[petsc-dev] configureLibrary fails for c++11 projects

Tue Mar 23 12:29:30 CDT 2021

And I think there are some flags that can't be used at link time [so
they have to go into CPPFLAGS and not CFLAGS - as CFLAGS gets used
with CLINKER aswell]

Satish

On Tue, 23 Mar 2021, Satish Balay via petsc-dev wrote:

> I'm not sure if we can eliminate preprocessing. [mpi.h detection is
> one place where its used - don't remember others - perhaps detection
> of most includes? - some externalpacakges need them listed
> separately?]
> 
> And as long as we need preprocessing as a separate step [and some
> compile flags give errors when used with processor] - we'll need
> separate PPFLAGS.
> 
> 
> Satish
> 
> On Tue, 23 Mar 2021, Junchao Zhang wrote:
> 
> > Can we combine CXXPPFLAGS and CXXFLAGS into one CXXFLAGS?
> > --Junchao Zhang
> > 
> > 
> > On Tue, Mar 23, 2021 at 11:38 AM Patrick Sanan <patrick.sanan at gmail.com>
> > wrote:
> > 
> > > I had a related (I think) issue trying to build with Kokkos. Those headers
> > > throw an #error if they're expecting OpenMP and the compiler doesn't have
> > > the OpenMP flag. I have an open MR here (number 60^2!) which thus adds the
> > > OpenMP flag to the CXXPPFLAGS:
> > > https://gitlab.com/petsc/petsc/-/merge_requests/3600
> > >
> > >
> > > My collaborator at CSCS was testing with the latest Kokkos and ran into an
> > > even hairier version of this problem trying to use CUDA - the Kokkos
> > > headers now apparently check that you're using nvcc. He has some workaround
> > > which I'll review and hopefully be able to submit.
> > >
> > >
> > > Am 23.03.2021 um 17:04 schrieb Stefano Zampini <stefano.zampini at gmail.com
> > > >:
> > >
> > > The check fails within buildsystem when running mpicc -E (which uses
> > > CXXPPFLAGS)  The package header needs c++11  to be included properly.
> > > C++11 is also needed at preprocessing time
> > >
> > > Il Mar 23 Mar 2021, 18:59 Satish Balay <balay at mcs.anl.gov> ha scritto:
> > >
> > >> -std=cxx11 for sure is a compile flag. But don't really know if its
> > >> also needed at pre-process stage and/or at link stage.
> > >>
> > >> And for compile stage both CXXFLAGS and CXXPPFLAGS should get
> > >> used. [PETSc makefiles make sure this is the case]
> > >>
> > >> And for link stage CXXFLAGS and LDFLAGS get used [but then sometimes
> > >> we have CLINKER, and FLINKER - and they certainly don't use CXXFLAGS -
> > >> so -std=cxx11 isn't really needed at link time?
> > >>
> > >> So the previous default of CXXPPFLAGS=-std=cxx11 looks reasonable to me.
> > >>
> > >> However if this project is not using PETSc makefiles - it should make
> > >> sure all compile flags are grabbed.
> > >>
> > >> # lib/petsc/conf/variables
> > >> PETSC_CXXCPPFLAGS       = ${PETSC_CC_INCLUDES} ${PETSCFLAGS}
> > >> ${CXXPP_FLAGS} ${CXXPPFLAGS}
> > >> CXXCPPFLAGS             = ${PETSC_CXXCPPFLAGS}
> > >> PETSC_CXXCOMPILE_SINGLE = ${CXX} -o $*.o -c ${CXX_FLAGS} ${CXXFLAGS}
> > >> ${CXXCPPFLAGS}
> > >>
> > >> # lib/petsc/conf/rules
> > >> .cpp.o .cxx.o .cc.o .C.o:
> > >>         ${PETSC_CXXCOMPILE_SINGLE} `pwd`/$<
> > >>
> > >> # gmakefile.test
> > >> PETSC_COMPILE.cxx = $(call quiet,CXX) -c $(CXX_FLAGS) $(CXXFLAGS)
> > >> $(CXXCPPFLAGS) $(CXX_DEPFLAGS)
> > >>
> > >> # lib/petsc/conf/test
> > >> LINK.cc = $(CXXLINKER) $(CXX_FLAGS) $(CXXFLAGS) $(CXXCPPFLAGS) $(LDFLAGS)
