1 //===- ConstraintSystem.h - A system of linear constraints. --------------===// 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 #ifndef LLVM_ANALYSIS_CONSTRAINTSYSTEM_H 10 #define LLVM_ANALYSIS_CONSTRAINTSYSTEM_H 11 12 #include "llvm/ADT/APInt.h" 13 #include "llvm/ADT/ArrayRef.h" 14 #include "llvm/ADT/STLExtras.h" 15 #include "llvm/ADT/SmallVector.h" 16 17 #include <string> 18 19 namespace llvm { 20 21 class ConstraintSystem { 22 /// Current linear constraints in the system. 23 /// An entry of the form c0, c1, ... cn represents the following constraint: 24 /// c0 >= v0 * c1 + .... + v{n-1} * cn 25 SmallVector<SmallVector<int64_t, 8>, 4> Constraints; 26 27 /// Current greatest common divisor for all coefficients in the system. 28 uint32_t GCD = 1; 29 30 // Eliminate constraints from the system using Fourier–Motzkin elimination. 31 bool eliminateUsingFM(); 32 33 /// Print the constraints in the system, using x0...xn as variable names. 34 void dump() const; 35 36 /// Returns true if there may be a solution for the constraints in the system. 37 bool mayHaveSolutionImpl(); 38 39 public: 40 bool addVariableRow(const SmallVector<int64_t, 8> &R) { 41 assert(Constraints.empty() || R.size() == Constraints.back().size()); 42 // If all variable coefficients are 0, the constraint does not provide any 43 // usable information. 44 if (all_of(makeArrayRef(R).drop_front(1), [](int64_t C) { return C == 0; })) 45 return false; 46 47 for (const auto &C : R) { 48 auto A = std::abs(C); 49 GCD = APIntOps::GreatestCommonDivisor({32, (uint32_t)A}, {32, GCD}) 50 .getZExtValue(); 51 } 52 Constraints.push_back(R); 53 return true; 54 } 55 56 bool addVariableRowFill(const SmallVector<int64_t, 8> &R) { 57 for (auto &CR : Constraints) { 58 while (CR.size() != R.size()) 59 CR.push_back(0); 60 } 61 return addVariableRow(R); 62 } 63 64 /// Returns true if there may be a solution for the constraints in the system. 65 bool mayHaveSolution(); 66 67 static SmallVector<int64_t, 8> negate(SmallVector<int64_t, 8> R) { 68 // The negated constraint R is obtained by multiplying by -1 and adding 1 to 69 // the constant. 70 R[0] += 1; 71 for (auto &C : R) 72 C *= -1; 73 return R; 74 } 75 76 bool isConditionImplied(SmallVector<int64_t, 8> R); 77 78 void popLastConstraint() { Constraints.pop_back(); } 79 80 /// Returns the number of rows in the constraint system. 81 unsigned size() const { return Constraints.size(); } 82 83 /// Print the constraints in the system, using \p Names as variable names. 84 void dump(ArrayRef<std::string> Names) const; 85 }; 86 } // namespace llvm 87 88 #endif // LLVM_ANALYSIS_CONSTRAINTSYSTEM_H 89