[PATCH, Fortran] Allow CHARACTER literals in assignments and DATA statements

Mark Eggleston mark.eggleston@codethink.co.uk
Tue Nov 5 09:55:00 GMT 2019 

On 25/10/2019 09:03, Tobias Burnus wrote:
> Hello Mark, hi all,
>
> On 10/21/19 4:40 PM, Mark Eggleston wrote:
>> This is an extension to support a legacy feature supported by other 
>> compilers such as flang and the sun compiler.  As I understand it 
>> this feature is associated with DEC so it enabled using 
>> -fdec-char-conversions and by -fdec.
>>
>> It allows character literals to be assigned to numeric (INTEGER, 
>> REAL, COMPLEX) and LOGICAL variables by direct assignment or in DATA 
>> statements.
>
>>     * arith.c (hollerith2representation): Use 
>> OPT_Wcharacter_truncation in
>>     call to gfc_warning.
>
> This has two effects: First, it permits to toggle the warning on and 
> off; secondly, it disables the warning by default. It is enabled by 
> -Wall, however. – I think that's acceptable: while Holleriths are less 
> transparent as normal strings, for normal strings the result is 
> identical.
>
>
>> + result->representation.string[result_len] = '\0'; /* For debugger  */
>
> Tiny nit: full stop after 'debugger'.
Done.
>
>
>> +/* Convert character to integer. The constant will be padded or 
>> truncated. */
>
> And here an extra space before '*/'.
Done.
>
>
>> +Allowing character literals to be used in a similar way to Hollerith 
>> constants
>> +is a non-standard extension.
>> +
>> +Character literals can be used in @code{DATA} statements and 
>> assignments with
>
> I wonder whether one should mention here explicitly that only 
> default-kind (i.e. kind=1) character strings are permitted. 
> Additionally, I wonder whether -fdec-char-conversion should be 
> mentioned here – without, it is not supported and the error message 
> doesn't point to this option.
>
Now mentions -fdec-char-conversion and kind=1.
>
>> +
>> +  /* Flang allows character conversions similar to Hollerith 
>> conversions
>> +     - the first characters will be turned into ascii values. */
>
> Is this Flang or DEC or …? I thought we talk about legacy support and 
> Flang is not really legacy.
>
>
Re-worded.
>> --- a/gcc/fortran/resolve.c
>> +++ b/gcc/fortran/resolve.c
>>   +  if ((gfc_numeric_ts (&lhs->ts) || lhs->ts.type == BT_LOGICAL)
>> +      && rhs->ts.type == BT_CHARACTER
>> +      && rhs->expr_type != EXPR_CONSTANT)
>> +    {
>> +      gfc_error ("Cannot convert %s to %s at %L", gfc_typename (rhs),
>> +         gfc_typename (lhs), &rhs->where);
>> +      return false;
>> +    }
>
> Maybe add a comment like:
> /* Happens with flag_dec_char_conversions for nonconstant strings.  */
> might help casual readers to understand where this if comes from.
>
Done.
>
>> @@ -331,8 +332,9 @@ gfc_conv_constant_to_tree (gfc_expr * expr)
>>               gfc_build_string_const (expr->representation.length,
>>                           expr->representation.string));
>>         if (!integer_zerop (tmp) && !integer_onep (tmp))
>> -        gfc_warning (0, "Assigning value other than 0 or 1 to LOGICAL"
>> -             " has undefined result at %L", &expr->where);
>> +        gfc_warning (OPT_Wsurprising, "Assigning value other than 0 
>> or 1 "
>> +                 "to LOGICAL has undefined result at %L",
>> +             &expr->where);
>
> I am not happy with this. We had odd issues with combining code 
> generated by gfortran and ifort and Booleans types ("logical"). 
> Namely, gfortran uses 0 and 1 – while ifort uses -1 and 0. When using 
> ".not. var", it is sufficient to flip a single bit – either the first 
> or the last bit – and it is sufficient to look only a single bit.
>
> Hence, one can get ".not. var .eqv. var".
>
> The same result one can get when assigning "-1" to logical. Hence, a 
> default warning makes more sense than -Wsurprising. At least, 
> -Wsurprising is enabled by default.
>
> Hence, I wonder whether your 'OPT_Wsurprising' or 
> 'flag_dec_char_conversions ? OPT_Wsurprising : 0' makes more sense.
>
The latter.
>
> Actually, I don't quickly see whether   4_'string'  (i.e. kind=4) 
> strings are rejected or not. The gfc_character2* functions all assume 
> kind=1 characters – while code like gfc_convert_constant or the 
> resolve.c code only looks at BT_CHARACTER.
> On the other hand, the add_conv calls in intrintrinsic.c's 
> add_conversions are only added for the default-character kind.
>
> In any case, can you add a test which checks that – even with 
> -fdec-char-conversion – assigning a 2_'string' and 4_'string' to a 
> integer/real/complex/logical will be rejected at compile time?
>
Did not add 2_'string' tests as 2 is not accepted as a valid kind for 
characters. The addition of 4_'string' in a data statement resulted in 
an ICE which has been fixed by only accepting characters of kind=1.
> Otherwise, it looks okay to me.
>
> Tobias
>
>
I noticed that warning were not produced for conversion to logicals, 
re-ordering of an if..else if sequence fixes that problem. Additional 
test cases have been added.