> > >>
> > >> Satish
> > >>
> > >>
> > >> On Tue, 23 Mar 2021, Junchao Zhang wrote:
> > >>
> > >> > I would rather directly change the project to use CXXFLAGS instead of
> > >> > CXXPPFLAGS.
> > >> >
> > >> > --Junchao Zhang
> > >> >
> > >> >
> > >> > On Tue, Mar 23, 2021 at 10:01 AM Satish Balay via petsc-dev <
> > >> > petsc-dev at mcs.anl.gov> wrote:
> > >> >
> > >> > > On Tue, 23 Mar 2021, Stefano Zampini wrote:
> > >> > >
> > >> > > > Just tried out of main, and and the include tests of a c++11
> > >> project fail
> > >> > > > Below my fix, if we agree on, I'll make a MR
> > >> > > >
> > >> > > > diff --git a/config/BuildSystem/config/compilers.py
> > >> > > > b/config/BuildSystem/config/compilers.py
> > >> > > > index c96967e..44e4657 100644
> > >> > > > --- a/config/BuildSystem/config/compilers.py
> > >> > > > +++ b/config/BuildSystem/config/compilers.py
> > >> > > > @@ -527,6 +527,8 @@ class Configure(config.base.Configure):
> > >> > > >          if self.setCompilers.checkCompilerFlag(flag, includes,
> > >> > > > body+body14):
> > >> > > >            newflag = getattr(self.setCompilers,LANG+'FLAGS') + ' ' +
> > >> > > flag #
> > >> > > > append flag to the old
> > >> > > >            setattr(self.setCompilers,LANG+'FLAGS',newflag)
> > >> > > > +          newflag = getattr(self.setCompilers,LANG+'PPFLAGS') + '
> > >> ' +
> > >> > > flag
> > >> > > > # append flag to the old
> > >> > > > +          setattr(self.setCompilers,LANG+'PPFLAGS',newflag)
> > >> > >
> > >> > >
> > >> > >
> > >> https://gitlab.com/petsc/petsc/commit/ead1aa4045d7bca177e78933b9ca25145fc3c574
> > >> > >
> > >> > >           self.setCompilers.CXXPPFLAGS += ' ' + flag
> > >> > >           newflag = getattr(self.setCompilers,LANG+'FLAGS') + ' ' +
> > >> flag #
> > >> > > append flag to the old
> > >> > >           setattr(self.setCompilers,LANG+'FLAGS',newflag)
> > >> > >
> > >> > > So the old code was setting 'PPFLAGS' - but this commit changed to
> > >> > > 'FLAGS'. Maybe this flag is needed at both compile time and link time?
> > >> > >
> > >> > > So this project is somehow using CXXPPFLAGS - but not CXXFLAGS?
> > >> > >
> > >> > > I'm fine with adding it to PPFLAGS - duplicate listing hopefully
> > >> shouldn't
> > >> > > cause grief.
> > >> > >
> > >> > > Satish
> > >> > >
> > >> > > >            cxxdialect = 'C++14'
> > >> > > >            self.addDefine('HAVE_'+LANG+'_DIALECT_CXX14',1)
> > >> > > >            self.addDefine('HAVE_'+LANG+'_DIALECT_CXX11',1)
> > >> > > > @@ -546,6 +548,8 @@ class Configure(config.base.Configure):
> > >> > > >          if self.setCompilers.checkCompilerFlag(flag, includes,
> > >> body):
> > >> > > >            newflag = getattr(self.setCompilers,LANG+'FLAGS') + ' ' +
> > >> > > flag #
> > >> > > > append flag to the old
> > >> > > >            setattr(self.setCompilers,LANG+'FLAGS',newflag)
> > >> > > > +          newflag = getattr(self.setCompilers,LANG+'PPFLAGS') + '
> > >> ' +
> > >> > > flag
> > >> > > > # append flag to the old
> > >> > > > +          setattr(self.setCompilers,LANG+'PPFLAGS',newflag)
> > >> > > >            cxxdialect = 'C++11'
> > >> > > >            self.addDefine('HAVE_'+LANG+'_DIALECT_CXX11',1)
> > >> > > >            break
> > >> > > >
> > >> > > >
> > >> > > >
> > >> > >
> > >> > >
> > >> >
> > >>
> > >>
> > >
> > 
> 