Patchwork [RFC,c++] fix PR 45329, provide information on overload resolution

login
register
mail settings
Submitter Nathan Froyd
Date Dec. 2, 2010, 10:09 p.m.
Message ID <20101202220946.GH18963@nightcrawler>
Download mbox | patch
Permalink /patch/74032/
State New
Headers show

Comments

Nathan Froyd - Dec. 2, 2010, 10:09 p.m.
On Fri, Nov 19, 2010 at 05:42:30PM -0500, Jason Merrill wrote:
> On 11/17/2010 03:46 PM, Nathan Froyd wrote:
> >There are two points at which I have not added rejection reasons.  One
> >of them--convert_class_to_reference--I have described in a comment.  The
> >second one is in add_function_candidate:
> >
> >   /* Kludge: When looking for a function from a subobject while generating
> >      an implicit copy/move constructor/operator=, don't consider anything
> >      that takes (a reference to) an unrelated type.  See c++/44909.  */
> 
> This should never lead to an error message, so I don't think we need
> to worry about it.  Well, it shouldn't once we re-enable implicit
> declaration of the copy constructor even with an explicit move
> constructor.

OK, thanks.  I will just leave it alone, then.

> >For the testcase above, a modified g++ prints:
> >
> >pr45329.C: In function 'int foo2(int)':
> >pr45329.C:26:7: error: no matching function for call to 'foo(int&)'
> >cc1plus: note: candidates are:
> >pr45329.C:7:5: note: int foo(int, int)
> >pr45329.C:7:5: note: candidate expects 2 arguments, 1 provided
> >pr45329.C:19:5: note: int foo(const S&)
> >pr45329.C:19:5: note: no known conversion for argument 1 from 'int' to 'const S&'
> >
> >which is a little friendlier.
> 
> Yes, but the cc1plus: line should have the source position of the
> call, and the rejection reason should be indented.

Yes, I noticed that the cc1plus bit looked a little funny.  The patch
below handles this by adding a location_t argument to print_z_candidates.

When you say "indented", do you mean like this:

pr45329.C: In function 'int foo2(int)':
pr45329.C:26:7: error: no matching function for call to 'foo(int&)'
pr45329.C:26:7: note: candidates are:
pr45329.C:7:5: note: int foo(int, int)
pr45329.C:7:5: note:   candidate expects 2 arguments, 1 provided
pr45329.C:19:5: note: int foo(const S&)
pr45329.C:19:5: note:   no known conversion for argument 1 from 'int' to 'const S&'

or do you mean something more radical?

Comments on the revised patch before I start tweaking testcases?

-Nathan

	PR c++/45329
	* cp-tree.h (location_at): Declare.
	* error.c (location_at): Export.
	* call.c (struct conversion): Document bad_p field.
	(enum rejection_reason_code): Define.
	(struct rejection_reason): Define.
	(struct z_candidate): Add `reason' field.
	(add_candidate): Add `reason' parameter.  Store it in CAND.
	(alloc_rejection, arity_rejection, arg_conversion_rejection):
	New functions.
	(bad_arg_conversion_rejection): New function.
	(convert_class_to_reference): Add comment.
	(add_function_candidate): Record rejection reason and pass it to
	add_candidate.
	(add_conv_candidate, build_builtin_candidate): Likewise.
	(add_template_candidate_real): Likewise.
	(print_z_candidate): Print CAND->REASON if it exists.  Adjust
	diagnostic strings.
	(print_z_candidates): Add location_t argument.  Adjust calling
	sequence for print_z_candidate. Print header line directly.
	(build_user_type_conversion_1): Add reason for rejection to
	CAND.  Adjust call to print_z_candidates.
	(build_new_function_call): Adjust call to print_z_candidates.
	(build_operator_new_call): Likewise.
	(build_op_call): Likewise.
	(build_conditional_expr): Likewise.
	(build_new_op): Likewise.
	(build_new_method_call): Likewise.
Jason Merrill - Dec. 3, 2010, 4:59 p.m.
On 12/02/2010 05:09 PM, Nathan Froyd wrote:
> When you say "indented", do you mean like this:
>
> pr45329.C: In function 'int foo2(int)':
> pr45329.C:26:7: error: no matching function for call to 'foo(int&)'
> pr45329.C:26:7: note: candidates are:
> pr45329.C:7:5: note: int foo(int, int)
> pr45329.C:7:5: note:   candidate expects 2 arguments, 1 provided
> pr45329.C:19:5: note: int foo(const S&)
> pr45329.C:19:5: note:   no known conversion for argument 1 from 'int' to 'const S&'

