LLVM  6.0.0svn
SparsePropagation.cpp
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1 //===- SparsePropagation.cpp - Sparse Conditional Property Propagation ----===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements an abstract sparse conditional propagation algorithm,
11 // modeled after SCCP, but with a customizable lattice function.
12 //
13 //===----------------------------------------------------------------------===//
14 
16 #include "llvm/IR/Constants.h"
17 #include "llvm/IR/Function.h"
18 #include "llvm/IR/Instructions.h"
19 #include "llvm/Support/Debug.h"
21 using namespace llvm;
22 
23 #define DEBUG_TYPE "sparseprop"
24 
25 //===----------------------------------------------------------------------===//
26 // AbstractLatticeFunction Implementation
27 //===----------------------------------------------------------------------===//
28 
30 
31 /// PrintValue - Render the specified lattice value to the specified stream.
33  if (V == UndefVal)
34  OS << "undefined";
35  else if (V == OverdefinedVal)
36  OS << "overdefined";
37  else if (V == UntrackedVal)
38  OS << "untracked";
39  else
40  OS << "unknown lattice value";
41 }
42 
43 //===----------------------------------------------------------------------===//
44 // SparseSolver Implementation
45 //===----------------------------------------------------------------------===//
46 
47 /// getOrInitValueState - Return the LatticeVal object that corresponds to the
48 /// value, initializing the value's state if it hasn't been entered into the
49 /// map yet. This function is necessary because not all values should start
50 /// out in the underdefined state... Arguments should be overdefined, and
51 /// constants should be marked as constants.
52 ///
53 SparseSolver::LatticeVal SparseSolver::getOrInitValueState(Value *V) {
54  DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(V);
55  if (I != ValueState.end()) return I->second; // Common case, in the map
56 
57  LatticeVal LV;
58  if (LatticeFunc->IsUntrackedValue(V))
59  return LatticeFunc->getUntrackedVal();
60  else if (Constant *C = dyn_cast<Constant>(V))
61  LV = LatticeFunc->ComputeConstant(C);
62  else if (Argument *A = dyn_cast<Argument>(V))
63  LV = LatticeFunc->ComputeArgument(A);
64  else if (!isa<Instruction>(V))
65  // All other non-instructions are overdefined.
66  LV = LatticeFunc->getOverdefinedVal();
67  else
68  // All instructions are underdefined by default.
69  LV = LatticeFunc->getUndefVal();
70 
71  // If this value is untracked, don't add it to the map.
72  if (LV == LatticeFunc->getUntrackedVal())
73  return LV;
74  return ValueState[V] = LV;
75 }
76 
77 /// UpdateState - When the state for some instruction is potentially updated,
78 /// this function notices and adds I to the worklist if needed.
79 void SparseSolver::UpdateState(Instruction &Inst, LatticeVal V) {
80  DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(&Inst);
81  if (I != ValueState.end() && I->second == V)
82  return; // No change.
83 
84  // An update. Visit uses of I.
85  ValueState[&Inst] = V;
86  InstWorkList.push_back(&Inst);
87 }
88 
89 /// MarkBlockExecutable - This method can be used by clients to mark all of
90 /// the blocks that are known to be intrinsically live in the processed unit.
91 void SparseSolver::MarkBlockExecutable(BasicBlock *BB) {
92  DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << "\n");
93  BBExecutable.insert(BB); // Basic block is executable!
94  BBWorkList.push_back(BB); // Add the block to the work list!
95 }
96 
97 /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
98 /// work list if it is not already executable...
99 void SparseSolver::markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
100  if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
101  return; // This edge is already known to be executable!
102 
103  DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName()
104  << " -> " << Dest->getName() << "\n");
105 
106  if (BBExecutable.count(Dest)) {
107  // The destination is already executable, but we just made an edge
108  // feasible that wasn't before. Revisit the PHI nodes in the block
109  // because they have potentially new operands.
110  for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
111  visitPHINode(*cast<PHINode>(I));
112 
113  } else {
114  MarkBlockExecutable(Dest);
115  }
116 }
117 
118 
119 /// getFeasibleSuccessors - Return a vector of booleans to indicate which
120 /// successors are reachable from a given terminator instruction.
121 void SparseSolver::getFeasibleSuccessors(TerminatorInst &TI,
122  SmallVectorImpl<bool> &Succs,
123  bool AggressiveUndef) {
124  Succs.resize(TI.getNumSuccessors());
125  if (TI.getNumSuccessors() == 0) return;
126 
127  if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
128  if (BI->isUnconditional()) {
129  Succs[0] = true;
130  return;
131  }
132 
133  LatticeVal BCValue;
134  if (AggressiveUndef)
135  BCValue = getOrInitValueState(BI->getCondition());
136  else
137  BCValue = getLatticeState(BI->getCondition());
138 
139  if (BCValue == LatticeFunc->getOverdefinedVal() ||
140  BCValue == LatticeFunc->getUntrackedVal()) {
141  // Overdefined condition variables can branch either way.
142  Succs[0] = Succs[1] = true;
143  return;
144  }
145 
146  // If undefined, neither is feasible yet.
