c++: Avoid -Wreturn-type warning if a template fn calls noreturn template fn [PR94742]

finish_call_expr already has code to set current_function_returns_abnormally
if a template calls a noreturn function, but on the following testcase it
doesn't call a FUNCTION_DECL, but TEMPLATE_DECL instead, in which case
we didn't check noreturn at all and just assumed it could return.

2020-04-25  Jakub Jelinek  <jakub@redhat.com>

	PR c++/94742
	* semantics.c (finish_call_expr): When looking if all overloads
	are noreturn, use STRIP_TEMPLATE to look through TEMPLATE_DECLs.

	* g++.dg/warn/Wreturn-type-12.C: New test.

gcc/cp/ChangeLog

+2020-04-25  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/94742
+	* semantics.c (finish_call_expr): When looking if all overloads
+	are noreturn, use STRIP_TEMPLATE to look through TEMPLATE_DECLs.
+
 2020-04-24  Martin Liska  <mliska@suse.cz>
 
 	* coroutines.cc: Fix compilation error for release checking

gcc/cp/semantics.c

@@ -2508,7 +2508,7 @@ finish_call_expr (tree fn, vec<tree, va_gc> **args, bool disallow_virtual,
 	      bool abnormal = true;
 	      for (lkp_iterator iter (fn); abnormal && iter; ++iter)
 		{
-		  tree fndecl = *iter;
+		  tree fndecl = STRIP_TEMPLATE (*iter);
 		  if (TREE_CODE (fndecl) != FUNCTION_DECL
 		      || !TREE_THIS_VOLATILE (fndecl))
 		    abnormal = false;

gcc/testsuite/ChangeLog

 2020-04-25  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/94742
+	* g++.dg/warn/Wreturn-type-12.C: New test.
+
 	PR tree-optimization/94734
 	PR tree-optimization/89430
 	* gcc.dg/tree-ssa/pr89430-1.c: Add xfail.

gcc/testsuite/g++.dg/warn/Wreturn-type-12.C

+// PR c++/94742
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wreturn-type" }
+
+template <class T>
+[[noreturn]] void
+foo (T const &t, char const *)
+{
+  throw T (t);
+}
+
+template <class U>
+int
+bar ()
+{
+  foo (42, __FUNCTION__);
+}	// { dg-bogus "no return statement in function returning non-void" }
+
+int
+main ()
+{
+  bar<long>();
+}