Yep.

Jason

Patch

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 6a11217..02037f6 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -84,6 +84,9 @@  struct conversion {
   BOOL_BITFIELD user_conv_p : 1;
   BOOL_BITFIELD ellipsis_p : 1;
   BOOL_BITFIELD this_p : 1;
+  /* True if this conversion would be permitted with a bending of
+     language standards, e.g. disregarding pointer qualifiers or
+     converting integers to pointers.  */
   BOOL_BITFIELD bad_p : 1;
   /* If KIND is ck_ref_bind ck_base_conv, true to indicate that a
      temporary should be created to hold the result of the
@@ -129,6 +132,7 @@  struct conversion {
 
 static struct obstack conversion_obstack;
 static bool conversion_obstack_initialized;
+struct rejection_reason;
 
 static struct z_candidate * tourney (struct z_candidate *);
 static int equal_functions (tree, tree);
@@ -151,7 +155,7 @@  static void op_error (enum tree_code, enum tree_code, tree, tree,
 static VEC(tree,gc) *resolve_args (VEC(tree,gc) *);
 static struct z_candidate *build_user_type_conversion_1 (tree, tree, int);
 static void print_z_candidate (const char *, struct z_candidate *);
-static void print_z_candidates (struct z_candidate *);
+static void print_z_candidates (location_t, struct z_candidate *);
 static tree build_this (tree);
 static struct z_candidate *splice_viable (struct z_candidate *, bool, bool *);
 static bool any_strictly_viable (struct z_candidate *);
@@ -190,7 +194,7 @@  static conversion *maybe_handle_ref_bind (conversion **);
 static void maybe_handle_implicit_object (conversion **);
 static struct z_candidate *add_candidate
 	(struct z_candidate **, tree, tree, const VEC(tree,gc) *, size_t,
-	 conversion **, tree, tree, int);
+	 conversion **, tree, tree, int, struct rejection_reason *);
 static tree source_type (conversion *);
 static void add_warning (struct z_candidate *, struct z_candidate *);
 static bool reference_compatible_p (tree, tree);
@@ -416,6 +420,45 @@  struct candidate_warning {
   candidate_warning *next;
 };
 
+/* Information for providing diagnostics about why overloading failed.  */
+
+enum rejection_reason_code {
+  rr_none,
+  rr_arity,
+  rr_arg_conversion,
+  rr_bad_arg_conversion
+};
+
+struct rejection_reason {
+  enum rejection_reason_code code;
+  union {
+    /* Information about an arity mismatch.  */
+    struct {
+      /* The expected number of arguments.  */
+      int expected;
+      /* The actual number of arguments in the call.  */
+      int actual;
+      /* Whether the call was a varargs call.  */
+      bool call_varargs_p;
+    } arity;
+    /* Information about an argument conversion mismatch.  */
+    struct {
+      /* The index of the argument, 0-based.  */
+      int n_arg;
+      /* The type of the actual argument.  */
+      tree from_type;
+      /* The type of the formal argument.  */
+      tree to_type;
+    } conversion;
+    /* Same, but for bad argument conversions.  */
+    struct {
+      int n_arg;
+      tree from_type;
+      tree to_type;
+    } bad_conversion;
+  } u;
+};
+
 struct z_candidate {
   /* The FUNCTION_DECL that will be called if this candidate is
      selected by overload resolution.  */
@@ -437,6 +480,7 @@  struct z_candidate {
      type.  */
   conversion *second_conv;
   int viable;
+  struct rejection_reason *reason;
   /* If FN is a member function, the binfo indicating the path used to
      qualify the name of FN at the call site.  This path is used to
      determine whether or not FN is accessible if it is selected by
@@ -518,6 +562,46 @@  conversion_obstack_alloc (size_t n)
   return p;
 }
 
