On 27/05/21 19:37 +0200, François Dumont via Libstdc++ wrote:
We have been talking for a long time of a debug mode with less impact
on performances.
We already have it, that's what _GLIBCXX_ASSERTIONS already is :-)
I propose to simply use the existing _GLIBCXX_ASSERTIONS macro.
libstdc++: [_GLIBCXX_ASSERTIONS] Activate basic debug checks
Use _GLIBCXX_ASSERTIONS as a _GLIBCXX_DEBUG light mode. When
defined it activates
all _GLIBCXX_DEBUG checks but skipping those requiring to loop
through the iterator
range unless in case of constexpr.
libstdc++-v3/ChangeLog:
* include/debug/debug.h [_GLIBCXX_ASSERTIONS]: Define
debug macros non-empty.
* include/debug/helper_functions.h: Cleanup comment about
removed _Iter_base.
* include/debug/functions.h (__skip_debug_runtime_check):
New, returns false if
_GLIBCXX_DEBUG is defined or if constant evaluated.
(__check_sorted, __check_partitioned_lower,
__check_partitioned_upper): Use latter.
Tested under Linux x64.
Ok to commit ?
François
diff --git a/libstdc++-v3/include/debug/debug.h
b/libstdc++-v3/include/debug/debug.h
index 116f2f023e2..2e6ce1c8a93 100644
--- a/libstdc++-v3/include/debug/debug.h
+++ b/libstdc++-v3/include/debug/debug.h
@@ -61,7 +61,7 @@ namespace __gnu_debug
struct _Safe_iterator;
}
-#ifndef _GLIBCXX_DEBUG
+#ifndef _GLIBCXX_ASSERTIONS
# define __glibcxx_requires_cond(_Cond,_Msg)
# define __glibcxx_requires_valid_range(_First,_Last)
diff --git a/libstdc++-v3/include/debug/functions.h
b/libstdc++-v3/include/debug/functions.h
index 6cac11f2abd..ee0eb877568 100644
--- a/libstdc++-v3/include/debug/functions.h
+++ b/libstdc++-v3/include/debug/functions.h
@@ -48,6 +48,25 @@ namespace __gnu_debug
template<typename _Sequence>
struct _Is_contiguous_sequence : std::__false_type { };
+ _GLIBCXX20_CONSTEXPR
Should this be simply _GLIBCXX_CONSTEXPR so that it can be constexpr
in C++14 mode too? Or are there are never any debug checks in
functions that are already constexpr in C++14 or C++17?
+ inline bool
+ __skip_debug_runtime_check()
+ {
+ // We could be here while only _GLIBCXX_ASSERTIONS has been
defined.
+ // In this case we skip expensive runtime checks, constexpr will
still
+ // be checked.
+ return
+#ifndef _GLIBCXX_DEBUG
+# if _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
+ !__builtin_is_constant_evaluated();
+# else
+ true;
+# endif
+#else
+ false;
+#endif
I think this would be simpler without the nesting, and without the
preprocessor checks halfway through the return statement:
#ifdef _GLIBCXX_DEBUG
return false;
#elif _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
return !__builtin_is_constant_evaluated();
#else
return true;
#endif
+ }
+
/* Checks that [first, last) is a valid range, and then returns
* __first. This routine is useful when we can't use a separate
* assertion statement because, e.g., we are in a constructor.
@@ -260,8 +279,9 @@ namespace __gnu_debug
inline bool
__check_sorted(const _InputIterator& __first, const
_InputIterator& __last)
{
- return __check_sorted_aux(__first, __last,
- std::__iterator_category(__first));
+ return __skip_debug_runtime_check()
+ || __check_sorted_aux(__first, __last,
+ std::__iterator_category(__first));
Currently this function is never called at all ifndef _GLIBCXX_DEBUG.
With this change, it's going to be present for _GLIBCXX_ASSERTIONS,
and if it isn't inlined it's going to explode the code size.
Some linux distros are already building the entire distro with
_GLIBCXX_ASSERTIONS so I think we need to be quite careful about this
kind of large change affecting every algo.
So maybe we shouldn't enable these checks via _GLIBCXX_ASSERTIONS, but
a new macro.
