[committed] libstdc++: Fix -Wshift-count-overflow warning in std::bitset

[committed] libstdc++: Fix -Wshift-count-overflow warning in std::bitset

[Jonathan Wakely]

Tested x86_64-linux and aarch64-linux. Pushed to trunk.

-- >8 --

This shift only happens if the unsigned long long type is wider than
unsigned long but the compiler warns when it sees the shift, without
caring if it's reachable.

Use the preprocessor to compare the sizes and just reuse _M_to_ulong()
if sizeof(long) == sizeof(long long).

libstdc++-v3/ChangeLog:

	* include/std/bitset (_Base_bitset::_M_do_to_ullong): Avoid
	-Wshift-count-overflow warning.
---
 libstdc++-v3/include/std/bitset | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/libstdc++-v3/include/std/bitset b/libstdc++-v3/include/std/bitset
index c169269698a..3243c649731 100644
--- a/libstdc++-v3/include/std/bitset
+++ b/libstdc++-v3/include/std/bitset
@@ -320,17 +320,18 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
     _GLIBCXX14_CONSTEXPR unsigned long long
     _Base_bitset<_Nw>::_M_do_to_ullong() const
     {
-      const bool __dw = sizeof(unsigned long long) > sizeof(unsigned long);
-      for (size_t __i = 1 + __dw; __i < _Nw; ++__i)
+#if __SIZEOF_LONG_LONG__ == __SIZEOF_LONG__
+      return _M_do_to_ulong();
+#else
+      for (size_t __i = 2; __i < _Nw; ++__i)
 	if (_M_w[__i])
 	  __throw_overflow_error(__N("_Base_bitset::_M_do_to_ullong"));
 
-      if (__dw)
-	return _M_w[0] + (static_cast<unsigned long long>(_M_w[1])
+      return _M_w[0] + (static_cast<unsigned long long>(_M_w[1])
 			  << _GLIBCXX_BITSET_BITS_PER_WORD);
-      return _M_w[0];
-    }
 #endif
+    }
+#endif // C++11
 
   template<size_t _Nw>
     _GLIBCXX14_CONSTEXPR size_t
-- 
2.43.0