1 #include "clang/Analysis/Analyses/LiveVariables.h"
2 #include "clang/AST/Stmt.h"
3 #include "clang/Analysis/CFG.h"
4 #include "clang/Analysis/AnalysisContext.h"
5 #include "clang/AST/StmtVisitor.h"
7 #include "llvm/ADT/PostOrderIterator.h"
8 #include "llvm/ADT/DenseMap.h"
14 using namespace clang;
18 // FIXME: This is copy-pasted from ThreadSafety.c. I wanted a patch that
19 // contained working code before refactoring the implementation of both
22 llvm::BitVector VisitedBlockIDs;
25 // po_iterator requires this iterator, but the only interface needed is the
26 // value_type typedef.
28 typedef const CFGBlock *value_type;
32 CFGBlockSet(const CFG *G) : VisitedBlockIDs(G->getNumBlockIDs(), false) {}
34 /// \brief Set the bit associated with a particular CFGBlock.
35 /// This is the important method for the SetType template parameter.
36 bool insert(const CFGBlock *Block) {
37 // Note that insert() is called by po_iterator, which doesn't check to make
38 // sure that Block is non-null. Moreover, the CFGBlock iterator will
39 // occasionally hand out null pointers for pruned edges, so we catch those
42 return false; // if an edge is trivially false.
43 if (VisitedBlockIDs.test(Block->getBlockID()))
45 VisitedBlockIDs.set(Block->getBlockID());
49 /// \brief Check if the bit for a CFGBlock has been already set.
50 /// This method is for tracking visited blocks in the main threadsafety loop.
51 /// Block must not be null.
52 bool alreadySet(const CFGBlock *Block) {
53 return VisitedBlockIDs.test(Block->getBlockID());
57 /// \brief We create a helper class which we use to iterate through CFGBlocks in
58 /// the topological order.
59 class TopologicallySortedCFG {
60 typedef llvm::po_iterator<const CFG*, CFGBlockSet, true> po_iterator;
62 std::vector<const CFGBlock*> Blocks;
64 typedef llvm::DenseMap<const CFGBlock *, unsigned> BlockOrderTy;
65 BlockOrderTy BlockOrder;
69 typedef std::vector<const CFGBlock*>::reverse_iterator iterator;
71 TopologicallySortedCFG(const CFG *CFGraph) {
72 Blocks.reserve(CFGraph->getNumBlockIDs());
73 CFGBlockSet BSet(CFGraph);
75 for (po_iterator I = po_iterator::begin(CFGraph, BSet),
76 E = po_iterator::end(CFGraph, BSet); I != E; ++I) {
77 BlockOrder[*I] = Blocks.size() + 1;
83 return Blocks.rbegin();
91 return begin() == end();
94 struct BlockOrderCompare;
95 friend struct BlockOrderCompare;
97 struct BlockOrderCompare {
98 const TopologicallySortedCFG &TSC;
100 BlockOrderCompare(const TopologicallySortedCFG &tsc) : TSC(tsc) {}
102 bool operator()(const CFGBlock *b1, const CFGBlock *b2) const {
103 TopologicallySortedCFG::BlockOrderTy::const_iterator b1It = TSC.BlockOrder.find(b1);
104 TopologicallySortedCFG::BlockOrderTy::const_iterator b2It = TSC.BlockOrder.find(b2);
106 unsigned b1V = (b1It == TSC.BlockOrder.end()) ? 0 : b1It->second;
107 unsigned b2V = (b2It == TSC.BlockOrder.end()) ? 0 : b2It->second;
112 BlockOrderCompare getComparator() const {
113 return BlockOrderCompare(*this);
117 class DataflowWorklist {
118 SmallVector<const CFGBlock *, 20> worklist;
119 llvm::BitVector enqueuedBlocks;
120 TopologicallySortedCFG TSC;
122 DataflowWorklist(const CFG &cfg)
123 : enqueuedBlocks(cfg.getNumBlockIDs()),
126 void enqueueBlock(const CFGBlock *block);
127 void enqueueSuccessors(const CFGBlock *block);
128 void enqueuePredecessors(const CFGBlock *block);
130 const CFGBlock *dequeue();
137 void DataflowWorklist::enqueueBlock(const clang::CFGBlock *block) {
138 if (block && !enqueuedBlocks[block->getBlockID()]) {
