Re: [PATCH] Fortran: improve attribute conflict checking [PR93635]

[Harald Anlauf <anlauf@gmx.de>]

Hi Mikael,

Am 09.05.24 um 21:51 schrieb Mikael Morin:
> Hello,
> 
> Le 06/05/2024 à 21:33, Harald Anlauf a écrit :
>> Dear all,
>>
>> I've been contemplating whether to submit the attached patch.
>> It addresses an ICE-on-invalid as reported in the PR, and also
>> fixes an accepts-invalid (see testcase), plus maybe some more,
>> related due to incomplete checking of symbol attribute conflicts.
>>
>> The fix does not fully address the general issue, which is
>> analyzed by Steve: some of the checks do depend on the selected
>> Fortran standard, and under circumstances such as in the testcase
>> the checking of other, standard-version-independent conflicts
>> simply does not occur.
>>
>> Steve's solution would fix that, but unfortunately leads to issues
>> with error recovery in notoriously fragile parts of the FE: e.g.
>> testcase pr87907.f90 needs adjusting, and minor variations
>> of it will lead to various other horrendous ICEs that remind
>> of existing PRs where parsing or resolution goes sideways.
>>
>> I therefore propose a much simpler approach: move - if possible -
>> selected of the standard-version-dependent checks after the
>> version-independent ones.  I think this could help in getting more
>> consistent error reporting and recovery.  However, I did *not*
>> move those checks that are critical when processing interfaces.
>> (-> pr87907.f90 / (sub)modules)
>>
> Your patch looks clean, but I'm concerned that the order of the checks 
> should be the important ones first, regardless of their standard 
> version.  I'm trying to look at the ICE caused by your other tentative 
> patch at https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93635#c6 but I 
> can't reproduce the problem.  Do you by any chance have around some of 
> the variations causing "horrendous" ICEs?

Oh, that's easy.  Just move the block

   conf_std (allocatable, dummy, GFC_STD_F2003);
   conf_std (allocatable, function, GFC_STD_F2003);
   conf_std (allocatable, result, GFC_STD_F2003);

towards the end of the gfc_check_conflict before the return true.

While the error messages for the original gfortran.dg/pr87907.f90
look harmless, commenting out the main program p I get:

pr87907.f90:15:18:

    15 |       subroutine g(x)   ! { dg-error "mismatch in argument" }
       |                  1
Error: FUNCTION attribute conflicts with SUBROUTINE attribute in 'g' at (1)
f951: internal compiler error: Segmentation fault
0x13b8ec2 crash_signal
         ../../gcc-trunk/gcc/toplev.cc:319
0xba530e free_sym_tree
         ../../gcc-trunk/gcc/fortran/symbol.cc:4026
0xba5319 free_sym_tree
         ../../gcc-trunk/gcc/fortran/symbol.cc:4026
0xba5319 free_sym_tree
         ../../gcc-trunk/gcc/fortran/symbol.cc:4026
0xba5319 free_sym_tree
         ../../gcc-trunk/gcc/fortran/symbol.cc:4026
0xba5609 gfc_free_namespace(gfc_namespace*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:4168
0xba39c1 gfc_free_symbol(gfc_symbol*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:3173
0xba3b89 gfc_release_symbol(gfc_symbol*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:3216
0xba5339 free_sym_tree
         ../../gcc-trunk/gcc/fortran/symbol.cc:4029
0xba5609 gfc_free_namespace(gfc_namespace*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:4168
0xba58ef gfc_symbol_done_2()
         ../../gcc-trunk/gcc/fortran/symbol.cc:4236
0xb12ec8 gfc_done_2()
         ../../gcc-trunk/gcc/fortran/misc.cc:387
0xb4ac7f clean_up_modules
         ../../gcc-trunk/gcc/fortran/parse.cc:7057
0xb4af02 translate_all_program_units
         ../../gcc-trunk/gcc/fortran/parse.cc:7122
0xb4b735 gfc_parse_file()
         ../../gcc-trunk/gcc/fortran/parse.cc:7413
0xbb626f gfc_be_parse_file
         ../../gcc-trunk/gcc/fortran/f95-lang.cc:241


Restoring the main program but simply adding "end subroutine g"
where it is naively expected gives:

pr87907.f90:15:18:

    15 |       subroutine g(x)   ! { dg-error "mismatch in argument" }
       |                  1
Error: FUNCTION attribute conflicts with SUBROUTINE attribute in 'g' at (1)
pr87907.f90:16:9:

    16 |       end subroutine g
       |         1
Error: Expecting END SUBMODULE statement at (1)
pr87907.f90:20:7:

    20 |    use m                ! { dg-error "has a type" }
       |       1
    21 |    integer :: x = 3
    22 |    call g(x)            ! { dg-error "which is not consistent 
with" }
       | 
     2
Error: 'g' at (1) has a type, which is not consistent with the CALL at (2)
f951: internal compiler error: in gfc_free_namespace, at 
fortran/symbol.cc:4164
0xba55e1 gfc_free_namespace(gfc_namespace*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:4164
0xba39c1 gfc_free_symbol(gfc_symbol*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:3173
0xba3b89 gfc_release_symbol(gfc_symbol*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:3216
0xba5339 free_sym_tree
         ../../gcc-trunk/gcc/fortran/symbol.cc:4029
0xba5609 gfc_free_namespace(gfc_namespace*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:4168
0xba58ef gfc_symbol_done_2()
         ../../gcc-trunk/gcc/fortran/symbol.cc:4236
0xb12ec8 gfc_done_2()
         ../../gcc-trunk/gcc/fortran/misc.cc:387
0xb4ac7f clean_up_modules
         ../../gcc-trunk/gcc/fortran/parse.cc:7057
0xb4af02 translate_all_program_units
         ../../gcc-trunk/gcc/fortran/parse.cc:7122
0xb4b735 gfc_parse_file()
         ../../gcc-trunk/gcc/fortran/parse.cc:7413
0xbb626f gfc_be_parse_file
         ../../gcc-trunk/gcc/fortran/f95-lang.cc:241

Now adding -std=f2018 to the compiler flags I get:

pr87907.f90:15:18:

    15 |       subroutine g(x)   ! { dg-error "mismatch in argument" }
       |                  1
Error: FUNCTION attribute conflicts with SUBROUTINE attribute in 'g' at (1)
pr87907.f90:16:9:

    16 |       end subroutine g
       |         1
Error: Expecting END SUBMODULE statement at (1)
pr87907.f90:20:7:

    20 |    use m                ! { dg-error "has a type" }
       |       1
    21 |    integer :: x = 3
    22 |    call g(x)            ! { dg-error "which is not consistent 
with" }
       | 
     2
Error: 'g' at (1) has a type, which is not consistent with the CALL at (2)
free(): invalid pointer
f951: internal compiler error: Aborted
0x13b8ec2 crash_signal
         ../../gcc-trunk/gcc/toplev.cc:319
0xba584f gfc_free_namespace(gfc_namespace*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:4207
0xba39c1 gfc_free_symbol(gfc_symbol*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:3173
0xba3b89 gfc_release_symbol(gfc_symbol*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:3216
0xba5339 free_sym_tree
         ../../gcc-trunk/gcc/fortran/symbol.cc:4029
0xba5609 gfc_free_namespace(gfc_namespace*&)
         ../../gcc-trunk/gcc/fortran/symbol.cc:4168
0xba58ef gfc_symbol_done_2()
         ../../gcc-trunk/gcc/fortran/symbol.cc:4236
0xb12ec8 gfc_done_2()
         ../../gcc-trunk/gcc/fortran/misc.cc:387
0xb4ac7f clean_up_modules
         ../../gcc-trunk/gcc/fortran/parse.cc:7057
0xb4af02 translate_all_program_units
         ../../gcc-trunk/gcc/fortran/parse.cc:7122
0xb4b735 gfc_parse_file()
         ../../gcc-trunk/gcc/fortran/parse.cc:7413
0xbb626f gfc_be_parse_file
         ../../gcc-trunk/gcc/fortran/f95-lang.cc:241

I'll stop here...

We currently do not recover well from errors, and the prevention
of corrupted namespaces is apparently a goal we aim at.

Cheers,
Harald

>> The patch therefore does not require any testsuite update and
>> should not give any other surprises, so it should be very safe.
>> The plan is also to leave the PR open for the time being.
>>
>> Regtesting on x86_64-pc-linux-gnu.  OK for mainline?
>>
>> Thanks,
>> Harald
>>
> 
>