c++: always check arity before deduction

This simple patch extends the r12-3271-gf1e73199569287 optimization
to happen for deduction without explicit template arguments as well.
The motivation for this is to accept testcases such as conv20.C and
ttp40.C below, which don't use explicit template arguments but for
which unnecessary template instantiation during deduction could be
avoided if we uniformly pruned overloads according to arity early.
This incidentally causes us to accept one reduced testcase from
PR c++/84075, but the underlying issue there remains at large.

As a nice side effect, this change causes the "candidate expects N
argument(s)" note during overload resolution failure to point to the
template candidate instead of the call site, which seems like an
improvement along the lines of r14-309-g14e881eb030509.

gcc/cp/ChangeLog:

	* call.cc (add_template_candidate_real): Check arity even
	when there are no explicit template arguments.  Combine the
	two adjacent '!obj' tests into one.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/vt-57397-1.C: Expect "candidate expects ... N
	argument(s)" at the declaration site instead of the call site.
	* g++.dg/cpp0x/vt-57397-2.C: Likewise.
	* g++.dg/overload/template5.C: Likewise.
	* g++.dg/template/local6.C: Likewise.
	* g++.dg/template/conv20.C: New test.
	* g++.dg/template/ttp40.C: New test.

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 399345307ea33dc67b3226343b4d00a7de52cee8..2bbaeee039d4c95d906be3f0870e43f630909129 100644 (file)
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -3535,13 +3535,13 @@ add_template_candidate_real (struct z_candidate **candidates, tree tmpl,
     }
   gcc_assert (ia == nargs_without_in_chrg);
 
-  if (!obj && explicit_targs)
+  if (!obj)
     {
       /* Check that there's no obvious arity mismatch before proceeding with
         deduction.  This avoids substituting explicit template arguments
-        into the template (which could result in an error outside the
-        immediate context) when the resulting candidate would be unviable
-        anyway.  */
+        into the template or e.g. derived-to-base parm/arg unification
+        (which could result in an error outside the immediate context) when
+        the resulting candidate would be unviable anyway.  */
       int min_arity = 0, max_arity = 0;
       tree parms = TYPE_ARG_TYPES (TREE_TYPE (tmpl));
       parms = skip_artificial_parms_for (tmpl, parms);
@@ -3571,11 +3571,7 @@ add_template_candidate_real (struct z_candidate **candidates, tree tmpl,
          reason = arity_rejection (NULL_TREE, max_arity, ia);
          goto fail;
        }
-    }
 
-  errs = errorcount+sorrycount;
-  if (!obj)
-    {
       convs = alloc_conversions (nargs);
 
       if (shortcut_bad_convs
@@ -3602,6 +3598,8 @@ add_template_candidate_real (struct z_candidate **candidates, tree tmpl,
            }
        }
     }
+
+  errs = errorcount+sorrycount;
   fn = fn_type_unification (tmpl, explicit_targs, targs,
                            args_without_in_chrg,
                            nargs_without_in_chrg,

diff --git a/gcc/testsuite/g++.dg/cpp0x/vt-57397-1.C b/gcc/testsuite/g++.dg/cpp0x/vt-57397-1.C
index 440bea5b2f75c99524f62e20ba641a1b03ca6a21..bac3b64ad7e8bc420c2ba7cb480432574b9092cf 100644 (file)
--- a/gcc/testsuite/g++.dg/cpp0x/vt-57397-1.C
+++ b/gcc/testsuite/g++.dg/cpp0x/vt-57397-1.C
@@ -3,20 +3,20 @@
 
 template<class T1, class... Tn>
 void foo(T1, Tn...);
+// { dg-message "candidate expects at least 1 argument, 0 provided" "" { target *-*-* } .-1 }
 
 template<class T1, class T2, class... Tn>
 void bar(T1, T2, Tn...);
+// { dg-message "candidate expects at least 2 arguments, 0 provided" "" { target *-*-* } .-1 }
+// { dg-message "candidate expects at least 2 arguments, 1 provided" "" { target *-*-* } .-2 }
 
 int main()
 {
   foo();   // { dg-error "no matching" }
-  // { dg-message "candidate expects at least 1 argument, 0 provided" "" { target *-*-* } .-1 }
   foo(1);
   foo(1, 2);
   bar();   // { dg-error "no matching" }
-  // { dg-message "candidate expects at least 2 arguments, 0 provided" "" { target *-*-* } .-1 }
   bar(1);  // { dg-error "no matching" }
-  // { dg-message "candidate expects at least 2 arguments, 1 provided" "" { target *-*-* } .-1 }
   bar(1, 2);
   bar(1, 2, 3);
 }

diff --git a/gcc/testsuite/g++.dg/cpp0x/vt-57397-2.C b/gcc/testsuite/g++.dg/cpp0x/vt-57397-2.C
index 1a99e22c5cb26c2d86509375cee4793f92f046cc..22b19ef6c1a08a0bd038f5a7391cc36b292a596a 100644 (file)
--- a/gcc/testsuite/g++.dg/cpp0x/vt-57397-2.C
+++ b/gcc/testsuite/g++.dg/cpp0x/vt-57397-2.C
@@ -3,21 +3,21 @@
 
