c++: Set the locus of the function result decl

gcc/cp/ChangeLog:

	* decl.cc (grokdeclarator): Build RESULT_DECL.
	(start_preparsed_function): Copy location from template.
	* semantics.cc (apply_deduced_return_type): Handle
	arg != current_function_decl.
	* method.cc (implicitly_declare_fn): Use it.

gcc/ChangeLog:

	* function.cc (init_function_start): Use DECL_RESULT location
	for -Waggregate-return warning.

gcc/testsuite/ChangeLog:

	* g++.dg/diagnostic/return-type-loc1.C: New test.

Co-authored-by: Jason Merrill <jason@redhat.com>

gcc/cp/decl.cc

@@ -14772,6 +14772,19 @@ grokdeclarator (const cp_declarator *declarator,
 	else if (constinit_p)
 	  DECL_DECLARED_CONSTINIT_P (decl) = true;
       }
+    else if (TREE_CODE (decl) == FUNCTION_DECL)
+      {
+	/* If we saw a return type, record its location.  */
+	location_t loc = declspecs->locations[ds_type_spec];
+	if (loc != UNKNOWN_LOCATION)
+	  {
+	    tree restype = TREE_TYPE (TREE_TYPE (decl));
+	    tree resdecl = build_decl (loc, RESULT_DECL, 0, restype);
+	    DECL_ARTIFICIAL (resdecl) = 1;
+	    DECL_IGNORED_P (resdecl) = 1;
+	    DECL_RESULT (decl) = resdecl;
+	  }
+      }
 
     /* Record constancy and volatility on the DECL itself .  There's
        no need to do this when processing a template; we'll do this
@@ -17326,9 +17339,17 @@ start_preparsed_function (tree decl1, tree attrs, int flags)
 
   if (DECL_RESULT (decl1) == NULL_TREE)
     {
-      tree resdecl;
+      /* In a template instantiation, copy the return type location.  When
+	 parsing, the location will be set in grokdeclarator.  */
+      location_t loc = input_location;
+      if (DECL_TEMPLATE_INSTANTIATION (decl1))
+	{
+	  tree tmpl = template_for_substitution (decl1);
+	  if (tree res = DECL_RESULT (DECL_TEMPLATE_RESULT (tmpl)))
+	    loc = DECL_SOURCE_LOCATION (res);
+	}
 
-      resdecl = build_decl (input_location, RESULT_DECL, 0, restype);
+      tree resdecl = build_decl (loc, RESULT_DECL, 0, restype);
       DECL_ARTIFICIAL (resdecl) = 1;
       DECL_IGNORED_P (resdecl) = 1;
       DECL_RESULT (decl1) = resdecl;

gcc/cp/method.cc

@@ -3079,7 +3079,7 @@ implicitly_declare_fn (special_function_kind kind, tree type,
     {
       fn = copy_operator_fn (pattern_fn, EQ_EXPR);
       DECL_ARTIFICIAL (fn) = 1;
-      TREE_TYPE (fn) = change_return_type (boolean_type_node, TREE_TYPE (fn));
+      apply_deduced_return_type (fn, boolean_type_node);
       return fn;
     }
 

gcc/cp/semantics.cc

@@ -12325,24 +12325,23 @@ apply_deduced_return_type (tree fco, tree return_type)
   /* We already have a DECL_RESULT from start_preparsed_function.
      Now we need to redo the work it and allocate_struct_function
      did to reflect the new type.  */
-  gcc_assert (current_function_decl == fco);
-  result = build_decl (input_location, RESULT_DECL, NULL_TREE,
+  result = build_decl (DECL_SOURCE_LOCATION (result), RESULT_DECL, NULL_TREE,
 		       TYPE_MAIN_VARIANT (return_type));
   DECL_ARTIFICIAL (result) = 1;
   DECL_IGNORED_P (result) = 1;
   cp_apply_type_quals_to_decl (cp_type_quals (return_type),
                                result);
-
   DECL_RESULT (fco) = result;
 
   if (!processing_template_decl)
-    {
-      bool aggr = aggregate_value_p (result, fco);
+    if (function *fun = DECL_STRUCT_FUNCTION (fco))
+      {
+	bool aggr = aggregate_value_p (result, fco);
 #ifdef PCC_STATIC_STRUCT_RETURN
-      cfun->returns_pcc_struct = aggr;
+	fun->returns_pcc_struct = aggr;
 #endif
-      cfun->returns_struct = aggr;
-    }
+	fun->returns_struct = aggr;
+      }
 }
 
 /* DECL is a local variable or parameter from the surrounding scope of a

gcc/function.cc

@@ -4997,7 +4997,8 @@ init_function_start (tree subr)
   /* Warn if this value is an aggregate type,
      regardless of which calling convention we are using for it.  */
   if (AGGREGATE_TYPE_P (TREE_TYPE (DECL_RESULT (subr))))
-    warning (OPT_Waggregate_return, "function returns an aggregate");
+    warning_at (DECL_SOURCE_LOCATION (DECL_RESULT (subr)),
+		OPT_Waggregate_return, "function returns an aggregate");
 }
 
 /* Expand code to verify the stack_protect_guard.  This is invoked at

gcc/testsuite/g++.dg/diagnostic/return-type-loc1.C

@@ -0,0 +1,20 @@
+// { dg-do compile { target c++11 } }
+// { dg-additional-options -Waggregate-return }
+
+struct B { int i,j; };
+
+template <class T>
+struct A
+{
+  template <class U>
+  U				// { dg-warning "aggregate" }
+  f() { return {}; }
+};
+
+int main()
+{
+  A<int>().f<B>();		// { dg-warning "aggregate" }
+}
+
+B				// { dg-warning "aggregate" }
+g() { return {}; }