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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.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_SPARSEPROPAGATION_H
+#define LLVM_ANALYSIS_SPARSEPROPAGATION_H
+
+#include "llvm/IR/Instructions.h"
+#include "llvm/Support/Debug.h"
+#include <set>
+
+#define DEBUG_TYPE "sparseprop"
+
+namespace llvm {
+
+/// A template for translating between LLVM Values and LatticeKeys. Clients must
+/// provide a specialization of LatticeKeyInfo for their LatticeKey type.
+template <class LatticeKey> struct LatticeKeyInfo {
+ // static inline Value *getValueFromLatticeKey(LatticeKey Key);
+ // static inline LatticeKey getLatticeKeyFromValue(Value *V);
+};
+
+template <class LatticeKey, class LatticeVal,
+ class KeyInfo = LatticeKeyInfo<LatticeKey>>
+class SparseSolver;
+
+/// 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 current requirement is that lattice values must be
+/// copyable. At the moment, nothing tries to avoid copying. Additionally,
+/// lattice keys must be able to be used as keys of a mapping data structure.
+/// Internally, the generic solver currently uses a DenseMap to map lattice keys
+/// to lattice values. If the lattice key is a non-standard type, a
+/// specialization of DenseMapInfo must be provided.
+template <class LatticeKey, class LatticeVal> class AbstractLatticeFunction {
+private:
+ LatticeVal UndefVal, OverdefinedVal, UntrackedVal;
+
+public:
+ AbstractLatticeFunction(LatticeVal undefVal, LatticeVal overdefinedVal,
+ LatticeVal untrackedVal) {
+ UndefVal = undefVal;
+ OverdefinedVal = overdefinedVal;
+ UntrackedVal = untrackedVal;
+ }
+
+ virtual ~AbstractLatticeFunction() = default;
+
+ LatticeVal getUndefVal() const { return UndefVal; }
+ LatticeVal getOverdefinedVal() const { return OverdefinedVal; }
+ LatticeVal getUntrackedVal() const { return UntrackedVal; }
+
+ /// IsUntrackedValue - If the specified LatticeKey is obviously uninteresting
+ /// to the analysis (i.e., it would always return UntrackedVal), this
+ /// function can return true to avoid pointless work.
+ virtual bool IsUntrackedValue(LatticeKey Key) { return false; }
+
+ /// ComputeLatticeVal - Compute and return a LatticeVal corresponding to the
+ /// given LatticeKey.
+ virtual LatticeVal ComputeLatticeVal(LatticeKey Key) {
+ return getOverdefinedVal();
+ }
+
+ /// 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; }
+
+ /// 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 - Compute the LatticeKeys that change as a result
+ /// of executing instruction \p I. Their associated LatticeVals are store in
+ /// \p ChangedValues.
+ virtual void
+ ComputeInstructionState(Instruction &I,
+ DenseMap<LatticeKey, LatticeVal> &ChangedValues,
+ SparseSolver<LatticeKey, LatticeVal> &SS) = 0;
+
+ /// PrintLatticeVal - Render the given LatticeVal to the specified stream.
+ virtual void PrintLatticeVal(LatticeVal LV, raw_ostream &OS);
+
+ /// PrintLatticeKey - Render the given LatticeKey to the specified stream.
+ virtual void PrintLatticeKey(LatticeKey Key, raw_ostream &OS);
+
+ /// GetValueFromLatticeVal - If the given LatticeVal is representable as an
+ /// LLVM value, return it; otherwise, return nullptr. If a type is given, the
+ /// returned value must have the same type. This function is used by the
+ /// generic solver in attempting to resolve branch and switch conditions.
+ virtual Value *GetValueFromLatticeVal(LatticeVal LV, Type *Ty = nullptr) {
+ return nullptr;
+ }
+};
+
+/// SparseSolver - This class is a general purpose solver for Sparse Conditional
+/// Propagation with a programmable lattice function.
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+class SparseSolver {
+
+ /// LatticeFunc - This is the object that knows the lattice and how to
+ /// compute transfer functions.
+ AbstractLatticeFunction<LatticeKey, LatticeVal> *LatticeFunc;
+
+ /// ValueState - Holds the LatticeVals associated with LatticeKeys.
+ DenseMap<LatticeKey, LatticeVal> ValueState;
+
+ /// BBExecutable - Holds the basic blocks that are executable.
+ SmallPtrSet<BasicBlock *, 16> BBExecutable;
+
+ /// ValueWorkList - Holds values that should be processed.
+ SmallVector<Value *, 64> ValueWorkList;
+
+ /// BBWorkList - Holds basic blocks that should be processed.