147  if (BCValue == LatticeFunc->getUndefVal())
148  return;
149 
150  Constant *C = LatticeFunc->GetConstant(BCValue, BI->getCondition(), *this);
151  if (!C || !isa<ConstantInt>(C)) {
152  // Non-constant values can go either way.
153  Succs[0] = Succs[1] = true;
154  return;
155  }
156 
157  // Constant condition variables mean the branch can only go a single way
158  Succs[C->isNullValue()] = true;
159  return;
160  }
161 
162  if (isa<InvokeInst>(TI)) {
163  // Invoke instructions successors are always executable.
164  // TODO: Could ask the lattice function if the value can throw.
165  Succs[0] = Succs[1] = true;
166  return;
167  }
168 
169  if (isa<IndirectBrInst>(TI)) {
170  Succs.assign(Succs.size(), true);
171  return;
172  }
173 
174  SwitchInst &SI = cast<SwitchInst>(TI);
175  LatticeVal SCValue;
176  if (AggressiveUndef)
177  SCValue = getOrInitValueState(SI.getCondition());
178  else
179  SCValue = getLatticeState(SI.getCondition());
180 
181  if (SCValue == LatticeFunc->getOverdefinedVal() ||
182  SCValue == LatticeFunc->getUntrackedVal()) {
183  // All destinations are executable!
184  Succs.assign(TI.getNumSuccessors(), true);
185  return;
186  }
187 
188  // If undefined, neither is feasible yet.
189  if (SCValue == LatticeFunc->getUndefVal())
190  return;
191 
192  Constant *C = LatticeFunc->GetConstant(SCValue, SI.getCondition(), *this);
193  if (!C || !isa<ConstantInt>(C)) {
194  // All destinations are executable!
195  Succs.assign(TI.getNumSuccessors(), true);
196  return;
197  }
198  SwitchInst::CaseHandle Case = *SI.findCaseValue(cast<ConstantInt>(C));
199  Succs[Case.getSuccessorIndex()] = true;
200 }
201 
202 
203 /// isEdgeFeasible - Return true if the control flow edge from the 'From'
204 /// basic block to the 'To' basic block is currently feasible...
206  bool AggressiveUndef) {
207  SmallVector<bool, 16> SuccFeasible;
208  TerminatorInst *TI = From->getTerminator();
209  getFeasibleSuccessors(*TI, SuccFeasible, AggressiveUndef);
210 
211  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
212  if (TI->getSuccessor(i) == To && SuccFeasible[i])
213  return true;
214 
215  return false;
216 }
217 
218 void SparseSolver::visitTerminatorInst(TerminatorInst &TI) {
219  SmallVector<bool, 16> SuccFeasible;
220  getFeasibleSuccessors(TI, SuccFeasible, true);
221 
222  BasicBlock *BB = TI.getParent();
223 
224  // Mark all feasible successors executable...
225  for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
226  if (SuccFeasible[i])
227  markEdgeExecutable(BB, TI.getSuccessor(i));
228 }
229 
230 void SparseSolver::visitPHINode(PHINode &PN) {
231  // The lattice function may store more information on a PHINode than could be
232  // computed from its incoming values. For example, SSI form stores its sigma
233  // functions as PHINodes with a single incoming value.
234  if (LatticeFunc->IsSpecialCasedPHI(&PN)) {
235  LatticeVal IV = LatticeFunc->ComputeInstructionState(PN, *this);
236  if (IV != LatticeFunc->getUntrackedVal())
237  UpdateState(PN, IV);
238  return;
239  }
240 
241  LatticeVal PNIV = getOrInitValueState(&PN);
242  LatticeVal Overdefined = LatticeFunc->getOverdefinedVal();
243 
244  // If this value is already overdefined (common) just return.
245  if (PNIV == Overdefined || PNIV == LatticeFunc->getUntrackedVal())
246  return; // Quick exit
247 
248  // Super-extra-high-degree PHI nodes are unlikely to ever be interesting,
249  // and slow us down a lot. Just mark them overdefined.
250  if (PN.getNumIncomingValues() > 64) {
251  UpdateState(PN, Overdefined);
252  return;
253  }
254 
255  // Look at all of the executable operands of the PHI node. If any of them
256  // are overdefined, the PHI becomes overdefined as well. Otherwise, ask the
257  // transfer function to give us the merge of the incoming values.
258  for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
259  // If the edge is not yet known to be feasible, it doesn't impact the PHI.
260  if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent(), true))
261  continue;
262 
263  // Merge in this value.
264  LatticeVal OpVal = getOrInitValueState(PN.getIncomingValue(i));
265  if (OpVal != PNIV)
266  PNIV = LatticeFunc->MergeValues(PNIV, OpVal);
267 
268  if (PNIV == Overdefined)
269  break; // Rest of input values don't matter.
270  }
271 
272  // Update the PHI with the compute value, which is the merge of the inputs.
273  UpdateState(PN, PNIV);
274 }
275 
276 
277 void SparseSolver::visitInst(Instruction &I) {
278  // PHIs are handled by the propagation logic, they are never passed into the
279  // transfer functions.
