Re: [PATCH 2/5] c++: Set the locus of the function result decl

[Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>]

On Thu, 17 Nov 2022 09:53:32 -0500
Jason Merrill <jason@redhat.com> wrote:

> On 11/17/22 03:56, Bernhard Reutner-Fischer wrote:
> > 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.  
> 
> Hmm, it should get set by your patch, since templates go through 
> start_function like normal functions.
> 
> > 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))))  
> 
> This condition is true only for the template definition, for which you 
> haven't gotten to your start_function change yet.
> 
> Instead, you want to copy the location for instantiations, i.e. check 
> DECL_TEMPLATE_INSTANTIATION instead of !DECL_USE_TEMPLATE.

No, that makes no difference.
But really I'm not interested in the template case, i only mentioned
them because they don't work and in case somebody wanted to have correct
locations.
I remember just frustration when i looked at those a year ago.

Is the hunk for normal functions OK for trunk?

thanks,

> 
> > +      DECL_SOURCE_LOCATION (DECL_RESULT (decl1))
> > +	= DECL_SOURCE_LOCATION (  
> 
> Open paren goes on the new line.
> 
> > +	    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;
> >>>    }
> >>>    \f
> >>>    /* Returns true iff an EH_SPEC_BLOCK should be created in the body of  
> >>  
> >   
>