+/* Allocate rejection reasons.  */
+
+static struct rejection_reason *
+alloc_rejection (enum rejection_reason_code code)
+{
+  struct rejection_reason *p;
+  p = (struct rejection_reason *) conversion_obstack_alloc (sizeof *p);
+  p->code = code;
+  return p;
+}
+
+static struct rejection_reason *
+arity_rejection (int expected, int actual)
+{
+  struct rejection_reason *r = alloc_rejection (rr_arity);
+  r->u.arity.expected = expected;
+  r->u.arity.actual = actual;
+  return r;
+}
+
+static struct rejection_reason *
+arg_conversion_rejection (int n_arg, tree from, tree to)
+{
+  struct rejection_reason *r = alloc_rejection (rr_arg_conversion);
+  r->u.conversion.n_arg = n_arg;
+  r->u.conversion.from_type = from;
+  r->u.conversion.to_type = to;
+  return r;
+}
+
+static struct rejection_reason *
+bad_arg_conversion_rejection (int n_arg, tree from, tree to)
+{
+  struct rejection_reason *r = alloc_rejection (rr_bad_arg_conversion);
+  r->u.bad_conversion.n_arg = n_arg;
+  r->u.bad_conversion.from_type = from;
+  r->u.bad_conversion.to_type = to;
+  return r;
+}
+
 /* Dynamically allocate a conversion.  */
 
 static conversion *
@@ -1147,6 +1231,10 @@  convert_class_to_reference (tree reference_type, tree s, tree expr, int flags)
 	  if (TREE_CODE (t2) != REFERENCE_TYPE
 	      || !reference_compatible_p (t, TREE_TYPE (t2)))
 	    {
+	      /* No need to set cand->reason here; this is most likely
+		 an ambiguous match.  If it's not, either this candidate
+		 will win, or we will have identified a reason for it
+		 losing already.  */
 	      cand->viable = 0;
 	    }
 	  else
@@ -1557,7 +1645,7 @@  add_candidate (struct z_candidate **candidates,
 	       tree fn, tree first_arg, const VEC(tree,gc) *args,
 	       size_t num_convs, conversion **convs,
 	       tree access_path, tree conversion_path,
-	       int viable)
+	       int viable, struct rejection_reason *reason)
 {
   struct z_candidate *cand = (struct z_candidate *)
     conversion_obstack_alloc (sizeof (struct z_candidate));
@@ -1570,12 +1658,28 @@  add_candidate (struct z_candidate **candidates,
   cand->access_path = access_path;
   cand->conversion_path = conversion_path;
   cand->viable = viable;
+  cand->reason = reason;
   cand->next = *candidates;
   *candidates = cand;
 
   return cand;
 }
 
+/* Return the number of remaining arguments in the parameter list
+   beginning with ARG.  */
+
+static int
+remaining_arguments (tree arg)
+{
+  int n;
+
+  for (n = 0; arg != NULL_TREE && arg != void_list_node;
+       arg = TREE_CHAIN (arg))
+    n++;
+
+  return n;
+}
+
 /* Create an overload candidate for the function or method FN called
    with the argument list FIRST_ARG/ARGS and add it to CANDIDATES.
    FLAGS is passed on to implicit_conversion.
@@ -1598,6 +1702,7 @@  add_function_candidate (struct z_candidate **candidates,
   tree orig_first_arg = first_arg;
   int skip;
   int viable = 1;
+  struct rejection_reason *reason = NULL;
 