139 enqueuedBlocks[block->getBlockID()] = true;
140 worklist.push_back(block);
144 void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) {
145 const unsigned OldWorklistSize = worklist.size();
146 for (CFGBlock::const_succ_iterator I = block->succ_begin(),
147 E = block->succ_end(); I != E; ++I) {
151 if (OldWorklistSize == 0 || OldWorklistSize == worklist.size())
157 void DataflowWorklist::enqueuePredecessors(const clang::CFGBlock *block) {
158 const unsigned OldWorklistSize = worklist.size();
159 for (CFGBlock::const_pred_iterator I = block->pred_begin(),
160 E = block->pred_end(); I != E; ++I) {
164 if (OldWorklistSize == 0 || OldWorklistSize == worklist.size())
170 void DataflowWorklist::sortWorklist() {
171 std::sort(worklist.begin(), worklist.end(), TSC.getComparator());
175 const CFGBlock *DataflowWorklist::dequeue() {
176 if (worklist.empty())
178 const CFGBlock *b = worklist.back();
180 enqueuedBlocks[b->getBlockID()] = false;
185 class LiveVariablesImpl {
187 AnalysisContext &analysisContext;
188 std::vector<LiveVariables::LivenessValues> cfgBlockValues;
189 llvm::ImmutableSet<const Stmt *>::Factory SSetFact;
190 llvm::ImmutableSet<const VarDecl *>::Factory DSetFact;
191 llvm::DenseMap<const CFGBlock *, LiveVariables::LivenessValues> blocksEndToLiveness;
192 llvm::DenseMap<const CFGBlock *, LiveVariables::LivenessValues> blocksBeginToLiveness;
193 llvm::DenseMap<const Stmt *, LiveVariables::LivenessValues> stmtsToLiveness;
194 llvm::DenseMap<const DeclRefExpr *, unsigned> inAssignment;
195 const bool killAtAssign;
197 LiveVariables::LivenessValues
198 merge(LiveVariables::LivenessValues valsA,
199 LiveVariables::LivenessValues valsB);
201 LiveVariables::LivenessValues runOnBlock(const CFGBlock *block,
202 LiveVariables::LivenessValues val,
203 LiveVariables::Observer *obs = 0);
205 void dumpBlockLiveness(const SourceManager& M);
207 LiveVariablesImpl(AnalysisContext &ac, bool KillAtAssign)
208 : analysisContext(ac),
209 SSetFact(false), // Do not canonicalize ImmutableSets by default.
210 DSetFact(false), // This is a *major* performance win.
211 killAtAssign(KillAtAssign) {}
215 static LiveVariablesImpl &getImpl(void *x) {
216 return *((LiveVariablesImpl *) x);
219 //===----------------------------------------------------------------------===//
220 // Operations and queries on LivenessValues.
221 //===----------------------------------------------------------------------===//
223 bool LiveVariables::LivenessValues::isLive(const Stmt *S) const {
224 return liveStmts.contains(S);
227 bool LiveVariables::LivenessValues::isLive(const VarDecl *D) const {
228 return liveDecls.contains(D);
232 template <typename SET>
233 SET mergeSets(SET A, SET B) {
237 for (typename SET::iterator it = B.begin(), ei = B.end(); it != ei; ++it) {
244 LiveVariables::LivenessValues
245 LiveVariablesImpl::merge(LiveVariables::LivenessValues valsA,
246 LiveVariables::LivenessValues valsB) {
248 llvm::ImmutableSetRef<const Stmt *>
249 SSetRefA(valsA.liveStmts.getRootWithoutRetain(), SSetFact.getTreeFactory()),
250 SSetRefB(valsB.liveStmts.getRootWithoutRetain(), SSetFact.getTreeFactory());
253 llvm::ImmutableSetRef<const VarDecl *>
254 DSetRefA(valsA.liveDecls.getRootWithoutRetain(), DSetFact.getTreeFactory()),
255 DSetRefB(valsB.liveDecls.getRootWithoutRetain(), DSetFact.getTreeFactory());
258 SSetRefA = mergeSets(SSetRefA, SSetRefB);
259 DSetRefA = mergeSets(DSetRefA, DSetRefB);
261 // asImmutableSet() canonicalizes the tree, allowing us to do an easy
262 // comparison afterwards.
