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//===- SparsePropagation.h - Sparse Conditional Property Propagation ------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file implements an abstract sparse conditional propagation algorithm,
// modeled after SCCP, but with a customizable lattice function.
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include <set>
#include <vector>
namespace llvm {
class Value;
class Constant;
class Argument;
class Instruction;
class PHINode;
class TerminatorInst;
class BasicBlock;
class Function;
class SparseSolver;
class raw_ostream;
template<typename T> class SmallVectorImpl;
/// AbstractLatticeFunction - This class is implemented by the dataflow instance
/// to specify what the lattice values are and how they handle merges etc.
/// This gives the client the power to compute lattice values from instructions,
/// constants, etc. The requirement is that lattice values must all fit into
/// a void*. If a void* is not sufficient, the implementation should use this
/// pointer to be a pointer into a uniquing set or something.
class AbstractLatticeFunction {
typedef void *LatticeVal;
LatticeVal UndefVal, OverdefinedVal, UntrackedVal;
AbstractLatticeFunction(LatticeVal undefVal, LatticeVal overdefinedVal,
LatticeVal untrackedVal) {
UndefVal = undefVal;
OverdefinedVal = overdefinedVal;
UntrackedVal = untrackedVal;
virtual ~AbstractLatticeFunction();
LatticeVal getUndefVal() const { return UndefVal; }
LatticeVal getOverdefinedVal() const { return OverdefinedVal; }
LatticeVal getUntrackedVal() const { return UntrackedVal; }
/// IsUntrackedValue - If the specified Value is something that is obviously
/// uninteresting to the analysis (and would always return UntrackedVal),
/// this function can return true to avoid pointless work.
virtual bool IsUntrackedValue(Value *V) {
return false;
/// ComputeConstant - Given a constant value, compute and return a lattice
/// value corresponding to the specified constant.
virtual LatticeVal ComputeConstant(Constant *C) {
return getOverdefinedVal(); // always safe
/// IsSpecialCasedPHI - Given a PHI node, determine whether this PHI node is
/// one that the we want to handle through ComputeInstructionState.
virtual bool IsSpecialCasedPHI(PHINode *PN) {
return false;
/// GetConstant - If the specified lattice value is representable as an LLVM
/// constant value, return it. Otherwise return null. The returned value
/// must be in the same LLVM type as Val.
virtual Constant *GetConstant(LatticeVal LV, Value *Val, SparseSolver &SS) {
return nullptr;
/// ComputeArgument - Given a formal argument value, compute and return a
/// lattice value corresponding to the specified argument.
virtual LatticeVal ComputeArgument(Argument *I) {
return getOverdefinedVal(); // always safe
/// MergeValues - Compute and return the merge of the two specified lattice
/// values. Merging should only move one direction down the lattice to
/// guarantee convergence (toward overdefined).
virtual LatticeVal MergeValues(LatticeVal X, LatticeVal Y) {
return getOverdefinedVal(); // always safe, never useful.
/// ComputeInstructionState - Given an instruction and a vector of its operand
/// values, compute the result value of the instruction.
virtual LatticeVal ComputeInstructionState(Instruction &I, SparseSolver &SS) {
return getOverdefinedVal(); // always safe, never useful.
/// PrintValue - Render the specified lattice value to the specified stream.
virtual void PrintValue(LatticeVal V, raw_ostream &OS);
/// SparseSolver - This class is a general purpose solver for Sparse Conditional
/// Propagation with a programmable lattice function.
class SparseSolver {
typedef AbstractLatticeFunction::LatticeVal LatticeVal;
/// LatticeFunc - This is the object that knows the lattice and how to do
/// compute transfer functions.
AbstractLatticeFunction *LatticeFunc;
DenseMap<Value*, LatticeVal> ValueState; // The state each value is in.
SmallPtrSet<BasicBlock*, 16> BBExecutable; // The bbs that are executable.
std::vector<Instruction*> InstWorkList; // Worklist of insts to process.
std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
/// KnownFeasibleEdges - Entries in this set are edges which have already had
/// PHI nodes retriggered.
typedef std::pair<BasicBlock*,BasicBlock*> Edge;
std::set<Edge> KnownFeasibleEdges;
SparseSolver(const SparseSolver&) LLVM_DELETED_FUNCTION;
void operator=(const SparseSolver&) LLVM_DELETED_FUNCTION;
explicit SparseSolver(AbstractLatticeFunction *Lattice)
: LatticeFunc(Lattice) {}
~SparseSolver() {
delete LatticeFunc;
/// Solve - Solve for constants and executable blocks.
void Solve(Function &F);
void Print(Function &F, raw_ostream &OS) const;
/// getLatticeState - Return the LatticeVal object that corresponds to the
/// value. If an value is not in the map, it is returned as untracked,
/// unlike the getOrInitValueState method.
LatticeVal getLatticeState(Value *V) const {
DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V);
return I != ValueState.end() ? I->second : LatticeFunc->getUntrackedVal();
/// getOrInitValueState - Return the LatticeVal object that corresponds to the
/// value, initializing the value's state if it hasn't been entered into the
/// map yet. This function is necessary because not all values should start
/// out in the underdefined state... Arguments should be overdefined, and
/// constants should be marked as constants.
LatticeVal getOrInitValueState(Value *V);
/// isEdgeFeasible - Return true if the control flow edge from the 'From'
/// basic block to the 'To' basic block is currently feasible. If
/// AggressiveUndef is true, then this treats values with unknown lattice
/// values as undefined. This is generally only useful when solving the
/// lattice, not when querying it.
bool isEdgeFeasible(BasicBlock *From, BasicBlock *To,
bool AggressiveUndef = false);
/// isBlockExecutable - Return true if there are any known feasible
/// edges into the basic block. This is generally only useful when
/// querying the lattice.
bool isBlockExecutable(BasicBlock *BB) const {
return BBExecutable.count(BB);
/// UpdateState - When the state for some instruction is potentially updated,
/// this function notices and adds I to the worklist if needed.
void UpdateState(Instruction &Inst, LatticeVal V);
/// MarkBlockExecutable - This method can be used by clients to mark all of
/// the blocks that are known to be intrinsically live in the processed unit.
void MarkBlockExecutable(BasicBlock *BB);
/// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
/// work list if it is not already executable.
void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest);
/// getFeasibleSuccessors - Return a vector of booleans to indicate which
/// successors are reachable from a given terminator instruction.
void getFeasibleSuccessors(TerminatorInst &TI, SmallVectorImpl<bool> &Succs,
bool AggressiveUndef);
void visitInst(Instruction &I);
void visitPHINode(PHINode &I);
void visitTerminatorInst(TerminatorInst &TI);
} // end namespace llvm