https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94632
--- Comment #3 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:f83adb68ed9cef1fbd4c16447eb4e89676df9f62 commit r10-7787-gf83adb68ed9cef1fbd4c16447eb4e89676df9f62 Author: Patrick Palka <ppa...@redhat.com> Date: Sat Apr 18 06:22:21 2020 -0400 c++: spec_hasher::equal and PARM_DECLs [PR94632] In the testcase below, during specialization of c<int>::d, we build two identical specializations of the parameter type b<decltype(e)::k> -- one when substituting into c<int>::d's TYPE_ARG_TYPES and another when substituting into c<int>::d's DECL_ARGUMENTS. We don't reuse the first specialization the second time around as a consequence of the fix for PR c++/56247 which made PARM_DECLs always compare different from one another during spec_hasher::equal. As a result, when looking up existing specializations of 'b', spec_hasher::equal considers the template argument decltype(e')::k to be different from decltype(e'')::k, where e' and e'' are the result of two calls to tsubst_copy on the PARM_DECL e. Since the two specializations are considered different due to the mentioned fix, their TYPE_CANONICAL points to themselves even though they are otherwise identical types, and this triggers an ICE in maybe_rebuild_function_decl_type when comparing the TYPE_ARG_TYPES of c<int>::d to its DECL_ARGUMENTS. This patch fixes this issue at the spec_hasher::equal level by ignoring the 'comparing_specializations' flag in cp_tree_equal whenever the DECL_CONTEXTs of the two parameters are identical. This seems to be a sufficient condition to be able to correctly compare PARM_DECLs structurally. (This also subsumes the CONSTRAINT_VAR_P check since constraint variables all have empty, and therefore identical, DECL_CONTEXTs.) gcc/cp/ChangeLog: PR c++/94632 * tree.c (cp_tree_equal) <case PARM_DECL>: Ignore comparing_specializations if the parameters' contexts are identical. gcc/testsuite/ChangeLog: PR c++/94632 * g++.dg/template/canon-type-14.C: New test.
