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[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

llvm-svn: 246266
This commit is contained in:
Eric Fiselier 2015-08-28 03:02:37 +00:00
parent ad5ca2245e
commit 8465ea4440
1 changed files with 10 additions and 2 deletions
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12
libcxx/include/string
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@ -3795,7 +3795,11 @@ bool
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 @@ bool
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!=