From ce784fdea4185d1fd7a23b5560455a6352c0295e Mon Sep 17 00:00:00 2001 From: Nikolas Klauser Date: Wed, 1 Oct 2025 09:18:48 +0200 Subject: [PATCH] Reapply "[libc++] Avoid constructing additional objects when using map::at" (#160738) This reverts commit b86aaacf28b358b187071bc87075f1faa2d65c4e. The issue in LLVM has been fixed now. --- libcxx/include/CMakeLists.txt | 2 + libcxx/include/__algorithm/comp.h | 4 ++ libcxx/include/__functional/is_transparent.h | 8 +++ libcxx/include/__functional/operations.h | 18 +++++++ .../include/__functional/ranges_operations.h | 7 +++ libcxx/include/__tree | 4 +- .../is_generic_transparent_comparator.h | 30 +++++++++++ .../include/__type_traits/make_transparent.h | 48 +++++++++++++++++ libcxx/include/map | 54 ++++++++++++++++--- libcxx/include/module.modulemap.in | 2 + libcxx/include/string | 16 ++++++ .../containers/associative/map.bench.cpp | 13 +++++ .../associative/unordered_map.bench.cpp | 13 +++++ 13 files changed, 211 insertions(+), 8 deletions(-) create mode 100644 libcxx/include/__type_traits/is_generic_transparent_comparator.h create mode 100644 libcxx/include/__type_traits/make_transparent.h diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt index e050362abb658..ddace8bf8c728 100644 --- a/libcxx/include/CMakeLists.txt +++ b/libcxx/include/CMakeLists.txt @@ -839,6 +839,7 @@ set(files __type_traits/is_floating_point.h __type_traits/is_function.h __type_traits/is_fundamental.h + __type_traits/is_generic_transparent_comparator.h __type_traits/is_implicit_lifetime.h __type_traits/is_implicitly_default_constructible.h __type_traits/is_integral.h @@ -881,6 +882,7 @@ set(files __type_traits/make_32_64_or_128_bit.h __type_traits/make_const_lvalue_ref.h __type_traits/make_signed.h + __type_traits/make_transparent.h __type_traits/make_unsigned.h __type_traits/maybe_const.h __type_traits/nat.h diff --git a/libcxx/include/__algorithm/comp.h b/libcxx/include/__algorithm/comp.h index ab3c598418828..38e2fb9f5e744 100644 --- a/libcxx/include/__algorithm/comp.h +++ b/libcxx/include/__algorithm/comp.h @@ -11,6 +11,7 @@ #include <__config> #include <__type_traits/desugars_to.h> +#include <__type_traits/is_generic_transparent_comparator.h> #include <__type_traits/is_integral.h> #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) @@ -48,6 +49,9 @@ inline const bool __desugars_to_v<__less_tag, __less<>, _Tp, _Tp> = true; template inline const bool __desugars_to_v<__totally_ordered_less_tag, __less<>, _Tp, _Tp> = is_integral<_Tp>::value; +template <> +inline const bool __is_generic_transparent_comparator_v<__less<> > = true; + _LIBCPP_END_NAMESPACE_STD #endif // _LIBCPP___ALGORITHM_COMP_H diff --git a/libcxx/include/__functional/is_transparent.h b/libcxx/include/__functional/is_transparent.h index 567df1a662f54..c2c6fbce2465b 100644 --- a/libcxx/include/__functional/is_transparent.h +++ b/libcxx/include/__functional/is_transparent.h @@ -29,6 +29,14 @@ inline const bool __is_transparent_v<_Tp, _Key, __void_t(arg))`. +// +// This is different from `__is_transparent_v`, which is only a property of the comparator and doesn't provide +// additional semantic guarantees. +template +inline const bool __is_transparently_comparable_v = false; + _LIBCPP_END_NAMESPACE_STD #endif // _LIBCPP___FUNCTIONAL_IS_TRANSPARENT diff --git a/libcxx/include/__functional/operations.h b/libcxx/include/__functional/operations.h index 7b0ea11db5844..7f315ca851c08 100644 --- a/libcxx/include/__functional/operations.h +++ b/libcxx/include/__functional/operations.h @@ -15,7 +15,9 @@ #include <__functional/unary_function.h> #include <__fwd/functional.h> #include <__type_traits/desugars_to.h> +#include <__type_traits/is_generic_transparent_comparator.h> #include <__type_traits/is_integral.h> +#include <__type_traits/make_transparent.h> #include <__utility/forward.h> #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) @@ -377,6 +379,14 @@ struct less { typedef void is_transparent; }; +template +struct __make_transparent > { + using type _LIBCPP_NODEBUG = less<>; +}; + +template <> +inline const bool __is_generic_transparent_comparator_v> = true; + template inline const bool __desugars_to_v<__less_tag, less<>, _Tp, _Up> = true; @@ -466,6 +476,14 @@ struct greater { template inline const bool __desugars_to_v<__greater_tag, greater<>, _Tp, _Up> = true; + +template +struct __make_transparent> { + using type _LIBCPP_NODEBUG = greater<>; +}; + +template <> +inline const bool __is_generic_transparent_comparator_v> = true; #endif // Logical operations diff --git a/libcxx/include/__functional/ranges_operations.h b/libcxx/include/__functional/ranges_operations.h index df95843e7c9af..dc9da061af264 100644 --- a/libcxx/include/__functional/ranges_operations.h +++ b/libcxx/include/__functional/ranges_operations.h @@ -14,6 +14,7 @@ #include <__concepts/totally_ordered.h> #include <__config> #include <__type_traits/desugars_to.h> +#include <__type_traits/is_generic_transparent_comparator.h> #include <__utility/forward.h> #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) @@ -108,6 +109,12 @@ inline const bool __desugars_to_v<__less_tag, ranges::less, _Tp, _Up> = true; template inline const bool __desugars_to_v<__greater_tag, ranges::greater, _Tp, _Up> = true; +template <> +inline const bool __is_generic_transparent_comparator_v = true; + +template <> +inline const bool __is_generic_transparent_comparator_v = true; + #endif // _LIBCPP_STD_VER >= 20 _LIBCPP_END_NAMESPACE_STD diff --git a/libcxx/include/__tree b/libcxx/include/__tree index 61c910c52c536..ef960d481cb7b 100644 --- a/libcxx/include/__tree +++ b/libcxx/include/__tree @@ -34,6 +34,7 @@ #include <__type_traits/is_same.h> #include <__type_traits/is_specialization.h> #include <__type_traits/is_swappable.h> +#include <__type_traits/make_transparent.h> #include <__type_traits/remove_const.h> #include <__utility/forward.h> #include <__utility/lazy_synth_three_way_comparator.h> @@ -1749,7 +1750,8 @@ __tree<_Tp, _Compare, _Allocator>::__find_equal(const _Key& __v) { } __node_base_pointer* __node_ptr = __root_ptr(); - auto __comp = __lazy_synth_three_way_comparator<_Compare, _Key, value_type>(value_comp()); + auto&& __transparent = std::__as_transparent(value_comp()); + auto __comp = __lazy_synth_three_way_comparator<__make_transparent_t<_Compare>, _Key, value_type>(__transparent); while (true) { auto __comp_res = __comp(__v, __nd->__get_value()); diff --git a/libcxx/include/__type_traits/is_generic_transparent_comparator.h b/libcxx/include/__type_traits/is_generic_transparent_comparator.h new file mode 100644 index 0000000000000..fd02c0b0423d1 --- /dev/null +++ b/libcxx/include/__type_traits/is_generic_transparent_comparator.h @@ -0,0 +1,30 @@ +//===----------------------------------------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// + +#ifndef _LIBCPP___TYPE_TRAITS_IS_GENERIC_TRANSPARENT_COMPARATOR_H +#define _LIBCPP___TYPE_TRAITS_IS_GENERIC_TRANSPARENT_COMPARATOR_H + +#include <__config> + +#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) +# pragma GCC system_header +#endif + +_LIBCPP_BEGIN_NAMESPACE_STD + +// This traits returns true if the given _Comparator is known to accept any two types for compaison. This is separate +// from `__is_transparent_v`, since that only enables overloads of specific functions, but doesn't give any semantic +// guarantees. This trait guarantess that the comparator simply calls the appropriate comparison functions for any two +// types. + +template +inline const bool __is_generic_transparent_comparator_v = false; + +_LIBCPP_END_NAMESPACE_STD + +#endif // _LIBCPP___TYPE_TRAITS_IS_GENERIC_TRANSPARENT_COMPARATOR_H diff --git a/libcxx/include/__type_traits/make_transparent.h b/libcxx/include/__type_traits/make_transparent.h new file mode 100644 index 0000000000000..4d3207a807fa7 --- /dev/null +++ b/libcxx/include/__type_traits/make_transparent.h @@ -0,0 +1,48 @@ +//===----------------------------------------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// + +#ifndef _LIBCPP___TYPE_TRAITS_MAKE_TRANSPARENT_H +#define _LIBCPP___TYPE_TRAITS_MAKE_TRANSPARENT_H + +#include <__config> +#include <__type_traits/enable_if.h> +#include <__type_traits/is_empty.h> +#include <__type_traits/is_same.h> + +#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) +# pragma GCC system_header +#endif + +_LIBCPP_BEGIN_NAMESPACE_STD + +// __make_transparent tries to create a transparent comparator from its non-transparent counterpart, e.g. obtain +// `less<>` from `less`. This is useful in cases where conversions can be avoided (e.g. a string literal to a +// std::string). + +template +struct __make_transparent { + using type _LIBCPP_NODEBUG = _Comparator; +}; + +template +using __make_transparent_t _LIBCPP_NODEBUG = typename __make_transparent<_Comparator>::type; + +template >::value, int> = 0> +_LIBCPP_HIDE_FROM_ABI _Comparator& __as_transparent(_Comparator& __comp) { + return __comp; +} + +template >::value, int> = 0> +_LIBCPP_HIDE_FROM_ABI __make_transparent_t<_Comparator> __as_transparent(_Comparator&) { + static_assert(is_empty<_Comparator>::value); + return __make_transparent_t<_Comparator>(); +} + +_LIBCPP_END_NAMESPACE_STD + +#endif // _LIBCPP___TYPE_TRAITS_MAKE_TRANSPARENT_H diff --git a/libcxx/include/map b/libcxx/include/map index a63dfec910aae..035f913bd3497 100644 --- a/libcxx/include/map +++ b/libcxx/include/map @@ -600,7 +600,10 @@ erase_if(multimap& c, Predicate pred); // C++20 # include <__ranges/from_range.h> # include <__tree> # include <__type_traits/container_traits.h> +# include <__type_traits/desugars_to.h> # include <__type_traits/is_allocator.h> +# include <__type_traits/is_convertible.h> +# include <__type_traits/make_transparent.h> # include <__type_traits/remove_const.h> # include <__type_traits/type_identity.h> # include <__utility/forward.h> @@ -666,6 +669,11 @@ public: # endif }; +template +struct __make_transparent<__map_value_compare<_Key, _MapValueT, _Compare> > { + using type _LIBCPP_NODEBUG = __map_value_compare<_Key, _MapValueT, __make_transparent_t<_Compare> >; +}; + # if _LIBCPP_STD_VER >= 14 template struct __lazy_synth_three_way_comparator<__map_value_compare<_Key, _MapValueT, _Compare>, _MapValueT, _MapValueT> { @@ -1048,6 +1056,24 @@ public: _LIBCPP_HIDE_FROM_ABI mapped_type& operator[](key_type&& __k); # endif + template >, int> = 0> + _LIBCPP_HIDE_FROM_ABI mapped_type& at(_Arg&& __arg) { + auto [_, __child] = __tree_.__find_equal(__arg); + if (__child == nullptr) + std::__throw_out_of_range("map::at: key not found"); + return static_cast<__node_pointer>(__child)->__get_value().second; + } + + template >, int> = 0> + _LIBCPP_HIDE_FROM_ABI const mapped_type& at(_Arg&& __arg) const { + auto [_, __child] = __tree_.