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348 lines
12 KiB
C++
348 lines
12 KiB
C++
//===- SparsePropagation.cpp - Sparse Conditional Property Propagation ----===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements an abstract sparse conditional propagation algorithm,
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// modeled after SCCP, but with a customizable lattice function.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/SparsePropagation.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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#define DEBUG_TYPE "sparseprop"
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//===----------------------------------------------------------------------===//
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// AbstractLatticeFunction Implementation
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//===----------------------------------------------------------------------===//
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AbstractLatticeFunction::~AbstractLatticeFunction() {}
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/// PrintValue - Render the specified lattice value to the specified stream.
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void AbstractLatticeFunction::PrintValue(LatticeVal V, raw_ostream &OS) {
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if (V == UndefVal)
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OS << "undefined";
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else if (V == OverdefinedVal)
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OS << "overdefined";
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else if (V == UntrackedVal)
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OS << "untracked";
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else
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OS << "unknown lattice value";
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}
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//===----------------------------------------------------------------------===//
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// SparseSolver Implementation
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//===----------------------------------------------------------------------===//
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/// getOrInitValueState - Return the LatticeVal object that corresponds to the
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/// value, initializing the value's state if it hasn't been entered into the
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/// map yet. This function is necessary because not all values should start
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/// out in the underdefined state... Arguments should be overdefined, and
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/// constants should be marked as constants.
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///
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SparseSolver::LatticeVal SparseSolver::getOrInitValueState(Value *V) {
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DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(V);
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if (I != ValueState.end()) return I->second; // Common case, in the map
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LatticeVal LV;
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if (LatticeFunc->IsUntrackedValue(V))
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return LatticeFunc->getUntrackedVal();
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else if (Constant *C = dyn_cast<Constant>(V))
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LV = LatticeFunc->ComputeConstant(C);
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else if (Argument *A = dyn_cast<Argument>(V))
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LV = LatticeFunc->ComputeArgument(A);
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else if (!isa<Instruction>(V))
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// All other non-instructions are overdefined.
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LV = LatticeFunc->getOverdefinedVal();
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else
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// All instructions are underdefined by default.
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LV = LatticeFunc->getUndefVal();
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// If this value is untracked, don't add it to the map.
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if (LV == LatticeFunc->getUntrackedVal())
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return LV;
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return ValueState[V] = LV;
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}
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/// UpdateState - When the state for some instruction is potentially updated,
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/// this function notices and adds I to the worklist if needed.
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void SparseSolver::UpdateState(Instruction &Inst, LatticeVal V) {
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DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(&Inst);
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if (I != ValueState.end() && I->second == V)
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return; // No change.
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// An update. Visit uses of I.
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ValueState[&Inst] = V;
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InstWorkList.push_back(&Inst);
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}
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/// MarkBlockExecutable - This method can be used by clients to mark all of
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/// the blocks that are known to be intrinsically live in the processed unit.
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void SparseSolver::MarkBlockExecutable(BasicBlock *BB) {
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DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << "\n");
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BBExecutable.insert(BB); // Basic block is executable!
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BBWorkList.push_back(BB); // Add the block to the work list!
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}
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/// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
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/// work list if it is not already executable...
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void SparseSolver::markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
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if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
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return; // This edge is already known to be executable!
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DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName()
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<< " -> " << Dest->getName() << "\n");
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if (BBExecutable.count(Dest)) {
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// The destination is already executable, but we just made an edge
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// feasible that wasn't before. Revisit the PHI nodes in the block
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// because they have potentially new operands.
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for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
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visitPHINode(*cast<PHINode>(I));
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} else {
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MarkBlockExecutable(Dest);
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}
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}
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/// getFeasibleSuccessors - Return a vector of booleans to indicate which
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/// successors are reachable from a given terminator instruction.
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void SparseSolver::getFeasibleSuccessors(TerminatorInst &TI,
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SmallVectorImpl<bool> &Succs,
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bool AggressiveUndef) {
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Succs.resize(TI.getNumSuccessors());
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if (TI.getNumSuccessors() == 0) return;
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if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
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if (BI->isUnconditional()) {
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Succs[0] = true;
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return;
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}
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LatticeVal BCValue;
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if (AggressiveUndef)
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BCValue = getOrInitValueState(BI->getCondition());
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else
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BCValue = getLatticeState(BI->getCondition());
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if (BCValue == LatticeFunc->getOverdefinedVal() ||
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BCValue == LatticeFunc->getUntrackedVal()) {
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// Overdefined condition variables can branch either way.
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Succs[0] = Succs[1] = true;
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return;
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}
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// If undefined, neither is feasible yet.
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if (BCValue == LatticeFunc->getUndefVal())
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return;
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Constant *C = LatticeFunc->GetConstant(BCValue, BI->getCondition(), *this);
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if (!C || !isa<ConstantInt>(C)) {
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// Non-constant values can go either way.
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Succs[0] = Succs[1] = true;
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return;
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}
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// Constant condition variables mean the branch can only go a single way
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Succs[C->isNullValue()] = true;
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return;
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}
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if (isa<InvokeInst>(TI)) {
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// Invoke instructions successors are always executable.
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// TODO: Could ask the lattice function if the value can throw.
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Succs[0] = Succs[1] = true;
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return;
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}
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if (isa<IndirectBrInst>(TI)) {
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Succs.assign(Succs.size(), true);
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return;
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}
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SwitchInst &SI = cast<SwitchInst>(TI);
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LatticeVal SCValue;
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if (AggressiveUndef)
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SCValue = getOrInitValueState(SI.getCondition());
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else
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SCValue = getLatticeState(SI.getCondition());
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if (SCValue == LatticeFunc->getOverdefinedVal() ||
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SCValue == LatticeFunc->getUntrackedVal()) {
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// All destinations are executable!
