c++: ICE with concepts TS multiple auto deduction [PR101886]

In extract_autos_r, we need to recompute TYPE_CANONICAL for the template
type parameter after adjusting its index, otherwise we end up with a
comptypes ICE for the below testcase.  Note that such in-place type
adjustment isn't generally safe to do since the type could be the
TYPE_CANONICAL of another (unadjusted) type, but in this case the
canonical auto (of some level and 0 index) is the first auto (of that
level) that's created, and so any auto that we do end up adjusting can't
be the canonical one.

	PR c++/101886

gcc/cp/ChangeLog:

	* pt.cc (extract_autos_r): Recompute TYPE_CANONICAL after
	adjusting the template type parameter's index.  Simplify
	by using TEMPLATE_TYPE_IDX.  Add some sanity checks.

gcc/testsuite/ChangeLog:

	* g++.dg/concepts/auto5.C: New test.

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 2516cca590ee0015daccdd7a07c5f7e3d85f6830..2b7b3756b68b39d4165c7fe9444d4a299f90b1ac 100644 (file)
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -29243,18 +29243,24 @@ extract_autos_r (tree t, void *data)
     {
       /* All the autos were built with index 0; fix that up now.  */
       tree *p = hash.find_slot (t, INSERT);
-      unsigned idx;
+      int idx;
       if (*p)
        /* If this is a repeated constrained-type-specifier, use the index we
           chose before.  */
-       idx = TEMPLATE_PARM_IDX (TEMPLATE_TYPE_PARM_INDEX (*p));
+       idx = TEMPLATE_TYPE_IDX (*p);
       else
        {
          /* Otherwise this is new, so use the current count.  */
          *p = t;
          idx = hash.elements () - 1;
        }
-      TEMPLATE_PARM_IDX (TEMPLATE_TYPE_PARM_INDEX (t)) = idx;
+      if (idx != TEMPLATE_TYPE_IDX (t))
+       {
+         gcc_checking_assert (TEMPLATE_TYPE_IDX (t) == 0);
+         gcc_checking_assert (TYPE_CANONICAL (t) != t);
+         TEMPLATE_TYPE_IDX (t) = idx;
+         TYPE_CANONICAL (t) = canonical_type_parameter (t);
+       }
     }
 
   /* Always keep walking.  */

diff --git a/gcc/testsuite/g++.dg/concepts/auto5.C b/gcc/testsuite/g++.dg/concepts/auto5.C
new file mode 100644 (file)
index 0000000..f1d653e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/auto5.C
@@ -0,0 +1,9 @@
+// PR c++/101886
+// { dg-do compile { target c++17_only } }
+// { dg-options "-fconcepts-ts" }
+
+template<typename...> struct A { };
+
+A<int, int> a;
+A<auto, auto> b1 = a;
+A<auto, auto> b2 = a;