[libcxx] Optimize away unneeded length calculation in basic_string::compare(const char*)
Summary:
This patch optimizes basic_string::compare to use strcmp when the default char_traits has been given.
See PR19900 for more information. https://llvm.org/bugs/show_bug.cgi?id=19900
Reviewers: mclow.lists
Subscribers: bkramer, cfe-commits
Differential Revision: http://reviews.llvm.org/D12355
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@246266 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/string b/include/string
index 372522c..504f9e1 100644
--- a/include/string
+++ b/include/string
@@ -3795,7 +3795,11 @@
operator==(const _CharT* __lhs,
const basic_string<_CharT, _Traits, _Allocator>& __rhs) _NOEXCEPT
{
- return __rhs.compare(__lhs) == 0;
+ typedef basic_string<_CharT, _Traits, _Allocator> _String;
+ _LIBCPP_ASSERT(__lhs != nullptr, "operator==(char*, basic_string): received nullptr");
+ size_t __lhs_len = _Traits::length(__lhs);
+ if (__lhs_len != __rhs.size()) return false;
+ return __rhs.compare(0, _String::npos, __lhs, __lhs_len) == 0;
}
template<class _CharT, class _Traits, class _Allocator>
@@ -3804,7 +3808,11 @@
operator==(const basic_string<_CharT,_Traits,_Allocator>& __lhs,
const _CharT* __rhs) _NOEXCEPT
{
- return __lhs.compare(__rhs) == 0;
+ typedef basic_string<_CharT, _Traits, _Allocator> _String;
+ _LIBCPP_ASSERT(__rhs != nullptr, "operator==(basic_string, char*): received nullptr");
+ size_t __rhs_len = _Traits::length(__rhs);
+ if (__rhs_len != __lhs.size()) return false;
+ return __lhs.compare(0, _String::npos, __rhs, __rhs_len) == 0;
}
// operator!=
