https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103706
--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-11 branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:d3950a70da6814206eef1946c289b5652ecc9986 commit r11-9838-gd3950a70da6814206eef1946c289b5652ecc9986 Author: Patrick Palka <ppa...@redhat.com> Date: Tue Feb 8 08:46:32 2022 -0500 c++: lambda in pack expansion using pack in constraint [PR103706] Here when expanding the pack expansion pattern containing a constrained lambda, the template argument for each Ts is an ARGUMENT_PACK_SELECT, which we store inside the lambda's LAMBDA_EXPR_REGEN_INFO. Then during satisfaction of the lambda's constraint C<Ts> the satisfaction cache uses this argument as part of the key to the corresponding sat_entry, but iterative_hash_template_arg and template_args_equal deliberately don't handle ARGUMENT_PACK_SELECT. Since it's wrong to preserve ARGUMENT_PACK_SELECT inside a hash table due to its instability (as documented in iterative_hash_template_arg), this patch helps make sure the satisfaction cache doesn't see such trees by resolving ARGUMENT_PACK_SELECT arguments before adding them to LAMBDA_EXPR_REGEN_INFO. PR c++/103706 gcc/cp/ChangeLog: * pt.c (preserve_args): New function. (tsubst_lambda_expr): Use it when setting LAMBDA_EXPR_REGEN_INFO. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/concepts-lambda19.C: New test. (cherry picked from commit db5f1c17031ad8a898d77121f1e0e0141306e22a)
