(no subject)

[Centurion]

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HI, I am new in gcc codebase. Can you explain please why we can't just use
TREE_TYPE(parm) for TEMLATE_TEMPLATE_PARM and why DECL_INITIAL is needed
for it? I tried to debug Bug 114377 and it seems to work fine. Thanks

--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -11032,10 +11032,7 @@ find_template_parameter_info::found (tree parm)
 {
   if (TREE_CODE (parm) == TREE_LIST)
     parm = TREE_VALUE (parm);
-  if (TREE_CODE (parm) == TYPE_DECL)
-    parm = TREE_TYPE (parm);
-  else
-    parm = DECL_INITIAL (parm);
+  parm = TREE_TYPE(parm);
   gcc_checking_assert (TEMPLATE_PARM_P (parm));
   return parms.contains (parm);
 }

Re: your mail

[Segher Boessenkool]

On Thu, Mar 21, 2024 at 07:12:23PM +0400, Centurion via Gcc-help wrote:
> HI, I am new in gcc codebase. Can you explain please why we can't just use
> TREE_TYPE(parm) for TEMLATE_TEMPLATE_PARM and why DECL_INITIAL is needed
> for it? I tried to debug Bug 114377 and it seems to work fine. Thanks

You cannot use TREE_TYPE if that would just access nonsense data.

The wrong thing might still work, in many cases.  If you have no
substantiation why your proposed change would work fine, chances are it
does not.  Sorry.


Segher


> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -11032,10 +11032,7 @@ find_template_parameter_info::found (tree parm)
>  {
>    if (TREE_CODE (parm) == TREE_LIST)
>      parm = TREE_VALUE (parm);
> -  if (TREE_CODE (parm) == TYPE_DECL)
> -    parm = TREE_TYPE (parm);
> -  else
> -    parm = DECL_INITIAL (parm);
> +  parm = TREE_TYPE(parm);
>    gcc_checking_assert (TEMPLATE_PARM_P (parm));
>    return parms.contains (parm);
>  }

Re: your mail

[Centurion]

[-- Attachment #1: Type: text/plain, Size: 2770 bytes --]

```
bool
find_template_parameter_info::found (tree parm)
{
  if (TREE_CODE (parm) == TREE_LIST)
    parm = TREE_VALUE (parm);
  if (TREE_CODE (parm) == TYPE_DECL)
    parm = TREE_TYPE (parm);
  else
    parm = DECL_INITIAL (parm);
  gcc_checking_assert (TEMPLATE_PARM_P (parm));
  return parms.contains (parm);
}
```

Is there a reason why TREE_TYPE used only for TYPE_DECL, but not for
TEMPLATE_DECL ? process_template_parm initializes DECL_INITIAL for non type
template parameters, but  TYPE_DECL and TEMPLATE_DECL, stayed with nullptr,
on the other hand as I understood it always initializes TREE_TYPE.

cp/pt.cc::tree process_template_parm:
```
 if (parm && TREE_CODE (parm) == TEMPLATE_DECL)
{
 t = cxx_make_type (TEMPLATE_TEMPLATE_PARM);
...
 TREE_TYPE (result) = t;
...
}
      else
{
 t = cxx_make_type (TEMPLATE_TYPE_PARM);
 /* parm is either IDENTIFIER_NODE or NULL_TREE.  */
 decl = build_decl (parm_loc,
    TYPE_DECL, parm, t);
}
```
In other similar pieces of code the condition is for both for TYPE_DECL and
TEMLATE_DECL:

cp/pt.cc::tree template_parm_to_arg:
```
 if (DECL_P (t) && DECL_TEMPLATE_PARM_P (t))
    {
      if (TREE_CODE (t) == TYPE_DECL
 || TREE_CODE (t) == TEMPLATE_DECL)
t = TREE_TYPE (t);
      else
t = DECL_INITIAL (t);
    }
```
cp/pt.cc::tree get_template_parm_index:
```
if (TREE_CODE (parm) == PARM_DECL
      || TREE_CODE (parm) == CONST_DECL)
    parm = DECL_INITIAL (parm);
  else if (TREE_CODE (parm) == TYPE_DECL
  || TREE_CODE (parm) == TEMPLATE_DECL)
    parm = TREE_TYPE (parm);
```

Sorry if I ask stupid question.

On Thu, Mar 21, 2024 at 7:28 PM Segher Boessenkool <
segher@kernel.crashing.org> wrote:

> On Thu, Mar 21, 2024 at 07:12:23PM +0400, Centurion via Gcc-help wrote:
> > HI, I am new in gcc codebase. Can you explain please why we can't just
> use
> > TREE_TYPE(parm) for TEMLATE_TEMPLATE_PARM and why DECL_INITIAL is needed
> > for it? I tried to debug Bug 114377 and it seems to work fine. Thanks
>
> You cannot use TREE_TYPE if that would just access nonsense data.
>
> The wrong thing might still work, in many cases.  If you have no
> substantiation why your proposed change would work fine, chances are it
> does not.  Sorry.
>
>
> Segher
>
>
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -11032,10 +11032,7 @@ find_template_parameter_info::found (tree parm)
> >  {
> >    if (TREE_CODE (parm) == TREE_LIST)
> >      parm = TREE_VALUE (parm);
> > -  if (TREE_CODE (parm) == TYPE_DECL)
> > -    parm = TREE_TYPE (parm);
> > -  else
> > -    parm = DECL_INITIAL (parm);
> > +  parm = TREE_TYPE(parm);
> >    gcc_checking_assert (TEMPLATE_PARM_P (parm));
> >    return parms.contains (parm);
> >  }
>