   /* At this point we should not see any functions which haven't been
      explicitly declared, except for friend functions which will have
@@ -1638,11 +1743,19 @@  add_function_candidate (struct z_candidate **candidates,
     }
 
   if (i < len && parmnode)
-    viable = 0;
+    {
+      int remaining = remaining_arguments (parmnode);
+      viable = 0;
+      reason = arity_rejection (i + remaining, len);
+    }
 
   /* Make sure there are default args for the rest of the parms.  */
   else if (!sufficient_parms_p (parmnode))
-    viable = 0;
+    {
+      int remaining = remaining_arguments (parmnode);
+      viable = 0;
+      reason = arity_rejection (i + remaining, len);
+    }
 
   /* Kludge: When looking for a function from a subobject while generating
      an implicit copy/move constructor/operator=, don't consider anything
@@ -1679,7 +1792,7 @@  add_function_candidate (struct z_candidate **candidates,
 
   for (i = 0; i < len; ++i)
     {
-      tree arg, argtype;
+      tree arg, argtype, to_type;
       conversion *t;
       int is_this;
 
@@ -1746,11 +1859,13 @@  add_function_candidate (struct z_candidate **candidates,
 
 	  t = implicit_conversion (parmtype, argtype, arg,
 				   /*c_cast_p=*/false, lflags);
+	  to_type = parmtype;
 	}
       else
 	{
 	  t = build_identity_conv (argtype, arg);
 	  t->ellipsis_p = true;
+	  to_type = argtype;
 	}
 
       if (t && is_this)
@@ -1760,16 +1875,20 @@  add_function_candidate (struct z_candidate **candidates,
       if (! t)
 	{
 	  viable = 0;
+	  reason = arg_conversion_rejection (i, argtype, to_type);
 	  break;
 	}
 
       if (t->bad_p)
-	viable = -1;
+	{
+	  viable = -1;
+	  reason = bad_arg_conversion_rejection (i, argtype, to_type);
+	}
     }
 
  out:
   return add_candidate (candidates, fn, orig_first_arg, args, len, convs,
-			access_path, conversion_path, viable);
+			access_path, conversion_path, viable, reason);
 }
 
 /* Create an overload candidate for the conversion function FN which will
@@ -1793,6 +1912,7 @@  add_conv_candidate (struct z_candidate **candidates, tree fn, tree obj,
   int i, len, viable, flags;
   tree parmlist, parmnode;
   conversion **convs;
+  struct rejection_reason *reason;
 
   for (parmlist = totype; TREE_CODE (parmlist) != FUNCTION_TYPE; )
     parmlist = TREE_TYPE (parmlist);
@@ -1803,6 +1923,7 @@  add_conv_candidate (struct z_candidate **candidates, tree fn, tree obj,
   parmnode = parmlist;
   viable = 1;
   flags = LOOKUP_IMPLICIT;
+  reason = NULL;
 
   /* Don't bother looking up the same type twice.  */
   if (*candidates && (*candidates)->fn == totype)
@@ -1810,7 +1931,7 @@  add_conv_candidate (struct z_candidate **candidates, tree fn, tree obj,
 
   for (i = 0; i < len; ++i)
     {
-      tree arg, argtype;
+      tree arg, argtype, convert_type = NULL_TREE;
       conversion *t;
 
       if (i == 0)
@@ -1823,17 +1944,24 @@  add_conv_candidate (struct z_candidate **candidates, tree fn, tree obj,
       argtype = lvalue_type (arg);
 
       if (i == 0)
-	t = implicit_conversion (totype, argtype, arg, /*c_cast_p=*/false,
-				 flags);
+	{
+	  t = implicit_conversion (totype, argtype, arg, /*c_cast_p=*/false,
+				   flags);
+	  convert_type = totype;
+	}
       else if (parmnode == void_list_node)
 	break;
       else if (parmnode)
-	t = implicit_conversion (TREE_VALUE (parmnode), argtype, arg,
-				 /*c_cast_p=*/false, flags);
+	{
+	  t = implicit_conversion (TREE_VALUE (parmnode), argtype, arg,
+				   /*c_cast_p=*/false, flags);
+	  convert_type = TREE_VALUE (parmnode);
+	}
       else
 	{
 	  t = build_identity_conv (argtype, arg);
 	  t->ellipsis_p = true;
+	  convert_type = argtype;
 	}
 
