[Bug c++/109531] [13 Regression] Checking ICE with hash table checking failed: equal operator returns true for a pair of values with a different hash value since r13-3292-gc2565a31c1622a

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109531

--- Comment #12 from Patrick Palka <ppalka at gcc dot gnu.org> ---
I suppose we're just neglecting to canonicalize a bound ttp's substituted args
before determining its canonical type.  Adding a call to coerce_template_parms
or canonicalize_type_argument seems to fix it:

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index fcc8e0d1d57..5ff91414f69 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -16285,9 +16285,18 @@ tsubst (tree t, tree args, tsubst_flags_t complain,
tree in_decl)
                      return error_mark_node;
                    tree argvec = tsubst (TI_ARGS (tinfo), args,
                                          complain, in_decl);
+                   // this fixes it
+                   tree tparms = DECL_INNERMOST_TEMPLATE_PARMS (tmpl);
+                   argvec = coerce_template_parms (tparms, argvec,
+                                                   tmpl, complain);
                    if (argvec == error_mark_node)
                      return error_mark_node;

+                   // or this
+                   for (tree& arg : tree_vec_range (argvec))
+                     if (TYPE_P (arg))
+                       arg = canonicalize_type_argument (arg, complain);
+
                    TEMPLATE_TEMPLATE_PARM_TEMPLATE_INFO (r)
                      = build_template_info (tmpl, argvec);
                  }