Line data Source code
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 :
15 : #include "llvm/Analysis/SparsePropagation.h"
16 : #include "llvm/ADT/DenseMap.h"
17 : #include "llvm/ADT/SmallVector.h"
18 : #include "llvm/IR/Argument.h"
19 : #include "llvm/IR/BasicBlock.h"
20 : #include "llvm/IR/Constant.h"
21 : #include "llvm/IR/Constants.h"
22 : #include "llvm/IR/Function.h"
23 : #include "llvm/IR/InstrTypes.h"
24 : #include "llvm/IR/Instruction.h"
25 : #include "llvm/IR/Instructions.h"
26 : #include "llvm/IR/User.h"
27 : #include "llvm/Support/Casting.h"
28 : #include "llvm/Support/Debug.h"
29 : #include "llvm/Support/raw_ostream.h"
30 :
31 : using namespace llvm;
32 :
33 : #define DEBUG_TYPE "sparseprop"
34 :
35 : //===----------------------------------------------------------------------===//
36 : // AbstractLatticeFunction Implementation
37 : //===----------------------------------------------------------------------===//
38 :
39 : AbstractLatticeFunction::~AbstractLatticeFunction() = default;
40 :
41 : /// PrintValue - Render the specified lattice value to the specified stream.
42 0 : void AbstractLatticeFunction::PrintValue(LatticeVal V, raw_ostream &OS) {
43 0 : if (V == UndefVal)
44 0 : OS << "undefined";
45 0 : else if (V == OverdefinedVal)
46 0 : OS << "overdefined";
47 0 : else if (V == UntrackedVal)
48 0 : OS << "untracked";
49 : else
50 0 : OS << "unknown lattice value";
51 0 : }
52 :
53 : //===----------------------------------------------------------------------===//
54 : // SparseSolver Implementation
55 : //===----------------------------------------------------------------------===//
56 :
57 : /// getOrInitValueState - Return the LatticeVal object that corresponds to the
58 : /// value, initializing the value's state if it hasn't been entered into the
59 : /// map yet. This function is necessary because not all values should start
60 : /// out in the underdefined state... Arguments should be overdefined, and
61 : /// constants should be marked as constants.
62 0 : SparseSolver::LatticeVal SparseSolver::getOrInitValueState(Value *V) {
63 0 : DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(V);
64 0 : if (I != ValueState.end()) return I->second; // Common case, in the map
65 :
66 : LatticeVal LV;
67 0 : if (LatticeFunc->IsUntrackedValue(V))
68 0 : return LatticeFunc->getUntrackedVal();
69 0 : else if (Constant *C = dyn_cast<Constant>(V))
70 0 : LV = LatticeFunc->ComputeConstant(C);
71 0 : else if (Argument *A = dyn_cast<Argument>(V))
72 0 : LV = LatticeFunc->ComputeArgument(A);
73 0 : else if (!isa<Instruction>(V))
74 : // All other non-instructions are overdefined.
75 0 : LV = LatticeFunc->getOverdefinedVal();
76 : else
77 : // All instructions are underdefined by default.
78 0 : LV = LatticeFunc->getUndefVal();
79 :
80 : // If this value is untracked, don't add it to the map.
81 0 : if (LV == LatticeFunc->getUntrackedVal())
82 : return LV;
83 0 : return ValueState[V] = LV;
84 : }
85 :
86 : /// UpdateState - When the state for some instruction is potentially updated,
87 : /// this function notices and adds I to the worklist if needed.
88 0 : void SparseSolver::UpdateState(Instruction &Inst, LatticeVal V) {
89 0 : DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(&Inst);
90 0 : if (I != ValueState.end() && I->second == V)
91 0 : return; // No change.
92 :
93 : // An update. Visit uses of I.
94 0 : ValueState[&Inst] = V;
95 0 : InstWorkList.push_back(&Inst);
96 : }
97 :
98 : /// MarkBlockExecutable - This method can be used by clients to mark all of
99 : /// the blocks that are known to be intrinsically live in the processed unit.
100 0 : void SparseSolver::MarkBlockExecutable(BasicBlock *BB) {
101 : DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << "\n");
102 0 : BBExecutable.insert(BB); // Basic block is executable!
103 0 : BBWorkList.push_back(BB); // Add the block to the work list!
104 0 : }
105 :
106 : /// markEdgeExecutable - Mark a basic block as executable, adding it to the BB
107 : /// work list if it is not already executable...
108 0 : void SparseSolver::markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
109 0 : if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
110 : return; // This edge is already known to be executable!
111 :
112 : DEBUG(dbgs() << "Marking Edge Executable: " << Source->getName()
113 : << " -> " << Dest->getName() << "\n");
114 :
115 0 : if (BBExecutable.count(Dest)) {
116 : // The destination is already executable, but we just made an edge
117 : // feasible that wasn't before. Revisit the PHI nodes in the block
118 : // because they have potentially new operands.