       convs[i] = t;
@@ -1841,7 +1969,10 @@  add_conv_candidate (struct z_candidate **candidates, tree fn, tree obj,
 	break;
 
       if (t->bad_p)
-	viable = -1;
+	{
+	  viable = -1;
+	  reason = bad_arg_conversion_rejection (i, argtype, convert_type);
+	}
 
       if (i == 0)
 	continue;
@@ -1851,13 +1982,21 @@  add_conv_candidate (struct z_candidate **candidates, tree fn, tree obj,
     }
 
   if (i < len)
-    viable = 0;
+    {
+      int remaining = remaining_arguments (parmnode);
+      viable = 0;
+      reason = arity_rejection (i + remaining, len);
+    }
 
   if (!sufficient_parms_p (parmnode))
-    viable = 0;
+    {
+      int remaining = remaining_arguments (parmnode);
+      viable = 0;
+      reason = arity_rejection (i + remaining, len);
+    }
 
   return add_candidate (candidates, totype, first_arg, arglist, len, convs,
-			access_path, conversion_path, viable);
+			access_path, conversion_path, viable, reason);
 }
 
 static void
@@ -1870,6 +2009,7 @@  build_builtin_candidate (struct z_candidate **candidates, tree fnname,
   size_t num_convs;
   int viable = 1, i;
   tree types[2];
+  struct rejection_reason *reason = NULL;
 
   types[0] = type1;
   types[1] = type2;
@@ -1897,9 +2037,13 @@  build_builtin_candidate (struct z_candidate **candidates, tree fnname,
 	  viable = 0;
 	  /* We need something for printing the candidate.  */
 	  t = build_identity_conv (types[i], NULL_TREE);
+	  reason = arg_conversion_rejection (i, argtypes[i], types[i]);
 	}
       else if (t->bad_p)
-	viable = 0;
+	{
+	  viable = 0;
+	  reason = bad_arg_conversion_rejection (i, argtypes[i], types[i]);
+	}
       convs[i] = t;
     }
 
@@ -1913,14 +2057,18 @@  build_builtin_candidate (struct z_candidate **candidates, tree fnname,
       if (t)
 	convs[0] = t;
       else
-	viable = 0;
+	{
+	  viable = 0;
+	  reason = arg_conversion_rejection (0, argtypes[2],
+					     boolean_type_node);
+	}
     }
 
   add_candidate (candidates, fnname, /*first_arg=*/NULL_TREE, /*args=*/NULL,
 		 num_convs, convs,
 		 /*access_path=*/NULL_TREE,
 		 /*conversion_path=*/NULL_TREE,
-		 viable);
+		 viable, reason);
 }
 
 static bool
@@ -2572,6 +2720,7 @@  add_template_candidate_real (struct z_candidate **candidates, tree tmpl,
   struct z_candidate *cand;
   int i;
   tree fn;
+  struct rejection_reason *reason = NULL;
 
   /* We don't do deduction on the in-charge parameter, the VTT
      parameter or 'this'.  */
@@ -2690,7 +2839,7 @@  add_template_candidate_real (struct z_candidate **candidates, tree tmpl,
   return cand;
  fail:
   return add_candidate (candidates, tmpl, first_arg, arglist, nargs, NULL,
-			access_path, conversion_path, 0);
+			access_path, conversion_path, 0, reason);
 }
 
