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[analysis] Implement Flat lattice (WebAssembly#6039)
Given a type `T`, `Flat<T>` is the lattice where none of the values of `T` are comparable except with themselves, but they are all greater than a common bottom element not in `T` and less than a common top element also not in `T`.
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| /* | ||
| * Copyright 2023 WebAssembly Community Group participants | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
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| #ifndef wasm_analysis_lattices_flat_h | ||
| #define wasm_analysis_lattices_flat_h | ||
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| #include <variant> | ||
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| #if __cplusplus >= 202002L | ||
| #include <concepts> | ||
| #endif | ||
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| #include "../lattice.h" | ||
| #include "support/utilities.h" | ||
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| namespace wasm::analysis { | ||
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| #if __cplusplus >= 202002L | ||
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| template<typename T> | ||
| concept Flattenable = std::copyable<T> && std::equality_comparable<T>; | ||
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| // Given a type T, Flat<T> is the lattice where none of the values of T are | ||
| // comparable except with themselves, but they are all greater than a common | ||
| // bottom element not in T and less than a common top element also not in T. | ||
| template<Flattenable T> | ||
| #else | ||
| template<typename T> | ||
| #endif | ||
| struct Flat { | ||
| private: | ||
| struct Bot {}; | ||
| struct Top {}; | ||
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| public: | ||
| struct Element : std::variant<Bot, T, Top> { | ||
| bool isBottom() const noexcept { return std::get_if<Bot>(this); } | ||
| bool isTop() const noexcept { return std::get_if<Top>(this); } | ||
| const T* getVal() const noexcept { return std::get_if<T>(this); } | ||
| T* getVal() noexcept { return std::get_if<T>(this); } | ||
| }; | ||
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| Element getBottom() const noexcept { return Element{Bot{}}; } | ||
| Element getTop() const noexcept { return Element{Top{}}; } | ||
| Element get(T&& val) const noexcept { return Element{std::move(val)}; } | ||
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| LatticeComparison compare(const Element& a, const Element& b) const noexcept { | ||
| if (a.index() < b.index()) { | ||
| return LESS; | ||
| } else if (a.index() > b.index()) { | ||
| return GREATER; | ||
| } else if (auto pA = a.getVal(); pA && *pA != *b.getVal()) { | ||
| return NO_RELATION; | ||
| } else { | ||
| return EQUAL; | ||
| } | ||
| } | ||
| bool join(Element& self, const Element& other) const noexcept { | ||
| switch (compare(self, other)) { | ||
| case LESS: | ||
| self = other; | ||
| return true; | ||
| case NO_RELATION: | ||
| self = Element{Top{}}; | ||
| return true; | ||
| case GREATER: | ||
| case EQUAL: | ||
| return false; | ||
| } | ||
| WASM_UNREACHABLE("unexpected comparison result"); | ||
| } | ||
| }; | ||
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| #if __cplusplus >= 202002L | ||
| static_assert(Lattice<Flat<int>>); | ||
| #endif | ||
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| } // namespace wasm::analysis | ||
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| #endif // wasm_analysis_lattices_flat_h |
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