https://gcc.gnu.org/g:92216cbc59b3a4566d49de5dfa059b70b03d639a
commit r15-6385-g92216cbc59b3a4566d49de5dfa059b70b03d639a
Author: Jakub Jelinek <ja...@redhat.com>
Date: Fri Dec 20 10:17:56 2024 +0100
c++: Fix up maybe_unused attribute handling [PR110345]
When adding test coverage for maybe_unused attribute, I've run into
several things:
1) similarly to deprecated attribute, the attribute shouldn't pedantically
appertain to types other than class/enumeration definitions
2) similarly to deprecated attribute, the attribute shouldn't pedantically
appertain to unnamed bit-fields
3) the standard says that it can appertain to identifier labels, but
we handled it silently also on case and default labels
4) I've run into a weird spurious error on
int f [[maybe_unused]];
int & [[maybe_unused]] i = f;
int && [[maybe_unused]] j = 0;
The problem was that we create an attribute variant for the int &
type, then create an attribute variant for the int && type, and
the type_canon_hash hashing just thought those 2 are the same,
so used int & [[maybe_unused]] type for j rather than
int && [[maybe_unused]]. As TYPE_REF_IS_RVALUE is a flag in the
generic code, it was easily possible to hash that flag and compare
it
2024-12-19 Jakub Jelinek <ja...@redhat.com>
PR c++/110345
gcc/
* tree.cc (type_hash_canon_hash): Hash TYPE_REF_IS_RVALUE for
REFERENCE_TYPE.
(type_cache_hasher::equal): Compare TYPE_REF_IS_RVALUE for
REFERENCE_TYPE.
gcc/cp/
* tree.cc (handle_maybe_unused_attribute): New function.
(std_attributes): Use handle_maybe_unused_attribute instead
of handle_unused_attribute for maybe_unused attribute.
gcc/testsuite/
* g++.dg/cpp0x/attr-maybe_unused1.C: New test.
* g++.dg/cpp0x/alignas21.C: Add test for int && alignas (int).
Diff:
---
gcc/cp/tree.cc | 23 +++-
gcc/testsuite/g++.dg/cpp0x/alignas21.C | 1 +
gcc/testsuite/g++.dg/cpp0x/attr-maybe_unused1.C | 148 ++++++++++++++++++++++++
gcc/tree.cc | 8 +-
4 files changed, 178 insertions(+), 2 deletions(-)
diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 12d0831e4c4c..9b181be6237f 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -5162,6 +5162,27 @@ handle_std_deprecated_attribute (tree *node, tree name,
tree args, int flags,
return ret;
}
+/* The C++17 [[maybe_unused]] attribute mostly maps to the GNU unused
+ attribute. */
+
+static tree
+handle_maybe_unused_attribute (tree *node, tree name, tree args, int flags,
+ bool *no_add_attrs)
+{
+ tree t = *node;
+ tree ret = handle_unused_attribute (node, name, args, flags, no_add_attrs);
+ if (TYPE_P (*node) && t != *node)
+ pedwarn (input_location, OPT_Wattributes,
+ "%qE on a type other than class or enumeration definition", name);
+ else if (TREE_CODE (*node) == FIELD_DECL && DECL_UNNAMED_BIT_FIELD (*node))
+ pedwarn (input_location, OPT_Wattributes, "%qE on unnamed bit-field",
+ name);
+ else if (TREE_CODE (*node) == LABEL_DECL && DECL_NAME (*node) == NULL_TREE)
+ pedwarn (input_location, OPT_Wattributes,
+ "%qE on %<case%> or %<default%> label", name);
+ return ret;
+}
+
/* Table of valid C++ attributes. */
static const attribute_spec cxx_gnu_attributes[] =
{
@@ -5188,7 +5209,7 @@ static const attribute_spec std_attributes[] =
{ "deprecated", 0, 1, false, false, false, false,
handle_std_deprecated_attribute, NULL },
