PR c++/87603 - constexpr functions are no longer noexcept.

* constexpr.c (is_sub_constant_expr): Remove unused function.
	* cp-tree.h (is_sub_constant_expr): Remove declaration.
	* except.c (check_noexcept_r): Don't consider a call to a constexpr
	function noexcept.

	* g++.dg/cpp0x/constexpr-noexcept.C: Adjust the expected result.
	* g++.dg/cpp0x/constexpr-noexcept3.C: Likewise.
	* g++.dg/cpp0x/constexpr-noexcept4.C: Likewise.
	* g++.dg/cpp0x/constexpr-noexcept8.C: New test.
	* g++.dg/cpp0x/inh-ctor32.C: Remove dg-message.
	* g++.dg/cpp1y/constexpr-noexcept1.C: New test.

From-SVN: r270320

gcc/cp/ChangeLog

@@ -3,6 +3,12 @@
 	* except.c (build_noexcept_spec): Use build_converted_constant_bool_expr
 	instead of perform_implicit_conversion_flags.
 
+	PR c++/87603 - constexpr functions are no longer noexcept.
+	* constexpr.c (is_sub_constant_expr): Remove unused function.
+	* cp-tree.h (is_sub_constant_expr): Remove declaration.
+	* except.c (check_noexcept_r): Don't consider a call to a constexpr
+	function noexcept.
+
 2019-04-11  Jakub Jelinek  <jakub@redhat.com>
 
 	PR translation/90035

gcc/cp/constexpr.c

@@ -5423,27 +5423,6 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
   return r;
 }
 
-/* Returns true if T is a valid subexpression of a constant expression,
-   even if it isn't itself a constant expression.  */
-
-bool
-is_sub_constant_expr (tree t)
-{
-  bool non_constant_p = false;
-  bool overflow_p = false;
-  hash_map <tree, tree> map;
-  HOST_WIDE_INT constexpr_ops_count = 0;
-
-  constexpr_ctx ctx
-    = { NULL, &map, NULL, NULL, NULL, NULL, &constexpr_ops_count,
-	true, true, false };
-
-  instantiate_constexpr_fns (t);
-  cxx_eval_constant_expression (&ctx, t, false, &non_constant_p,
-				&overflow_p);
-  return !non_constant_p && !overflow_p;
-}
-
 /* If T represents a constant expression returns its reduced value.
    Otherwise return error_mark_node.  If T is dependent, then
    return NULL.  */

gcc/cp/cp-tree.h

@@ -7720,7 +7720,6 @@ extern tree fold_non_dependent_init		(tree,
 						 tsubst_flags_t = tf_warning_or_error,
 						 bool = false);
 extern tree fold_simple				(tree);
-extern bool is_sub_constant_expr                (tree);
 extern bool reduced_constant_expression_p       (tree);
 extern bool is_instantiation_of_constexpr       (tree);
 extern bool var_in_constexpr_fn                 (tree);

gcc/cp/except.c

@@ -1128,11 +1128,14 @@ check_noexcept_r (tree *tp, int * /*walk_subtrees*/, void * /*data*/)
 	      && (DECL_ARTIFICIAL (fn)
 		  || nothrow_libfn_p (fn)))
 	    return TREE_NOTHROW (fn) ? NULL_TREE : fn;
-	  /* A call to a constexpr function is noexcept if the call
+	  /* We used to treat a call to a constexpr function as noexcept if
-	     is a constant expression.  */
+	     the call was a constant expression (CWG 1129).  This has changed
-	  if (DECL_DECLARED_CONSTEXPR_P (fn)
+	     in P0003 whereby noexcept has no special rule for constant
-	      && is_sub_constant_expr (t))
+	     expressions anymore.  Since the current behavior is important for
-	    return NULL_TREE;
+	     certain library functionality, we treat this as a DR, therefore
+	     adjusting the behavior for C++11 and C++14.  Previously, we had
+	     to evaluate the noexcept-specifier's operand here, but that could
+	     cause instantiations that would fail.  */
 	}
       if (!TYPE_NOTHROW_P (type))
 	return fn;

gcc/testsuite/ChangeLog

@@ -1,3 +1,13 @@
+2019-04-12  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/87603 - constexpr functions are no longer noexcept.
+	* g++.dg/cpp0x/constexpr-noexcept.C: Adjust the expected result.
+	* g++.dg/cpp0x/constexpr-noexcept3.C: Likewise.
+	* g++.dg/cpp0x/constexpr-noexcept4.C: Likewise.
+	* g++.dg/cpp0x/constexpr-noexcept8.C: New test.
+	* g++.dg/cpp0x/inh-ctor32.C: Remove dg-message.
+	* g++.dg/cpp1y/constexpr-noexcept1.C: New test.
+
 2019-04-12  Marek Polacek  <polacek@redhat.com>
 
 	* g++.dg/cpp0x/noexcept30.C: Tweak dg-error.

