[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]

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 <tob...@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++] = ' ';
 	}
     }