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