https://gcc.gnu.org/g:4d86e4cda01aa3ab60de164a8492a99bc9ca1f70
commit r16-2093-g4d86e4cda01aa3ab60de164a8492a99bc9ca1f70
Author: Luc Grosheintz <luc.groshei...@gmail.com>
Date: Fri Jul 4 10:29:43 2025 +0200
libstdc++: Check prerequisites of layout_*::operator().
Previously, the prerequisite that the arguments passed to operator() are
a multi-dimensional index (of extents()) was not checked.
Both mapping::operator() and mdspan::operator[] have the same
prerequisite. Since, mdspan must check the prerequisite for user-defined
layout mappings, the preference is to check in mdspan.
Because out-of-bounds accesses are very common it's nevertheless useful
to check the prerequisite in mapping::operator(). This is relevant for
cases where the layout mappings are used without mdspan. This commit
checks the prerequisites via _GLIBCXX_DEBUG_ASSERTs and adds the required
tests.
More discussion in the email chain starting at:
https://gcc.gnu.org/pipermail/libstdc++/2025-July/062265.html
libstdc++-v3/ChangeLog:
* include/std/mdspan: Check prerequisites of
layout_*::operator() with _GLIBCXX_DEBUG_ASSERTs.
* testsuite/23_containers/mdspan/layouts/debug/out_of_bounds_neg.cc:
Add tests for prerequisites.
Reviewed-by: Tomasz Kamiński <tkami...@redhat.com>
Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
Diff:
---
libstdc++-v3/include/std/mdspan | 5 ++++
.../mdspan/layouts/debug/out_of_bounds_neg.cc | 30 ++++++++++++++++++++++
2 files changed, 35 insertions(+)
diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index 4a06fb2d3a86..1fdcae634419 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -441,6 +441,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_IndexType __mult = 1;
auto __update = [&, __pos = 0u](_IndexType __idx) mutable
{
+ _GLIBCXX_DEBUG_ASSERT(cmp_less(__idx, __exts.extent(__pos)));
__res += __idx * __mult;
__mult *= __exts.extent(__pos);
++__pos;
@@ -651,6 +652,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
auto __update = [&, __pos = __exts.rank()](_IndexType) mutable
{
--__pos;
+ _GLIBCXX_DEBUG_ASSERT(cmp_less(__ind_arr[__pos],
+ __exts.extent(__pos)));
__res += __ind_arr[__pos] * __mult;
__mult *= __exts.extent(__pos);
};
@@ -822,6 +825,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
auto __update = [&, __pos = 0u](_IndexType __idx) mutable
{
+ _GLIBCXX_DEBUG_ASSERT(cmp_less(__idx,
+ __m.extents().extent(__pos)));
__res += __idx * __m.stride(__pos++);
};
(__update(__indices), ...);
diff --git
a/libstdc++-v3/testsuite/23_containers/mdspan/layouts/debug/out_of_bounds_neg.cc
b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/debug/out_of_bounds_neg.cc
new file mode 100644
index 000000000000..fb8ff01e8aa2
--- /dev/null
+++
b/libstdc++-v3/testsuite/23_containers/mdspan/layouts/debug/out_of_bounds_neg.cc
@@ -0,0 +1,30 @@
+// { dg-do compile { target c++23 } }
+// { dg-require-debug-mode "" }
+#include<mdspan>
+
+template<typename Layout>
+ constexpr bool
+ test_out_of_bounds_1d()
+ {
+ auto m = typename Layout::mapping<std::extents<int, 0>>{};
+ (void) m(0); // { dg-error "expansion of" }
+ return true;
+ }
+static_assert(test_out_of_bounds_1d<std::layout_left>()); // { dg-error
"expansion of" }
+static_assert(test_out_of_bounds_1d<std::layout_right>()); // { dg-error
"expansion of" }
+static_assert(test_out_of_bounds_1d<std::layout_stride>()); // { dg-error
"expansion of" }
+
+template<typename Layout>
+ constexpr bool
+ test_out_of_bounds_3d()
+ {
+ auto m = typename Layout::mapping<std::extents<int, 3, 5, 7>>{};
+ (void) m(2, 5, 5); // { dg-error "expansion of" }
+ return true;
+ }
+static_assert(test_out_of_bounds_3d<std::layout_left>()); // { dg-error
"expansion of" }
+static_assert(test_out_of_bounds_3d<std::layout_right>()); // { dg-error
"expansion of" }
+static_assert(test_out_of_bounds_3d<std::layout_stride>()); // { dg-error
"expansion of" }
+
+// { dg-prune-output "non-constant condition for static assertion" }
+// { dg-prune-output "__glibcxx_assert" }
