The facility (with the original shorter name) has been in use on the
contracts development branch for almost a year, and has been tested in
isolation on x86_64-darwin and powerpc64le-linux.
OK for trunk?
thanks
Iain
--- 8< ---
This implements the library parts of P1494 as amended by P3641. For GCC the
compiler itself treats stdio operations as equivalent to the observable
checkpoint and thus it does not appear to be necessary to add calls to those
functions (it will not alter the outcome).
This adds the facility for C++26, although there is no reason, in principle,
that it would not work back to C++11 at least.
PR c++/119060
libstdc++-v3/ChangeLog:
* include/bits/version.h (__glibcxx_observable_checkpoint,
__cpp_lib_observable_checkpoint,
__glibcxx_want_observable_checkpoint): New.
* include/std/utility: Add std::observable_checkpoint().
Signed-off-by: Iain Sandoe <i...@sandoe.co.uk>
---
libstdc++-v3/include/bits/version.h | 10 ++++++++++
libstdc++-v3/include/std/utility | 19 +++++++++++++++++++
2 files changed, 29 insertions(+)
diff --git a/libstdc++-v3/include/bits/version.h
b/libstdc++-v3/include/bits/version.h
index c7569f42773..a1afbf44c8e 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -2123,6 +2123,16 @@
#endif /* !defined(__cpp_lib_unreachable) &&
defined(__glibcxx_want_unreachable) */
#undef __glibcxx_want_unreachable
+#if !defined(__cpp_lib_observable_checkpoint)
+# if (__cplusplus >= 202400L) &&
(__has_builtin(__builtin_observable_checkpoint))
+# define __glibcxx_observable_checkpoint 202506L
+# if defined(__glibcxx_want_all) ||
defined(__glibcxx_want_observable_checkpoint)
+# define __cpp_lib_observable_checkpoint 202506L
+# endif
+# endif
+#endif /* !defined(__cpp_lib_observable_checkpoint) &&
defined(__glibcxx_want_observable_checkpoint) */
+#undef __glibcxx_want_observable_checkpoint
+
#if !defined(__cpp_lib_algorithm_default_value_type)
# if (__cplusplus > 202302L)
# define __glibcxx_algorithm_default_value_type 202403L
diff --git a/libstdc++-v3/include/std/utility b/libstdc++-v3/include/std/utility
index 8a85ccfd09b..4a33a369f9c 100644
--- a/libstdc++-v3/include/std/utility
+++ b/libstdc++-v3/include/std/utility
@@ -98,6 +98,7 @@
#define __glibcxx_want_tuple_element_t
#define __glibcxx_want_tuples_by_type
#define __glibcxx_want_unreachable
+#define __glibcxx_want_observable_checkpoint
#define __glibcxx_want_tuple_like
#define __glibcxx_want_constrained_equality
#include <bits/version.h>
@@ -234,6 +235,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
#endif
+
+#ifdef __cpp_lib_observable_checkpoint // C++ >= 26
+ /// Informs the compiler that prior actions are considered observable.
+ /**
+ * This may be used to limit the extent to which optimisations based on the
+ * assumed unreachability of undefined behaviour can propagate to earlier
+ * code.
+ *
+ * @since C++26
+ */
+ [[__gnu__::__always_inline__]]
+ inline void
+ observable_checkpoint() _GLIBCXX_NOTHROW
+ {
+ return __builtin_observable_checkpoint();
+ }
+#endif
+
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
--
2.39.2 (Apple Git-143)
