1 //===- WatchedLiteralsSolver.h ----------------------------------*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file defines a SAT solver implementation that can be used by dataflow 10 // analyses. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_WATCHEDLITERALSSOLVER_H 15 #define LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_WATCHEDLITERALSSOLVER_H 16 17 #include "clang/Analysis/FlowSensitive/Formula.h" 18 #include "clang/Analysis/FlowSensitive/Solver.h" 19 #include "llvm/ADT/ArrayRef.h" 20 #include <limits> 21 22 namespace clang { 23 namespace dataflow { 24 25 /// A SAT solver that is an implementation of Algorithm D from Knuth's The Art 26 /// of Computer Programming Volume 4: Satisfiability, Fascicle 6. It is based on 27 /// the Davis-Putnam-Logemann-Loveland (DPLL) algorithm, keeps references to a 28 /// single "watched" literal per clause, and uses a set of "active" variables 29 /// for unit propagation. 30 class WatchedLiteralsSolver : public Solver { 31 // Count of the iterations of the main loop of the solver. This spans *all* 32 // calls to the underlying solver across the life of this object. It is 33 // reduced with every (non-trivial) call to the solver. 34 // 35 // We give control over the abstract count of iterations instead of concrete 36 // measurements like CPU cycles or time to ensure deterministic results. 37 std::int64_t MaxIterations = std::numeric_limits<std::int64_t>::max(); 38 39 public: 40 WatchedLiteralsSolver() = default; 41 42 // `Work` specifies a computational limit on the solver. Units of "work" 43 // roughly correspond to attempts to assign a value to a single 44 // variable. Since the algorithm is exponential in the number of variables, 45 // this is the most direct (abstract) unit to target. 46 explicit WatchedLiteralsSolver(std::int64_t WorkLimit) 47 : MaxIterations(WorkLimit) {} 48 49 Result solve(llvm::ArrayRef<const Formula *> Vals) override; 50 51 // The solver reached its maximum number of iterations. 52 bool reachedLimit() const { return MaxIterations == 0; } 53 }; 54 55 } // namespace dataflow 56 } // namespace clang 57 58 #endif // LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_WATCHEDLITERALSSOLVER_H 59