1//===- SparsePropagation.h - Sparse Conditional Property Propagation ------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements an abstract sparse conditional propagation algorithm, 11// modeled after SCCP, but with a customizable lattice function. 12// 13//===----------------------------------------------------------------------===// 14 15#ifndef LLVM_ANALYSIS_SPARSEPROPAGATION_H 16#define LLVM_ANALYSIS_SPARSEPROPAGATION_H 17 18#include "llvm/ADT/DenseMap.h" 19#include "llvm/ADT/SmallPtrSet.h" 20#include "llvm/IR/BasicBlock.h" 21#include <set> 22#include <vector> 23 24namespace llvm { 25class Value; 26class Constant; 27class Argument; 28class Instruction; 29class PHINode; 30class TerminatorInst; 31class BasicBlock; 32class Function; 33class SparseSolver; 34class raw_ostream; 35 36template <typename T> class SmallVectorImpl; 37 38/// AbstractLatticeFunction - This class is implemented by the dataflow instance 39/// to specify what the lattice values are and how they handle merges etc. 40/// This gives the client the power to compute lattice values from instructions, 41/// constants, etc. The requirement is that lattice values must all fit into 42/// a void*. If a void* is not sufficient, the implementation should use this 43/// pointer to be a pointer into a uniquing set or something. 44/// 45class AbstractLatticeFunction { 46public: 47 typedef void *LatticeVal; 48 49private: 50 LatticeVal UndefVal, OverdefinedVal, UntrackedVal; 51 52public: 53 AbstractLatticeFunction(LatticeVal undefVal, LatticeVal overdefinedVal, 54 LatticeVal untrackedVal) { 55 UndefVal = undefVal; 56 OverdefinedVal = overdefinedVal; 57 UntrackedVal = untrackedVal; 58 } 59 virtual ~AbstractLatticeFunction(); 60 61 LatticeVal getUndefVal() const { return UndefVal; } 62 LatticeVal getOverdefinedVal() const { return OverdefinedVal; } 63 LatticeVal getUntrackedVal() const { return UntrackedVal; } 64 65 /// IsUntrackedValue - If the specified Value is something that is obviously 66 /// uninteresting to the analysis (and would always return UntrackedVal), 67 /// this function can return true to avoid pointless work. 68 virtual bool IsUntrackedValue(Value *V) { return false; } 69 70 /// ComputeConstant - Given a constant value, compute and return a lattice 71 /// value corresponding to the specified constant. 72 virtual LatticeVal ComputeConstant(Constant *C) { 73 return getOverdefinedVal(); // always safe 74 } 75 76 /// IsSpecialCasedPHI - Given a PHI node, determine whether this PHI node is 77 /// one that the we want to handle through ComputeInstructionState. 78 virtual bool IsSpecialCasedPHI(PHINode *PN) { return false; } 79 80 /// GetConstant - If the specified lattice value is representable as an LLVM 81 /// constant value, return it. Otherwise return null. The returned value 82 /// must be in the same LLVM type as Val. 83 virtual Constant *GetConstant(LatticeVal LV, Value *Val, SparseSolver &SS) { 84 return nullptr; 85 } 86 87 /// ComputeArgument - Given a formal argument value, compute and return a 88 /// lattice value corresponding to the specified argument. 89 virtual LatticeVal ComputeArgument(Argument *I) { 90 return getOverdefinedVal(); // always safe 91 } 92 93 /// MergeValues - Compute and return the merge of the two specified lattice 94 /// values. Merging should only move one direction down the lattice to 95 /// guarantee convergence (toward overdefined). 96 virtual LatticeVal MergeValues(LatticeVal X, LatticeVal Y) { 97 return getOverdefinedVal(); // always safe, never useful. 98 } 99 100 /// ComputeInstructionState - Given an instruction and a vector of its operand 101 /// values, compute the result value of the instruction. 102 virtual LatticeVal ComputeInstructionState(Instruction &I, SparseSolver &SS) { 103 return getOverdefinedVal(); // always safe, never useful. 104 } 105 106 /// PrintValue - Render the specified lattice value to the specified stream. 