https://gcc.gnu.org/g:1b7cfa715c6c02db6ef587c87757d7792fc43423
commit r15-3993-g1b7cfa715c6c02db6ef587c87757d7792fc43423
Author: Giuseppe D'Angelo <giuseppe.dang...@kdab.com>
Date: Tue Oct 1 13:31:00 2024 +0200
c++: introduce __builtin_is_virtual_base_of
P2985R0 (C++26) introduces std::is_virtual_base_of; this is the compiler
builtin that will back up the library trait (which strictly requires
compiler support).
The name has been chosen to match LLVM/MSVC's, as per the discussion
here:
https://github.com/llvm/llvm-project/issues/98310
The actual user-facing type trait in libstdc++ will be added later.
gcc/cp/ChangeLog:
* constraint.cc (diagnose_trait_expr): New diagnostic.
* cp-trait.def (IS_VIRTUAL_BASE_OF): New builtin.
* cp-tree.h (enum base_access_flags): Add a new flag to be
able to request a search for a virtual base class.
* cxx-pretty-print.cc (pp_cxx_userdef_literal): Update the
list of GNU extensions to the grammar.
* search.cc (struct lookup_base_data_s): Add a field to
request searching for a virtual base class.
(dfs_lookup_base): Add the ability to look for a virtual
base class.
(lookup_base): Forward the flag to dfs_lookup_base.
* semantics.cc (trait_expr_value): Implement the builtin
by calling lookup_base with the new flag.
(finish_trait_expr): Handle the new builtin.
gcc/ChangeLog:
* doc/extend.texi: Document the new
__builtin_is_virtual_base_of builtin; amend the docs for
__is_base_of.
gcc/testsuite/ChangeLog:
* g++.dg/ext/is_virtual_base_of.C: New test.
* g++.dg/ext/is_virtual_base_of_diagnostic.C: New test.
Signed-off-by: Giuseppe D'Angelo <giuseppe.dang...@kdab.com>
Reviewed-by: Jason Merrill <ja...@redhat.com>
Diff:
---
gcc/doc/extend.texi | 15 ++
gcc/cp/cp-tree.h | 3 +-
gcc/cp/constraint.cc | 3 +
gcc/cp/cxx-pretty-print.cc | 2 +
gcc/cp/search.cc | 15 +-
gcc/cp/semantics.cc | 12 ++
gcc/testsuite/g++.dg/ext/is_virtual_base_of.C | 163 +++++++++++++++++++++
.../g++.dg/ext/is_virtual_base_of_diagnostic.C | 15 ++
gcc/cp/cp-trait.def | 1 +
9 files changed, 225 insertions(+), 4 deletions(-)
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index f0d8eb59dded..f46c3df33030 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -29984,12 +29984,27 @@ If @var{base_type} is a base class of
@var{derived_type}
Top-level cv-qualifications of @var{base_type} and
@var{derived_type} are ignored. For the purposes of this trait, a
class type is considered is own base.
+The trait is @code{true} even if @var{base_type} is an ambiguous or
+inaccessible base class of @var{derived_type}.
Requires: if @code{__is_class (base_type)} and @code{__is_class (derived_type)}
are @code{true} and @var{base_type} and @var{derived_type} are not the same
type (disregarding cv-qualifiers), @var{derived_type} shall be a complete
type. A diagnostic is produced if this requirement is not met.
@enddefbuiltin
+@defbuiltin{bool __builtin_is_virtual_base_of (@var{base_type},
@var{derived_type})}
+If @var{base_type} is a virtual base class of @var{derived_type}
+([class.derived], [class.mi]) then the trait is @code{true},
+otherwise it is @code{false}.
+Top-level cv-qualifications of @var{base_type} and
+@var{derived_type} are ignored.
+The trait is @code{true} even if @var{base_type} is an ambiguous or
+inaccessible virtual base class of @var{derived_type}.
+Requires: if @code{__is_class (base_type)} and @code{__is_class (derived_type)}
+are @code{true}, @var{derived_type} shall be a complete
+type. A diagnostic is produced if this requirement is not met.
