c++: equivalence of non-dependent calls [PR107461]

After r13-5684-g59e0376f607805 the (pruned) callee of a non-dependent
CALL_EXPR is a bare FUNCTION_DECL rather than ADDR_EXPR of FUNCTION_DECL.
This innocent change revealed that cp_tree_equal doesn't first check
dependence of a CALL_EXPR before treating a FUNCTION_DECL callee as a
dependent name, which leads to us incorrectly accepting the first two
testcases below and rejecting the third:

 * In the first testcase, cp_tree_equal incorrectly returns true for
   the two non-dependent CALL_EXPRs f(0) and f(0) (whose CALL_EXPR_FN
   are different FUNCTION_DECLs) which causes us to treat #2 as a
   redeclaration of #1.

 * Same issue in the second testcase, for f<int*>() and f<char>().

 * In the third testcase, cp_tree_equal incorrectly returns true for
   f<int>() and f<void(*)(int)>() which causes us to conflate the two
   dependent specializations A<decltype(f<int>()(U()))> and
   A<decltype(f<void(*)(int)>()(U()))>.

This patch fixes this by making called_fns_equal treat two callees as
dependent names only if the overall CALL_EXPRs are dependent, via a new
convenience function call_expr_dependent_name that is like dependent_name
but also checks dependence of the overall CALL_EXPR.

	PR c++/107461

gcc/cp/ChangeLog:

	* cp-tree.h (call_expr_dependent_name): Declare.
	* pt.cc (iterative_hash_template_arg) <case CALL_EXPR>: Use
	call_expr_dependent_name instead of dependent_name.
	* tree.cc (call_expr_dependent_name): Define.
	(called_fns_equal): Adjust to take two CALL_EXPRs instead of
	CALL_EXPR_FNs thereof.  Use call_expr_dependent_name instead
	of dependent_name.
	(cp_tree_equal) <case CALL_EXPR>: Adjust call to called_fns_equal.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/overload5.C: New test.
	* g++.dg/cpp0x/overload5a.C: New test.
	* g++.dg/cpp0x/overload6.C: New test.

gcc/cp/cp-tree.h

@@ -7902,6 +7902,7 @@ extern tree lookup_maybe_add			(tree fns, tree lookup,
 extern int is_overloaded_fn			(tree) ATTRIBUTE_PURE;
 extern bool really_overloaded_fn		(tree) ATTRIBUTE_PURE;
 extern tree dependent_name			(tree);
+extern tree call_expr_dependent_name		(tree);
 extern tree maybe_get_fns			(tree) ATTRIBUTE_PURE;
 extern tree get_fns				(tree) ATTRIBUTE_PURE;
 extern tree get_first_fn			(tree) ATTRIBUTE_PURE;

gcc/cp/pt.cc

@@ -1841,7 +1841,7 @@ iterative_hash_template_arg (tree arg, hashval_t val)
     case CALL_EXPR:
       {
 	tree fn = CALL_EXPR_FN (arg);
-	if (tree name = dependent_name (fn))
+	if (tree name = call_expr_dependent_name (arg))
 	  {
 	    if (TREE_CODE (fn) == TEMPLATE_ID_EXPR)
 	      val = iterative_hash_template_arg (TREE_OPERAND (fn, 1), val);

gcc/cp/tree.cc

@@ -2608,6 +2608,18 @@ dependent_name (tree x)
   return NULL_TREE;
 }
 
+/* Like dependent_name, but instead takes a CALL_EXPR and also checks
+   its dependence.  */
+
+tree
+call_expr_dependent_name (tree x)
+{
+  if (TREE_TYPE (x) != NULL_TREE)
+    /* X isn't dependent, so its callee isn't a dependent name.  */
+    return NULL_TREE;
+  return dependent_name (CALL_EXPR_FN (x));
+}
+
 /* Returns true iff X is an expression for an overloaded function
    whose type cannot be known without performing overload
    resolution.  */
@@ -3870,16 +3882,18 @@ decl_internal_context_p (const_tree decl)
   return !TREE_PUBLIC (decl);
 }
 
-/* Subroutine of cp_tree_equal: t1 and t2 are the CALL_EXPR_FNs of two
-   CALL_EXPRS.  Return whether they are equivalent.  */
+/* Subroutine of cp_tree_equal: t1 and t2 are two CALL_EXPRs.
+   Return whether their CALL_EXPR_FNs are equivalent.  */
 
 static bool
 called_fns_equal (tree t1, tree t2)
 {
   /* Core 1321: dependent names are equivalent even if the overload sets
      are different.  But do compare explicit template arguments.  */
-  tree name1 = dependent_name (t1);
-  tree name2 = dependent_name (t2);
+  tree name1 = call_expr_dependent_name (t1);
+  tree name2 = call_expr_dependent_name (t2);
+  t1 = CALL_EXPR_FN (t1);
+  t2 = CALL_EXPR_FN (t2);
   if (name1 || name2)
     {
       tree targs1 = NULL_TREE, targs2 = NULL_TREE;
@@ -4037,7 +4051,7 @@ cp_tree_equal (tree t1, tree t2)
 	if (KOENIG_LOOKUP_P (t1) != KOENIG_LOOKUP_P (t2))
 	  return false;
 
-	if (!called_fns_equal (CALL_EXPR_FN (t1), CALL_EXPR_FN (t2)))
+	if (!called_fns_equal (t1, t2))
 	  return false;
 
 	call_expr_arg_iterator iter1, iter2;

gcc/testsuite/g++.dg/cpp0x/overload5.C

@@ -0,0 +1,12 @@
+// PR c++/107461
+// { dg-do compile { target c++11 } }
+
+int f(...);
+template<class T> decltype(T() + f(0)) g(); // #1
+
+char f(int);
+template<class T> decltype(T() + f(0)) g(); // #2, distinct from #1
+
+int main() {
+  g<int>(); // { dg-error "ambiguous" }
+}

gcc/testsuite/g++.dg/cpp0x/overload5a.C

@@ -0,0 +1,10 @@
+// PR c++/107461
+// { dg-do compile { target c++11 } }
+
+template<class T> T f();
+template<class T> decltype(T() + f<int*>()) g(); // #1
+template<class T> decltype(T() + f<char>()) g(); // #2, distinct from #1
+
+int main() {
+  g<int>(); // { dg-error "ambiguous" }
+}

gcc/testsuite/g++.dg/cpp0x/overload6.C

@@ -0,0 +1,16 @@
+// PR c++/107461
+// { dg-do compile { target c++11 } }
+
+template<class T> T f();
+
+template<class> struct A { };
+
+template<class T> struct B {
+  template<class U, class = A<decltype(f<T>()(U()))>>
+  static void g(U);
+};
+
+int main() {
+  B<int> b;
+  B<void(*)(int)>::g(0); // { dg-bogus "no match" }
+}