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

@@ -10,4 +10,7 @@ constexpr T value(T t) noexcept(is_funny<T>::value) { return t; } // Line 7
 
 constexpr bool ok = noexcept(value(42));
 
-static_assert(ok, "Assertion failure");
+// We used to treat a call to a constexpr function as noexcept if
+// the call was a constant expression.  We no longer do since
+// c++/87603.
+static_assert(!ok, "Assertion failure");

gcc/testsuite/g++.dg/cpp0x/constexpr-noexcept3.C

@@ -2,6 +2,8 @@
 
 constexpr int f(int i) { return i; }
 #define SA(X) static_assert (X, #X)
-SA(noexcept(f(42)));
+/* We used to assert that the following *is* noexcept, but this has changed
+   in c++/87603.  */
+SA(!noexcept(f(42)));
 int j;
 SA(!noexcept(f(j)));

gcc/testsuite/g++.dg/cpp0x/constexpr-noexcept4.C

@@ -1,6 +1,7 @@
 // { dg-do compile { target c++11 } }
-// A call is noexcept if it is a valid subexpression of a constant
+// We used to treat a call to a constexpr function as noexcept if
-// expression, even if it is not itself a constant expression.
+// the call was a constant expression.  We no longer do since
+// c++/87603.
 
 #define SA(X) static_assert(X,#X)
 
@@ -9,6 +10,6 @@ constexpr const int* f(const int *p) { return p; }
 int main()
 {
   constexpr int i = 42;
-  SA(noexcept(*f(&i)));
+  SA(!noexcept(*f(&i)));
-  SA(noexcept(f(&i)));
+  SA(!noexcept(f(&i)));
 }

gcc/testsuite/g++.dg/cpp0x/constexpr-noexcept8.C

@@ -0,0 +1,10 @@
+// PR c++/87603
+// { dg-do compile { target c++11 } }
+
+struct Y { };
+
+          bool operator<(Y a, Y b) { return false; }
+constexpr bool operator>(Y a, Y b) { return false; }
+
+static_assert(!noexcept(Y{} > Y{}), "");
+static_assert(!noexcept(Y{} < Y{}), "");

gcc/testsuite/g++.dg/cpp0x/inh-ctor32.C

@@ -168,7 +168,7 @@ namespace derived_ctor {
       };
       struct bar : boo {
 	template <typename ...T>
-	constexpr bar(T ... args) : boo(args...) {} // { dg-message "sorry, unimplemented: passing arguments to ellipsis" }
+	constexpr bar(T ... args) : boo(args...) {}
       };
       void f() noexcept(noexcept(bar{0,1}));
     }
@@ -200,12 +200,12 @@ namespace derived_ctor {
       };
       struct bor : boo {
 	template <typename ...T>
-	constexpr bor(T ... args) : boo(args...) {} // { dg-message "sorry, unimplemented: passing arguments to ellipsis" }
+	constexpr bor(T ... args) : boo(args...) {}
       };
       struct bar : bor {
 	using bor::bor;
       };
-      void f() noexcept(noexcept(bar{0,1})); // { dg-message "'constexpr' expansion" }
+      void f() noexcept(noexcept(bar{0,1}));
     }
 
     namespace no_constexpr_noninherited_ctor {

gcc/testsuite/g++.dg/cpp1y/constexpr-noexcept1.C

@@ -0,0 +1,12 @@
+// PR c++/87603
+// { dg-do compile { target c++14 } }
+
+template<typename T>
+struct basic_string_view
+{
+  constexpr basic_string_view(T p) noexcept { (void) p.i; }
+};
+
+struct X { } x;
+
+bool b = noexcept(basic_string_view<X>{x});