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Extracted pass_in_reg machinery to a dedicated header.
Added more documentation links. Minor debug build bug fixes.
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| #pragma once | ||
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| #include <psi/build/disable_warnings.hpp> | ||
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| #include <boost/config.hpp> | ||
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| #include <ranges> | ||
| #include <span> | ||
| #include <string> | ||
| #include <string_view> | ||
| #include <type_traits> | ||
| //------------------------------------------------------------------------------ | ||
| namespace psi::vm | ||
| { | ||
| //------------------------------------------------------------------------------ | ||
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| PSI_WARNING_DISABLE_PUSH() | ||
| PSI_WARNING_MSVC_DISABLE( 5030 ) // unrecognized attribute | ||
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| //////////////////////////////////////////////////////////////////////////////// | ||
| // Modern(ized) attempt at 'automatized' boost::call_traits primarily to support | ||
| // efficient transparent comparators & non-inlined generic lookup functions | ||
| // which cause neither unnecessary copies of non-trivial types nor pass-by-ref | ||
| // of trivial ones. | ||
| // Largely still WiP... | ||
| // Essentially this is 'explicit IPA SROA'. | ||
| // https://gcc.gnu.org/onlinedocs/gccint/passes-and-files-of-the-compiler/inter-procedural-optimization-passes.html | ||
| //////////////////////////////////////////////////////////////////////////////// | ||
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| template <typename T> | ||
| bool constexpr can_be_passed_in_reg | ||
| { | ||
| ( | ||
| std::is_trivial_v<T> && | ||
| ( sizeof( T ) <= 2 * sizeof( void * ) ) // assuming a sane ABI like SysV (ignoring the MS x64 disaster) | ||
| ) | ||
| #if defined( __GNUC__ ) || defined( __clang__ ) | ||
| || // detect SIMD types (this could also produce false positives for large compiler-native vectors that do not fit into the register file) | ||
| requires{ __builtin_convertvector( T{}, T ); } | ||
| #endif | ||
| // This is certainly not an exhaustive list/'trait' - certain types that can | ||
| // be passed in reg cannot be detected as such by existing compiler | ||
| // functionality, e.g. Homogeneous Vector Aggregates | ||
| // https://devblogs.microsoft.com/cppblog/introducing-vector-calling-convention | ||
| // users are encouraged to provide specializations for such types. | ||
| }; // can_be_passed_in_reg | ||
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| template <typename T> | ||
| struct optimal_const_ref { using type = T const &; }; | ||
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| template <typename Char> | ||
| struct optimal_const_ref<std::basic_string<Char>> { using type = std::basic_string_view<Char>; }; | ||
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| template <std::ranges::contiguous_range Rng> | ||
| struct optimal_const_ref<Rng> { using type = std::span<std::ranges::range_value_t<Rng> const>; }; | ||
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| template <typename T> | ||
| struct [[ clang::trivial_abi ]] pass_in_reg | ||
| { | ||
| static auto constexpr pass_by_val{ can_be_passed_in_reg<T> }; | ||
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| using value_type = T; | ||
| using stored_type = std::conditional_t<pass_by_val, T, typename optimal_const_ref<T>::type>; | ||
| BOOST_FORCEINLINE | ||
| constexpr pass_in_reg( auto const &... args ) noexcept requires requires { stored_type{ args... }; } : value{ args... } {} | ||
| constexpr pass_in_reg( pass_in_reg const & ) noexcept = default; | ||
| constexpr pass_in_reg( pass_in_reg && ) noexcept = default; | ||
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| stored_type value; | ||
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| [[ gnu::pure ]] BOOST_FORCEINLINE | ||
| constexpr operator stored_type const &() const noexcept { return value; } | ||
| }; // pass_in_reg | ||
| template <typename T> | ||
| pass_in_reg( T ) -> pass_in_reg<T>; | ||
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| template <typename T> | ||
| struct [[ clang::trivial_abi ]] pass_rv_in_reg | ||
| { | ||
| static auto constexpr pass_by_val{ can_be_passed_in_reg<T> }; | ||
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| using value_type = T; | ||
| using stored_type = std::conditional_t<pass_by_val, T, T &&>; | ||
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| constexpr pass_rv_in_reg( T && u ) noexcept : value{ std::move( u ) } {} // move for not-trivially-moveable yet trivial_abi types (that can be passed in reg) | ||
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| stored_type value; | ||
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| [[ gnu::pure ]] BOOST_FORCEINLINE constexpr operator stored_type const & () const & noexcept { return value ; } | ||
| [[ gnu::pure ]] BOOST_FORCEINLINE constexpr operator stored_type &&() && noexcept { return std::move( value ); } | ||
| }; // pass_rv_in_reg | ||
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| template <typename T> bool constexpr reg { can_be_passed_in_reg<T> }; | ||
| template <typename T> bool constexpr reg<pass_in_reg <T>>{ true }; | ||
| template <typename T> bool constexpr reg<pass_rv_in_reg<T>>{ true }; | ||
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| template <typename T> | ||
| concept Reg = reg<T>; | ||
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| // 'Explicit IPA SROA' / pass-in-reg helper end | ||
| //////////////////////////////////////////////////////////////////////////////// | ||
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| PSI_WARNING_DISABLE_POP() | ||
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| //------------------------------------------------------------------------------ | ||
| } // namespace psi::vm | ||
| //------------------------------------------------------------------------------ |
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