__find_equal(__arg); + if (__child == nullptr) + std::__throw_out_of_range("map::at: key not found"); + return static_cast<__node_pointer>(__child)->__get_value().second; + } + _LIBCPP_HIDE_FROM_ABI mapped_type& at(const key_type& __k); _LIBCPP_HIDE_FROM_ABI const mapped_type& at(const key_type& __k) const; @@ -1242,11 +1268,15 @@ public: _LIBCPP_HIDE_FROM_ABI iterator find(const key_type& __k) { return __tree_.find(__k); } _LIBCPP_HIDE_FROM_ABI const_iterator find(const key_type& __k) const { return __tree_.find(__k); } # if _LIBCPP_STD_VER >= 14 - template , int> = 0> + template || __is_transparently_comparable_v<_Compare, key_type, _K2>, + int> = 0> _LIBCPP_HIDE_FROM_ABI iterator find(const _K2& __k) { return __tree_.find(__k); } - template , int> = 0> + template || __is_transparently_comparable_v<_Compare, key_type, _K2>, + int> = 0> _LIBCPP_HIDE_FROM_ABI const_iterator find(const _K2& __k) const { return __tree_.find(__k); } @@ -1262,7 +1292,9 @@ public: # if _LIBCPP_STD_VER >= 20 _LIBCPP_HIDE_FROM_ABI bool contains(const key_type& __k) const { return find(__k) != end(); } - template , int> = 0> + template || __is_transparently_comparable_v<_Compare, key_type, _K2>, + int> = 0> _LIBCPP_HIDE_FROM_ABI bool contains(const _K2& __k) const { return find(__k) != end(); } @@ -1271,12 +1303,16 @@ public: _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.lower_bound(__k); } _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const { return __tree_.lower_bound(__k); } # if _LIBCPP_STD_VER >= 14 - template , int> = 0> + template || __is_transparently_comparable_v<_Compare, key_type, _K2>, + int> = 0> _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const _K2& __k) { return __tree_.lower_bound(__k); } - template , int> = 0> + template || __is_transparently_comparable_v<_Compare, key_type, _K2>, + int> = 0> _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const _K2& __k) const { return __tree_.lower_bound(__k); } @@ -1285,11 +1321,15 @@ public: _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.upper_bound(__k); } _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const { return __tree_.upper_bound(__k); } # if _LIBCPP_STD_VER >= 14 - template , int> = 0> + template || __is_transparently_comparable_v<_Compare, key_type, _K2>, + int> = 0> _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const _K2& __k) { return __tree_.upper_bound(__k); } - template , int> = 0> + template || __is_transparently_comparable_v<_Compare, key_type, _K2>, + int> = 0> _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const _K2& __k) const { return __tree_.upper_bound(__k); } diff --git a/libcxx/include/module.modulemap.in b/libcxx/include/module.modulemap.in index 93d43f8d7e195..894093b409e11 100644 --- a/libcxx/include/module.modulemap.in +++ b/libcxx/include/module.modulemap.in @@ -200,6 +200,7 @@ module std_core [system] { header "__type_traits/is_fundamental.h" export std_core.type_traits.integral_constant } + module is_generic_transparent_comparator { header "__type_traits/is_generic_transparent_comparator.h" } module is_implicit_lifetime { header "__type_traits/is_implicit_lifetime.h" export std_core.type_traits.integral_constant @@ -353,6 +354,7 @@ module std_core [system] { module make_32_64_or_128_bit { header "__type_traits/make_32_64_or_128_bit.h" } module make_const_lvalue_ref { header "__type_traits/make_const_lvalue_ref.h" } module make_signed { header "__type_traits/make_signed.h" } + module