+@enddefbuiltin
+
@defbuiltin{bool __is_class (@var{type})}
If @var{type} is a cv-qualified class type, and not a union type
([basic.compound]) the trait is @code{true}, else it is @code{false}.
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 39c065eecf6d..c5d02567cb4b 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -5723,7 +5723,8 @@ enum base_access_flags {
ba_unique = 1 << 0, /* Must be a unique base. */
ba_check_bit = 1 << 1, /* Check access. */
ba_check = ba_unique | ba_check_bit,
- ba_ignore_scope = 1 << 2 /* Ignore access allowed by local scope. */
+ ba_ignore_scope = 1 << 2, /* Ignore access allowed by local scope. */
+ ba_require_virtual = 1 << 3 /* Require a virtual base. */
};
/* This type is used for parameters and variables which hold
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index ebfcdefd2841..cf0e5d37571c 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3291,6 +3291,9 @@ diagnose_trait_expr (tree expr, tree args)
case CPTK_IS_UNION:
inform (loc, " %qT is not a union", t1);
break;
+ case CPTK_IS_VIRTUAL_BASE_OF:
+ inform (loc, " %qT is not a virtual base of %qT", t1, t2);
+ break;
case CPTK_IS_VOLATILE:
inform (loc, " %qT is not a volatile type", t1);
break;
diff --git a/gcc/cp/cxx-pretty-print.cc b/gcc/cp/cxx-pretty-print.cc
index e690354e08e9..41e6bdfdda50 100644
--- a/gcc/cp/cxx-pretty-print.cc
+++ b/gcc/cp/cxx-pretty-print.cc
@@ -418,6 +418,8 @@ pp_cxx_userdef_literal (cxx_pretty_printer *pp, tree t)
__builtin_offsetof ( type-id, offsetof-expression )
__builtin_addressof ( expression )
+ __builtin_is_virtual_base_of ( type-id , type-id )
+
__has_nothrow_assign ( type-id )
__has_nothrow_constructor ( type-id )
__has_nothrow_copy ( type-id )
diff --git a/gcc/cp/search.cc b/gcc/cp/search.cc
index 6a21a25272b2..b0421ee05247 100644
--- a/gcc/cp/search.cc
+++ b/gcc/cp/search.cc
@@ -65,6 +65,7 @@ struct lookup_base_data_s
bool repeated_base; /* Whether there are repeated bases in the
hierarchy. */
bool want_any; /* Whether we want any matching binfo. */
+ bool require_virtual; /* Whether we require a virtual path. */
};
/* Worker function for lookup_base. See if we've found the desired
@@ -93,11 +94,18 @@ dfs_lookup_base (tree binfo, void *data_)
if (SAME_BINFO_TYPE_P (BINFO_TYPE (binfo), data->base))
{
+ const bool via_virtual
+ = binfo_via_virtual (binfo, data->t) != NULL_TREE;
+
+ if (data->require_virtual && !via_virtual)
+ /* Skip this result if we require virtual inheritance
+ and this is not a virtual base. */
+ return dfs_skip_bases;
+
if (!data->binfo)
{
data->binfo = binfo;
- data->via_virtual
- = binfo_via_virtual (data->binfo, data->t) != NULL_TREE;
+ data->via_virtual = via_virtual;
if (!data->repeated_base)
/* If there are no repeated bases, we can stop now. */
@@ -124,7 +132,7 @@ dfs_lookup_base (tree binfo, void *data_)
}
/* Prefer one via a non-virtual path. */
- if (!binfo_via_virtual (binfo, data->t))
+ if (!via_virtual)
{
data->binfo = binfo;
data->via_virtual = false;
@@ -271,6 +279,7 @@ lookup_base (tree t, tree base, base_access access,
