https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107539
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:a4e577b044d69977f93b2cb7769dc991eadf2cf0 commit r13-4453-ga4e577b044d69977f93b2cb7769dc991eadf2cf0 Author: Patrick Palka <ppa...@redhat.com> Date: Thu Dec 1 20:11:53 2022 -0500 c++: comptypes ICE with BOUND_TEMPLATE_TEMPLATE_PARMs [PR107539] Here we end up giving the two BOUND_TEMPLATE_TEMPLATE_PARMs C<decltype(f::t)> and C<decltype(g::t)> the same TYPE_CANONICAL because the hash table that interns TYPE_CANONICAL for template type parameters doesn't set the comparing_specializations flag which controls how PARM_DECLs from different contexts compare equal. Later, from spec_hasher::equal for the corresponding two specializations A<C<decltype(f::t)>> and A<C<decltype(g::t)>>, we compare the two bound ttps with comparing_specializations set hence they now (structurally) compare different despite having the same TYPE_CANONICAL, and so we get the error: internal compiler error: same canonical type node for different types 'C<decltype (t)>' and 'C<decltype (t)>' This suggests that we should be setting comparing_specializations from ctp_hasher::equal to match spec_hasher::equal. But doing so introduces a separate ICE in cpp2a/concepts-placeholder3.C: internal compiler error: canonical types differ for identical types 'auto [requires ::same_as<<placeholder>, decltype(f::x)>]' and 'auto [requires ::same_as<<placeholder>, decltype(g::x)>]' because norm_hasher::equal doesn't set comparing_specializations either. I'm not sure when exactly we need to set comparing_specializations given what it controls (TYPENAME_TYPE equality/hashing and PARM_DECL equality) but it seems to be the conservative choice to set the flag wherever we have a global hash table that relies on type equality. To that end this patch sets comparing_specializations in ctp_hasher and norm_hasher, as well as in atom_hasher and sat_hasher for good measure. This turns out to be a compile time win of about 2% in some concepts tests, probably because of the improved TYPENAME_TYPE hashing enabled by the flag. PR c++/107539 gcc/cp/ChangeLog: * constraint.cc (norm_hasher::hash, norm_hasher::equal): Set comparing_specializations. (sat_hasher::hash, sat_hasher::equal): Likewise. * cp-tree.h (atom_hasher::hash, atom_hasher::equal): Likewise. * pt.cc (ctp_hasher::hash, ctp_hasher::equal): Likewise. gcc/testsuite/ChangeLog: * g++.dg/template/canon-type-19.C: New test.
