Re: nvptx: Adjust 'scan-assembler' in 'gfortran.dg/weak-1.f90' (was: Support for NOINLINE attribute)

[Harald Anlauf <anlauf@gmx.de>]

Hi Thomas,

On 2/14/23 10:35, Thomas Schwinge wrote:
> Hi!
> 
> On 2023-02-13T18:50:23+0100, Harald Anlauf via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>> Pushed as:
>>
>> commit 086a1df4374962787db37c1f0d1bd9beb828f9e3
> 
>> On 2/12/23 22:28, Harald Anlauf via Gcc-patches wrote:
>>> There is one thing I cannot test, which is the handling of weak symbols
>>> on other platforms.  A quick glance at the C testcases suggests that
>>> someone with access to either an NVPTX or MingGW target might tell
>>> whether that particular target should be excluded.
> 
> Indeed nvptx does use a different assembler syntax; I've pushed to
> master branch commit 8d8175869ca94c600e64e27b7676787b2a398f6e
> "nvptx: Adjust 'scan-assembler' in 'gfortran.dg/weak-1.f90'", see
> attached.

thanks for taking care of this.

> And I'm curious, is '!GCC$ ATTRIBUTES weak' meant to be used only for
> weak definitions (like in 'gfortran.dg/weak-1.f90'), or also for weak
> declarations (which, for example, in the C world then evaluate to
> zero-address unless actually defined)?  When I did a quick experiment,
> that didn't seem to work?  (But may be my fault, of course.)
> 
> And, orthogonally: is '!GCC$ ATTRIBUTES weak' meant to be used only for
> subroutines (like in 'gfortran.dg/weak-1.f90') and also functions (I
> suppose; test case?), or also for weak "data" in some way (which, for
> example, in the C world then evaluates to a zero-address unless actually
> defined)?

It also works for functions, e.g.

integer function f ()
!GCC$ ATTRIBUTES weak :: f
   print *, "weak f"
   f = 0
end

Regarding symbols beyond procedures (subroutines, functions),
I had a look at what Crayftn supports.  Its manpage has:

```
WEAK

Syntax and use of the WEAK directive.
!DIR$ WEAK procedure_name[, procedure_name] ...
!DIR$ WEAK procedure_name= stub_name[, procedure_name1= stub_name1] ...

[...]

The WEAK directive supports the following arguments:

procedure_name
     A weak object in the form of a variable or procedure.
stub_name
     A stub procedure that exists in the code. The stub_name will be 
called if a strong reference does not exist for procedure_name. The 
stub_name procedure must have the same name and dummy argument list as 
procedure_name.
```

However, testing e.g. with a module variable either gave an
error message or assembly that suggests that this does not work,
at least not with version cce/14.0.0.

> Could help to at least add a few more test cases, and clarify the
> documentation?

I'm not sure whether we need to support weak symbols other than
procedures in gfortran.  Maybe Rimvydas can comment on this.

We could clarify the documentation an reject e.g. variables
using:

diff --git a/gcc/fortran/trans-decl.cc b/gcc/fortran/trans-decl.cc
index ff64588b9a8..75c04ad7ece 100644
--- a/gcc/fortran/trans-decl.cc
+++ b/gcc/fortran/trans-decl.cc
@@ -814,6 +814,13 @@ gfc_finish_var_decl (tree decl, gfc_symbol * sym)
        && (TREE_STATIC (decl) || DECL_EXTERNAL (decl)))
      set_decl_tls_model (decl, decl_default_tls_model (decl));

+  if ((sym->attr.ext_attr & (1 << EXT_ATTR_WEAK))
+      && sym->attr.flavor != FL_PROCEDURE)
+    {
+      gfc_error ("Symbol %qs at %L has the WEAK attribute but is not a "
+                "procedure", sym->name, &sym->declared_at);
+    }
+
    gfc_finish_decl_attrs (decl, &sym->attr);
  }

This would reject code like

module m
   integer :: i, j
!GCC$ ATTRIBUTES weak :: j
end

weak-1.f90:18:17:

    18 |   integer :: i, j
       |                 1
Error: Symbol 'j' at (1) has the WEAK attribute but is not a procedure

Comments and thoughts?

Cheers,
Harald

> 
> Grüße
>   Thomas
> 
> 
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