[libcxx-commits] [libcxx] [libc++] std::cmp_less and other integer comparison functions could be improved (PR #151332)

[via libcxx-commits]

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@@ -28,7 +29,13 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <__signed_or_unsigned_integer _Tp, __signed_or_unsigned_integer _Up>
 _LIBCPP_HIDE_FROM_ABI constexpr bool cmp_equal(_Tp __t, _Up __u) noexcept {
-  if constexpr (is_signed_v<_Tp> == is_signed_v<_Up>)
+  if constexpr (sizeof(_Tp) < sizeof(int) && sizeof(_Up) < sizeof(int)) {
+    _LIBCPP_ASSUME(__t < numeric_limits<int>::max() && __u < numeric_limits<int>::max());
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kisuhorikka wrote:

[Previous bench](https://quick-bench.com/q/BcqNhwMMj53O4xg6MQvhKe9PWok) shows slower results when converting parameters from `short` to `long long`. The performance is better if parameters are converted to `int`. https://quick-bench.com/q/q87HT8ePhR1AqI_Gy3Zj6rbElp8

However, the above results are based on clang 15 (I neglected this before unfortunately), and the difference seems vanished on clang 17. https://quick-bench.com/q/q0Q-bgFsVQyqe8QiDTiPHkawIu4

Though the little difference between speed, the assembly for `int` is shorter than `long long`, and `_LIBCPP_ASSUME` seems no work now. https://godbolt.org/z/a5s3zx64W

https://github.com/llvm/llvm-project/pull/151332