make_transparent { header "__type_traits/make_transparent.h" } module make_unsigned { header "__type_traits/make_unsigned.h" } module maybe_const { header "__type_traits/maybe_const.h" } module nat { header "__type_traits/nat.h" } diff --git a/libcxx/include/string b/libcxx/include/string index cfd6861e5c9c2..dc562e0207630 100644 --- a/libcxx/include/string +++ b/libcxx/include/string @@ -600,6 +600,7 @@ basic_string operator""s( const char32_t *str, size_t len ); # include <__debug_utils/sanitizers.h> # include <__format/enable_insertable.h> # include <__functional/hash.h> +# include <__functional/is_transparent.h> # include <__functional/unary_function.h> # include <__fwd/string.h> # include <__iterator/bounded_iter.h> @@ -628,6 +629,7 @@ basic_string operator""s( const char32_t *str, size_t len ); # include <__type_traits/is_allocator.h> # include <__type_traits/is_array.h> # include <__type_traits/is_convertible.h> +# include <__type_traits/is_generic_transparent_comparator.h> # include <__type_traits/is_nothrow_assignable.h> # include <__type_traits/is_nothrow_constructible.h> # include <__type_traits/is_replaceable.h> @@ -2567,6 +2569,20 @@ struct __default_three_way_comparator, bas }; # endif +template +inline const bool __is_transparently_comparable_v<_Comparator, + basic_string<_CharT, _Traits, _Alloc>, + const _CharT*, + __enable_if_t<__is_generic_transparent_comparator_v<_Comparator> > > = + true; + +template +inline const bool __is_transparently_comparable_v<_Comparator, + basic_string<_CharT, _Traits, _Alloc>, + _CharT[_Np], + __enable_if_t<__is_generic_transparent_comparator_v<_Comparator> > > = + true; + # if _LIBCPP_STD_VER >= 17 template , diff --git a/libcxx/test/benchmarks/containers/associative/map.bench.cpp b/libcxx/test/benchmarks/containers/associative/map.bench.cpp index bd664dbb56ee7..142229ae64cad 100644 --- a/libcxx/test/benchmarks/containers/associative/map.bench.cpp +++ b/libcxx/test/benchmarks/containers/associative/map.bench.cpp @@ -16,6 +16,19 @@ #include "../../GenerateInput.h" #include "benchmark/benchmark.h" +static void BM_map_find_string_literal(benchmark::State& state) { + std::map map; + map.emplace("Something very very long to show a long string situation", 1); + map.emplace("Something Else", 2); + + for (auto _ : state) { + benchmark::DoNotOptimize(map); + benchmark::DoNotOptimize(map.find("Something very very long to show a long string situation")); + } +} + +BENCHMARK(BM_map_find_string_literal); + template struct support::adapt_operations> { using ValueType = typename std::map::value_type; diff --git a/libcxx/test/benchmarks/containers/associative/unordered_map.bench.cpp b/libcxx/test/benchmarks/containers/associative/unordered_map.bench.cpp index 57adec2d214d4..d670c531910ea 100644 --- a/libcxx/test/benchmarks/containers/associative/unordered_map.bench.cpp +++ b/libcxx/test/benchmarks/containers/associative/unordered_map.bench.cpp @@ -15,6 +15,19 @@ #include "../../GenerateInput.h" #include "benchmark/benchmark.h" +static void BM_map_find_string_literal(benchmark::State& state) { + std::unordered_map map; + map.emplace("Something very very long to show a long string situation", 1); + map.emplace("Something Else", 2); + + for (auto _ : state) { + benchmark::DoNotOptimize(map); + benchmark::DoNotOptimize(map.find("Something very very long to show a long string situation")); + } +} + +BENCHMARK(BM_map_find_string_literal); + template struct support::adapt_operations> { using ValueType = typename std::unordered_map::value_type;