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Succs.assign(TI.getNumSuccessors(), true);
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return;
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}
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// If undefined, neither is feasible yet.
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if (SCValue == LatticeFunc->getUndefVal())
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return;
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Constant *C = LatticeFunc->GetConstant(SCValue, SI.getCondition(), *this);
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if (!C || !isa<ConstantInt>(C)) {
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// All destinations are executable!
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Succs.assign(TI.getNumSuccessors(), true);
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return;
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}
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SwitchInst::CaseIt Case = SI.findCaseValue(cast<ConstantInt>(C));
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Succs[Case.getSuccessorIndex()] = true;
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}
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/// isEdgeFeasible - Return true if the control flow edge from the 'From'
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/// basic block to the 'To' basic block is currently feasible...
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bool SparseSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To,
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bool AggressiveUndef) {
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SmallVector<bool, 16> SuccFeasible;
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TerminatorInst *TI = From->getTerminator();
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getFeasibleSuccessors(*TI, SuccFeasible, AggressiveUndef);
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for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
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if (TI->getSuccessor(i) == To && SuccFeasible[i])
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return true;
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return false;
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}
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void SparseSolver::visitTerminatorInst(TerminatorInst &TI) {
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SmallVector<bool, 16> SuccFeasible;
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getFeasibleSuccessors(TI, SuccFeasible, true);
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BasicBlock *BB = TI.getParent();
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// Mark all feasible successors executable...
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for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
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if (SuccFeasible[i])
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markEdgeExecutable(BB, TI.getSuccessor(i));
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}
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void SparseSolver::visitPHINode(PHINode &PN) {
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// The lattice function may store more information on a PHINode than could be
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// computed from its incoming values. For example, SSI form stores its sigma
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// functions as PHINodes with a single incoming value.
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if (LatticeFunc->IsSpecialCasedPHI(&PN)) {
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LatticeVal IV = LatticeFunc->ComputeInstructionState(PN, *this);
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if (IV != LatticeFunc->getUntrackedVal())
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UpdateState(PN, IV);
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return;
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}
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LatticeVal PNIV = getOrInitValueState(&PN);
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LatticeVal Overdefined = LatticeFunc->getOverdefinedVal();
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// If this value is already overdefined (common) just return.
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if (PNIV == Overdefined || PNIV == LatticeFunc->getUntrackedVal())
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return; // Quick exit
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// Super-extra-high-degree PHI nodes are unlikely to ever be interesting,
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// and slow us down a lot. Just mark them overdefined.
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if (PN.getNumIncomingValues() > 64) {
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UpdateState(PN, Overdefined);
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return;
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}
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// Look at all of the executable operands of the PHI node. If any of them
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// are overdefined, the PHI becomes overdefined as well. Otherwise, ask the
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// transfer function to give us the merge of the incoming values.
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for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
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// If the edge is not yet known to be feasible, it doesn't impact the PHI.
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if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent(), true))
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continue;
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// Merge in this value.
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LatticeVal OpVal = getOrInitValueState(PN.getIncomingValue(i));
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if (OpVal != PNIV)
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PNIV = LatticeFunc->MergeValues(PNIV, OpVal);
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if (PNIV == Overdefined)
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break; // Rest of input values don't matter.
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}
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// Update the PHI with the compute value, which is the merge of the inputs.
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UpdateState(PN, PNIV);
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}
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void SparseSolver::visitInst(Instruction &I) {
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// PHIs are handled by the propagation logic, they are never passed into the
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// transfer functions.
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if (PHINode *PN = dyn_cast<PHINode>(&I))
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return visitPHINode(*PN);
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// Otherwise, ask the transfer function what the result is. If this is
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// something that we care about, remember it.
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LatticeVal IV = LatticeFunc->ComputeInstructionState(I, *this);
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if (IV != LatticeFunc->getUntrackedVal())
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UpdateState(I, IV);
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if (TerminatorInst *TI = dyn_cast<TerminatorInst>(&I))
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visitTerminatorInst(*TI);
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}
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void SparseSolver::Solve(Function &F) {
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MarkBlockExecutable(&F.getEntryBlock());
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// Process the work lists until they are empty!
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while (!BBWorkList.empty() || !InstWorkList.empty()) {
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// Process the instruction work list.
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while (!InstWorkList.empty()) {
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Instruction *I = InstWorkList.back();
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InstWorkList.pop_back();
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DEBUG(dbgs() << "\nPopped off I-WL: " << *I << "\n");
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// "I" got into the work list because it made a transition. See if any
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// users are both live and in need of updating.
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for (User *U : I->users()) {
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Instruction *UI = cast<Instruction>(U);
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if (BBExecutable.count(UI->getParent())) // Inst is executable?
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visitInst(*UI);
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}
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}
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// Process the basic block work list.
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while (!BBWorkList.empty()) {
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BasicBlock *BB = BBWorkList.back();
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BBWorkList.pop_back();
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DEBUG(dbgs() << "\nPopped off BBWL: " << *BB);
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// Notify all instructions in this basic block that they are newly
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// executable.
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for (Instruction &I : *BB)
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visitInst(I);
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}
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}
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}
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void SparseSolver::Print(Function &F, raw_ostream &OS) const {
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OS << "\nFUNCTION: " << F.getName() << "\n";
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for (auto &BB : F) {
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if (!BBExecutable.count(&BB))
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OS << "INFEASIBLE: ";
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OS << "\t";
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if (BB.hasName())
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OS << BB.getName() << ":\n";
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else
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OS << "; anon bb\n";
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for (auto &I : BB) {
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LatticeFunc->PrintValue(getLatticeState(&I), OS);
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OS << I << "\n";
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}
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OS << "\n";
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}
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}
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