data.repeated_base = (offset == -1) && CLASSTYPE_REPEATED_BASE_P (t);
data.want_any = access == ba_any;
data.offset = offset;
+ data.require_virtual = (access & ba_require_virtual);
dfs_walk_once (t_binfo, dfs_lookup_base, NULL, &data);
binfo = data.binfo;
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 0cb46c1986ca..0370d81de01f 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12932,6 +12932,11 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree
type2)
case CPTK_IS_UNION:
return type_code1 == UNION_TYPE;
+ case CPTK_IS_VIRTUAL_BASE_OF:
+ return (NON_UNION_CLASS_TYPE_P (type1) && NON_UNION_CLASS_TYPE_P (type2)
+ && lookup_base (type2, type1, ba_require_virtual,
+ NULL, tf_none) != NULL_TREE);
+
case CPTK_IS_VOLATILE:
return CP_TYPE_VOLATILE_P (type1);
@@ -13154,6 +13159,13 @@ finish_trait_expr (location_t loc, cp_trait_kind kind,
tree type1, tree type2)
return error_mark_node;
break;
+ case CPTK_IS_VIRTUAL_BASE_OF:
+ if (NON_UNION_CLASS_TYPE_P (type1) && NON_UNION_CLASS_TYPE_P (type2)
+ && !complete_type_or_else (type2, NULL_TREE))
+ /* We already issued an error. */
+ return error_mark_node;
+ break;
+
case CPTK_IS_ARRAY:
case CPTK_IS_BOUNDED_ARRAY:
case CPTK_IS_CLASS:
diff --git a/gcc/testsuite/g++.dg/ext/is_virtual_base_of.C
b/gcc/testsuite/g++.dg/ext/is_virtual_base_of.C
new file mode 100644
index 000000000000..775a35393885
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_virtual_base_of.C
@@ -0,0 +1,163 @@
+// { dg-do run }
+#include <cassert>
+
+class A1
+{
+ double a;
+ double b;
+};
+
+class A2
+{
+ double a;
+ double b;
+};
+
+class B
+: private A1 { };
+
+class C
+: private A1, private A2 { };
+
+class VD1
+: public virtual A1 { };
+
+class VD2
+: protected virtual A1 { };
+
+class VD3
+: private virtual A1 { };
+
+class D
+: public B, public VD1 { };
+
+class VDMultiple1
+: public virtual A1, public A2 { };
+
+class VDMultiple2
+: public virtual A1, public virtual A2 { };
+
+template <typename T>
+class VDTemplate : public virtual T { };
+
+// example from from [class.mi]
+namespace class_mi
+{
+class B { int b; };
+class X : virtual public B { int x; };
+class Y : virtual public B { int y; };
+class Z : public B { int z; };
+class AA : public X, public Y, public Z { int aa; };
+}
+
+union U
+{
+ double a;
+ double b;
+};
+
+template<typename T, typename U>
+ bool
+ f()
+ { return __builtin_is_virtual_base_of(T, U); }
+
+template<typename T, typename U>
+ class My
+ {
+ public:
+ bool
+ f()
+ { return !!__builtin_is_virtual_base_of(T, U); }
+ };
+
+template<typename T, typename U>
+ class My2
+ {
+ public:
+ static const bool trait = __builtin_is_virtual_base_of(T, U);
+ };
+
+template<typename T, typename U>
+ const bool My2<T, U>::trait;
+
+template<typename T, typename U, bool b = __builtin_is_virtual_base_of(T, U)>
+ struct My3_help
+ { static const bool trait = b; };
+
+template<typename T, typename U, bool b>
+ const bool My3_help<T, U, b>::trait;
+
+template<typename T, typename U>
+ class My3
+ {
+ public:
+ bool
