https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92687
--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:867cbadb912ab75d0eaf919a3f992595e508482b commit r14-9258-g867cbadb912ab75d0eaf919a3f992595e508482b Author: Jakub Jelinek <ja...@redhat.com> Date: Fri Mar 1 16:59:08 2024 +0100 c++: Fix up decltype of non-dependent structured binding decl in template [PR92687] finish_decltype_type uses DECL_HAS_VALUE_EXPR_P (expr) check for DECL_DECOMPOSITION_P (expr) to determine if it is array/struct/vector/complex etc. subobject proxy case vs. structured binding using std::tuple_{size,element}. For non-templates or when templates are already instantiated, that works correctly, finalized DECL_DECOMPOSITION_P non-base vars indeed have DECL_VALUE_EXPR in the former case and don't have it in the latter. It works fine for dependent structured bindings as well, cp_finish_decomp in that case creates DECLTYPE_TYPE tree and defers the handling until instantiation. As the testcase shows, this doesn't work for the non-dependent structured binding case in templates, because DECL_HAS_VALUE_EXPR_P is set in that case always; cp_finish_decomp ends with: if (processing_template_decl) { for (unsigned int i = 0; i < count; i++) if (!DECL_HAS_VALUE_EXPR_P (v[i])) { tree a = build_nt (ARRAY_REF, decl, size_int (i), NULL_TREE, NULL_TREE); SET_DECL_VALUE_EXPR (v[i], a); DECL_HAS_VALUE_EXPR_P (v[i]) = 1; } } and those artificial ARRAY_REFs are used in various places during instantiation to find out what base the DECL_DECOMPOSITION_P VAR_DECLs have and their positions. The following patch fixes that by changing lookup_decomp_type, such that it doesn't ICE when called on a DECL_DECOMPOSITION_P var which isn't in a hash table, but returns NULL_TREE in that case, and for processing_template_decl asserts DECL_HAS_VALUE_EXPR_P is non-NULL and just calls lookup_decomp_type. If it returns non-NULL, it is a structured binding using tuple and its result is returned, otherwise it falls through to returning unlowered_expr_type (expr) because it is an array, structure etc. subobject proxy. For !processing_template_decl it keeps doing what it did before, DECL_HAS_VALUE_EXPR_P meaning it is an array/structure etc. subobject proxy, otherwise the tuple case. 2024-03-01 Jakub Jelinek <ja...@redhat.com> PR c++/92687 * decl.cc (lookup_decomp_type): Return NULL_TREE if decomp_type_table doesn't have entry for V. * semantics.cc (finish_decltype_type): If ptds.saved, assert DECL_HAS_VALUE_EXPR_P is true and decide on tuple vs. non-tuple based on if lookup_decomp_type is NULL or not. * g++.dg/cpp1z/decomp59.C: New test.