{ "maybe_unused", 0, 0, false, false, false, false,
- handle_unused_attribute, NULL },
+ handle_maybe_unused_attribute, NULL },
{ "nodiscard", 0, 1, false, false, false, false,
handle_nodiscard_attribute, NULL },
{ "no_unique_address", 0, 0, true, false, false, false,
diff --git a/gcc/testsuite/g++.dg/cpp0x/alignas21.C
b/gcc/testsuite/g++.dg/cpp0x/alignas21.C
index b7be7c5ce926..3d3059a4e02c 100644
--- a/gcc/testsuite/g++.dg/cpp0x/alignas21.C
+++ b/gcc/testsuite/g++.dg/cpp0x/alignas21.C
@@ -81,6 +81,7 @@ int g2 alignas (int) [2];
int corge () alignas (int); // { dg-error "'alignas' on a
type other than class" }
int *alignas (int) h; // { dg-error "'alignas' on a
type other than class" }
int & alignas (int) i = f; // { dg-error "'alignas' on a
type other than class" }
+int && alignas (int) j = 0; // { dg-error "'alignas' on a
type other than class" }
int S::* alignas (int) k; // { dg-error "'alignas' on a
type other than class" }
auto l = sizeof (int [2] alignas (int)); // { dg-error "'alignas' on a
type other than class" }
int freddy (alignas (int) int a, // { dg-error "alignment may
not be specified for 'a'" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/attr-maybe_unused1.C
b/gcc/testsuite/g++.dg/cpp0x/attr-maybe_unused1.C
new file mode 100644
index 000000000000..c2c2d36b5797
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/attr-maybe_unused1.C
@@ -0,0 +1,148 @@
+// C++ 26 P2552R3 - On the ignorability of standard attributes
+// { dg-do compile { target c++11 } }
+
+int arr[2];
+struct S { int a, b; };
+S arr2[2];
+
+void
+foo (int n)
+{
+ [[maybe_unused]] int x1;
+ [[maybe_unused ("foobar")]] int x2; // { dg-error "'maybe_unused'
attribute does not take any arguments" }
+ // { dg-error "expected
primary-expression before 'int'" "" { target *-*-* } .-1 }
+ [[maybe_unused (0)]] int x3; // { dg-error "'maybe_unused'
attribute does not take any arguments" }
+ // { dg-error "expected
primary-expression before 'int'" "" { target *-*-* } .-1 }
+
+ auto a = [] [[maybe_unused]] () {};
+ auto b = [] constexpr [[maybe_unused]] {}; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+ // { dg-error "parameter
declaration before lambda declaration specifiers only optional with" "" {
target c++20_down } .-1 }
+ // { dg-error "'constexpr'
lambda only available with" "" { target c++14_down } .-2 }
+ auto c = [] noexcept [[maybe_unused]] {}; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+ // { dg-error "parameter
declaration before lambda exception specification only optional with" "" {
target c++20_down } .-1 }
+ auto d = [] () [[maybe_unused]] {}; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+ auto e = new int [n] [[maybe_unused]]; // { dg-warning "attributes
ignored on outermost array type in new expression" }
+ auto e2 = new int [n] [[maybe_unused]] [42]; // { dg-warning "attributes
ignored on outermost array type in new expression" }
+ auto f = new int [n][42] [[maybe_unused]]; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+ [[maybe_unused]]; // { dg-warning "attributes at
the beginning of statement are ignored" }
+ [[maybe_unused]] {} // { dg-warning "attributes at
the beginning of statement are ignored" }
+ [[maybe_unused]] if (true) {} // { dg-warning
"attributes at the beginning of statement are ignored" }
