Re: [PATCH] ipa-icf: skip variables with body_removed

["Martin Liška" <mliska@suse.cz>]

On 5/19/22 17:02, Jan Hubicka wrote:
>> Similarly to cgraph_nodes, it may happen that body_removed is set
>> during merging of symbols.
>>
>> 	PR ipa/105600
>>
>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
>>
>> Ready to be installed?
>> Thanks,
>> Martin
>>
>> gcc/ChangeLog:
>>
>> 	* ipa-icf.cc (sem_item_optimizer::filter_removed_items):
>> 	Skip variables with body_removed.
>> ---
>>  gcc/ipa-icf.cc | 7 ++++---
>>  1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/gcc/ipa-icf.cc b/gcc/ipa-icf.cc
>> index 765ae746745..6528a7a10b2 100644
>> --- a/gcc/ipa-icf.cc
>> +++ b/gcc/ipa-icf.cc
>> @@ -2411,10 +2411,11 @@ sem_item_optimizer::filter_removed_items (void)
>>  	    {
>>  	      /* Filter out non-readonly variables.  */
>>  	      tree decl = item->decl;
>> -	      if (TREE_READONLY (decl))
>> -		filtered.safe_push (item);
>> -	      else
>> +	      varpool_node *vnode = static_cast <sem_variable *>(item)->get_node ();
>> +	      if (!TREE_READONLY (decl) || vnode->body_removed)
>>  		remove_item (item);
>> +	      else
>> +		filtered.safe_push (item);
> 
> So the situation here is that we merge symbols but keep syntactic alias
> because the declarations are not compatible (have different attributes
> perhaps because of fortify source)?

The test-case is more about a constexpr symbol or so, I'm not familiar enough
with these modern C++.

cgraph_node looks like:

(gdb) p item->node->debug()
_ZN8nlohmann6detail12static_constINS0_10to_json_fnEE5valueE/10 (value) @0x7ffff7fb3200
  Type: variable
  Body removed by symtab_remove_unreachable_nodes
  Visibility: externally_visible semantic_interposition preempted_reg external public weak comdat comdat_group:_ZN8nlohmann6detail12static_constINS0_10to_json_fnEE5valueE one_only
  References: 
  Referring: _Z7to_jsonRN8nlohmann10basic_jsonISt3mapSt6vectorNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEblmiSaNS_14adl_serializerES2_IhSaIhEEEERK8Settings/1 (addr) _Z7to_jsonRN8nlohmann10basic_jsonISt3mapSt6vectorNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEblmiSaNS_14adl_serializerES2_IhSaIhEEEERK8Settings/1 (addr) 
  Read from file: a.o
  Availability: not_available
  Varpool flags: initialized read-only


> 
> Will ICF still see through the aliases and do merging?

No.

> I think you can
> craft a testcase by triggering the attribute mismatch and see what
> happens.  At the time we implemented ICF these aliases did not exists,
> so maybe some TLC is needed here.

Please come up with such test case :)

Thanks,
Martin

> 
> Honza