 
@@ -2811,38 +2960,74 @@  equal_functions (tree fn1, tree fn2)
 static void
 print_z_candidate (const char *msgstr, struct z_candidate *candidate)
 {
+  const char *msg = (msgstr == NULL
+		     ? ""
+		     : ACONCAT ((msgstr, " ", NULL)));
+
   if (TREE_CODE (candidate->fn) == IDENTIFIER_NODE)
     {
       if (candidate->num_convs == 3)
-	inform (input_location, "%s %D(%T, %T, %T) <built-in>", msgstr, candidate->fn,
+	inform (input_location, "%s%D(%T, %T, %T) <built-in>", msg, candidate->fn,
 		candidate->convs[0]->type,
 		candidate->convs[1]->type,
 		candidate->convs[2]->type);
       else if (candidate->num_convs == 2)
-	inform (input_location, "%s %D(%T, %T) <built-in>", msgstr, candidate->fn,
+	inform (input_location, "%s%D(%T, %T) <built-in>", msg, candidate->fn,
 		candidate->convs[0]->type,
 		candidate->convs[1]->type);
       else
-	inform (input_location, "%s %D(%T) <built-in>", msgstr, candidate->fn,
+	inform (input_location, "%s%D(%T) <built-in>", msg, candidate->fn,
 		candidate->convs[0]->type);
     }
   else if (TYPE_P (candidate->fn))
-    inform (input_location, "%s %T <conversion>", msgstr, candidate->fn);
+    inform (input_location, "%s%T <conversion>", msg, candidate->fn);
   else if (candidate->viable == -1)
-    inform (input_location, "%s %+#D <near match>", msgstr, candidate->fn);
+    inform (input_location, "%s%+#D <near match>", msg, candidate->fn);
   else if (DECL_DELETED_FN (STRIP_TEMPLATE (candidate->fn)))
-    inform (input_location, "%s %+#D <deleted>", msgstr, candidate->fn);
+    inform (input_location, "%s%+#D <deleted>", msg, candidate->fn);
   else
-    inform (input_location, "%s %+#D", msgstr, candidate->fn);
+    inform (input_location, "%s%+#D", msg, candidate->fn);
+  /* Give the user some information about why this candidate failed.  */
+  if (candidate->reason != NULL)
+    {
+      struct rejection_reason *r = candidate->reason;
+      location_t loc = location_of (candidate->fn);
+
+      switch (r->code)
+	{
+	case rr_arity:
+	  inform_n (loc, r->u.arity.expected,
+		    "  candidate expects %d argument, %d provided",
+		    "  candidate expects %d arguments, %d provided",
+		    r->u.arity.expected, r->u.arity.actual);
+	  break;
+	case rr_arg_conversion:
+	  inform (loc,
+		  "  no known conversion for argument %d from %qT to %qT",
+		  r->u.conversion.n_arg+1, r->u.conversion.from_type,
+		  r->u.conversion.to_type);
+	  break;
+	case rr_bad_arg_conversion:
+	  inform (loc,
+		  "  no known conversion for argument %d from %qT to %qT",
+		  r->u.bad_conversion.n_arg+1, r->u.bad_conversion.from_type,
+		  r->u.bad_conversion.to_type);
+	  break;
+	case rr_none:
+	default:
+	  /* This candidate didn't have any issues or we failed to
+	     handle a particular code.  Either way...  */
+	  gcc_unreachable ();
+	}
+    }
 }
 
 static void
-print_z_candidates (struct z_candidate *candidates)
+print_z_candidates (location_t loc, struct z_candidate *candidates)
 {
-  const char *str;
   struct z_candidate *cand1;
   struct z_candidate **cand2;
-  char *spaces;
+  int n_candidates;
 
   if (!candidates)
     return;
@@ -2884,14 +3069,12 @@  print_z_candidates (struct z_candidate *candidates)
 	}
     }
 
-  str = candidates->next ? _("candidates are:") :  _("candidate is:");
-  spaces = NULL;
+  for (n_candidates = 0, cand1 = candidates; cand1; cand1 = cand1->next)
+    n_candidates++;
+
+  inform_n (loc, n_candidates, "candidate is:", "candidates are:");
   for (; candidates; candidates = candidates->next)
-    {
-      print_z_candidate (spaces ? spaces : str, candidates);
-      spaces = spaces ? spaces : get_spaces (str);
-    }
-  free (spaces);
+    print_z_candidate (NULL, candidates);
 }
 