+ f()
+ { return My3_help<T, U>::trait; }
+ };
+
+#define PTEST(T, U) (__builtin_is_virtual_base_of(T, U) && f<T, U>() \
+ && My<T, U>().f() && My2<T, U>::trait && My3<T, U>().f())
+
+#define NTEST(T, U) (!__builtin_is_virtual_base_of(T, U) && !f<T, U>() \
+ && !My<T, U>().f() && !My2<T, U>::trait && !My3<T, U>().f())
+
+int main()
+{
+ assert (NTEST (int, A1));
+ assert (NTEST (A1, void));
+ assert (NTEST (A1, A1));
+ assert (NTEST (A1*, A1*));
+ assert (NTEST (A1&, A1&));
+ assert (NTEST (A1, B));
+ assert (NTEST (B, A1));
+ assert (NTEST (A1, C));
+ assert (NTEST (A2, C));
+ assert (NTEST (C, A1));
+ assert (NTEST (A1, const B));
+ assert (NTEST (const B, A1));
+ assert (NTEST (A1, volatile C));
+ assert (NTEST (volatile A2, const C));
+ assert (NTEST (const volatile C, A1));
+
+ assert (PTEST (A1, VD1));
+ assert (PTEST (A1, VD2));
+ assert (PTEST (A1, VD3));
+
+ assert (PTEST (A1, const VD1));
+ assert (PTEST (A1, const VD2));
+ assert (PTEST (A1, const VD3));
+
+ assert (PTEST (const A1, VD1));
+ assert (PTEST (const A1, VD2));
+ assert (PTEST (const A1, VD3));
+
+ assert (PTEST (const A1, const VD1));
+ assert (PTEST (const A1, const VD2));
+ assert (PTEST (const A1, const VD3));
+
+ assert (NTEST (A2, VD1));
+ assert (NTEST (A2, VD2));
+ assert (NTEST (A2, VD3));
+
+ assert (PTEST (A1, D));
+
+ assert (PTEST (A1, VDMultiple1));
+ assert (PTEST (A1, VDMultiple2));
+ assert (NTEST (A2, VDMultiple1));
+ assert (PTEST (A2, VDMultiple2));
+
+ assert (PTEST (A1, VDTemplate<A1>));
+ assert (NTEST (A2, VDTemplate<A1>));
+ assert (NTEST (A1, VDTemplate<A2>));
+
+ assert (NTEST (class_mi::B, class_mi::B));
+ assert (PTEST (class_mi::B, class_mi::X));
+ assert (PTEST (class_mi::B, class_mi::Y));
+ assert (NTEST (class_mi::B, class_mi::Z));
+ assert (PTEST (class_mi::B, class_mi::AA));
+
+ assert (NTEST (U, U));
+
+ return 0;
+}
diff --git a/gcc/testsuite/g++.dg/ext/is_virtual_base_of_diagnostic.C
b/gcc/testsuite/g++.dg/ext/is_virtual_base_of_diagnostic.C
new file mode 100644
index 000000000000..a50459afdca9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_virtual_base_of_diagnostic.C
@@ -0,0 +1,15 @@
+class A
+{ };
+
+class B; // { dg-message "forward declaration" }
+
+union C
+{ };
+
+union D;
+
+void f()
+{
+ __builtin_is_virtual_base_of(A, B); // { dg-error "incomplete type" }
+ __builtin_is_virtual_base_of(C, D);
+}
diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
index 0721ecdf3f05..6aaca13c5e90 100644
--- a/gcc/cp/cp-trait.def
+++ b/gcc/cp/cp-trait.def
@@ -100,6 +100,7 @@ DEFTRAIT_EXPR (IS_TRIVIALLY_CONSTRUCTIBLE,
"__is_trivially_constructible", -1)
DEFTRAIT_EXPR (IS_TRIVIALLY_COPYABLE, "__is_trivially_copyable", 1)
DEFTRAIT_EXPR (IS_UNBOUNDED_ARRAY, "__is_unbounded_array", 1)
DEFTRAIT_EXPR (IS_UNION, "__is_union", 1)
+DEFTRAIT_EXPR (IS_VIRTUAL_BASE_OF, "__builtin_is_virtual_base_of", 2)
DEFTRAIT_EXPR (IS_VOLATILE, "__is_volatile", 1)
DEFTRAIT_EXPR (RANK, "__array_rank", 1)
DEFTRAIT_EXPR (REF_CONSTRUCTS_FROM_TEMPORARY,
"__reference_constructs_from_temporary", 2)
