https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101886
--- Comment #5 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:8aa045c97485d75e0b6eb1068464c0ddaa6beacb commit r13-4810-g8aa045c97485d75e0b6eb1068464c0ddaa6beacb Author: Patrick Palka <ppa...@redhat.com> Date: Tue Dec 20 17:02:37 2022 -0500 c++, tree: walk TREE_VEC (and VECTOR_CST) in natural order [PR101886] Unfortunately the extract_autos_r fix in r13-4799-ga7c8036b26082d is derailed by the fact that walk_tree_1 currently walks the elements of a TREE_VEC in reverse, which means for A<auto, auto> in the below testcase extract_autos_r ends up adjusting the TEMPLATE_TYPE_IDX of the first auto instead of the second one, and the first auto is the canonical auto of level 2 (and index 0), so we rightfully trigger the sanity check added in that commit. It seems TREE_VEC and VECTOR_CST are the only trees we walk in reverse, and this has been the case since r21884 whence the original version of walk_tree_1 was introduced. But that's arguably unnatural and not consistent with how we walk all other compound trees such as CONSTRUCTORs and EXPR_P trees in forward order. So this patch makes walk_tree_1 walk TREE_VEC (and VECTOR_CST) in forward order as well, which fixes the testcase. Doing so revealed that keep_template_parm grows the list of found template parameters from the front, which previously compensated for the TREE_VEC behavior, so now we should grow it from the back. PR c++/101886 gcc/cp/ChangeLog: * pt.cc (find_template_parameter_info::parm_list_tail): New data member. (keep_template_parm): Use parm_list_tail to append rather than prepend to parm_list. gcc/ChangeLog: * tree.cc (walk_tree_1) <case TREE_VEC>: Walk the elements in forward instead of reverse order. <case VECTOR_CST>: Likewise. gcc/testsuite/ChangeLog: * g++.dg/concepts/diagnostic12.C: Adjust expected order of template parameters within pretty printed parameter mapping. * g++.dg/concepts/auto6.C: New test.