263 return LiveVariables::LivenessValues(SSetRefA.asImmutableSet(),
264 DSetRefA.asImmutableSet());
267 bool LiveVariables::LivenessValues::equals(const LivenessValues &V) const {
268 return liveStmts == V.liveStmts && liveDecls == V.liveDecls;
271 //===----------------------------------------------------------------------===//
273 //===----------------------------------------------------------------------===//
275 static bool isAlwaysAlive(const VarDecl *D) {
276 return D->hasGlobalStorage();
279 bool LiveVariables::isLive(const CFGBlock *B, const VarDecl *D) {
280 return isAlwaysAlive(D) || getImpl(impl).blocksEndToLiveness[B].isLive(D);
283 bool LiveVariables::isLive(const Stmt *S, const VarDecl *D) {
284 return isAlwaysAlive(D) || getImpl(impl).stmtsToLiveness[S].isLive(D);
287 bool LiveVariables::isLive(const Stmt *Loc, const Stmt *S) {
288 return getImpl(impl).stmtsToLiveness[Loc].isLive(S);
291 //===----------------------------------------------------------------------===//
292 // Dataflow computation.
293 //===----------------------------------------------------------------------===//
296 class TransferFunctions : public StmtVisitor<TransferFunctions> {
297 LiveVariablesImpl &LV;
298 LiveVariables::LivenessValues &val;
299 LiveVariables::Observer *observer;
300 const CFGBlock *currentBlock;
302 TransferFunctions(LiveVariablesImpl &im,
303 LiveVariables::LivenessValues &Val,
304 LiveVariables::Observer *Observer,
305 const CFGBlock *CurrentBlock)
306 : LV(im), val(Val), observer(Observer), currentBlock(CurrentBlock) {}
308 void VisitBinaryOperator(BinaryOperator *BO);
309 void VisitBlockExpr(BlockExpr *BE);
310 void VisitDeclRefExpr(DeclRefExpr *DR);
311 void VisitDeclStmt(DeclStmt *DS);
312 void VisitObjCForCollectionStmt(ObjCForCollectionStmt *OS);
313 void VisitUnaryExprOrTypeTraitExpr(UnaryExprOrTypeTraitExpr *UE);
314 void VisitUnaryOperator(UnaryOperator *UO);
319 static const VariableArrayType *FindVA(QualType Ty) {
320 const Type *ty = Ty.getTypePtr();
321 while (const ArrayType *VT = dyn_cast<ArrayType>(ty)) {
322 if (const VariableArrayType *VAT = dyn_cast<VariableArrayType>(VT))
323 if (VAT->getSizeExpr())
326 ty = VT->getElementType().getTypePtr();
332 void TransferFunctions::Visit(Stmt *S) {
334 observer->observeStmt(S, currentBlock, val);
336 StmtVisitor<TransferFunctions>::Visit(S);
339 val.liveStmts = LV.SSetFact.remove(val.liveStmts, S);
342 // Mark all children expressions live.
344 switch (S->getStmtClass()) {
347 case Stmt::StmtExprClass: {
348 // For statement expressions, look through the compound statement.
349 S = cast<StmtExpr>(S)->getSubStmt();
352 case Stmt::CXXMemberCallExprClass: {
353 // Include the implicit "this" pointer as being live.
354 CXXMemberCallExpr *CE = cast<CXXMemberCallExpr>(S);
355 if (Expr *ImplicitObj = CE->getImplicitObjectArgument()) {
356 ImplicitObj = ImplicitObj->IgnoreParens();
357 val.liveStmts = LV.SSetFact.add(val.liveStmts, ImplicitObj);
361 case Stmt::DeclStmtClass: {
362 const DeclStmt *DS = cast<DeclStmt>(S);
363 if (const VarDecl *VD = dyn_cast<VarDecl>(DS->getSingleDecl())) {
364 for (const VariableArrayType* VA = FindVA(VD->getType());
365 VA != 0; VA = FindVA(VA->getElementType())) {
366 val.liveStmts = LV.SSetFact.add(val.liveStmts,
367 VA->getSizeExpr()->IgnoreParens());
372 // FIXME: These cases eventually shouldn't be needed.
373 case Stmt::ExprWithCleanupsClass: {
374 S = cast<ExprWithCleanups>(S)->getSubExpr();
377 case Stmt::CXXBindTemporaryExprClass: {
378 S = cast<CXXBindTemporaryExpr>(S)->getSubExpr();
381 case Stmt::UnaryExprOrTypeTraitExprClass: {
382 // No need to unconditionally visit subexpressions.