280  if (PHINode *PN = dyn_cast<PHINode>(&I))
281  return visitPHINode(*PN);
282 
283  // Otherwise, ask the transfer function what the result is. If this is
284  // something that we care about, remember it.
285  LatticeVal IV = LatticeFunc->ComputeInstructionState(I, *this);
286  if (IV != LatticeFunc->getUntrackedVal())
287  UpdateState(I, IV);
288 
289  if (TerminatorInst *TI = dyn_cast<TerminatorInst>(&I))
290  visitTerminatorInst(*TI);
291 }
292 
294  MarkBlockExecutable(&F.getEntryBlock());
295 
296  // Process the work lists until they are empty!
297  while (!BBWorkList.empty() || !InstWorkList.empty()) {
298  // Process the instruction work list.
299  while (!InstWorkList.empty()) {
300  Instruction *I = InstWorkList.back();
301  InstWorkList.pop_back();
302 
303  DEBUG(dbgs() << "\nPopped off I-WL: " << *I << "\n");
304 
305  // "I" got into the work list because it made a transition. See if any
306  // users are both live and in need of updating.
307  for (User *U : I->users()) {
308  Instruction *UI = cast<Instruction>(U);
309  if (BBExecutable.count(UI->getParent())) // Inst is executable?
310  visitInst(*UI);
311  }
312  }
313 
314  // Process the basic block work list.
315  while (!BBWorkList.empty()) {
316  BasicBlock *BB = BBWorkList.back();
317  BBWorkList.pop_back();
318 
319  DEBUG(dbgs() << "\nPopped off BBWL: " << *BB);
320 
321  // Notify all instructions in this basic block that they are newly
322  // executable.
323  for (Instruction &I : *BB)
324  visitInst(I);
325  }
326  }
327 }
328 
330  OS << "\nFUNCTION: " << F.getName() << "\n";
331  for (auto &BB : F) {
332  if (!BBExecutable.count(&BB))
333  OS << "INFEASIBLE: ";
334  OS << "\t";
335  if (BB.hasName())
336  OS << BB.getName() << ":\n";
337  else
338  OS << "; anon bb\n";
339  for (auto &I : BB) {
340  LatticeFunc->PrintValue(getLatticeState(&I), OS);
341  OS << I << "\n";
342  }
343 
344  OS << "\n";
345  }
346 }
347 
uint64_t CallInst * C
LatticeVal getOrInitValueState(Value *V)
getOrInitValueState - Return the LatticeVal object that corresponds to the value, initializing the va...
This class represents an incoming formal argument to a Function.
Definition: Argument.h:30
void Solve(Function &F)
Solve - Solve for constants and executable blocks.
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
bool isEdgeFeasible(BasicBlock *From, BasicBlock *To, bool AggressiveUndef=false)
isEdgeFeasible - Return true if the control flow edge from the &#39;From&#39; basic block to the &#39;To&#39; basic b...
BasicBlock * getSuccessor(unsigned idx) const
Return the specified successor.
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:136
Value * getCondition() const
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:252
void assign(size_type NumElts, const T &Elt)
Definition: SmallVector.h:427
bool isNullValue() const
Return true if this is the value that would be returned by getNullValue.
Definition: Constants.cpp:86
#define F(x, y, z)
Definition: MD5.cpp:55
const BasicBlock & getEntryBlock() const
Definition: Function.h:564
Subclasses of this class are all able to terminate a basic block.
Definition: InstrTypes.h:54
* if(!EatIfPresent(lltok::kw_thread_local)) return false
ParseOptionalThreadLocal := /*empty.
bool hasName() const
Definition: Value.h:251
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
Conditional or Unconditional Branch instruction.
This is an important base class in LLVM.
Definition: Constant.h:42
This file contains the declarations for the subclasses of Constant, which represent the different fla...
#define A
Definition: LargeTest.cpp:12
const Instruction & back() const
Definition: BasicBlock.h:266
Value * getIncomingValue(unsigned i) const
Return incoming value number x.
Iterator for intrusive lists based on ilist_node.
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:864
unsigned getNumIncomingValues() const
Return the number of incoming edges.
CaseIt findCaseValue(const ConstantInt *C)
Search all of the case values for the specified constant.
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:132
virtual void PrintValue(LatticeVal V, raw_ostream &OS)
PrintValue - Render the specified lattice value to the specified stream.
iterator_range< user_iterator > users()
Definition: Value.h:395
unsigned getSuccessorIndex() const
Returns TerminatorInst&#39;s successor index for current case successor.
void Print(Function &F, raw_ostream &OS) const
StringRef getName() const
Return a constant reference to the value&#39;s name.
Definition: Value.cpp:218
BasicBlock * getIncomingBlock(unsigned i) const
Return incoming basic block number i.
#define I(x, y, z)
Definition: MD5.cpp:58
Multiway switch.
unsigned getNumSuccessors() const
Return the number of successors that this terminator has.
LLVM Value Representation.
Definition: Value.h:73
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:44
#define DEBUG(X)
Definition: Debug.h:118
const TerminatorInst * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.cpp:120
const BasicBlock * getParent() const
Definition: Instruction.h:66
void resize(size_type N)
Definition: SmallVector.h:355