On 3/1/24 02:55, Jakub Jelinek wrote:
On Thu, Feb 29, 2024 at 12:50:47PM +0100, Jakub Jelinek wrote: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.Another option would be to change tree lookup_decomp_type (tree v) { - return *decomp_type_table->get (v); + if (tree *slot = decomp_type_table->get (v)) + return *slot; + return NULL_TREE; } and in finish_decl_decomp either just in the ptds.saved case or always try to lookup_decomp_type, if it returns non-NULL, return what it returned, otherwise return unlowered_expr_type (expr). I guess it would be cleaner, I thought it would be more costly due to the hash table lookup, but now that I think about it again, DECL_VALUE_EXPR is a hash table lookup as well. So maybe then + if (ptds.saved) + { + gcc_checking_assert (DECL_HAS_VALUE_EXPR_P (expr)); + /* DECL_HAS_VALUE_EXPR_P is always set if + processing_template_decl. If lookup_decomp_type + returns non-NULL, it is the tuple case. */ + if (tree ret = lookup_decomp_type (expr)) + return ret; + } if (DECL_HAS_VALUE_EXPR_P (expr)) /* Expr is an array or struct subobject proxy, handle bit-fields properly. */ return unlowered_expr_type (expr); else /* Expr is a reference variable for the tuple case. */ return lookup_decomp_type (expr);Here is a variant of the patch which does that. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Or the other version, or adding some flag to the DECL_DECOMPOSITION_P decls? 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. --- gcc/cp/decl.cc.jj 2024-02-28 23:20:01.004751204 +0100 +++ gcc/cp/decl.cc 2024-02-29 20:03:11.087218176 +0100 @@ -9262,7 +9262,9 @@ static GTY((cache)) decl_tree_cache_map tree lookup_decomp_type (tree v) { - return *decomp_type_table->get (v); + if (tree *slot = decomp_type_table->get (v)) + return *slot; + return NULL_TREE; }/* Mangle a decomposition declaration if needed. Arguments like--- gcc/cp/semantics.cc.jj 2024-02-28 22:57:08.101800588 +0100 +++ gcc/cp/semantics.cc 2024-02-29 20:04:51.936880622 +0100 @@ -11804,6 +11804,15 @@ finish_decltype_type (tree expr, bool id access expression). */ if (DECL_DECOMPOSITION_P (expr)) { + if (ptds.saved) + { + gcc_checking_assert (DECL_HAS_VALUE_EXPR_P (expr)); + /* DECL_HAS_VALUE_EXPR_P is always set if + processing_template_decl. If lookup_decomp_type + returns non-NULL, it is the tuple case. */ + if (tree ret = lookup_decomp_type (expr)) + return ret; + } if (DECL_HAS_VALUE_EXPR_P (expr)) /* Expr is an array or struct subobject proxy, handle bit-fields properly. */ --- gcc/testsuite/g++.dg/cpp1z/decomp59.C.jj 2024-02-29 20:02:17.467929327 +0100 +++ gcc/testsuite/g++.dg/cpp1z/decomp59.C 2024-02-29 20:02:17.467929327 +0100 @@ -0,0 +1,63 @@ +// PR c++/92687 +// { dg-do compile { target c++11 } } +// { dg-options "" } + +namespace std { + template<typename T> struct tuple_size; + template<int, typename> struct tuple_element; +} + +struct A { + int i; + template <int I> int& get() { return i; } +}; + +template<> struct std::tuple_size<A> { static const int value = 2; }; +template<int I> struct std::tuple_element<I,A> { using type = int; }; + +template<typename T> +struct is_reference { + static const bool value = false; +}; + +template<typename T> +struct is_reference<T&> +{ + static const bool value = true; +}; + +template<typename T> +struct is_reference<T&&> +{ + static const bool value = true; +}; + +template<int N> +void +foo () +{ + auto [x, y] = A {}; // { dg-warning "structured bindings only available with" "" { target c++14_down } } + static_assert (!is_reference<decltype (x)>::value, ""); +} + +void +bar () +{ + auto [x, y] = A {}; // { dg-warning "structured bindings only available with" "" { target c++14_down } } + static_assert (!is_reference<decltype (x)>::value, ""); +} + +template<typename T> +void +baz () +{ + auto [x, y] = T {}; // { dg-warning "structured bindings only available with" "" { target c++14_down } } + static_assert (!is_reference<decltype (x)>::value, ""); +} + +void +qux () +{ + foo<0> (); + baz<A> (); +} Jakub
