c++: reduce redundant deprecated warnings

If a template uses a deprecated function, we should warn there and not also
whenever the template is instantiated.  I implement this by suppressing
the warning at the location; then to make this also work with modules, I
need to make sure to set TREE_NO_WARNING so that the warning spec for this
location gets recorded.

And then I noticed that has_warning_spec was broken such that if it
returned true than get_nowarn_spec would always return null.

gcc/cp/ChangeLog:

	* decl2.cc (cp_handle_deprecated_or_unavailable): Avoid redundant
	warning.
	* call.cc (build_over_call): Set TREE_NO_WARNING for calls
	to deprecated functions.
	* semantics.cc (finish_call_expr): Propagate TREE_NO_WARNING.

gcc/ChangeLog:

	* warning-control.cc (has_warning_spec): Fix handling of
	get_no_warning_bit.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/deprecated-21.C: New test.
	* g++.dg/modules/warn-spec-2_a.C: New test.
	* g++.dg/modules/warn-spec-2_b.C: New test.

gcc/cp/call.cc

@@ -10004,6 +10004,11 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
       SET_EXPR_LOCATION (expr, input_location);
       if (TREE_THIS_VOLATILE (fn) && cfun)
 	current_function_returns_abnormally = 1;
+      if (TREE_DEPRECATED (fn)
+	  && warning_suppressed_at (input_location,
+				    OPT_Wdeprecated_declarations))
+	/* Make the expr consistent with the location.  */
+	TREE_NO_WARNING (expr) = true;
       if (immediate_invocation_p (fn))
 	{
 	  tree obj_arg = NULL_TREE, exprimm = expr;
@@ -10704,6 +10709,14 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
       if (TREE_CODE (c) == CALL_EXPR)
 	suppress_warning (c /* Suppress all warnings.  */);
     }
+  else if (TREE_DEPRECATED (fn)
+	   && warning_suppressed_at (input_location,
+				     OPT_Wdeprecated_declarations))
+    {
+      tree c = extract_call_expr (call);
+      if (TREE_CODE (c) == CALL_EXPR)
+	TREE_NO_WARNING (c) = true;
+    }
 
   return call;
 }

gcc/cp/decl2.cc

@@ -5943,7 +5943,12 @@ cp_handle_deprecated_or_unavailable (tree decl, tsubst_flags_t complain)
 	}
     }
   else
+    {
+      if (!warning_suppressed_at (input_location,
+				  OPT_Wdeprecated_declarations))
 	warned = warn_deprecated_use (decl, NULL_TREE);
+      suppress_warning_at (input_location, OPT_Wdeprecated_declarations);
+    }
 
   return warned;
 }

gcc/cp/semantics.cc

@@ -3313,11 +3313,12 @@ finish_call_expr (tree fn, vec<tree, va_gc> **args, bool disallow_virtual,
 	  orig_fn = sel_fn;
 	}
 
-      result = build_call_vec (TREE_TYPE (result), orig_fn, orig_args);
-      SET_EXPR_LOCATION (result, input_location);
-      KOENIG_LOOKUP_P (result) = koenig_p;
+      tree r = build_call_vec (TREE_TYPE (result), orig_fn, orig_args);
+      SET_EXPR_LOCATION (r, input_location);
+      KOENIG_LOOKUP_P (r) = koenig_p;
+      TREE_NO_WARNING (r) = TREE_NO_WARNING (result);
       release_tree_vector (orig_args);
-      result = convert_from_reference (result);
+      result = convert_from_reference (r);
     }
 
   return result;

gcc/testsuite/g++.dg/modules/warn-spec-2_a.C

@@ -0,0 +1,11 @@
+// { dg-additional-options -fmodules }
+
+export module M;
+
+[[deprecated]] void depr_fn() {}
+
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+
+export {
+  template <class T> void f(T) { depr_fn(); }
+}

gcc/testsuite/g++.dg/modules/warn-spec-2_b.C

@@ -0,0 +1,8 @@
+// { dg-additional-options -fmodules }
+
+import M;
+
+int main()
+{
+  f(42);
+}

gcc/testsuite/g++.dg/warn/deprecated-21.C

@@ -0,0 +1,12 @@
+// { dg-do compile { target c++11 } }
+
+[[deprecated]] void depr_fn() {}
+
+template <class T> void f(T) {
+  depr_fn();			// { dg-warning "deprecated" }
+}
+
+int main()
+{
+  f(42);
+}

gcc/warning-control.cc

@@ -262,7 +262,7 @@ copy_warning (gimple *to, const gimple *from)
 bool has_warning_spec (const_tree t)
 {
   const location_t loc = get_location (t);
-  return !RESERVED_LOCATION_P (loc) && !get_no_warning_bit (t);
+  return !RESERVED_LOCATION_P (loc) && get_no_warning_bit (t);
 }
 
 /* Retrieve warning dispostion bitmap for tree streaming.  */