 /* USER_SEQ is a user-defined conversion sequence, beginning with a
@@ -3128,9 +3311,18 @@  build_user_type_conversion_1 (tree totype, tree expr, int flags)
 	  cand->second_conv = ics;
 
 	  if (!ics)
-	    cand->viable = 0;
+	    {
+	      tree rettype = TREE_TYPE (TREE_TYPE (cand->fn));
+	      cand->viable = 0;
+	      cand->reason = arg_conversion_rejection (-1, rettype, totype);
+	    }
 	  else if (cand->viable == 1 && ics->bad_p)
-	    cand->viable = -1;
+	    {
+	      tree rettype = TREE_TYPE (TREE_TYPE (cand->fn));
+	      cand->viable = -1;
+	      cand->reason
+		= bad_arg_conversion_rejection (-1, rettype, totype);
+	    }
 	}
     }
 
@@ -3145,7 +3337,7 @@  build_user_type_conversion_1 (tree totype, tree expr, int flags)
 	{
 	  error ("conversion from %qT to %qT is ambiguous",
 		    fromtype, totype);
-	  print_z_candidates (candidates);
+	  print_z_candidates (location_of (expr), candidates);
 	}
 
       cand = candidates;	/* any one will do */
@@ -3392,19 +3584,21 @@  build_new_function_call (tree fn, VEC(tree,gc) **args, bool koenig_p,
     {
       if (complain & tf_error)
 	{
+	  tree name;
 	  if (!any_viable_p && candidates && ! candidates->next
 	      && (TREE_CODE (candidates->fn) == FUNCTION_DECL))
 	    return cp_build_function_call_vec (candidates->fn, args, complain);
 	  if (TREE_CODE (fn) == TEMPLATE_ID_EXPR)
 	    fn = TREE_OPERAND (fn, 0);
+	  name = DECL_NAME (OVL_CURRENT (fn));
 	  if (!any_viable_p)
 	    error ("no matching function for call to %<%D(%A)%>",
-		   DECL_NAME (OVL_CURRENT (fn)), build_tree_list_vec (*args));
+		   name, build_tree_list_vec (*args));
 	  else
 	    error ("call of overloaded %<%D(%A)%> is ambiguous",
-		   DECL_NAME (OVL_CURRENT (fn)), build_tree_list_vec (*args));
+		   name, build_tree_list_vec (*args));
 	  if (candidates)
-	    print_z_candidates (candidates);
+	    print_z_candidates (location_of (name), candidates);
 	}
       result = error_mark_node;
     }
@@ -3462,14 +3656,15 @@  build_operator_new_call (tree fnname, VEC(tree,gc) **args,
      and give up.  */
   if (!cand)
     {
+      tree name = DECL_NAME (OVL_CURRENT (fns));
       if (!any_viable_p)
 	error ("no matching function for call to %<%D(%A)%>",
-	       DECL_NAME (OVL_CURRENT (fns)), build_tree_list_vec (*args));
+	       name, build_tree_list_vec (*args));
       else
 	error ("call of overloaded %<%D(%A)%> is ambiguous",
-	       DECL_NAME (OVL_CURRENT (fns)), build_tree_list_vec (*args));
+	       name, build_tree_list_vec (*args));
       if (candidates)
-	print_z_candidates (candidates);
+	print_z_candidates (location_of (name), candidates);
       return error_mark_node;
     }
 
