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89 lines
2.8 KiB
C++
89 lines
2.8 KiB
C++
//===- ConstraintSystem.h - A system of linear constraints. --------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_CONSTRAINTSYSTEM_H
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#define LLVM_ANALYSIS_CONSTRAINTSYSTEM_H
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#include "llvm/ADT/APInt.h"
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallVector.h"
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#include <string>
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namespace llvm {
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class ConstraintSystem {
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/// Current linear constraints in the system.
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/// An entry of the form c0, c1, ... cn represents the following constraint:
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/// c0 >= v0 * c1 + .... + v{n-1} * cn
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SmallVector<SmallVector<int64_t, 8>, 4> Constraints;
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/// Current greatest common divisor for all coefficients in the system.
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uint32_t GCD = 1;
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// Eliminate constraints from the system using Fourier–Motzkin elimination.
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bool eliminateUsingFM();
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/// Print the constraints in the system, using x0...xn as variable names.
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void dump() const;
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/// Returns true if there may be a solution for the constraints in the system.
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bool mayHaveSolutionImpl();
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public:
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bool addVariableRow(const SmallVector<int64_t, 8> &R) {
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assert(Constraints.empty() || R.size() == Constraints.back().size());
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// If all variable coefficients are 0, the constraint does not provide any
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// usable information.
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if (all_of(makeArrayRef(R).drop_front(1), [](int64_t C) { return C == 0; }))
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return false;
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for (const auto &C : R) {
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auto A = std::abs(C);
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GCD = APIntOps::GreatestCommonDivisor({32, (uint32_t)A}, {32, GCD})
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.getZExtValue();
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}
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Constraints.push_back(R);
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return true;
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}
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bool addVariableRowFill(const SmallVector<int64_t, 8> &R) {
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for (auto &CR : Constraints) {
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while (CR.size() != R.size())
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CR.push_back(0);
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}
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return addVariableRow(R);
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}
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/// Returns true if there may be a solution for the constraints in the system.
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bool mayHaveSolution();
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static SmallVector<int64_t, 8> negate(SmallVector<int64_t, 8> R) {
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// The negated constraint R is obtained by multiplying by -1 and adding 1 to
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// the constant.
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R[0] += 1;
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for (auto &C : R)
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C *= -1;
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return R;
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}
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bool isConditionImplied(SmallVector<int64_t, 8> R);
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void popLastConstraint() { Constraints.pop_back(); }
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/// Returns the number of rows in the constraint system.
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unsigned size() const { return Constraints.size(); }
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/// Print the constraints in the system, using \p Names as variable names.
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void dump(ArrayRef<std::string> Names) const;
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};
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} // namespace llvm
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#endif // LLVM_ANALYSIS_CONSTRAINTSYSTEM_H
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