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

[Lisandro Dalcin]

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.
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