[petsc-dev] Issue with dependency generation in GCC 9

[Matthew Knepley]

On Mon, Jan 20, 2020 at 7:06 AM Lisandro Dalcin <dalcinl at gmail.com> wrote:

> On Mon, 20 Jan 2020 at 14:14, Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Mon, Jan 20, 2020 at 3:06 AM Lisandro Dalcin <dalcinl at gmail.com>
>> wrote:
>>
>>> I'm using GCC 9 from Fedora 31. A few things have changed regarding
>>> dependency generation, and things are now broken for PETSc. I do not have a
>>> clean solution to propose.
>>>
>>> The problem is the way targets are emitted :
>>>
>>> $ head -n 3 arch-linux2-c-debug/obj/sys/objects/init.d
>>> init.o: /home/devel/petsc/dev/src/sys/objects/init.c \
>>>  /home/devel/petsc/dev/include/petscsys.h \
>>>  /home/devel/petsc/dev/arch-linux2-c-debug/include/petscconf.h \
>>>
>>> GCC now generates a bare "init.o" target. Using GCC 8 in a Manjaro box I
>>> get instead:
>>>
>>> $ head -n 3 arch-linux2-c-debug/obj/sys/objects/init.d
>>> arch-linux2-c-debug/obj/sys/objects/init.o: \
>>>  /home/devel/petsc/src/sys/objects/init.c \
>>>  /home/devel/petsc/include/petscsys.h \
>>>
>>> These differences totally break our use of dependencies:
>>>
>>> $ touch include/petscsys.h
>>> $ make
>>> ...
>>> gmake[2]: Nothing to be done for 'all'.
>>> ...
>>>
>>>
>>> My quick workaround so far has been to add this in makefiles:
>>>
>>> C_DEPFLAGS   += -MT $@
>>> CXX_DEPFLAGS += -MT $@
>>> FC_DEPFLAGS  += -MT $@
>>>
>>> From the GCC info page
>>>
>>> '-MT TARGET'
>>>
>>>      Change the target of the rule emitted by dependency generation.  By
>>>      default CPP takes the name of the main input file, deletes any
>>>      directory components and any file suffix such as '.c', and appends
>>>      the platform's usual object suffix.  The result is the target.
>>>
>>>      An '-MT' option sets the target to be exactly the string you
>>>      specify.  If you want multiple targets, you can specify them as a
>>>      single argument to '-MT', or use multiple '-MT' options.
>>>
>>>      For example, '-MT '$(objpfx)foo.o'' might give
>>>
>>>           $(objpfx)foo.o: foo.c
>>>
>>
>> Why is my GCC 9.1 not doing this?
>>
>> master *$:/PETSc3/petsc/petsc-dev$ head -n 3
>> arch-master-debug/obj/sys/objects/init.d
>> arch-master-debug/obj/sys/objects/init.o: \
>>   /PETSc3/petsc/petsc-dev/src/sys/objects/init.c \
>>   /PETSc3/petsc/petsc-dev/include/petscsys.h \
>> master *$:/PETSc3/petsc/petsc-dev$ head -n 3
>> arch-master-gcc-debug/obj/sys/objects/init.d
>> arch-master-gcc-debug/obj/sys/objects/init.o: \
>>  /PETSc3/petsc/petsc-dev/src/sys/objects/init.c \
>>  /PETSc3/petsc/petsc-dev/include/petscsys.h \
>> master *$:/PETSc3/petsc/petsc-dev$ /PETSc3/petsc/gcc/bin/mpicc -show
>> /Users/knepley/MacSoftware/bin/ccache /usr/local/gcc-9.1/bin/gcc-9.1
>> -fstack-protector -g3 -Wl,-flat_namespace -Wl,-commons,use_dy
>> libs -I/PETSc3/petsc/gcc/include -L/PETSc3/petsc/gcc/lib -lmpi -lpmpi
>> master *$:/PETSc3/petsc/petsc-dev$ /usr/local/gcc-9.1/bin/gcc-9.1
>> --version
>> gcc-9.1 (GCC) 9.1.0
>> Copyright (C) 2019 Free Software Foundation, Inc.
>>
>> This is free software; see the source for copying conditions.  There is NO
>> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
>> PURPOSE.
>>
>>
> Maybe this is a regression in GCC 9.2 ? The thing is that the behavior
> seems consistent with the documentation.
>
> $ gcc --version
> gcc (GCC) 9.2.1 20190827 (Red Hat 9.2.1-1)
> Copyright (C) 2019 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>

That is why I wondered. Could they have changed this between 9.1 and 9.2?
It seems like a large change.

   Matt

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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