cgraph: flatten and same_body aliases [PR96078]

The patch for PR92372 made us start warning about a flatten attribute on an
alias.  But in the case of C++ 'tor base/complete variants, the user didn't
create the alias.  If the alias target also has the attribute, the alias
points to a flattened function, so we shouldn't warn.

gcc/ChangeLog:

	PR c++/96078
	* cgraphunit.c (process_function_and_variable_attributes): Don't
	warn about flatten on an alias if the target also has it.
	* cgraph.h (symtab_node::get_alias_target_tree): New.

gcc/testsuite/ChangeLog:

	PR c++/96078
	* g++.dg/ext/attr-flatten1.C: New test.

1 files changed, 14 insertions, 0 deletions

diff --git a/gcc/cgraph.h b/gcc/cgraph.h
index 47b5c02..4a1f899 100644
--- a/gcc/cgraph.h
+++ b/gcc/cgraph.h
@@ -319,6 +319,9 @@ public:
   /* Return node that alias is aliasing.  */
   inline symtab_node *get_alias_target (void);
 
+  /* Return DECL that alias is aliasing.  */
+  inline tree get_alias_target_tree ();
+
   /* Set section for symbol and its aliases.  */
   void set_section (const char *section);
 
@@ -2665,6 +2668,17 @@ symtab_node::get_alias_target (void)
   return ref->referred;
 }
 
+/* Return the DECL (or identifier) that alias is aliasing.  Unlike the above,
+   this works whether or not the alias has been analyzed already.  */
+
+inline tree
+symtab_node::get_alias_target_tree ()
+{
+  if (alias_target)
+    return alias_target;
+  return get_alias_target ()->decl;
+}
+
 /* Return next reachable static symbol with initializer after the node.  */
 
 inline symtab_node *