Lunderberg commented on code in PR #13130: URL: https://github.com/apache/tvm/pull/13130#discussion_r1021747479
########## src/tir/analysis/control_flow_graph.h: ########## @@ -0,0 +1,458 @@ +/* + * 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 control_flow_graph.h + * \brief Utility for extracting and interacting with buffer touch points + */ + +#include <tvm/arith/analyzer.h> +#include <tvm/arith/int_solver.h> +#include <tvm/runtime/container/array.h> +#include <tvm/tir/buffer.h> +#include <tvm/tir/stmt.h> +#include <tvm/tir/var.h> + +#include <unordered_map> +#include <utility> +#include <vector> + +#ifndef TVM_TIR_ANALYSIS_CONTROL_FLOW_GRAPH_H_ +#define TVM_TIR_ANALYSIS_CONTROL_FLOW_GRAPH_H_ + +namespace tvm { +namespace tir { + +/*! \brief Represents an interaction with a buffer */ +struct BufferTouch { + enum class AccessType { + Read, + Write, + Assume, + }; + + BufferTouch(Buffer buffer, PrimExpr predicate, PrimExpr value) + : buffer(buffer), + predicate(predicate), + value(value), + loop_var_expressions({}), + touch_type(AccessType::Assume) {} + + BufferTouch(Buffer buffer, PrimExpr predicate, PrimExpr value, + std::vector<std::pair<Var, PrimExpr>> loop_var_expressions, AccessType touch_type) + : buffer(buffer), + predicate(predicate), + value(value), + loop_var_expressions(loop_var_expressions), + touch_type(touch_type) {} + + /*! \brief The buffer being touched */ + Buffer buffer; + + /*! \brief A predicate that is true when this touch applies + * + * May be in terms of axis variables to indicate touches that impact + * only a portion of a buffer. + */ + PrimExpr predicate; + + /*! \brief The value in this buffer after the touch + * + * May be in terms of axis variables to indicate a known + * non-constant value. May be in terms of a BufferLoad to indicate + * an unknown value. + */ + PrimExpr value; + + /*! \brief Active loops during the buffer touch + * + * Used to construct boolean expressions indicating whether the loop + * iteration that performs this touch has been reached. + */ + std::vector<std::pair<Var, PrimExpr>> loop_var_expressions; + + /*! \brief How the buffer was interacted with + * + * When used as a constraint (e.g. in BufferState), should use + * Assume. + */ + AccessType touch_type{AccessType::Assume}; + + PrimExpr BeforeLoopIteration() const; + PrimExpr AtLoopIteration() const; + PrimExpr AfterLoopIteration() const; + + /* \brief Checks if this touch affects a subset of indices of another + * + * Returns true if the indices accessed by this touch are a subset + * of predicate is true can be proven to be a subset of the other + * subset. Returns false if it cannot be proven to be a subset of + * ther other subset. + */ + bool IsSubsetOf(const BufferTouch& other, arith::Analyzer* analyzer) const; + + /* \brief Checks if this touch affects distinct indicates from another + * + * Returns true if it can be proven that the two predicates cannot + * be simultaneously true. Returns false if it cannot be proven + * that the two predicates are distinct. + */ + bool IsDistinctFrom(const BufferTouch& other, arith::Analyzer* analyzer) const; + + /* \brief Checks if this touch affects distinct indicates from another + * + * Returns true if it can be proven that the two predicates cannot + * be simultaneously true. Returns false if it cannot be proven + * that the two predicates are distinct. + */ + bool IsEquivalentTo(const BufferTouch& other, arith::Analyzer* analyzer) const; + + friend std::ostream& operator<<(std::ostream& os, const BufferTouch& expr); +}; + +/*! \brief Represents the known state of buffers at a specific point */ +class BufferState { + public: + /*! Default constructor + * + * Initialize the buffer state with no known information. + */ + BufferState() {} + + /*! \brief Replace BufferLoad instances with known values + * + * \param expr The expression to be updated. + * + * \param axis_var_lookup A map from buffer to the variables + * representing positions along the buffer's axes. + * + * \param analyzer The analyzer to use when validating a + * constraint's predicate. + * + * \returns The modified expression. If no substitutions are made, + * the original expression is returned. + */ + PrimExpr SubstituteKnownBufferValues(PrimExpr expr, + const Map<Buffer, Array<Var>>& axis_var_lookup, + arith::Analyzer* analyzer) const; + + /*! \brief Apply a condition to all known constraints + * + * For example, when propagating pre-loop constraints into the body + * of a loop, add a condition that the loop iterator is zero. + * + * \param condition The condition to apply + */ + void AddCondition(const PrimExpr& condition); + + /*! \brief Perform a variable substitution for all constraints + * + * For example, when propagating constraints from the end of a loop + * to the beginning, replace `i` with `i-1`. + * + * \param var_remap The variable remapping to apply. + */ + void Substitute(const Map<Var, PrimExpr>& var_remap, arith::Analyzer* analyzer); + + /*! \brief Simplify the predicate of all constraints + * + * \param analyzer The analyzer with which to simplify + */ + void Simplify(arith::Analyzer* analyzer); + + /*! \brief Update the known buffer values based on buffer touches + * + * For any Write or Assume touches, update the known values. For + * any Read touches, ignore. Used to determine known values at the + * end of a series of a control flow block, given the known values + * at the start. + * + * \param axis_var_lookup A map from buffer to the variables + * representing positions along the buffer's axes. + * + * \param touch_points The buffer touch points to apply + * + * \param analyzer The analyzer to use for simplifications + */ + void ApplyTouches(const Map<Buffer, Array<Var>>& axis_var_lookup, + const std::vector<BufferTouch>& touch_points, arith::Analyzer* analyzer); + + void BackpropUnusedIndices(const Map<Buffer, Array<Var>>& axis_var_lookup, + const std::vector<BufferTouch>& touch_points, + arith::Analyzer* analyzer); + + /*! \brief Remove free parameters from the constraints + * + * \param free_predicate_parameters + * + * \param analyzer The analyzer with which to simplify after removal + */ + void RemoveFreeParameters(const Map<Var, Range>& free_predicate_parameters, + arith::Analyzer* analyzer); + + /*! \brief Check if two buffer states are equivalent + * + * \param other + * + * \param analyzer The analyzer used to check equality of PrimExpr + * + * \return True if the two states are provably equivalent, false otherwise. + */ + bool IsEquivalentTo(const BufferState& other, arith::Analyzer* analyzer) const; + + /* \brief Add known values provided by another state + * + * \param other The state with which to merge constraints + * + * \param analyzer The analyzer with which to simplify the result + */ + void Union(const BufferState& other, arith::Analyzer* analyzer); + + /* \brief Remove all known values not consistent with another state + * + * \param other The state with which to merge constraints + * + * \param analyzer The analyzer with which to simplify the result + */ + void Intersection(const BufferState& other, arith::Analyzer* analyzer); + + friend std::ostream& operator<<(std::ostream& os, const BufferState&); + + private: + friend class ControlFlowGraph; + /*! \brief The known constraints */ + std::vector<BufferTouch> constraints; +}; + +class ControlFlowGraph { Review Comment: And added. -- This is an automated message from the Apache Git Service. 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