On May 15, 2020 11:53:42 PM GMT+02:00, Jason Merrill <ja...@redhat.com> wrote: >On 5/15/20 2:21 PM, Richard Biener wrote: >> 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. > >Building stage 1 with -std=c++11 -pedantic-errors works with 8.3.1, but > >fails pretty badly with 4.8.5, > >>> 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. > >It doesn't seem to be, so I've made that change. > >>>> 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. > >This patch uses a test from the autoconf archive to add any needed >flags. Tested with GCC 4.8.5 and clang 3.4.2 (with the above stage 1 >-std=c++11 disabled). > >>>> 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? > >True, but the new test should cover that case. > >OK for trunk?
OK if there are no further comments over the weekend. Thanks, Richard.
