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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/103769] [11/12 Regression] checking ICE in
 hashtab_chk_error with alias template and pack expansion after r11-7931
Date: Fri, 07 Jan 2022 09:27:22 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103769

--- Comment #7 from Martin Li=C5=A1ka <marxin at gcc dot gnu.org> ---
With:

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 0fa4a162354..9a8bfa51049 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -45,6 +45,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gcc-rich-location.h"
 #include "selftest.h"
 #include "target.h"
+#include "print-tree.h"

 /* The type of functions taking a tree, and some additional data, and
    returning an int.  */
@@ -9902,6 +9903,9 @@ lookup_template_class_1 (tree d1, tree arglist, tree
in_decl, tree context,
       elt.args =3D arglist;
       elt.spec =3D NULL_TREE;
       hash =3D spec_hasher::hash (&elt);
+      debug_tree (arglist);
+      fprintf (stderr, "hashing %p, %p: %d\n", arglist, gen_tmpl, hash);
+
       entry =3D type_specializations->find_with_hash (&elt, hash);

       if (entry)

I see:

./xg++ -B. --param=3Dhash-table-verification-limit=3D10000 -O1
~/Programming/testcases/pr103769.C -c
 <tree_vec 0x7ffff77059e0 length:1
    elt:0 <template_type_parm 0x7ffff770e348 Args VOID
        align:8 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
0x7ffff770ed20
       index 0 level 1 orig_level 1
        chain <type_decl 0x7ffff75d4ab0 Args>>>
hashing 0x7ffff77059e0, 0x7ffff7722000: -913564281
 <tree_vec 0x7ffff7705b00 length:1
    elt:0 <type_argument_pack 0x7ffff770e5e8
        type <tree_vec 0x7ffff7705b20 length:1 elt:0 <type_pack_expansion
0x7ffff770e540>>
        VOID
        align:8 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
0x7ffff770e5e8>>
hashing 0x7ffff7705b00, 0x7ffff7722080: -1965388615
 <tree_vec 0x7ffff7705ce0 length:1
    elt:0 <type_argument_pack 0x7ffff77280a8
        type <tree_vec 0x7ffff7705d00 length:1 elt:0 <type_pack_expansion
0x7ffff770e498>>
        VOID
        align:8 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
0x7ffff77280a8>>
hashing 0x7ffff7705ce0, 0x7ffff7722080: 683150001


verification fails for:

(gdb) p **entry
$2 =3D {
  tmpl =3D <template_decl 0x7ffff7722080 s>,
  args =3D <tree_vec 0x7ffff7705b00>,
  spec =3D <record_type 0x7ffff770e690 s>
}
(gdb) p *comparable
$3 =3D {
  tmpl =3D <template_decl 0x7ffff7722080 s>,
  args =3D <tree_vec 0x7ffff7705ce0>,
  spec =3D <tree 0x0>
}

So as seen, comp_template_args (e1->args, e2->args)) return true, while the
hash values
are different at the place where I dump them.=