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-//===- SparsePropagation.cpp - 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/Analysis/SparsePropagation.h"
-#include "llvm/IR/Constants.h"
-#include "llvm/IR/Function.h"
-#include "llvm/IR/Instructions.h"
-#include "llvm/Support/Debug.h"
-#include "llvm/Support/raw_ostream.h"
-using namespace llvm;
-
-#define DEBUG_TYPE "sparseprop"
-
-//===----------------------------------------------------------------------===//
-// AbstractLatticeFunction Implementation
-//===----------------------------------------------------------------------===//
-
-AbstractLatticeFunction::~AbstractLatticeFunction() {}
-
-/// PrintValue - Render the specified lattice value to the specified stream.
-void AbstractLatticeFunction::PrintValue(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";
-}
-
-//===----------------------------------------------------------------------===//
-// SparseSolver Implementation
-//===----------------------------------------------------------------------===//
-
-/// 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.
-///
-SparseSolver::LatticeVal SparseSolver::getOrInitValueState(Value *V) {
- DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(V);
- if (I != ValueState.end()) return I->second; // Common case, in the map
-
- LatticeVal LV;
- if (LatticeFunc->IsUntrackedValue(V))
- return LatticeFunc->getUntrackedVal();
- else if (Constant *C = dyn_cast<Constant>(V))
- LV = LatticeFunc->ComputeConstant(C);
- else if (Argument *A = dyn_cast<Argument>(V))
- LV = LatticeFunc->ComputeArgument(A);
- else if (!isa<Instruction>(V))
- // All other non-instructions are overdefined.
- LV = LatticeFunc->getOverdefinedVal();
- else
- // All instructions are underdefined by default.
- LV = LatticeFunc->getUndefVal();
-
- // If this value is untracked, don't add it to the map.
- if (LV == LatticeFunc->getUntrackedVal())
- return LV;
- return ValueState[V] = LV;
-}
-
-/// UpdateState - When the state for some instruction is potentially updated,
-/// this function notices and adds I to the worklist if needed.
-void SparseSolver::UpdateState(Instruction &Inst, LatticeVal V) {
- DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(&Inst);
- if (I != ValueState.end() && I->second == V)
- return; // No change.
-
- // An update. Visit uses of I.
- ValueState[&Inst] = V;
- InstWorkList.push_back(&Inst);
-}
-
-/// 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 SparseSolver::MarkBlockExecutable(BasicBlock *BB) {
- DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << "\n");
- BBExecutable.insert(BB); // Basic block is executable!
- BBWorkList.push_back(BB); // Add the block to the work list!
-}
-
-/// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
-/// work list if it is not already executable...
-void SparseSolver::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);
- }
-}
-
-
-/// getFeasibleSuccessors - Return a vector of booleans to indicate which
-/// successors are reachable from a given terminator instruction.
-void SparseSolver::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 = getOrInitValueState(BI->getCondition());
- else
- BCValue = getLatticeState(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 = LatticeFunc->GetConstant(BCValue, BI->getCondition(), *this);
- 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 (isa<InvokeInst>(TI)) {
- // Invoke instructions successors are always executable.
- // TODO: Could ask the lattice function if the value can throw.
- Succs[0] = Succs[1] = true;
- return;
- }
-
- if (isa<IndirectBrInst>(TI)) {
- Succs.assign(Succs.size(), true);
- return;
- }
-
- SwitchInst &SI = cast<SwitchInst>(TI);
- LatticeVal SCValue;
- if (AggressiveUndef)
- SCValue = getOrInitValueState(SI.getCondition());
- else
- SCValue = getLatticeState(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 = LatticeFunc->GetConstant(SCValue, SI.getCondition(), *this);
- 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;
-}
-
-
-/// isEdgeFeasible - Return true if the control flow edge from the 'From'
-/// basic block to the 'To' basic block is currently feasible...
-bool SparseSolver::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;
-}
-
-void SparseSolver::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));
-}
-
-void SparseSolver::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)) {
- LatticeVal IV = LatticeFunc->ComputeInstructionState(PN, *this);
- if (IV != LatticeFunc->getUntrackedVal())
- UpdateState(PN, IV);
- return;
- }
-
- LatticeVal PNIV = getOrInitValueState(&PN);
- 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(PN, 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 = getOrInitValueState(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(PN, PNIV);
-}
-
-
-void SparseSolver::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.
- LatticeVal IV = LatticeFunc->ComputeInstructionState(I, *this);
- if (IV != LatticeFunc->getUntrackedVal())
- UpdateState(I, IV);
-
- if (TerminatorInst *TI = dyn_cast<TerminatorInst>(&I))
- visitTerminatorInst(*TI);
-}
-
-void SparseSolver::Solve(Function &F) {
- MarkBlockExecutable(&F.getEntryBlock());
-
- // Process the work lists until they are empty!
- while (!BBWorkList.empty() || !InstWorkList.empty()) {
- // Process the instruction work list.
- while (!InstWorkList.empty()) {
- Instruction *I = InstWorkList.back();
- InstWorkList.pop_back();
-
- DEBUG(dbgs() << "\nPopped off I-WL: " << *I << "\n");
-
- // "I" 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 : I->users()) {
- Instruction *UI = cast<Instruction>(U);
- if (BBExecutable.count(UI->getParent())) // Inst is executable?
- visitInst(*UI);
- }
- }
-
- // 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);
- }
- }
-}
-
-void SparseSolver::Print(Function &F, raw_ostream &OS) const {
- OS << "\nFUNCTION: " << F.getName() << "\n";
- for (auto &BB : F) {
- if (!BBExecutable.count(&BB))
- OS << "INFEASIBLE: ";
- OS << "\t";
- if (BB.hasName())
- OS << BB.getName() << ":\n";
- else
- OS << "; anon bb\n";
- for (auto &I : BB) {
- LatticeFunc->PrintValue(getLatticeState(&I), OS);
- OS << I << "\n";
- }
-
- OS << "\n";
- }
-}
-
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