@@ -3619,7 +3814,7 @@  build_op_call (tree obj, VEC(tree,gc) **args, tsubst_flags_t complain)
         {
           error ("no match for call to %<(%T) (%A)%>", TREE_TYPE (obj),
 		 build_tree_list_vec (*args));
-          print_z_candidates (candidates);
+          print_z_candidates (location_of (TREE_TYPE (obj)), candidates);
         }
       result = error_mark_node;
     }
@@ -3632,7 +3827,7 @@  build_op_call (tree obj, VEC(tree,gc) **args, tsubst_flags_t complain)
             {
               error ("call of %<(%T) (%A)%> is ambiguous", 
                      TREE_TYPE (obj), build_tree_list_vec (*args));
-              print_z_candidates (candidates);
+              print_z_candidates (location_of (TREE_TYPE (obj)), candidates);
             }
 	  result = error_mark_node;
 	}
@@ -4051,7 +4246,7 @@  build_conditional_expr (tree arg1, tree arg2, tree arg3,
           if (complain & tf_error)
             {
               op_error (COND_EXPR, NOP_EXPR, arg1, arg2, arg3, FALSE);
-              print_z_candidates (candidates);
+              print_z_candidates (location_of (arg1), candidates);
             }
 	  return error_mark_node;
 	}
@@ -4061,7 +4256,7 @@  build_conditional_expr (tree arg1, tree arg2, tree arg3,
           if (complain & tf_error)
             {
               op_error (COND_EXPR, NOP_EXPR, arg1, arg2, arg3, FALSE);
-              print_z_candidates (candidates);
+              print_z_candidates (location_of (arg1), candidates);
             }
 	  return error_mark_node;
 	}
@@ -4580,7 +4775,7 @@  build_new_op (enum tree_code code, int flags, tree arg1, tree arg2, tree arg3,
 		    /* ... Otherwise, report the more generic
 		       "no matching operator found" error */
 		    op_error (code, code2, arg1, arg2, arg3, FALSE);
-		    print_z_candidates (candidates);
+		    print_z_candidates (location_of (arg1), candidates);
 		  }
 	    }
 	  result = error_mark_node;
@@ -4595,7 +4790,7 @@  build_new_op (enum tree_code code, int flags, tree arg1, tree arg2, tree arg3,
 	  if ((flags & LOOKUP_COMPLAIN) && (complain & tf_error))
 	    {
 	      op_error (code, code2, arg1, arg2, arg3, TRUE);
-	      print_z_candidates (candidates);
+	      print_z_candidates (location_of (arg1), candidates);
 	    }
 	  result = error_mark_node;
 	}
@@ -6655,7 +6850,7 @@  build_new_method_call (tree instance, tree fns, VEC(tree,gc) **args,
 	      if (free_p)
 		free (pretty_name);
 	    }
-	  print_z_candidates (candidates);
+	  print_z_candidates (location_of (name), candidates);
 	}
       call = error_mark_node;
     }
@@ -6676,7 +6871,7 @@  build_new_method_call (tree instance, tree fns, VEC(tree,gc) **args,
 		arglist = TREE_CHAIN (arglist);
 	      error ("call of overloaded %<%s(%A)%> is ambiguous", pretty_name,
 		     arglist);
-	      print_z_candidates (candidates);
+	      print_z_candidates (location_of (name), candidates);
 	      if (free_p)
 		free (pretty_name);
 	    }
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 23f594c..0a5afdf 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -4907,6 +4907,7 @@  extern void print_instantiation_context		(void);
 extern void maybe_warn_variadic_templates       (void);
 extern void maybe_warn_cpp0x			(cpp0x_warn_str str);
 extern bool pedwarn_cxx98                       (location_t, int, const char *, ...) ATTRIBUTE_GCC_DIAG(3,4);
+extern location_t location_of                   (tree);
 
 /* in except.c */
 extern void init_exception_processing		(void);
diff --git a/gcc/cp/error.c b/gcc/cp/error.c
index 2676966..614e462 100644
--- a/gcc/cp/error.c
+++ b/gcc/cp/error.c
@@ -97,7 +97,6 @@  static void cp_print_error_function (diagnostic_context *, diagnostic_info *);
 
 static bool cp_printer (pretty_printer *, text_info *, const char *,
 			int, bool, bool, bool);
-static location_t location_of (tree);
 
 void
 init_error (void)
@@ -2458,7 +2457,7 @@  lang_decl_name (tree decl, int v, bool translate)
 
 /* Return the location of a tree passed to %+ formats.  */
 
-static location_t
+location_t
 location_of (tree t)
 {
   if (TREE_CODE (t) == PARM_DECL && DECL_CONTEXT (t))