119 0 : for (BasicBlock::iterator I = Dest->begin(); isa<PHINode>(I); ++I)
120 0 : visitPHINode(*cast<PHINode>(I));
121 : } else {
122 0 : MarkBlockExecutable(Dest);
123 : }
124 : }
125 :
126 : /// getFeasibleSuccessors - Return a vector of booleans to indicate which
127 : /// successors are reachable from a given terminator instruction.
128 0 : void SparseSolver::getFeasibleSuccessors(TerminatorInst &TI,
129 : SmallVectorImpl<bool> &Succs,
130 : bool AggressiveUndef) {
131 0 : Succs.resize(TI.getNumSuccessors());
132 0 : if (TI.getNumSuccessors() == 0) return;
133 :
134 0 : if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
135 0 : if (BI->isUnconditional()) {
136 0 : Succs[0] = true;
137 0 : return;
138 : }
139 :
140 : LatticeVal BCValue;
141 0 : if (AggressiveUndef)
142 0 : BCValue = getOrInitValueState(BI->getCondition());
143 : else
144 0 : BCValue = getLatticeState(BI->getCondition());
145 :
146 0 : if (BCValue == LatticeFunc->getOverdefinedVal() ||
147 0 : BCValue == LatticeFunc->getUntrackedVal()) {
148 : // Overdefined condition variables can branch either way.
149 0 : Succs[0] = Succs[1] = true;
150 0 : return;
151 : }
152 :
153 : // If undefined, neither is feasible yet.
154 0 : if (BCValue == LatticeFunc->getUndefVal())
155 : return;
156 :
157 0 : Constant *C = LatticeFunc->GetConstant(BCValue, BI->getCondition(), *this);
158 0 : if (!C || !isa<ConstantInt>(C)) {
159 : // Non-constant values can go either way.
160 0 : Succs[0] = Succs[1] = true;
161 0 : return;
162 : }
163 :
164 : // Constant condition variables mean the branch can only go a single way
165 0 : Succs[C->isNullValue()] = true;
166 0 : return;
167 : }
168 :
169 0 : if (isa<InvokeInst>(TI)) {
170 : // Invoke instructions successors are always executable.
171 : // TODO: Could ask the lattice function if the value can throw.
172 0 : Succs[0] = Succs[1] = true;
173 0 : return;
174 : }
175 :
176 0 : if (isa<IndirectBrInst>(TI)) {
177 0 : Succs.assign(Succs.size(), true);
178 0 : return;
179 : }
180 :
181 0 : SwitchInst &SI = cast<SwitchInst>(TI);
182 : LatticeVal SCValue;
183 0 : if (AggressiveUndef)
184 0 : SCValue = getOrInitValueState(SI.getCondition());
185 : else
186 0 : SCValue = getLatticeState(SI.getCondition());
187 :
188 0 : if (SCValue == LatticeFunc->getOverdefinedVal() ||
189 0 : SCValue == LatticeFunc->getUntrackedVal()) {
190 : // All destinations are executable!
191 0 : Succs.assign(TI.getNumSuccessors(), true);
192 0 : return;
193 : }
194 :
195 : // If undefined, neither is feasible yet.
196 0 : if (SCValue == LatticeFunc->getUndefVal())
197 : return;
198 :
199 0 : Constant *C = LatticeFunc->GetConstant(SCValue, SI.getCondition(), *this);
200 0 : if (!C || !isa<ConstantInt>(C)) {
201 : // All destinations are executable!
202 0 : Succs.assign(TI.getNumSuccessors(), true);
203 0 : return;
204 : }
205 0 : SwitchInst::CaseHandle Case = *SI.findCaseValue(cast<ConstantInt>(C));
206 0 : Succs[Case.getSuccessorIndex()] = true;
207 : }
208 :
209 : /// isEdgeFeasible - Return true if the control flow edge from the 'From'
210 : /// basic block to the 'To' basic block is currently feasible...
211 0 : bool SparseSolver::isEdgeFeasible(BasicBlock *From, BasicBlock *To,
212 : bool AggressiveUndef) {
213 0 : SmallVector<bool, 16> SuccFeasible;
214 0 : TerminatorInst *TI = From->getTerminator();
215 0 : getFeasibleSuccessors(*TI, SuccFeasible, AggressiveUndef);
216 :
217 0 : for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
218 0 : if (TI->getSuccessor(i) == To && SuccFeasible[i])
219 : return true;
220 :
221 : return false;
222 : }
223 :
224 0 : void SparseSolver::visitTerminatorInst(TerminatorInst &TI) {
225 0 : SmallVector<bool, 16> SuccFeasible;
226 0 : getFeasibleSuccessors(TI, SuccFeasible, true);
227 :
228 0 : BasicBlock *BB = TI.getParent();
229 :
230 : // Mark all feasible successors executable...
231 0 : for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
232 0 : if (SuccFeasible[i])
233 0 : markEdgeExecutable(BB, TI.getSuccessor(i));
234 0 : }
235 :
236 0 : void SparseSolver::visitPHINode(PHINode &PN) {
237 : // The lattice function may store more information on a PHINode than could be
238 : // computed from its incoming values. For example, SSI form stores its sigma
239 : // functions as PHINodes with a single incoming value.