+ SmallVector<BasicBlock *, 64> BBWorkList;
+
+ using Edge = std::pair<BasicBlock *, BasicBlock *>;
+
+ /// KnownFeasibleEdges - Entries in this set are edges which have already had
+ /// PHI nodes retriggered.
+ std::set<Edge> KnownFeasibleEdges;
+
+public:
+ explicit SparseSolver(
+ AbstractLatticeFunction<LatticeKey, LatticeVal> *Lattice)
+ : LatticeFunc(Lattice) {}
+ SparseSolver(const SparseSolver &) = delete;
+ SparseSolver &operator=(const SparseSolver &) = delete;
+
+ /// Solve - Solve for constants and executable blocks.
+ void Solve();
+
+ void Print(raw_ostream &OS) const;
+
+ /// getExistingValueState - Return the LatticeVal object corresponding to the
+ /// given value from the ValueState map. If the value is not in the map,
+ /// UntrackedVal is returned, unlike the getValueState method.
+ LatticeVal getExistingValueState(LatticeKey Key) const {
+ auto I = ValueState.find(Key);
+ return I != ValueState.end() ? I->second : LatticeFunc->getUntrackedVal();
+ }
+
+ /// getValueState - Return the LatticeVal object corresponding to the given
+ /// value from the ValueState map. If the value is not in the map, its state
+ /// is initialized.
+ LatticeVal getValueState(LatticeKey Key);
+
+ /// 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);
+ }
+
+ /// 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);
+
+private:
+ /// UpdateState - When the state of some LatticeKey is potentially updated to
+ /// the given LatticeVal, this function notices and adds the LLVM value
+ /// corresponding the key to the work list, if needed.
+ void UpdateState(LatticeKey Key, LatticeVal LV);
+
+ /// 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);
+};
+
+//===----------------------------------------------------------------------===//
+// AbstractLatticeFunction Implementation
+//===----------------------------------------------------------------------===//
+
+template <class LatticeKey, class LatticeVal>
+void AbstractLatticeFunction<LatticeKey, LatticeVal>::PrintLatticeVal(
+ LatticeVal V, raw_ostream &OS) {
+ if (V == UndefVal)
+ OS << "undefined";
+ else if (V == OverdefinedVal)
+ OS << "overdefined";
+ else if (V == UntrackedVal)
+ OS << "untracked";
+ else
+ OS << "unknown lattice value";
+}
+
+template <class LatticeKey, class LatticeVal>
+void AbstractLatticeFunction<LatticeKey, LatticeVal>::PrintLatticeKey(
+ LatticeKey Key, raw_ostream &OS) {
+ OS << "unknown lattice key";
+}
+
+//===----------------------------------------------------------------------===//
+// SparseSolver Implementation
+//===----------------------------------------------------------------------===//
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+LatticeVal
+SparseSolver<LatticeKey, LatticeVal, KeyInfo>::getValueState(LatticeKey Key) {
+ auto I = ValueState.find(Key);
+ if (I != ValueState.end())
+ return I->second; // Common case, in the map
+
+ if (LatticeFunc->IsUntrackedValue(Key))
+ return LatticeFunc->getUntrackedVal();
+ LatticeVal LV = LatticeFunc->ComputeLatticeVal(Key);
+
+ // If this value is untracked, don't add it to the map.
+ if (LV == LatticeFunc->getUntrackedVal())
+ return LV;
+ return ValueState[Key] = LV;
+}
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::UpdateState(LatticeKey Key,
+ LatticeVal LV) {
+ auto I = ValueState.find(Key);
+ if (I != ValueState.end() && I->second == LV)
+ return; // No change.
+
+ // Update the state of the given LatticeKey and add its corresponding LLVM
+ // value to the work list.
+ ValueState[Key] = LV;
+ if (Value *V = KeyInfo::getValueFromLatticeKey(Key))
+ ValueWorkList.push_back(V);
+}
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::MarkBlockExecutable(
+ BasicBlock *BB) {
+ if (!BBExecutable.insert(BB).second)
+ return;
+ DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << "\n");
+ BBWorkList.push_back(BB); // Add the block to the work list!
+}
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::markEdgeExecutable(
+ BasicBlock *Source, BasicBlock *Dest) {
+ if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
+ return; // This edge is already known to be executable!
+
+ DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName() << " -> "
+ << Dest->getName() << "\n");
+
+ if (BBExecutable.count(Dest)) {
+ // The destination is already executable, but we just made an edge
+ // feasible that wasn't before. Revisit the PHI nodes in the block
+ // because they have potentially new operands.
