re PR c++/47504 ([C++0x] some constexpr calculations erroneously overflow when…

re PR c++/47504 ([C++0x] some constexpr calculations erroneously overflow when using negative numbers)

	PR c++/47504
	* semantics.c (cxx_eval_constant_expression) [NOP_EXPR]: Don't let
	the conversion set TREE_OVERFLOW.

From-SVN: r171116

gcc/cp/ChangeLog

 2011-03-17  Jason Merrill  <jason@redhat.com>
 
+	PR c++/47504
+	* semantics.c (cxx_eval_constant_expression) [NOP_EXPR]: Don't let
+	the conversion set TREE_OVERFLOW.
+
 	Core 1212
 	* semantics.c (finish_decltype_type): Return T&& for xvalue.
 	* typeck.c (unlowered_expr_type): Preserve cv-quals.

gcc/cp/semantics.c

@@ -6991,6 +6991,11 @@ cxx_eval_constant_expression (const constexpr_call *call, tree t,
 	     conversion.  */
 	  return fold (t);
 	r = fold_build1 (TREE_CODE (t), to, op);
+	/* Conversion of an out-of-range value has implementation-defined
+	   behavior; the language considers it different from arithmetic
+	   overflow, which is undefined.  */
+	if (TREE_OVERFLOW_P (r) && !TREE_OVERFLOW_P (op))
+	  TREE_OVERFLOW (r) = false;
       }
       break;
 

gcc/testsuite/ChangeLog

+2011-03-17  Jason Merrill  <jason@redhat.com>
+
+	* g++.dg/cpp0x/constexpr-overflow2.C: New.
+	* g++.dg/cpp0x/constexpr-data2.C: Remove FIXME.
+
 2011-03-17  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gnat.dg/specs/elab2.ads: New test.

gcc/testsuite/g++.dg/cpp0x/constexpr-data2.C

@@ -44,5 +44,4 @@ extern template struct A3<int, 510>;
 
 // Use.
 A3<int, 1111> a31;
-// FIXME should this be an error?
 A3<char, 9999> a32;		// { dg-warning "overflow" }

gcc/testsuite/g++.dg/cpp0x/constexpr-overflow2.C

+// PR c++/47504
+// { dg-options -std=c++0x }
+
+char constexpr sub(char arg)
+{ return char(arg - char(1)); }
+
+int main()
+{ static char constexpr m = sub(-1); }