107 virtual void PrintValue(LatticeVal V, raw_ostream &OS); 108}; 109 110/// SparseSolver - This class is a general purpose solver for Sparse Conditional 111/// Propagation with a programmable lattice function. 112/// 113class SparseSolver { 114 typedef AbstractLatticeFunction::LatticeVal LatticeVal; 115 116 /// LatticeFunc - This is the object that knows the lattice and how to do 117 /// compute transfer functions. 118 AbstractLatticeFunction *LatticeFunc; 119 120 DenseMap<Value *, LatticeVal> ValueState; // The state each value is in. 121 SmallPtrSet<BasicBlock *, 16> BBExecutable; // The bbs that are executable. 122 123 std::vector<Instruction *> InstWorkList; // Worklist of insts to process. 124 125 std::vector<BasicBlock *> BBWorkList; // The BasicBlock work list 126 127 /// KnownFeasibleEdges - Entries in this set are edges which have already had 128 /// PHI nodes retriggered. 129 typedef std::pair<BasicBlock*,BasicBlock*> Edge; 130 std::set<Edge> KnownFeasibleEdges; 131 132 SparseSolver(const SparseSolver&) = delete; 133 void operator=(const SparseSolver&) = delete; 134 135public: 136 explicit SparseSolver(AbstractLatticeFunction *Lattice) 137 : LatticeFunc(Lattice) {} 138 ~SparseSolver() { delete LatticeFunc; } 139 140 /// Solve - Solve for constants and executable blocks. 141 /// 142 void Solve(Function &F); 143 144 void Print(Function &F, raw_ostream &OS) const; 145 146 /// getLatticeState - Return the LatticeVal object that corresponds to the 147 /// value. If an value is not in the map, it is returned as untracked, 148 /// unlike the getOrInitValueState method. 149 LatticeVal getLatticeState(Value *V) const { 150 DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V); 151 return I != ValueState.end() ? I->second : LatticeFunc->getUntrackedVal(); 152 } 153 154 /// getOrInitValueState - Return the LatticeVal object that corresponds to the 155 /// value, initializing the value's state if it hasn't been entered into the 156 /// map yet. This function is necessary because not all values should start 157 /// out in the underdefined state... Arguments should be overdefined, and 158 /// constants should be marked as constants. 159 /// 160 LatticeVal getOrInitValueState(Value *V); 161 162 /// isEdgeFeasible - Return true if the control flow edge from the 'From' 163 /// basic block to the 'To' basic block is currently feasible. If 164 /// AggressiveUndef is true, then this treats values with unknown lattice 165 /// values as undefined. This is generally only useful when solving the 166 /// lattice, not when querying it. 167 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To, 168 bool AggressiveUndef = false); 169 170 /// isBlockExecutable - Return true if there are any known feasible 171 /// edges into the basic block. This is generally only useful when 172 /// querying the lattice. 173 bool isBlockExecutable(BasicBlock *BB) const { 174 return BBExecutable.count(BB); 175 } 176 177private: 178 /// UpdateState - When the state for some instruction is potentially updated, 179 /// this function notices and adds I to the worklist if needed. 180 void UpdateState(Instruction &Inst, LatticeVal V); 181 182 /// MarkBlockExecutable - This method can be used by clients to mark all of 183 /// the blocks that are known to be intrinsically live in the processed unit. 184 void MarkBlockExecutable(BasicBlock *BB); 185 186 /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB 187 /// work list if it is not already executable. 188 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest); 189 190 /// getFeasibleSuccessors - Return a vector of booleans to indicate which 191 /// successors are reachable from a given terminator instruction. 192 void getFeasibleSuccessors(TerminatorInst &TI, SmallVectorImpl<bool> &Succs, 193 bool AggressiveUndef); 194 195 void visitInst(Instruction &I); 196 void visitPHINode(PHINode &I); 197 void visitTerminatorInst(TerminatorInst &TI); 198}; 199 200} // end namespace llvm 201 202#endif // LLVM_ANALYSIS_SPARSEPROPAGATION_H 203