re PR c++/57132 (spurious warning: division by zero [-Wdiv-by-zero] in if (m) res %=m;)

/cp
2013-05-01  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/57132
	* pt.c (tsubst_copy_and_build, MODOP_EXPR): Increase / decrease
	c_inhibit_evaluation_warnings around build_x_modify_expr call.

/testsuite
2013-05-01  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/57132
	* g++.dg/warn/Wdiv-by-zero-bogus-2.C: New.

From-SVN: r198504

gcc/cp/ChangeLog

 2013-05-01  Paolo Carlini  <paolo.carlini@oracle.com>
 
+	PR c++/57132
+	* pt.c (tsubst_copy_and_build, MODOP_EXPR): Increase / decrease
+	c_inhibit_evaluation_warnings around build_x_modify_expr call.
+
+2013-05-01  Paolo Carlini  <paolo.carlini@oracle.com>
+
 	PR c++/57092
 	* semantics.c (finish_decltype_type): Handle instantiated template
 	non-type arguments.

gcc/cp/pt.c

@@ -13810,7 +13810,11 @@ tsubst_copy_and_build (tree t,
 
     case MODOP_EXPR:
       {
-	tree r = build_x_modify_expr
+	tree r;
+
+	++c_inhibit_evaluation_warnings;
+
+	r = build_x_modify_expr
 	  (EXPR_LOCATION (t),
 	   RECUR (TREE_OPERAND (t, 0)),
 	   TREE_CODE (TREE_OPERAND (t, 1)),
@@ -13824,6 +13828,9 @@ tsubst_copy_and_build (tree t,
 	   here.  */
 	if (TREE_NO_WARNING (t))
 	  TREE_NO_WARNING (r) = TREE_NO_WARNING (t);
+
+	--c_inhibit_evaluation_warnings;
+
 	RETURN (r);
       }
 

gcc/testsuite/ChangeLog

+2013-05-01  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/57132
+	* g++.dg/warn/Wdiv-by-zero-bogus-2.C: New.
+
 2013-05-01  Vladimir Makarov  <vmakarov@redhat.com>
 
 	PR target/57091

gcc/testsuite/g++.dg/warn/Wdiv-by-zero-bogus-2.C

+// PR c++/57132
+
+template<unsigned m, unsigned a>
+struct mod 
+{
+  static unsigned calc(unsigned x) {
+    unsigned res = a * x;
+    if (m)
+      res %= m;
+    return res;
+  }
+};
+
+int main()
+{
+  mod<3,2>::calc(7);
+  mod<0,2>::calc(7);
+}