240 0 : if (LatticeFunc->IsSpecialCasedPHI(&PN)) {
241 0 : LatticeVal IV = LatticeFunc->ComputeInstructionState(PN, *this);
242 0 : if (IV != LatticeFunc->getUntrackedVal())
243 0 : UpdateState(PN, IV);
244 : return;
245 : }
246 :
247 0 : LatticeVal PNIV = getOrInitValueState(&PN);
248 0 : LatticeVal Overdefined = LatticeFunc->getOverdefinedVal();
249 :
250 : // If this value is already overdefined (common) just return.
251 0 : if (PNIV == Overdefined || PNIV == LatticeFunc->getUntrackedVal())
252 : return; // Quick exit
253 :
254 : // Super-extra-high-degree PHI nodes are unlikely to ever be interesting,
255 : // and slow us down a lot. Just mark them overdefined.
256 0 : if (PN.getNumIncomingValues() > 64) {
257 0 : UpdateState(PN, Overdefined);
258 0 : return;
259 : }
260 :
261 : // Look at all of the executable operands of the PHI node. If any of them
262 : // are overdefined, the PHI becomes overdefined as well. Otherwise, ask the
263 : // transfer function to give us the merge of the incoming values.
264 0 : for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
265 : // If the edge is not yet known to be feasible, it doesn't impact the PHI.
266 0 : if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent(), true))
267 0 : continue;
268 :
269 : // Merge in this value.
270 0 : LatticeVal OpVal = getOrInitValueState(PN.getIncomingValue(i));
271 0 : if (OpVal != PNIV)
272 0 : PNIV = LatticeFunc->MergeValues(PNIV, OpVal);
273 :
274 0 : if (PNIV == Overdefined)
275 : break; // Rest of input values don't matter.
276 : }
277 :
278 : // Update the PHI with the compute value, which is the merge of the inputs.
279 0 : UpdateState(PN, PNIV);
280 : }
281 :
282 0 : void SparseSolver::visitInst(Instruction &I) {
283 : // PHIs are handled by the propagation logic, they are never passed into the
284 : // transfer functions.
285 0 : if (PHINode *PN = dyn_cast<PHINode>(&I))
286 0 : return visitPHINode(*PN);
287 :
288 : // Otherwise, ask the transfer function what the result is. If this is
289 : // something that we care about, remember it.
290 0 : LatticeVal IV = LatticeFunc->ComputeInstructionState(I, *this);
291 0 : if (IV != LatticeFunc->getUntrackedVal())
292 0 : UpdateState(I, IV);
293 :
294 0 : if (TerminatorInst *TI = dyn_cast<TerminatorInst>(&I))
295 0 : visitTerminatorInst(*TI);
296 : }
297 :
298 0 : void SparseSolver::Solve(Function &F) {
299 0 : MarkBlockExecutable(&F.getEntryBlock());
300 :
301 : // Process the work lists until they are empty!
302 0 : while (!BBWorkList.empty() || !InstWorkList.empty()) {
303 : // Process the instruction work list.
304 0 : while (!InstWorkList.empty()) {
305 0 : Instruction *I = InstWorkList.back();
306 0 : InstWorkList.pop_back();
307 :
308 : DEBUG(dbgs() << "\nPopped off I-WL: " << *I << "\n");
309 :
310 : // "I" got into the work list because it made a transition. See if any
311 : // users are both live and in need of updating.
312 0 : for (User *U : I->users()) {
313 0 : Instruction *UI = cast<Instruction>(U);
314 0 : if (BBExecutable.count(UI->getParent())) // Inst is executable?
315 0 : visitInst(*UI);
316 : }
317 : }
318 :
319 : // Process the basic block work list.
320 0 : while (!BBWorkList.empty()) {
321 0 : BasicBlock *BB = BBWorkList.back();
322 0 : BBWorkList.pop_back();
323 :
324 : DEBUG(dbgs() << "\nPopped off BBWL: " << *BB);
325 :
326 : // Notify all instructions in this basic block that they are newly
327 : // executable.
328 0 : for (Instruction &I : *BB)
329 0 : visitInst(I);
330 : }
331 : }
332 0 : }
333 :
334 0 : void SparseSolver::Print(Function &F, raw_ostream &OS) const {
335 0 : OS << "\nFUNCTION: " << F.getName() << "\n";
336 0 : for (auto &BB : F) {
337 0 : if (!BBExecutable.count(&BB))
338 0 : OS << "INFEASIBLE: ";
339 0 : OS << "\t";
340 0 : if (BB.hasName())
341 0 : OS << BB.getName() << ":\n";
342 : else
343 0 : OS << "; anon bb\n";
344 0 : for (auto &I : BB) {
345 0 : LatticeFunc->PrintValue(getLatticeState(&I), OS);
346 0 : OS << I << "\n";
347 : }
348 :
349 0 : OS << "\n";
350 : }
351 0 : }
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