+ for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
+ visitPHINode(*cast<PHINode>(I));
+ } else {
+ MarkBlockExecutable(Dest);
+ }
+}
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::getFeasibleSuccessors(
+ TerminatorInst &TI, SmallVectorImpl<bool> &Succs, bool AggressiveUndef) {
+ Succs.resize(TI.getNumSuccessors());
+ if (TI.getNumSuccessors() == 0)
+ return;
+
+ if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
+ if (BI->isUnconditional()) {
+ Succs[0] = true;
+ return;
+ }
+
+ LatticeVal BCValue;
+ if (AggressiveUndef)
+ BCValue =
+ getValueState(KeyInfo::getLatticeKeyFromValue(BI->getCondition()));
+ else
+ BCValue = getExistingValueState(
+ KeyInfo::getLatticeKeyFromValue(BI->getCondition()));
+
+ if (BCValue == LatticeFunc->getOverdefinedVal() ||
+ BCValue == LatticeFunc->getUntrackedVal()) {
+ // Overdefined condition variables can branch either way.
+ Succs[0] = Succs[1] = true;
+ return;
+ }
+
+ // If undefined, neither is feasible yet.
+ if (BCValue == LatticeFunc->getUndefVal())
+ return;
+
+ Constant *C =
+ dyn_cast_or_null<Constant>(LatticeFunc->GetValueFromLatticeVal(
+ BCValue, BI->getCondition()->getType()));
+ if (!C || !isa<ConstantInt>(C)) {
+ // Non-constant values can go either way.
+ Succs[0] = Succs[1] = true;
+ return;
+ }
+
+ // Constant condition variables mean the branch can only go a single way
+ Succs[C->isNullValue()] = true;
+ return;
+ }
+
+ if (TI.isExceptional()) {
+ Succs.assign(Succs.size(), true);
+ return;
+ }
+
+ if (isa<IndirectBrInst>(TI)) {
+ Succs.assign(Succs.size(), true);
+ return;
+ }
+
+ SwitchInst &SI = cast<SwitchInst>(TI);
+ LatticeVal SCValue;
+ if (AggressiveUndef)
+ SCValue = getValueState(KeyInfo::getLatticeKeyFromValue(SI.getCondition()));
+ else
+ SCValue = getExistingValueState(
+ KeyInfo::getLatticeKeyFromValue(SI.getCondition()));
+
+ if (SCValue == LatticeFunc->getOverdefinedVal() ||
+ SCValue == LatticeFunc->getUntrackedVal()) {
+ // All destinations are executable!
+ Succs.assign(TI.getNumSuccessors(), true);
+ return;
+ }
+
+ // If undefined, neither is feasible yet.
+ if (SCValue == LatticeFunc->getUndefVal())
+ return;
+
+ Constant *C = dyn_cast_or_null<Constant>(LatticeFunc->GetValueFromLatticeVal(
+ SCValue, SI.getCondition()->getType()));
+ if (!C || !isa<ConstantInt>(C)) {
+ // All destinations are executable!
+ Succs.assign(TI.getNumSuccessors(), true);
+ return;
+ }
+ SwitchInst::CaseHandle Case = *SI.findCaseValue(cast<ConstantInt>(C));
+ Succs[Case.getSuccessorIndex()] = true;
+}
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+bool SparseSolver<LatticeKey, LatticeVal, KeyInfo>::isEdgeFeasible(
+ BasicBlock *From, BasicBlock *To, bool AggressiveUndef) {
+ SmallVector<bool, 16> SuccFeasible;
+ TerminatorInst *TI = From->getTerminator();
+ getFeasibleSuccessors(*TI, SuccFeasible, AggressiveUndef);
+
+ for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+ if (TI->getSuccessor(i) == To && SuccFeasible[i])
+ return true;
+
+ return false;
+}
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::visitTerminatorInst(
+ TerminatorInst &TI) {
+ SmallVector<bool, 16> SuccFeasible;
+ getFeasibleSuccessors(TI, SuccFeasible, true);
+
+ BasicBlock *BB = TI.getParent();
+
+ // Mark all feasible successors executable...
+ for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
+ if (SuccFeasible[i])
+ markEdgeExecutable(BB, TI.getSuccessor(i));
+}
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::visitPHINode(PHINode &PN) {
+ // The lattice function may store more information on a PHINode than could be
+ // computed from its incoming values. For example, SSI form stores its sigma
+ // functions as PHINodes with a single incoming value.
