On Tue, 15 Nov 2022 18:52:41 -0500
Jason Merrill <jason@redhat.com> wrote:

> On 11/12/22 13:45, Bernhard Reutner-Fischer wrote:
> > gcc/cp/ChangeLog:
> > 
> > 	* decl.cc (start_function): Set the result decl source location to
> > 	the location of the typespec.
> > 
> > ---
> > Bootstrapped and regtested on x86_86-unknown-linux with no regressions.
> > Ok for trunk?
> > 
> > Cc: Nathan Sidwell <nathan@acm.org>
> > Cc: Jason Merrill <jason@redhat.com>
> > ---
> >   gcc/cp/decl.cc | 15 ++++++++++++++-
> >   1 file changed, 14 insertions(+), 1 deletion(-)
> > 
> > diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> > index 6e98ea35a39..ed40815e645 100644
> > --- a/gcc/cp/decl.cc
> > +++ b/gcc/cp/decl.cc
> > @@ -17449,6 +17449,8 @@ start_function (cp_decl_specifier_seq *declspecs,
> >   		tree attrs)
> >   {
> >     tree decl1;
> > +  tree result;
> > +  bool ret;  
> 
> We now prefer to declare new variables as late as possible, usually when 
> they are initialized.

Moved. Ok like attached? Bootstrapped and regtested fine.

> >     decl1 = grokdeclarator (declarator, declspecs, FUNCDEF, 1, &attrs);
> >     invoke_plugin_callbacks (PLUGIN_START_PARSE_FUNCTION, decl1);
> > @@ -17461,7 +17463,18 @@ start_function (cp_decl_specifier_seq *declspecs,
> >       gcc_assert (same_type_p (TREE_TYPE (TREE_TYPE (decl1)),
> >   			     integer_type_node));
> >   
> > -  return start_preparsed_function (decl1, attrs, /*flags=*/SF_DEFAULT);
> > +  ret = start_preparsed_function (decl1, attrs, /*flags=*/SF_DEFAULT);
> > +
> > +  /* decl1 might be ggc_freed here.  */
> > +  decl1 = current_function_decl;
> > +
> > +  /* Set the result decl source location to the location of the typespec.  */
> > +  if (TREE_CODE (decl1) == FUNCTION_DECL
> > +      && declspecs->locations[ds_type_spec] != UNKNOWN_LOCATION
> > +      && (result = DECL_RESULT (decl1)) != NULL_TREE
> > +      && DECL_SOURCE_LOCATION (result) == input_location)
> > +    DECL_SOURCE_LOCATION (result) = declspecs->locations[ds_type_spec];  
> 
> One way to handle the template case would be for the code in 
> start_preparsed_function that sets DECL_RESULT to check whether decl1 is 
> a template instantiation, and in that case copy the location from the 
> template's DECL_RESULT, i.e.
> 
> DECL_RESULT (DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (decl1)))

Well, that would probably work if something would set the location of
that template result decl properly, which nothing does out of the box.

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index ed7226b82f0..65d78c82a2d 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -17230,6 +17231,17 @@ start_preparsed_function (tree decl1, tree attrs, int flags)
       cp_apply_type_quals_to_decl (cp_type_quals (restype), resdecl);
     }
 
+  /* Set the result decl source location to the location of the typespec.  */
+  if (DECL_RESULT (decl1)
+      && !DECL_USE_TEMPLATE (decl1)
+      && DECL_TEMPLATE_INFO (decl1)
+      && DECL_TI_TEMPLATE (decl1)
+      && DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (decl1))
+      && DECL_RESULT (DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (decl1))))
+      DECL_SOURCE_LOCATION (DECL_RESULT (decl1))
+	= DECL_SOURCE_LOCATION (
+	    DECL_RESULT (DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (decl1))));
+
   /* Record the decl so that the function name is defined.
      If we already have a decl for this name, and it is a FUNCTION_DECL,
      use the old decl.  */

(gdb) call inform(DECL_SOURCE_LOCATION (DECL_RESULT (decl1)), "decl1 result locus before")
../tmp4/return-narrow-2.cc:7:3: note: decl1 result locus before
    7 |   { return _M_finish != 0; }
      |   ^
(gdb) n
(gdb) call inform(DECL_SOURCE_LOCATION (DECL_RESULT (decl1)), "decl1 result locus from TI")
../tmp4/return-narrow-2.cc:7:3: note: decl1 result locus from TI
(gdb) p DECL_SOURCE_LOCATION (DECL_RESULT (decl1))
$1 = 267168

I'm leaving the template case alone for now, maybe i'm motivated later
on to again look at grokfndecl and/or grokmethod to fill in the proper
location. For starters i only need normal functions.
But many thanks for the hint on where the template stuff is, i thought
i would not need it at all but had hoped that there is a spot where
both declspec are at hand and something is "derived" from the templates.

> 
> > +  return ret;
> >   }
> >   
> >   /* Returns true iff an EH_SPEC_BLOCK should be created in the body of  
>