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

[Jason Merrill <jason@redhat.com>]

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.

> +      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
>>
>