https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65328
--- Comment #10 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:343d83c7a89d0c7a78139e685395228115a28f6e commit r13-1047-g343d83c7a89d0c7a78139e685395228115a28f6e Author: Patrick Palka <ppa...@redhat.com> Date: Fri Jun 10 16:10:02 2022 -0400 c++: improve TYPENAME_TYPE hashing [PR65328] For the testcase in this PR, compilation takes very long ultimately due to our poor hashing of TYPENAME_TYPE causing a huge number of collisions in the spec_hasher and typename_hasher tables. In spec_hasher, we don't hash the components of TYPENAME_TYPE, which means most TYPENAME_TYPE arguments end up contributing the same hash. This is the safe thing to do uniformly since structural_comptypes may try resolving a TYPENAME_TYPE via the current instantiation. But this behavior of structural_comptypes is suppressed from spec_hasher::equal via the comparing_specializations flag, which means spec_hasher::hash can assume it's disabled too. To that end, this patch makes spec_hasher::hash set the flag, and teaches iterative_hash_template_arg to hash the relevant components of TYPENAME_TYPE when the flag is set. And in typename_hasher, the hash function considers TYPE_IDENTIFIER instead of the more informative TYPENAME_TYPE_FULLNAME, which this patch fixes accordingly. After this patch, compile time for the testcase in the PR falls to around 30 seconds on my machine (down from dozens of minutes). PR c++/65328 gcc/cp/ChangeLog: * decl.cc (typename_hasher::hash): Add extra overloads. Use iterative_hash_object instead of htab_hash_pointer. Hash TYPENAME_TYPE_FULLNAME instead of TYPE_IDENTIFIER. (build_typename_type): Use typename_hasher::hash. * pt.cc (spec_hasher::hash): Add two-parameter overload. Set comparing_specializations around the call to hash_tmpl_and_args. (iterative_hash_template_arg) <case TYPENAME_TYPE>: When comparing_specializations, hash the TYPE_CONTEXT and TYPENAME_TYPE_FULLNAME. (tsubst_function_decl): Use spec_hasher::hash instead of hash_tmpl_and_args. (tsubst_template_decl): Likewise. (tsubst_decl): Likewise.