+ if (LatticeFunc->IsSpecialCasedPHI(&PN)) {
+ DenseMap<LatticeKey, LatticeVal> ChangedValues;
+ LatticeFunc->ComputeInstructionState(PN, ChangedValues, *this);
+ for (auto &ChangedValue : ChangedValues)
+ if (ChangedValue.second != LatticeFunc->getUntrackedVal())
+ UpdateState(ChangedValue.first, ChangedValue.second);
+ return;
+ }
+
+ LatticeKey Key = KeyInfo::getLatticeKeyFromValue(&PN);
+ LatticeVal PNIV = getValueState(Key);
+ LatticeVal Overdefined = LatticeFunc->getOverdefinedVal();
+
+ // If this value is already overdefined (common) just return.
+ if (PNIV == Overdefined || PNIV == LatticeFunc->getUntrackedVal())
+ return; // Quick exit
+
+ // Super-extra-high-degree PHI nodes are unlikely to ever be interesting,
+ // and slow us down a lot. Just mark them overdefined.
+ if (PN.getNumIncomingValues() > 64) {
+ UpdateState(Key, Overdefined);
+ return;
+ }
+
+ // Look at all of the executable operands of the PHI node. If any of them
+ // are overdefined, the PHI becomes overdefined as well. Otherwise, ask the
+ // transfer function to give us the merge of the incoming values.
+ for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
+ // If the edge is not yet known to be feasible, it doesn't impact the PHI.
+ if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent(), true))
+ continue;
+
+ // Merge in this value.
+ LatticeVal OpVal =
+ getValueState(KeyInfo::getLatticeKeyFromValue(PN.getIncomingValue(i)));
+ if (OpVal != PNIV)
+ PNIV = LatticeFunc->MergeValues(PNIV, OpVal);
+
+ if (PNIV == Overdefined)
+ break; // Rest of input values don't matter.
+ }
+
+ // Update the PHI with the compute value, which is the merge of the inputs.
+ UpdateState(Key, PNIV);
+}
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::visitInst(Instruction &I) {
+ // PHIs are handled by the propagation logic, they are never passed into the
+ // transfer functions.
+ if (PHINode *PN = dyn_cast<PHINode>(&I))
+ return visitPHINode(*PN);
+
+ // Otherwise, ask the transfer function what the result is. If this is
+ // something that we care about, remember it.
+ DenseMap<LatticeKey, LatticeVal> ChangedValues;
+ LatticeFunc->ComputeInstructionState(I, ChangedValues, *this);
+ for (auto &ChangedValue : ChangedValues)
+ if (ChangedValue.second != LatticeFunc->getUntrackedVal())
+ UpdateState(ChangedValue.first, ChangedValue.second);
+
+ if (TerminatorInst *TI = dyn_cast<TerminatorInst>(&I))
+ visitTerminatorInst(*TI);
+}
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::Solve() {
+ // Process the work lists until they are empty!
+ while (!BBWorkList.empty() || !ValueWorkList.empty()) {
+ // Process the value work list.
+ while (!ValueWorkList.empty()) {
+ Value *V = ValueWorkList.back();
+ ValueWorkList.pop_back();
+
+ DEBUG(dbgs() << "\nPopped off V-WL: " << *V << "\n");
+
+ // "V" got into the work list because it made a transition. See if any
+ // users are both live and in need of updating.
+ for (User *U : V->users())
+ if (Instruction *Inst = dyn_cast<Instruction>(U))
+ if (BBExecutable.count(Inst->getParent())) // Inst is executable?
+ visitInst(*Inst);
+ }
+
+ // Process the basic block work list.
+ while (!BBWorkList.empty()) {
+ BasicBlock *BB = BBWorkList.back();
+ BBWorkList.pop_back();
+
+ DEBUG(dbgs() << "\nPopped off BBWL: " << *BB);
+
+ // Notify all instructions in this basic block that they are newly
+ // executable.
+ for (Instruction &I : *BB)
+ visitInst(I);
+ }
+ }
+}
+
+template <class LatticeKey, class LatticeVal, class KeyInfo>
+void SparseSolver<LatticeKey, LatticeVal, KeyInfo>::Print(
+ raw_ostream &OS) const {
+ if (ValueState.empty())
+ return;
+
+ LatticeKey Key;
+ LatticeVal LV;
+
+ OS << "ValueState:\n";
+ for (auto &Entry : ValueState) {
+ std::tie(Key, LV) = Entry;
+ if (LV == LatticeFunc->getUntrackedVal())
+ continue;
+ OS << "\t";
+ LatticeFunc->PrintLatticeVal(LV, OS);
+ OS << ": ";
+ LatticeFunc->PrintLatticeKey(Key, OS);
+ OS << "\n";
+ }
+}
+} // end namespace llvm
+
+#undef DEBUG_TYPE
+
+#endif // LLVM_ANALYSIS_SPARSEPROPAGATION_H