 template<class T1, class... Tn, class... Tm>
 void foo(T1, Tn..., Tm...);
+// { dg-message "candidate expects at least 1 argument, 0 provided" "" { target *-*-* } .-1 }
 
 template<class T1, class T2, class... Tn, class... Tm>
 void bar(T1, T2, Tn..., Tm...);
+// { dg-message "candidate expects at least 2 arguments, 0 provided" "" { target *-*-* } .-1 }
+// { dg-message "candidate expects at least 2 arguments, 1 provided" "" { target *-*-* } .-2 }
 
 int main()
 {
   foo();   // { dg-error "no matching" }
-  // { dg-message "candidate expects at least 1 argument, 0 provided" "" { target *-*-* } .-1 }
   foo(1);
   foo(1, 2);
   foo(1, 2, 3);
   bar();   // { dg-error "no matching" }
-  // { dg-message "candidate expects at least 2 arguments, 0 provided" "" { target *-*-* } .-1 }
   bar(1);  // { dg-error "no matching" }
-  // { dg-message "candidate expects at least 2 arguments, 1 provided" "" { target *-*-* } .-1 }
   bar(1, 2);
   bar(1, 2, 3);
   bar(1, 2, 3, 4);

diff --git a/gcc/testsuite/g++.dg/overload/template5.C b/gcc/testsuite/g++.dg/overload/template5.C
index 902684059a8036725c7e3650880d874eb7970fe7..932c13bde3014be08de495f4701c5e3f0ccf533a 100644 (file)
--- a/gcc/testsuite/g++.dg/overload/template5.C
+++ b/gcc/testsuite/g++.dg/overload/template5.C
@@ -2,14 +2,14 @@
 
 template<typename T>
 int low(T a, T b, T c) { return a + b + c; } // { dg-message "template" }
+// { dg-message "(candidate|3 arguments, 2 provided)" "" { target *-*-* } .-1 }
 
 template<typename T>
 int high(T a, T b, T c) { return a + b + c; } // { dg-message "template" }
+// { dg-message "(candidate|3 arguments, 4 provided)" "" { target *-*-* } .-1 }
 
 void test (void)
 {
   low (5, 6);                  // { dg-error "no matching function" }
-  // { dg-message "(candidate|3 arguments, 2 provided)" "" { target *-*-* } .-1 }
   high (5, 6, 7, 8);           // { dg-error "no matching function" }
-  // { dg-message "(candidate|3 arguments, 4 provided)" "" { target *-*-* } .-1 }
 }

diff --git a/gcc/testsuite/g++.dg/template/conv20.C b/gcc/testsuite/g++.dg/template/conv20.C
new file mode 100644 (file)
index 0000000..202549a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/conv20.C
@@ -0,0 +1,17 @@
+// Verify we check arity early before deduction without explicit
+// template arguments.
+
+template<class T>
+struct A;
+
+template<class T>
+struct B : A<T> { };
+
+template<class T> void f(A<T>&, int); // #1
+template<class T> void f(B<T>&);      // #2
+
+int main() {
+  extern B<int> b;
+  ::f(b); // OK, deduction for #1 short-circuited and B<int> not instantiated,
+         // which would have resulted in a hard error
+}

diff --git a/gcc/testsuite/g++.dg/template/local6.C b/gcc/testsuite/g++.dg/template/local6.C
index 94c19be56a29e3b91e608a818c61813bbab6716a..d8ca5aa66ebbf1c90bae38e5cb3af3c2c3a758cf 100644 (file)
--- a/gcc/testsuite/g++.dg/template/local6.C
+++ b/gcc/testsuite/g++.dg/template/local6.C
@@ -1,11 +1,11 @@
 template <class T> struct PCVector2 // { dg-message "note" }
 {
-    template <class T2> PCVector2(const PCVector2<T> &cv) ; // { dg-message "note" }
+    template <class T2> PCVector2(const PCVector2<T> &cv) ; // { dg-message "candidate:" }
+    // { dg-message "(candidate|expects 1 argument, 2 provided|cannot convert)" "candidate note" { target *-*-* } .-1 }
 
     PCVector2<T> operator- (const PCVector2<T> &ov) const 
        { 
          return PCVector2<T>(ov.xFIELD, ov.yFIELD); // { dg-error "matching" }
-         // { dg-message "(candidate|expects 1 argument, 2 provided|cannot convert)" "candidate note" { target *-*-* } .-1 }
        }
 
     T xFIELD, yFIELD;

diff --git a/gcc/testsuite/g++.dg/template/ttp40.C b/gcc/testsuite/g++.dg/template/ttp40.C
new file mode 100644 (file)
index 0000000..9d68b9e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ttp40.C
@@ -0,0 +1,25 @@
+// Verify we check arity early before deduction without explicit
+// template arguments.
+// PR c++/84075
+
+template<class T>
+struct trait {
+  static const int value = T::value; // { dg-bogus "not a member of 'B'" }
+};
+
+template<class T, int N = trait<T>::value>
+struct A { };
+
+template<class T>
+void f(A<T, 42>, int); // #1
+
+struct B { };
+
+template<template<class> class TT>
+void f(TT<B>); // #2
+
+int main() {
+  A<int, 42> a;
+  f(a, 0); // OK, deduction for #2 short-circuited and A<B> not specialized,
+          // which would have resulted in a hard error
+}