C++ PATCH for c++/49082 (wrong merging of noexcept(false)) and DR 1073

[Jason Merrill <jason at redhat dot com>]

In my earlier change to support noexcept in merge_exception_specifiers, 
I failed to consider the case of combining noexcept(false) with 
noexcept(true) in the context of implicitly declared member functions; 
that combination needs to result in noexcept(false), not noexcept(true).

While I was looking at this I also implemented DR 1073, which dropped 
compatibility between noexcept(false) and a dynamic-exception-specification.

Tested x86_64-pc-linux-gnu, applying to trunk.
commit a69bb0ad268ae28dd1a15617d733b4d9cf10f493
Author: Jason Merrill <jason@redhat.com>
Date:   Fri May 20 15:34:15 2011 -0400

    	DR 1073
    	PR c++/49082
    	* typeck.c (comp_except_specs): noexcept(false) is not compatible
    	with throw(type-list).
    	* typeck2.c (merge_exception_specifiers): noexcept(false)
    	beats any more limited specification.

diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index d98c62b..7791efc 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -986,14 +986,14 @@ comp_except_specs (const_tree t1, const_tree t2, int exact)
   /* First handle noexcept.  */
   if (exact < ce_exact)
     {
-      /* noexcept(false) is compatible with any throwing dynamic-exc-spec
+      /* noexcept(false) is compatible with no exception-specification,
 	 and stricter than any spec.  */
       if (t1 == noexcept_false_spec)
-	return !nothrow_spec_p (t2) || exact == ce_derived;
-      /* Even a derived noexcept(false) is compatible with a throwing
-	 dynamic spec.  */
+	return t2 == NULL_TREE || exact == ce_derived;
+      /* Even a derived noexcept(false) is compatible with no
+	 exception-specification.  */
       if (t2 == noexcept_false_spec)
-	return !nothrow_spec_p (t1);
+	return t1 == NULL_TREE;
 
       /* Otherwise, if we aren't looking for an exact match, noexcept is
 	 equivalent to throw().  */
diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
index 26b9816..c2eff9e 100644
--- a/gcc/cp/typeck2.c
+++ b/gcc/cp/typeck2.c
@@ -1756,10 +1756,13 @@ add_exception_specifier (tree list, tree spec, int complain)
 tree
 merge_exception_specifiers (tree list, tree add)
 {
-  if (!list || !add)
-    return NULL_TREE;
+  /* No exception-specifier or noexcept(false) are less strict than
+     anything else.  Prefer the newer variant (LIST).  */
+  if (!list || list == noexcept_false_spec)
+    return list;
+  else if (!add || add == noexcept_false_spec)
+    return add;
   /* For merging noexcept(true) and throw(), take the more recent one (LIST).
-     A throw(type-list) spec takes precedence over a noexcept(false) spec.
      Any other noexcept-spec should only be merged with an equivalent one.
      So the !TREE_VALUE code below is correct for all cases.  */
   else if (!TREE_VALUE (add))
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept02.C b/gcc/testsuite/g++.dg/cpp0x/noexcept02.C
index 60015e7..ffbb091 100644
--- a/gcc/testsuite/g++.dg/cpp0x/noexcept02.C
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept02.C
@@ -10,9 +10,9 @@ void f();
 
 SA(!noexcept(f()));
 
-void g() throw (int);
-void g() noexcept(false);	// { dg-error "previous declaration" }
-void g();			// { dg-error "different exception" }
+void g() throw (int);		// { dg-error "previous declaration" }
+void g() noexcept(false);	// { dg-error "different exception" }
+void g();
 
 void h() throw();
 void h() noexcept;
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept03.C b/gcc/testsuite/g++.dg/cpp0x/noexcept03.C
index c759f6f..54e04f3 100644
--- a/gcc/testsuite/g++.dg/cpp0x/noexcept03.C
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept03.C
@@ -36,19 +36,6 @@ void f2(T a) noexcept (noexcept (f (a)))
 
 struct A { A() { } };		// { dg-warning "does not throw" }
 
-// throw(int) overrides noexcept(false) in either order.
-void h() throw (int, std::bad_exception);
-void h() noexcept (false)
-{
-  throw 1.0;
-}
-
-void i() noexcept (false);
-void i() throw (int, std::bad_exception)
-{
-  throw 1.0;
-}
-
 int main()
 {
   // noexcept(false) allows throw.
@@ -57,10 +44,6 @@ int main()
   try { f(A()); } catch (int) { }
   try { f2(A()); } catch (int) { }
 
-  std::set_unexpected (my_unexpected);
-  try { h(); } catch (std::bad_exception) { }
-  try { i(); } catch (std::bad_exception) { }
-
   std::set_terminate (my_terminate);
   // noexcept(noexcept(int())) == noexcept(true).
   try { f2(1); } catch (...) { }
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept08.C b/gcc/testsuite/g++.dg/cpp0x/noexcept08.C
index c450332..1df85ef 100644
--- a/gcc/testsuite/g++.dg/cpp0x/noexcept08.C
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept08.C
@@ -34,7 +34,7 @@ struct D: A
   void g() noexcept(false);	// { dg-error "looser" }
   void h() noexcept(false);	// { dg-error "looser" }
   void i() noexcept(false);
-  void j() noexcept(false);	// compatible; treated as throw(int)
+  void j() noexcept(false);	// { dg-error "looser" }
 };
 
 struct E: A
diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept10.C b/gcc/testsuite/g++.dg/cpp0x/noexcept10.C
new file mode 100644
index 0000000..058a387
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/noexcept10.C
@@ -0,0 +1,27 @@
+// PR c++/49082
+// { dg-options -std=c++0x }
+
+namespace std { template <class T> T&& declval() noexcept; }
+
+struct Base
+{
+  Base(const Base&) noexcept(false);
+  Base(Base&&) noexcept(false);
+ ~Base() noexcept(false);
+};
+
+struct Derived
+: Base
+{
+  // Derived(const Derived&) = default;
+  // Derived(Derived&&) = default;
+};
+
+static_assert(!noexcept(Base(std::declval<const Base&>())), "Error");
+static_assert(!noexcept(Derived(std::declval<const Derived&>())), "Error"); // Error
+
+static_assert(!noexcept(Base(std::declval<Base&&>())), "Error");
+static_assert(!noexcept(Derived(std::declval<Derived&&>())), "Error"); // Error
+
+static_assert(!noexcept(std::declval<Base&>().~Base()), "Error"); // OK
+static_assert(!noexcept(std::declval<Derived&>().~Derived()), "Error"); // Error