[Patch, committed] Fortran: Fix 'fn spec' for deferred character length (was: Re: [r12-4457 Regression] FAIL: gfortran.dg/deferred_type_param_6.f90 -Os execution test on Linux/x86_64)

[Tobias Burnus <tobias@codesourcery.com>]

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On 16.10.21 20:54, Jan Hubicka wrote:
> I wrote:
>> Fortran has for a long time 'character(len=5), allocatable" or
>> "character(len=*)". In the first case, the "5" can be ignored as both
>> caller and callee know the length. In the second case, the length is
>> determined by the argument, but it cannot be changed.
>>
>> Since a not-that-short while, 'len=:' together with allocatable/pointer
>> is supported.
>>
>> In the latter case, the value can be change when the array
>> association/allocation is changed.
>> ...
>> +      if (!sym->ts.u.cl->length
>> +          && ((sym->attr.allocatable && sym->attr.target)
>> +              || sym->attr.pointer))
>> +        spec[spec_len++] = '.';
>> +      if (!sym->ts.u.cl->length && sym->attr.allocatable)
>> +        spec[spec_len++] = 'w';
>> +      else
>> +        spec[spec_len++] = 'R';
> Also escaping is quite important bit of information so it would be
> good to figure out if it really can escape rather than playing safe.

The pointer to the string length variable itself does not escape,
only its integer string value:

subroutine foo(x)
   character(len=:), pointer :: x
   character(len=:), pointer :: y
   y => x
has in the dump:
   .y = *_x;
   y = (character(kind=1)[1:.y] *) *x;

Thus, 'w' can always be used.

Committed as obvious as r12-4511-gff0eec94e87dfb7dc387f120ca5ade2707aecf50

Tobias
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commit ff0eec94e87dfb7dc387f120ca5ade2707aecf50
Author: Tobias Burnus <tobias@codesourcery.com>
Date:   Tue Oct 19 16:38:56 2021 +0200

    Fortran: Fix 'fn spec' for deferred character length
    
    Shows now up with gfortran.dg/deferred_type_param_6.f90 due to more ME
    optimizations, causing fails without this commit.
    
    gcc/fortran/ChangeLog:
    
            * trans-types.c (create_fn_spec): For allocatable/pointer
            character(len=:), use 'w' not 'R' as fn spec for the length dummy
            argument.
---
 gcc/fortran/trans-types.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/gcc/fortran/trans-types.c b/gcc/fortran/trans-types.c
index 50fceebc941..42778067dbe 100644
--- a/gcc/fortran/trans-types.c
+++ b/gcc/fortran/trans-types.c
@@ -3014,7 +3014,11 @@ create_fn_spec (gfc_symbol *sym, tree fntype)
 	}
       if (sym->ts.type == BT_CHARACTER)
 	{
-	  spec[spec_len++] = 'R';
+	  if (!sym->ts.u.cl->length
+	      && (sym->attr.allocatable || sym->attr.pointer))
+	    spec[spec_len++] = 'w';
+	  else
+	    spec[spec_len++] = 'R';
 	  spec[spec_len++] = ' ';
 	}
     }