libstdc++: Disable __gnu_debug::__is_singular(T*) in constexpr [PR109517]

Because of PR c++/85944 we have several bugs where _GLIBCXX_DEBUG causes
errors for constexpr code. Although Bug 117966 could be fixed by
avoiding redundant debug checks in std::span, and Bug 106212 could be
fixed by avoiding redundant debug checks in std::array, there are many
more cases where similar __glibcxx_requires_valid_range checks fail to
compile and removing the checks everywhere isn't desirable.

This just disables the __gnu_debug::__check_singular(T*) check during
constant evaluation. Attempting to dereference a null pointer will
certainly fail during constant evaluation (if it doesn't fail then it's
a compiler bug and not the library's problem). Disabling this check
during constant evaluation shouldn't do any harm.

libstdc++-v3/ChangeLog:

	PR libstdc++/109517
	PR libstdc++/109976
	* include/debug/helper_functions.h (__valid_range_aux): Treat
	all input iterator ranges as valid during constant evaluation.

diff --git a/libstdc++-v3/include/debug/helper_functions.h b/libstdc++-v3/include/debug/helper_functions.h
index d686a29e8ee900143420c017ecf74bde3bc1f1cb..8d6a5fb41fb479fb5d423575ad33869b8a8a000f 100644 (file)
--- a/libstdc++-v3/include/debug/helper_functions.h
+++ b/libstdc++-v3/include/debug/helper_functions.h
@@ -168,6 +168,11 @@ namespace __gnu_debug
     __valid_range_aux(_InputIterator __first, _InputIterator __last,
                      std::input_iterator_tag)
     {
+      // FIXME: The checks for singular iterators fail during constant eval
+      // due to PR c++/85944. e.g. PR libstdc++/109517 and PR libstdc++/109976.
+      if (std::__is_constant_evaluated())
+       return true;
+
       return __first == __last
        || (!__gnu_debug::__check_singular(__first)
              && !__gnu_debug::__check_singular(__last));