1 //===- SparsePropagation.h - Sparse Conditional Property Propagation ------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements an abstract sparse conditional propagation algorithm,
11 // modeled after SCCP, but with a customizable lattice function.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_ANALYSIS_SPARSE_PROPAGATION_H
16 #define LLVM_ANALYSIS_SPARSE_PROPAGATION_H
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/SmallPtrSet.h"
36 template<typename T> class SmallVectorImpl;
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.
45 class AbstractLatticeFunction {
47 typedef void *LatticeVal;
49 LatticeVal UndefVal, OverdefinedVal, UntrackedVal;
51 AbstractLatticeFunction(LatticeVal undefVal, LatticeVal overdefinedVal,
52 LatticeVal untrackedVal) {
54 OverdefinedVal = overdefinedVal;
55 UntrackedVal = untrackedVal;
57 virtual ~AbstractLatticeFunction();
59 LatticeVal getUndefVal() const { return UndefVal; }
60 LatticeVal getOverdefinedVal() const { return OverdefinedVal; }
61 LatticeVal getUntrackedVal() const { return UntrackedVal; }
63 /// IsUntrackedValue - If the specified Value is something that is obviously
64 /// uninteresting to the analysis (and would always return UntrackedVal),
65 /// this function can return true to avoid pointless work.
66 virtual bool IsUntrackedValue(Value *V) {
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
76 /// GetConstant - If the specified lattice value is representable as an LLVM
77 /// constant value, return it. Otherwise return null. The returned value
78 /// must be in the same LLVM type as Val.
79 virtual Constant *GetConstant(LatticeVal LV, Value *Val, SparseSolver &SS) {
83 /// ComputeArgument - Given a formal argument value, compute and return a
84 /// lattice value corresponding to the specified argument.
85 virtual LatticeVal ComputeArgument(Argument *I) {
86 return getOverdefinedVal(); // always safe
89 /// MergeValues - Compute and return the merge of the two specified lattice
90 /// values. Merging should only move one direction down the lattice to
91 /// guarantee convergence (toward overdefined).
92 virtual LatticeVal MergeValues(LatticeVal X, LatticeVal Y) {
93 return getOverdefinedVal(); // always safe, never useful.
96 /// ComputeInstructionState - Given an instruction and a vector of its operand
97 /// values, compute the result value of the instruction.
98 virtual LatticeVal ComputeInstructionState(Instruction &I, SparseSolver &SS) {
99 return getOverdefinedVal(); // always safe, never useful.
102 /// PrintValue - Render the specified lattice value to the specified stream.
103 virtual void PrintValue(LatticeVal V, std::ostream &OS);
107 /// SparseSolver - This class is a general purpose solver for Sparse Conditional
108 /// Propagation with a programmable lattice function.
111 typedef AbstractLatticeFunction::LatticeVal LatticeVal;
113 /// LatticeFunc - This is the object that knows the lattice and how to do
114 /// compute transfer functions.
115 AbstractLatticeFunction *LatticeFunc;
117 LLVMContext *Context;
119 DenseMap<Value*, LatticeVal> ValueState; // The state each value is in.
120 SmallPtrSet<BasicBlock*, 16> BBExecutable; // The bbs that are executable.
122 std::vector<Instruction*> InstWorkList; // Worklist of insts to process.
124 std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
126 /// KnownFeasibleEdges - Entries in this set are edges which have already had
127 /// PHI nodes retriggered.
128 typedef std::pair<BasicBlock*,BasicBlock*> Edge;
129 std::set<Edge> KnownFeasibleEdges;
131 SparseSolver(const SparseSolver&); // DO NOT IMPLEMENT
132 void operator=(const SparseSolver&); // DO NOT IMPLEMENT
134 explicit SparseSolver(AbstractLatticeFunction *Lattice, LLVMContext *C)
135 : LatticeFunc(Lattice), Context(C) {}
140 /// Solve - Solve for constants and executable blocks.
142 void Solve(Function &F);
144 void Print(Function &F, std::ostream &OS) const;
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>::iterator I = ValueState.find(V);
151 return I != ValueState.end() ? I->second : LatticeFunc->getUntrackedVal();
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.
160 LatticeVal getOrInitValueState(Value *V);
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);
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);
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);
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);
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);
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);
195 void visitInst(Instruction &I);
196 void visitPHINode(PHINode &I);
197 void visitTerminatorInst(TerminatorInst &TI);
201 } // end namespace llvm
203 #endif // LLVM_ANALYSIS_SPARSE_PROPAGATION_H