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