PING^2 Re: [PATCH RFC] c++: lambda mangling alias issues [PR107897]

[Jason Merrill <jason@redhat.com>]

On 3/14/23 11:16, Jason Merrill wrote:
> On 3/8/23 11:54, Jason Merrill wrote:
>> On 3/8/23 11:15, Jason Merrill wrote:
>>> On 3/8/23 10:53, Jan Hubicka wrote:
>>>>> Tested x86_64-pc-linux-gnu.  Does this look good, or do we want to 
>>>>> factor the
>>>>> flag clearing into a symtab_node counterpart to cgraph_node::reset?
>>>>>
>>>>> -- 8< --
>>>>>
>>>>> In 107897, by the time we are looking at the mangling clash, the
>>>>> alias has already been removed from the symbol table by 
>>>>> analyze_functions,
>>>>> so we can't look at n->cpp_implicit_alias.  So just assume that 
>>>>> it's an
>>>>> alias if it's internal.
>>>>>
>>>>> In 108887 the problem is that removing the mangling alias from the 
>>>>> symbol
>>>>> table confuses analyze_functions, because it ended up as 
>>>>> first_analyzed
>>>>> somehow, so it becomes a dangling pointer.  Fixed by clearing 
>>>>> various flags
>>>>> to neutralize the alias.
>>>>>
>>>>>     PR c++/107897
>>>>>     PR c++/108887
>>>>>
>>>>> gcc/cp/ChangeLog:
>>>>>
>>>>>     * decl2.cc (record_mangling): Improve symbol table handling.
>>>>>
>>>>> gcc/testsuite/ChangeLog:
>>>>>
>>>>>     * g++.dg/cpp2a/concepts-lambda3.C: Use -flto if supported.
>>>>>     * g++.dg/cpp0x/lambda/lambda-mangle7.C: New test.
>>>>> ---
>>>>>   gcc/cp/decl2.cc                               | 25 +++++--
>>>>>   .../g++.dg/cpp0x/lambda/lambda-mangle7.C      | 70 
>>>>> +++++++++++++++++++
>>>>>   gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C |  1 +
>>>>>   3 files changed, 91 insertions(+), 5 deletions(-)
>>>>>   create mode 100644 
>>>>> gcc/testsuite/g++.dg/cpp0x/lambda/lambda-mangle7.C
>>>>>
>>>>> diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
>>>>> index 387e24542cd..e6e58b08de4 100644
>>>>> --- a/gcc/cp/decl2.cc
>>>>> +++ b/gcc/cp/decl2.cc
>>>>> @@ -4742,15 +4742,30 @@ record_mangling (tree decl, bool need_warning)
>>>>>       = mangled_decls->find_slot_with_hash (id, 
>>>>> IDENTIFIER_HASH_VALUE (id),
>>>>>                         INSERT);
>>>>> -  /* If this is already an alias, remove the alias, because the real
>>>>> +  /* If this is already an alias, cancel the alias, because the real
>>>>>        decl takes precedence.  */
>>>>>     if (*slot && DECL_ARTIFICIAL (*slot) && DECL_IGNORED_P (*slot))
>>>>> -    if (symtab_node *n = symtab_node::get (*slot))
>>>>> -      if (n->cpp_implicit_alias)
>>>>> +    {
>>>>> +      if (symtab_node *n = symtab_node::get (*slot))
>>>>>       {
>>>>> -      n->remove ();
>>>>> -      *slot = NULL_TREE;
>>>>> +      if (n->cpp_implicit_alias)
>>>>> +        {
>>>>> +          /* Actually removing the node isn't safe if other code 
>>>>> is already
>>>>> +         holding a pointer to it, so just neutralize it.  */
>>>>> +          n->remove_from_same_comdat_group ();
>>>>> +          n->analyzed = false;
>>>>> +          n->definition = false;
>>>>> +          n->alias = false;
>>>>> +          n->cpp_implicit_alias = false;
>>>> We have n->reset () for that which is used in similar situation when
>>>> frontends overwrites extern inline function by its different offline
>>>> implementation.
>>>
>>> The problem there is that reset() is a member of cgraph_node, not 
>>> symtab_node, and I need something that works for variables as well.
>>>
>>>> reset doesn't call remove_from_same_comdat_group probably because it 
>>>> was
>>>> never used on anything in comdat group.  So I think it would make sense
>>>> to call n->reset() here and add remove_from_same_comdat_group into 
>>>> that.
>>
>> How about moving it to symtab_node and using dyn_cast for the cgraph 
>> bits, like this:
> 
> Ping? (Patch in attachment in earlier message)
>