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

[Jason Merrill <jason@redhat.com>]

On 11/17/22 14:02, Bernhard Reutner-Fischer wrote:
> 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.

Hmm, when I stop there when processing the instantiation the template's 
DECL_RESULT has the right location information, e.g. for

template <class T> int f() { return 42; }

int main()
{
   f<int>();
}

#1  0x0000000000f950e8 in instantiate_body (pattern=<template_decl 
0x7ffff7ff5080 f>, args=<tree_vec 0x7fffe9712ae0>, d=<function_decl 
0x7fffe971e600 f>, nested_p=false) at /home/jason/gt/gcc/cp/pt.cc:26470
#0  start_preparsed_function (decl1=<function_decl 0x7fffe971e600 f>, 
attrs=<tree 0x0>, flags=1) at /home/jason/gt/gcc/cp/decl.cc:17252
(gdb) p expand_location (input_location)
$13 = {file = 0x4962370 "wa.C", line = 1, column = 24, data = 0x0, sysp 
= false}
(gdb) p expand_location (DECL_SOURCE_LOCATION (DECL_RESULT 
(DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (decl1)))))
$14 = {file = 0x4962370 "wa.C", line = 1, column = 20, data = 0x0, sysp 
= false}

> 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.

I'd like to get the template case right while we're looking at it.  I 
guess I can add that myself if you're done trying.

> Is the hunk for normal functions OK for trunk?

You also need a testcase for the desired behavior, with e.g.
{ dg-error "23:" }

> 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
>>>>   
>>>    
>>
>