+ [[maybe_unused]] while (false) {} // { dg-warning "attributes at
the beginning of statement are ignored" }
+ [[maybe_unused]] goto lab; // { dg-warning "attributes at
the beginning of statement are ignored" }
+ [[maybe_unused]] lab:;
+ [[maybe_unused]] try {} catch (int) {} // { dg-warning "attributes at
the beginning of statement are ignored" }
+ if ([[maybe_unused]] int x = 0) {}
+ switch (n)
+ {
+ [[maybe_unused]] case 1: // { dg-error "'maybe_unused'
on 'case' or 'default' label" }
+ [[maybe_unused]] break; // { dg-warning "attributes at
the beginning of statement are ignored" }
+ [[maybe_unused]] default: // { dg-error "'maybe_unused'
on 'case' or 'default' label" }
+ break;
+ }
+ for ([[maybe_unused]] auto a : arr) {}
+ for ([[maybe_unused]] auto [a, b] : arr2) {} // { dg-error "structured
bindings only available with" "" { target c++14_down } }
+ [[maybe_unused]] asm (""); // { dg-warning "attributes
ignored on 'asm' declaration" }
+ try {} catch ([[maybe_unused]] int x) {}
+ try {} catch ([[maybe_unused]] int) {}
+ try {} catch (int [[maybe_unused]] x) {} // { dg-warning "attribute
ignored" }
+ try {} catch (int [[maybe_unused]]) {} // { dg-warning "attribute
ignored" }
+ try {} catch (int x [[maybe_unused]]) {}
+}
+
+[[maybe_unused]] int bar ();
+using foobar [[maybe_unused]] = int;
+[[maybe_unused]] int a;
+[[maybe_unused]] auto [b, c] = arr; // { dg-error "structured
bindings only available with" "" { target c++14_down } }
+[[maybe_unused]]; // { dg-warning "attribute
ignored" }
+inline [[maybe_unused]] void baz () {} // { dg-warning "attribute
ignored" }
+ // { dg-error "standard
attributes in middle of decl-specifiers" "" { target *-*-* } .-1 }
+constexpr [[maybe_unused]] int qux () { return 0; } // { dg-warning
"attribute ignored" }
+ // { dg-error "standard
attributes in middle of decl-specifiers" "" { target *-*-* } .-1 }
+int [[maybe_unused]] d; // { dg-warning
"attribute ignored" }
+int const [[maybe_unused]] e = 1; // { dg-warning "attribute
ignored" }
+struct A {} [[maybe_unused]]; // { dg-warning "attribute
ignored in declaration of 'struct A'" }
+struct A [[maybe_unused]]; // { dg-warning "attribute
ignored" }
+struct A [[maybe_unused]] a1; // { dg-warning "attribute
ignored" }
+A [[maybe_unused]] a2; // { dg-warning "attribute
ignored" }
+enum B { B0 } [[maybe_unused]]; // { dg-warning
"attribute ignored in declaration of 'enum B'" }
+enum B [[maybe_unused]]; // { dg-warning "attribute
ignored" }
+enum B [[maybe_unused]] b1; // { dg-warning "attribute
ignored" }
+B [[maybe_unused]] b2; // { dg-warning "attribute
ignored" }
+struct [[maybe_unused]] C {};
+int f [[maybe_unused]];
+int g[2] [[maybe_unused]]; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+int g2 [[maybe_unused]] [2];
+int corge () [[maybe_unused]]; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+int *[[maybe_unused]] h; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+int & [[maybe_unused]] i = f; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+int && [[maybe_unused]] j = 0; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+int S::* [[maybe_unused]] k; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+auto l = sizeof (int [2] [[maybe_unused]]); // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+int freddy ([[maybe_unused]] int a,
