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* [gcc r14-9258] c++: Fix up decltype of non-dependent structured binding decl in template [PR92687]
@ 2024-03-01 16:28 Jakub Jelinek
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From: Jakub Jelinek @ 2024-03-01 16:28 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:867cbadb912ab75d0eaf919a3f992595e508482b
commit r14-9258-g867cbadb912ab75d0eaf919a3f992595e508482b
Author: Jakub Jelinek <jakub@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 <jakub@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.
Diff:
---
gcc/cp/decl.cc | 4 ++-
gcc/cp/semantics.cc | 9 +++++
gcc/testsuite/g++.dg/cpp1z/decomp59.C | 63 +++++++++++++++++++++++++++++++++++
3 files changed, 75 insertions(+), 1 deletion(-)
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 05e4600c7bb..993d7ef4d2b 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -9262,7 +9262,9 @@ static GTY((cache)) decl_tree_cache_map *decomp_type_table;
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
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 57840176863..adb1ba48d29 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -11804,6 +11804,15 @@ finish_decltype_type (tree expr, bool id_expression_or_member_access_p,
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. */
diff --git a/gcc/testsuite/g++.dg/cpp1z/decomp59.C b/gcc/testsuite/g++.dg/cpp1z/decomp59.C
new file mode 100644
index 00000000000..52a72fa9c08
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/decomp59.C
@@ -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> ();
+}
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