Hi,
On 12/04/19 20:29, Jason Merrill wrote:
On 4/11/19 11:20 AM, Paolo Carlini wrote:
Hi,
over the last few days I spent some time on this regression, which at
first seemed just a minor error-recovery issue, but then I noticed
that very slightly tweeking the original testcase uncovered a pretty
serious ICE on valid:
template<typename SX, typename ...XE> void
fk (XE..., int/*SW*/);
void
w9 (void)
{
fk<int> (0);
}
The regression has to do with the changes committed by Jason for
c++/86932, in particular with the condition in coerce_template_parms:
if (template_parameter_pack_p (TREE_VALUE (parm))
&& (arg || !(complain & tf_partial))
&& !(arg && ARGUMENT_PACK_P (arg)))
which has the additional (arg || !complain & tf_partial)) false for
the present testcase, thus the null arg is not changed into an empty
pack, thus later instantiate_template calls check_instantiated_args
which finds it still null and crashes. Now, likely some additional
analysis is in order, but for sure there is an important difference
between the testcase which came with c++/86932 and the above:
non-type vs type template parameter pack. It seems to me that the
kind of problem fixed in c++/86932 cannot occur with type packs,
because it boils down to a reference to a previous parm (full
disclosure: the comments and logic in fixed_parameter_pack_p helped
me a lot here). Thus I had the idea of simply restricting the scope
of the new condition above by adding an || TREE_CODE (TREE_VALUE
(parm)) == TYPE_DECL, which definitely leads to a clean testsuite and
a proper behavior on the new testcases, AFAICS. I'm attaching what I
tested on x86_64-linux.
I think the important property here is that it's non-terminal, not
that it's a type pack. We can't deduce anything for a non-terminal
pack, so we should go ahead and make an empty pack.
I see.
Then what about something bolder, like the below? Instead of fiddling
with the details of coerce_template_parms - how it handles the explicit
arguments - in fn_type_unification we deal with both parameter_pack ==
true and false in the same way when targ == NULL_TREE, thus we set
incomplete. Then, for the new testcases, since incomplete is true, there
is no jump to the deduced label and type_unification_real takes care of
making the empty pack - the same happens already when there are no
explicit arguments. Tested x86_64-linux. I also checked quite a few
other variants of the tests but nothing new, nothing interesting, showed
up...
Thanks, Paolo.
/////////////////////////
Index: cp/pt.c
===================================================================
--- cp/pt.c (revision 270364)
+++ cp/pt.c (working copy)
@@ -20176,21 +20176,17 @@ fn_type_unification (tree fn,
parameter_pack = TEMPLATE_PARM_PARAMETER_PACK (parm);
}
- if (!parameter_pack && targ == NULL_TREE)
+ if (targ == NULL_TREE)
/* No explicit argument for this template parameter. */
incomplete = true;
-
- if (parameter_pack && pack_deducible_p (parm, fn))
+ else if (parameter_pack && pack_deducible_p (parm, fn))
{
/* Mark the argument pack as "incomplete". We could
still deduce more arguments during unification.
We remove this mark in type_unification_real. */
- if (targ)
- {
- ARGUMENT_PACK_INCOMPLETE_P(targ) = 1;
- ARGUMENT_PACK_EXPLICIT_ARGS (targ)
- = ARGUMENT_PACK_ARGS (targ);
- }
+ ARGUMENT_PACK_INCOMPLETE_P(targ) = 1;
+ ARGUMENT_PACK_EXPLICIT_ARGS (targ)
+ = ARGUMENT_PACK_ARGS (targ);
/* We have some incomplete argument packs. */
incomplete = true;
Index: testsuite/g++.dg/cpp0x/pr89900-1.C
===================================================================
--- testsuite/g++.dg/cpp0x/pr89900-1.C (nonexistent)
+++ testsuite/g++.dg/cpp0x/pr89900-1.C (working copy)
@@ -0,0 +1,10 @@
+// { dg-do compile { target c++11 } }
+
+template<typename SX, typename ...XE> void
+fk (XE..., SW); // { dg-error "12:.SW. has not been declared" }
+
+void
+w9 (void)
+{
+ fk<int> (0);
+}
Index: testsuite/g++.dg/cpp0x/pr89900-2.C
===================================================================
--- testsuite/g++.dg/cpp0x/pr89900-2.C (nonexistent)
+++ testsuite/g++.dg/cpp0x/pr89900-2.C (working copy)
@@ -0,0 +1,10 @@
+// { dg-do compile { target c++11 } }
+
+template<typename SX, typename ...XE> void
+fk (XE..., int);
+
+void
+w9 (void)
+{
+ fk<int> (0);
+}
Index: testsuite/g++.dg/cpp0x/pr89900-3.C
===================================================================
--- testsuite/g++.dg/cpp0x/pr89900-3.C (nonexistent)
+++ testsuite/g++.dg/cpp0x/pr89900-3.C (working copy)
@@ -0,0 +1,10 @@
+// { dg-do compile { target c++11 } }
+
+template<typename ...XE> void
+fk (XE..., SW); // { dg-error "12:.SW. has not been declared" }
+
+void
+w9 (void)
+{
+ fk (0);
+}
Index: testsuite/g++.dg/cpp0x/pr89900-4.C
===================================================================
--- testsuite/g++.dg/cpp0x/pr89900-4.C (nonexistent)
+++ testsuite/g++.dg/cpp0x/pr89900-4.C (working copy)
@@ -0,0 +1,10 @@
+// { dg-do compile { target c++11 } }
+
+template<typename ...XE> void
+fk (XE..., int);
+
+void
+w9 (void)
+{
+ fk (0);
+}
