Lunderberg commented on code in PR #12972: URL: https://github.com/apache/tvm/pull/12972#discussion_r993682474
########## src/arith/conjunctive_normal_form.cc: ########## @@ -0,0 +1,415 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you 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. + */ + +/*! + * \file tvm/arith/conjunctive_normal_form.cc + */ + +#include "conjunctive_normal_form.h" + +#include <tvm/arith/analyzer.h> +#include <tvm/tir/expr.h> + +#include <optional> +#include <unordered_map> +#include <unordered_set> +#include <utility> +#include <vector> + +#include "pattern_match.h" +#include "rewrite_simplify.h" + +namespace tvm { +namespace arith { + +namespace { +/* \brief A utility for simplifying expressions using conjunctive/disjuctive normal forms */ +class AndOfOrs { + public: + /*! \brief Construct the simplifier + * + * Convert a PrimExpr to the internal representation. + * + * \param expr The PrimExpr to be simplified. + */ + explicit AndOfOrs(const PrimExpr& expr); + + /*! \brief Convert internal representation to PrimExpr */ + PrimExpr AsPrimExpr() const; + + /*! \brief Simplify the internal representation */ + void Simplify(Analyzer* analyzer); + + private: + /*! \brief Internal utility, simplify within each group of expressions + * + * For each pair of values within a chunk, attempt to simplify them into + * a single expression. + * + * For example, + * before = (a == 5) && ((b < 10) || (b > 10)) + * after = (a == 5) && ((b != 10) || false) + */ + void SimplifyWithinChunks(Analyzer* analyzer); + + /*! \brief Internal utility, simplify across groups of expressions + * + * For each pair of chunks, if the two chunks differ by only a single + * term, attempt to simplify those differing terms. + * + * For example, + * before = ((a == 5) || (b <= 10)) && ((a == 5) || (b >= 10)) + * after = ((a == 5) || (b == 10)) && ((a == 5) || true) + */ + void SimplifyAcrossChunks(Analyzer* analyzer); + + /*! \brief Remove instances of true/false from internal representation + * + * To avoid invalidating iterators, `SimplifyWithinChunks` and + * `SimplifyAcrossChunks` may replace keys, but may not remove keys from + * the internal representation. For example, `(a < 5) && (a < 10)` + * would be simplified to `(a < 5) && true`. The `Cleanup` function + * removes these leftover instances of true/false. + */ + void Cleanup(); + + /*! \brief Internal utility function used to convert to internal form */ + static void VisitAndExpressions(const PrimExpr& expr, + std::function<void(const PrimExpr&)> callback); + /*! \brief Internal utility function used to convert to internal form */ + static void VisitOrExpressions(const PrimExpr& expr, + std::function<void(const PrimExpr&)> callback); + + /* \brief Type-safe wrapper class that represents an PrimExpr + * + * Because integer indices are used frequently through this class, + * maintaining a separation between integer indices used to access + * specific elements of the internal representation, and unique + * identifiers used to represent expressions PrimExpr, is useful. + */ + enum class Key : size_t {}; + + /*! \brief Convert a PrimExpr to a Key */ + Key GetKey(const PrimExpr& expr); + + /*! \brief Convert a Key to a PrimExpr */ + PrimExpr GetExpr(Key key) const; + + /*! \brief Attempt to simplify (a && b) + * + * If successful, will overwrite the parameters `a` and `b` with the + * simplified form. + */ + void TrySimplifyOr(Key* a, Key* b, Analyzer* analyzer); + + /*! \brief Attempt to simplify (a || b) + * + * If successful, will overwrite the parameters `a` and `b` with the + * simplified form. + */ + void TrySimplifyAnd(Key* a, Key* b, Analyzer* analyzer); + + /*! \brief The internal representation + * + * `chunks[i][j]` is the j-th expression in the i-th OR-group. + */ + std::vector<std::vector<Key>> chunks; + + /*! \brief Mapping from internal Key to PrimExpr */ + std::unordered_map<Key, PrimExpr, StructuralHash, StructuralEqual> key_to_expr; + + /*! \brief Mapping from PrimExpr to internal Key */ + std::unordered_map<PrimExpr, Key, StructuralHash, StructuralEqual> expr_to_key; + + /*! \brief Cached key representing tir::Bool(true) */ + Key key_true; + + /*! \brief Cached key representing tir::Bool(false) */ + Key key_false; +}; + +AndOfOrs::AndOfOrs(const PrimExpr& expr) + : key_true(GetKey(Bool(true))), key_false(GetKey(Bool(false))) { + VisitAndExpressions(expr, [&](const PrimExpr& outer_expr) { + std::vector<Key> or_components; + VisitOrExpressions(outer_expr, [&](const PrimExpr& inner_expr) { + Key key = GetKey(inner_expr); + bool is_duplicate = std::any_of(or_components.begin(), or_components.end(), + [&](Key prev) { return prev == key; }); + if (!is_duplicate) { + or_components.push_back(key); + } + }); + + bool is_permutation = + std::any_of(chunks.begin(), chunks.end(), [&](const std::vector<Key>& prev_components) { + return or_components.size() == prev_components.size() && + std::is_permutation(prev_components.begin(), prev_components.end(), + or_components.begin()); + }); + if (!is_permutation) { + chunks.push_back(std::move(or_components)); + } + }); +} + +void AndOfOrs::VisitAndExpressions(const PrimExpr& expr, + std::function<void(const PrimExpr&)> callback) { + PVar<PrimExpr> x, y, z; + if ((x && y).Match(expr)) { + VisitAndExpressions(x.Eval(), callback); + VisitAndExpressions(y.Eval(), callback); + } else if ((x || y).Match(expr)) { + VisitAndExpressions(x.Eval(), [&](const PrimExpr& x_part) { + VisitAndExpressions(y.Eval(), [&](const PrimExpr& y_part) { callback(x_part || y_part); }); + }); + } else { + callback(expr); + } +} Review Comment: Good call, and updated. -- This is an automated message from the Apache Git Service. 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