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

23 Mar 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 <[email protected]>
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 <[email protected]
...
:
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 <[email protected]> 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 <
[email protected]> 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/ead1aa4045d7bca177e78933b9ca25145fc3c5...
...
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


    

Satish Balay

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