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 21 namespace clang { 22 namespace dataflow { 23 24 /// A SAT solver that is an implementation of Algorithm D from Knuth's The Art 25 /// of Computer Programming Volume 4: Satisfiability, Fascicle 6. It is based on 26 /// the Davis-Putnam-Logemann-Loveland (DPLL) algorithm [1], keeps references to 27 /// a single "watched" literal per clause, and uses a set of "active" variables 28 /// for unit propagation. 29 // 30 // [1] https://en.wikipedia.org/wiki/DPLL_algorithm 31 class WatchedLiteralsSolver : public Solver { 32 // Count of the iterations of the main loop of the solver. This spans *all* 33 // calls to the underlying solver across the life of this object. It is 34 // reduced with every (non-trivial) call to the solver. 35 // 36 // We give control over the abstract count of iterations instead of concrete 37 // measurements like CPU cycles or time to ensure deterministic results. 38 std::int64_t MaxIterations = std::numeric_limits<std::int64_t>::max(); 39 40 public: 41 WatchedLiteralsSolver() = default; 42 43 // `Work` specifies a computational limit on the solver. Units of "work" 44 // roughly correspond to attempts to assign a value to a single 45 // variable. Since the algorithm is exponential in the number of variables, 46 // this is the most direct (abstract) unit to target. WatchedLiteralsSolver(std::int64_t WorkLimit)47 explicit WatchedLiteralsSolver(std::int64_t WorkLimit) 48 : MaxIterations(WorkLimit) {} 49 50 Result solve(llvm::ArrayRef<const Formula *> Vals) override; 51 reachedLimit()52 bool reachedLimit() const override { return MaxIterations == 0; } 53 }; 54 55 } // namespace dataflow 56 } // namespace clang 57 58 #endif // LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_WATCHEDLITERALSSOLVER_H 59