https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486
--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:4806f9157a26cfd66c083bcc01596ff33009c0d6 commit r10-9743-g4806f9157a26cfd66c083bcc01596ff33009c0d6 Author: Patrick Palka <ppa...@redhat.com> Date: Wed Jul 29 22:06:41 2020 -0400 c++: alias_ctad_tweaks and constrained dguide [PR95486] In the below testcase, we're ICEing from alias_ctad_tweaks ultimately because the implied deduction guide for X's user-defined constructor already has constraints associated with it. We then carry over these constraints to 'fprime', the overlying deduction guide for the alias template Y, via tsubst_decl from alias_ctad_tweaks. Later in alias_ctad_tweaks we call get_constraints followed by set_constraints without doing remove_constraints in between, which triggers the !found assert in set_constraints. This patch fixes this issue by adding an intervening call to remove_constraints. gcc/cp/ChangeLog: PR c++/95486 * pt.c (alias_ctad_tweaks): Call remove_constraints before calling set_constraints. gcc/testsuite/ChangeLog: PR c++/95486 * g++.dg/cpp2a/class-deduction-alias3.C: New test. (cherry picked from commit 71141b1bd537cc516e485c834c2d36abba3f4544)