On May 15, 2020 7:30:38 PM GMT+02:00, Jason Merrill <ja...@redhat.com> wrote: >On Fri, May 15, 2020 at 3:15 AM Richard Biener ><richard.guent...@gmail.com> >wrote: > >> > +# When bootstrapping with GCC, build stage 1 in C++11 mode to >ensure >> that a >> > +# C++11 compiler can still start the bootstrap. >> > if test "$enable_bootstrap:$GXX" = "yes:yes"; then >> > + CXX="$CXX -std=gnu++11" >> >> So I just spotted this - since we're requiring a ISO C++11 compiler >> shouldn't >> we build stage1 with -std=c++11 rather than gnu++11 (whatever the >detailed >> differences are here)? Also not sure what level of -pedantic we'd >need to >> avoid GNU extensions even with -std=c++11. Of course there are (I >hope) >> a lot less GNU extensions for C++ than there were for C and hopefully >> no extra in gnu++11 compared to gnu++98 which we checked previously. >> > >When we first moved to C++ I tried using -std=c++98, but there were too >many places where we were assuming that if we're building with GCC, we >can >use GNU C extensions. > >I'll see if that's still a problem for -std=c++11. > >Note I think what's missing is some general blurb in our coding >conventions >> as to how much of C++11 we are supposed to use in non-infrastructure >parts >> of GCC (I expect things like hash-table.h to use more C++ features >than, >> say, tree-ssa-alias.c). >> >> There also does not seem to be a configure check which may present >> users with a more useful error message than later cryptic fail of >build? >> I suppose we cannot simply check __cplusplus for this, can we? Do >> other common host compilers need additional options to enable C++11? >> > >Good point, I'll add that. > > >> Should we try to second guess such flags via configury? For example >> GCC 4.8 defaults to -std=gnu++98 and the above only seems to apply >> to the bootstrap case so GCC 4.8 cannot be used to build cross >compilers >> without adjusting CC and CXX? >> > >Older GCC is still GCC and will get the flag automatically.
But yes:yes suggests that when building a cross compiler this doesn't apply? Richard. >Jason
