[Patch] (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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Hi Honza,

On 16.10.21 20:23, Jan Hubicka via Gcc-patches wrote:
>> FAIL: gfortran.dg/deferred_type_param_6.f90   -O1  execution test
>> FAIL: gfortran.dg/deferred_type_param_6.f90   -Os  execution test
> Sorry for the breakage.  This time it seems like bug in Fortran FE
> which was previously latent:
>
> __attribute__((fn spec (". . R ")))
> void subfunc (character(kind=1)[1:..__result] * & __result, integer(kind=8) * .__result)

...

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.

I attached a patch, which was not tested. I am not quite sure whether
the pointer address can actually escape or not - I think cannot but I
played safe.

Tobias
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Fortran: Fix fn spec for character-returning functions

gcc/fortran/ChangeLog
	* trans-types.c (create_fn_spec): For character-returning functions,
	set the hidden string-length argument to 'R' only when the "len=:",
	i.e. deferred length which goes alongside with allocatable/pointer.

diff --git a/gcc/fortran/trans-types.c b/gcc/fortran/trans-types.c
index 220976babb8..637d2c71d01 100644
--- a/gcc/fortran/trans-types.c
+++ b/gcc/fortran/trans-types.c
@@ -3008,7 +3008,14 @@ 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.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';
 	  spec[spec_len++] = ' ';
 	}
     }