Patchwork C++ PATCH to improve -Wnoexcept with templates

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Submitter Jason Merrill
Date Aug. 19, 2010, 4:52 p.m.
Message ID <4C6D6157.3010106@redhat.com>
Download mbox | patch
Permalink /patch/62201/
State New
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Comments

Jason Merrill - Aug. 19, 2010, 4:52 p.m.
A noexcept testcase I got from someone on the C++ committee led me to 
notice that -Wnoexcept wasn't warning about non-throwing functions that 
aren't defined yet, including templates.  This patch remembers such 
functions and checks them again at EOF.

Tested x86_64-pc-linux-gnu, applied to trunk.

Patch

commit 6630348bb4c308683991664058a972dca541a53f
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Aug 11 13:44:19 2010 -0400

    	* except.c (pending_noexcept, pending_noexcept_checks): New.
    	(perform_deferred_noexcept_checks): New.
    	(maybe_noexcept_warning): Split from...
    	(finish_noexcept_expr): ...here.  Adjust.
    	* decl2.c (cp_write_global_declarations): Call
    	perform_deferred_noexcept_checks.
    	* cp-tree.h: And declare it.

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index baa6656..dce28df 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -4883,6 +4883,7 @@  extern tree build_throw				(tree);
 extern int nothrow_libfn_p			(const_tree);
 extern void check_handlers			(tree);
 extern tree finish_noexcept_expr		(tree, tsubst_flags_t);
+extern void perform_deferred_noexcept_checks	(void);
 extern bool nothrow_spec_p			(const_tree);
 extern bool type_noexcept_p			(const_tree);
 extern bool type_throw_all_p			(const_tree);
diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index a768877..fed3452 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -3934,6 +3934,8 @@  cp_write_global_declarations (void)
 				      VEC_length (tree, pending_statics));
     }
 
+  perform_deferred_noexcept_checks ();
+
   /* Generate hidden aliases for Java.  */
   if (candidates)
     {
diff --git a/gcc/cp/except.c b/gcc/cp/except.c
index 79bab76..20b44e3 100644
--- a/gcc/cp/except.c
+++ b/gcc/cp/except.c
@@ -1069,6 +1069,51 @@  check_noexcept_r (tree *tp, int *walk_subtrees ATTRIBUTE_UNUSED,
   return NULL_TREE;
 }
 
+/* If a function that causes a noexcept-expression to be false isn't
+   defined yet, remember it and check it for TREE_NOTHROW again at EOF.  */
+
+typedef struct GTY(()) pending_noexcept {
+  tree fn;
+  location_t loc;
+} pending_noexcept;
+DEF_VEC_O(pending_noexcept);
+DEF_VEC_ALLOC_O(pending_noexcept,gc);
+static GTY(()) VEC(pending_noexcept,gc) *pending_noexcept_checks;
+
+/* FN is a FUNCTION_DECL that caused a noexcept-expr to be false.  Warn if
+   it can't throw.  */
+
+static void
+maybe_noexcept_warning (tree fn)
+{
+  if (TREE_NOTHROW (fn))
+    {
+      warning (OPT_Wnoexcept, "noexcept-expression evaluates to %<false%> "
+	       "because of a call to %qD", fn);
+      warning (OPT_Wnoexcept, "but %q+D does not throw; perhaps "
+	       "it should be declared %<noexcept%>", fn);
+    }
+}
+
+/* Check any functions that weren't defined earlier when they caused a
+   noexcept expression to evaluate to false.  */
+
+void
+perform_deferred_noexcept_checks (void)
+{
+  int i;
+  pending_noexcept *p;
+  location_t saved_loc = input_location;
+  for (i = 0;
+       VEC_iterate (pending_noexcept, pending_noexcept_checks, i, p);
+       ++i)
+    {
+      input_location = p->loc;
+      maybe_noexcept_warning (p->fn);
+    }
+  input_location = saved_loc;
+}
+
 /* Evaluate noexcept ( EXPR ).  */
 
 tree
@@ -1082,13 +1127,20 @@  finish_noexcept_expr (tree expr, tsubst_flags_t complain)
   fn = cp_walk_tree_without_duplicates (&expr, check_noexcept_r, 0);
   if (fn)
     {
-      if ((complain & tf_warning) && TREE_CODE (fn) == FUNCTION_DECL
-	  && TREE_NOTHROW (fn) && !DECL_ARTIFICIAL (fn))
+      if ((complain & tf_warning) && warn_noexcept
+	  && TREE_CODE (fn) == FUNCTION_DECL)
 	{
-	  warning (OPT_Wnoexcept, "noexcept-expression evaluates to %<false%> "
-		   "because of a call to %qD", fn);
-	  warning (OPT_Wnoexcept, "but %q+D does not throw; perhaps "
-		   "it should be declared %<noexcept%>", fn);
+	  if (!DECL_INITIAL (fn))
+	    {
+	      /* Not defined yet; check again at EOF.  */
+	      pending_noexcept *p
+		= VEC_safe_push (pending_noexcept, gc,
+				 pending_noexcept_checks, NULL);
+	      p->fn = fn;
+	      p->loc = input_location;
+	    }
+	  else
+	    maybe_noexcept_warning (fn);
 	}
       return boolean_false_node;
     }
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept09.C b/gcc/testsuite/g++.dg/cpp0x/noexcept09.C
new file mode 100644
index 0000000..2a4525c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept09.C
@@ -0,0 +1,14 @@ 
+// Test that -Wnoexcept works with templates
+// { dg-options "-std=c++0x -Wnoexcept" }
+
+template <class T>
+T f (T t) { return t; }		// { dg-warning "does not throw" }
+
+#define SA(X) static_assert(X, #X)
+
+SA (!noexcept(f(1)));		// { dg-warning "noexcept" }
+
+int main()
+{
+  f(1);				// Use f(int) so it gets instantiated
+}