From: Jonathan Wakely <jwakely@redhat.com>
Date: Wed, 8 Oct 2025 14:26:54 +0000 (+0100)
Subject: libstdc++: Extend constexpr if to C++14 in _Hashtable::_S_nothrow_move()
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ea05497d4a329f183ffb5428befc957c5522ef86;p=thirdparty%2Fgcc.git

libstdc++: Extend constexpr if to C++14 in _Hashtable::_S_nothrow_move()

We can use diagnostic pragmas to allow the constexpr if version of this
function to be used for C++14 as well. We still need the __and_ version
for C++11 because we can't use 'if' in constexpr functions at all before
C++14.

Also use the integral_constant::value static data member instead of
invoking integral_constant::operator(), as it's a tiny bit cheaper to
compiler.

libstdc++-v3/ChangeLog:

	* include/bits/hashtable.h (_Hashtable::_S_nothrow_move): Use
	diagnostic pragmas to allow constexpr if in C++14. Use value
	member instead of operator().

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
---

diff --git a/libstdc++-v3/include/bits/hashtable.h b/libstdc++-v3/include/bits/hashtable.h
index 20f9bd98d5b..b5a71f516f8 100644
--- a/libstdc++-v3/include/bits/hashtable.h
+++ b/libstdc++-v3/include/bits/hashtable.h
@@ -477,15 +477,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	static constexpr bool
 	_S_nothrow_move()
 	{
-#if __cplusplus <= 201402L
+#if __cpp_constexpr >= 201304 // >= C++14
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wc++17-extensions" // if constexpr
+	  if constexpr (_No_realloc)
+	    if constexpr (is_nothrow_copy_constructible<_Hash>::value)
+	      return is_nothrow_copy_constructible<_Equal>::value;
+	  return false;
+# pragma GCC diagnostic pop
+#else // In C++11 a constexpr function must be a single statement.
 	  return __and_<__bool_constant<_No_realloc>,
 			is_nothrow_copy_constructible<_Hash>,
 			is_nothrow_copy_constructible<_Equal>>::value;
-#else
-	  if constexpr (_No_realloc)
-	    if constexpr (is_nothrow_copy_constructible<_Hash>())
-	      return is_nothrow_copy_constructible<_Equal>();
-	  return false;
 #endif
 	}