code generation; I don't see any reason we should want to > > use these extended floating types in GCC itself at all. > > I turned it off because any gcc/*.cc that includes <limits> directly or > through eg. <math.h> throws: > > In file included from > <BUILD>/prev-x86_64-pc-linux-gnu/libstdc++-v3/include/bits/specfun.h:44, > from > <BUILD>/prev-x86_64-pc-linux-gnu/libstdc++-v3/include/cmath:3913, > from > <BUILD>/prev-x86_64-pc-linux-gnu/libstdc++-v3/include/math.h:36, > from ../../gcc/gcc/genautomata.cc:116: > <BUILD>/prev-x86_64-pc-linux-gnu/libstdc++-v3/include/limits:2107:30: error: > non-standard suffix on floating constant [-Werror=non-standard-suffix] > 2107 | return __extension__ 0x1.0p-16382Q; > | ^~~~~~~~~~~~~ > ... > > Should I add the flag selectively to affected files' build flags only?
The libstdc++ headers need to work for user applications without producing warnings with any default warning options, or with any non-default warnings options except maybe for very specialized ones - applications must not need to add -Wno-* options to get clean builds when including the headers installed by GCC. Host code in GCC is a user application for this purpose. If normal user code that includes <limits> gets this warning (built with an installed compiler), that needs fixing in some way. If not, what is different about how GCC uses its own libstdc++? (For example, it's important to include system headers with -isystem not -I, does GCC get this right when building with the libstdc++ from a previous stage of bootstrap?) -- Joseph S. Myers josmy...@redhat.com