Steve Kargl suggested a revision to the conversion warning adding 
"Nonstandard" to the text this has also been done.

Tested on x86_64 using make -j 8 check-fortran.

Please find attached the updated patch, the change logs follow. OK to 
commit?

regards,

Mark

gcc/fortran/ChangeLog

     Jim MacArthur  <jim.macarthur@codethink.co.uk>
     Mark Eggleston  <mark.eggleston@codethink.com>

     * arith.c (hollerith2representation): Use OPT_Wcharacter_truncation in
     call to gfc_warning.  Add character2representation, gfc_character2int,
     gfc_character2real, gfc_character2complex and gfc_character2logical.
     * arith.h: Add prototypes for gfc_character2int, gfc_character2real,
     gfc_character2complex and gfc_character2logical.
     * expr.c (gfc_check_assign): Return true if left hand side is numeric
     or logical and the right hand side is character and of kind=1.
     * gfortran.texi: Add -fdec-char-conversions.
     * intrinsic.c (add_conversions): Add conversions from character to
     integer, real, complex and logical types for their supported kinds.
     (gfc_convert_type_warn): Reorder if..else if.. sequence so that 
warnings
     are produced for conversion to logical.
     * invoke.texi: Add option to list of options.
     * invoke.texi: Add Character conversion subsection to Extensions
     section.
     * lang.opt: Add new option.
     * options.c (set_dec_flags): Add SET_BITFLAG for
     flag_dec_char_conversions.
     * resolve.c (resolve_ordindary_assign): Issue error if the left hand
     side is numeric or logical and the right hand side is a character
     variable.
     * simplify.c (gfc_convert_constant): Assign the conversion function
     depending on destination type.
     * trans-const.c (gfc_constant_to_tree): Use OPT_Wsurprising in
     gfc_warning allowing the warning to be switched off only if
     flag_dec_char_conversions is enabled.

gcc/testsuite/gfortran.dg

     Jim MacArthur <jim.macarthur@codethink.co.uk>
     Mark Eggleston <mark.eggleston@codethink.com>

     PR fortran/89103
     * gfortran.dg/dec_char_conversion_in_assignment_1.f90: New test.
     * gfortran.dg/dec_char_conversion_in_assignment_2.f90: New test.
     * gfortran.dg/dec_char_conversion_in_assignment_3.f90: New test.
     * gfortran.dg/dec_char_conversion_in_assignment_4.f90: New test.
     * gfortran.dg/dec_char_conversion_in_assignment_5.f90: New test.
     * gfortran.dg/dec_char_conversion_in_assignment_6.f90: New test.
     * gfortran.dg/dec_char_conversion_in_assignment_7.f90: New test.
     * gfortran.dg/dec_char_conversion_in_assignment_8.f90: New test.
     * gfortran.dg/dec_char_conversion_in_data_1.f90: New test.
     * gfortran.dg/dec_char_conversion_in_data_2.f90: New test.
     * gfortran.dg/dec_char_conversion_in_data_3.f90: New test.
     * gfortran.dg/dec_char_conversion_in_data_4.f90: New test.
     * gfortran.dg/dec_char_conversion_in_data_5.f90: New test.
     * gfortran.dg/dec_char_conversion_in_data_6.f90: New test.
     * gfortran.dg/dec_char_conversion_in_data_7.f90: New test.
     * gfortran.dg/hollerith5.f90: Add -Wsurprising to options.
     * gfortran.dg/hollerith_legacy.f90: Add -Wsurprising to options.
     * gfortran.dg/no_char_to_numeric_assign.f90: New test.

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