+ [[maybe_unused]] int,
+ [[maybe_unused]] int c = 0,
+ [[maybe_unused]] int = 0);
+void
+corge ([[maybe_unused]] int a,
+ [[maybe_unused]] int,
+ [[maybe_unused]] int c = 0,
+ [[maybe_unused]] int = 0)
+{
+}
+[[maybe_unused]] void
+garply ()
+{
+}
+int grault (int [[maybe_unused]] a, // { dg-warning "attribute
ignored" }
+ int [[maybe_unused]], // { dg-warning "attribute
ignored" }
+ int [[maybe_unused]] c = 0, // { dg-warning "attribute
ignored" }
+ int [[maybe_unused]] = 0); // { dg-warning "attribute
ignored" }
+void
+waldo (int [[maybe_unused]] a, // { dg-warning "attribute
ignored" }
+ int [[maybe_unused]], // { dg-warning "attribute
ignored" }
+ int [[maybe_unused]] c = 0, // { dg-warning "attribute
ignored" }
+ int [[maybe_unused]] = 0) // { dg-warning "attribute
ignored" }
+{
+}
+int plugh (int a [[maybe_unused]],
+ int b [[maybe_unused]] = 0);
+void
+thud (int a [[maybe_unused]],
+ int b [[maybe_unused]] = 0)
+{
+}
+enum [[maybe_unused]] D { D0 };
+enum class [[maybe_unused]] E { E0 };
+enum F {};
+enum [[maybe_unused]] F; // { dg-warning "type
attributes ignored after type is already defined" }
+enum G {
+ G0 [[maybe_unused]],
+ G1 [[maybe_unused]] = 2
+};
+namespace [[maybe_unused]] H { using H0 = int; }// { dg-warning
"'maybe_unused' attribute directive ignored" }
+namespace [[maybe_unused]] {} // { dg-warning "'maybe_unused'
attribute directive ignored" }
+[[maybe_unused]] using namespace H; // { dg-warning "'maybe_unused'
attribute directive ignored" }
+struct [[maybe_unused]] I
+{
+ [[maybe_unused]]; // { dg-error "declaration does
not declare anything" }
+ [[maybe_unused]] int i;
+ [[maybe_unused]] int foo ();
+ [[maybe_unused]] int bar () { return 1; }
+ [[maybe_unused]] int : 0; // { dg-error "'maybe_unused'
on unnamed bit-field" }
+ [[maybe_unused]] int i2 : 5;
+ [[maybe_unused]] static int i3;
+ static int i4;
+};
+[[maybe_unused]] int I::i4 = 0;
+struct J : [[maybe_unused]] C {}; // { dg-warning "attributes on
base specifiers are ignored" }
+#if __cpp_concepts >= 201907L
+template <typename T>
+concept K [[maybe_unused]] = requires { true; };// { dg-warning
"'maybe_unused' attribute ignored" "" { target c++20 } }
+#endif
+typedef int L [[maybe_unused]];
+template <typename T>
+struct M {};
+template <>
+struct [[maybe_unused]] M<int> { int m; };
+typedef int N[2] [[maybe_unused]]; // { dg-error "'maybe_unused'
on a type other than class or enumeration definition" }
+typedef int O [[maybe_unused]] [2];
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 322451139162..e3b5e56b828c 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -6120,6 +6120,10 @@ type_hash_canon_hash (tree type)
hstate.add_poly_int (TYPE_VECTOR_SUBPARTS (type));
break;
+ case REFERENCE_TYPE:
+ hstate.add_flag (TYPE_REF_IS_RVALUE (type));
+ break;
+
default:
break;
}
@@ -6162,7 +6166,6 @@ type_cache_hasher::equal (type_hash *a, type_hash *b)
case OPAQUE_TYPE:
case COMPLEX_TYPE:
case POINTER_TYPE:
- case REFERENCE_TYPE:
case NULLPTR_TYPE:
return true;
@@ -6252,6 +6255,9 @@ type_cache_hasher::equal (type_hash *a, type_hash *b)
break;
return false;
+ case REFERENCE_TYPE:
+ return TYPE_REF_IS_RVALUE (a->type) == TYPE_REF_IS_RVALUE (b->type);
+
default:
return false;
}
