Re: [PATCH] Allow new/delete operator deletion only for replaceable.

[Jan Hubicka <hubicka@ucw.cz>]

> From 2f8ba3418f10b41bb839aadb292447bd757238d0 Mon Sep 17 00:00:00 2001
> From: Martin Liska <mliska@suse.cz>
> Date: Tue, 7 Apr 2020 16:23:27 +0200
> Subject: [PATCH] Allow new/delete operator deletion only for replaceable.
> 
> gcc/ChangeLog:
> 
> 2020-04-07  Martin Liska  <mliska@suse.cz>
> 
> 	PR c++/94314
> 	* gimple.c (gimple_call_operator_delete_p): Rename to...
> 	(gimple_call_replaceable_operator_delete_p): ... this.
> 	Use DECL_IS_REPLACEABLE_OPERATOR_DELETE_P.
> 	* gimple.h (gimple_call_operator_delete_p): Rename to ...
> 	(gimple_call_replaceable_operator_delete_p): ... this.
> 	* tree-core.h (tree_function_decl): Add replaceable_operator
> 	flag.
> 	* tree-ssa-dce.c (mark_all_reaching_defs_necessary_1):
> 	Use DECL_IS_REPLACEABLE_OPERATOR_DELETE_P.
> 	(propagate_necessity): Use gimple_call_replaceable_operator_delete_p.
> 	(eliminate_unnecessary_stmts): Likewise.
> 	* tree-streamer-in.c (unpack_ts_function_decl_value_fields):
> 	Pack DECL_IS_REPLACEABLE_OPERATOR.
> 	* tree-streamer-out.c (pack_ts_function_decl_value_fields):
> 	Unpack the field here.
> 	* tree.h (DECL_IS_REPLACEABLE_OPERATOR): New.
> 	(DECL_IS_REPLACEABLE_OPERATOR_NEW_P): New.
> 	(DECL_IS_REPLACEABLE_OPERATOR_DELETE_P): New.
> 	* cgraph.c (cgraph_node::dump): Dump if an operator is replaceable.
> 	* ipa-icf.c (sem_item::compare_referenced_symbol_properties): Compare
> 	replaceable operator flags.
> 
> gcc/cp/ChangeLog:
> 
> 2020-04-07  Martin Liska  <mliska@suse.cz>
> 
> 	PR c++/94314
> 	* decl.c (duplicate_decls): Duplicate also DECL_IS_REPLACEABLE_OPERATOR.
> 	(cxx_init_decl_processing): Mark replaceable all implicitly defined
> 	operators.
> 
> gcc/lto/ChangeLog:
> 
> 2020-04-07  Martin Liska  <mliska@suse.cz>
> 
> 	PR c++/94314
> 	* lto-common.c (compare_tree_sccs_1): Compare also
> 	DECL_IS_REPLACEABLE_OPERATOR.
> 
> gcc/testsuite/ChangeLog:
> 
> 2020-04-07  Martin Liska  <mliska@suse.cz>
> 
> 	PR c++/94314
> 	* g++.dg/pr94314-2.C: New test.
> 	* g++.dg/pr94314-3.C: New test.
> 	* g++.dg/pr94314.C: New test.
> @@ -2368,6 +2368,8 @@ duplicate_decls (tree newdecl, tree olddecl, bool newdecl_is_friend)
>  	    DECL_SET_IS_OPERATOR_NEW (newdecl, true);
>  	  DECL_LOOPING_CONST_OR_PURE_P (newdecl)
>  	    |= DECL_LOOPING_CONST_OR_PURE_P (olddecl);
> +	  DECL_IS_REPLACEABLE_OPERATOR (newdecl)
> +	    |= DECL_IS_REPLACEABLE_OPERATOR (olddecl);
>  
>  	  if (merge_attr)
>  	    merge_attribute_bits (newdecl, olddecl);

I think you will also need to take care of decl copying tht happens in
the midle-end.  If we do ipa-cp clone of the replaceable operator I
guess we want to copy the flag since it is still new/delete
(removeing it in dce has still the same semantics)

However if we split the function, I think we want to remove the flag
from foo.part clone, or one would be able to again produce the examples
with broken reference counting by making ipa-split to separate the
refernece count and tail of the function.

I am not quite sure about the offloading done by openMP - I think that
one produces new decls.

Honza