387 for (Stmt::child_iterator it = S->child_begin(), ei = S->child_end();
389 if (Stmt *child = *it) {
390 if (Expr *Ex = dyn_cast<Expr>(child))
391 child = Ex->IgnoreParens();
393 val.liveStmts = LV.SSetFact.add(val.liveStmts, child);
398 void TransferFunctions::VisitBinaryOperator(BinaryOperator *B) {
399 if (B->isAssignmentOp()) {
400 if (!LV.killAtAssign)
403 // Assigning to a variable?
404 Expr *LHS = B->getLHS()->IgnoreParens();
406 if (DeclRefExpr *DR = dyn_cast<DeclRefExpr>(LHS))
407 if (const VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) {
408 // Assignments to references don't kill the ref's address
409 if (VD->getType()->isReferenceType())
412 if (!isAlwaysAlive(VD)) {
413 // The variable is now dead.
414 val.liveDecls = LV.DSetFact.remove(val.liveDecls, VD);
418 observer->observerKill(DR);
423 void TransferFunctions::VisitBlockExpr(BlockExpr *BE) {
424 AnalysisContext::referenced_decls_iterator I, E;
426 LV.analysisContext.getReferencedBlockVars(BE->getBlockDecl());
427 for ( ; I != E ; ++I) {
428 const VarDecl *VD = *I;
429 if (isAlwaysAlive(VD))
431 val.liveDecls = LV.DSetFact.add(val.liveDecls, VD);
435 void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *DR) {
436 if (const VarDecl *D = dyn_cast<VarDecl>(DR->getDecl()))
437 if (!isAlwaysAlive(D) && LV.inAssignment.find(DR) == LV.inAssignment.end())
438 val.liveDecls = LV.DSetFact.add(val.liveDecls, D);
441 void TransferFunctions::VisitDeclStmt(DeclStmt *DS) {
442 for (DeclStmt::decl_iterator DI=DS->decl_begin(), DE = DS->decl_end();
444 if (VarDecl *VD = dyn_cast<VarDecl>(*DI)) {
445 if (!isAlwaysAlive(VD))
446 val.liveDecls = LV.DSetFact.remove(val.liveDecls, VD);
450 void TransferFunctions::VisitObjCForCollectionStmt(ObjCForCollectionStmt *OS) {
451 // Kill the iteration variable.
453 const VarDecl *VD = 0;
455 Stmt *element = OS->getElement();
456 if (DeclStmt *DS = dyn_cast<DeclStmt>(element)) {
457 VD = cast<VarDecl>(DS->getSingleDecl());
459 else if ((DR = dyn_cast<DeclRefExpr>(cast<Expr>(element)->IgnoreParens()))) {
460 VD = cast<VarDecl>(DR->getDecl());
464 val.liveDecls = LV.DSetFact.remove(val.liveDecls, VD);
466 observer->observerKill(DR);
470 void TransferFunctions::
471 VisitUnaryExprOrTypeTraitExpr(UnaryExprOrTypeTraitExpr *UE)
473 // While sizeof(var) doesn't technically extend the liveness of 'var', it
474 // does extent the liveness of metadata if 'var' is a VariableArrayType.
475 // We handle that special case here.
476 if (UE->getKind() != UETT_SizeOf || UE->isArgumentType())
479 const Expr *subEx = UE->getArgumentExpr();
480 if (subEx->getType()->isVariableArrayType()) {
481 assert(subEx->isLValue());
482 val.liveStmts = LV.SSetFact.add(val.liveStmts, subEx->IgnoreParens());
486 void TransferFunctions::VisitUnaryOperator(UnaryOperator *UO) {
487 // Treat ++/-- as a kill.
488 // Note we don't actually have to do anything if we don't have an observer,
489 // since a ++/-- acts as both a kill and a "use".
493 switch (UO->getOpcode()) {
503 if (DeclRefExpr *DR = dyn_cast<DeclRefExpr>(UO->getSubExpr()->IgnoreParens()))
504 if (isa<VarDecl>(DR->getDecl())) {
505 // Treat ++/-- as a kill.
506 observer->observerKill(DR);
510 LiveVariables::LivenessValues
511 LiveVariablesImpl::runOnBlock(const CFGBlock *block,
512 LiveVariables::LivenessValues val,
513 LiveVariables::Observer *obs) {
515 TransferFunctions TF(*this, val, obs, block);
517 // Visit the terminator (if any).
518 if (const Stmt *term = block->getTerminator())
519 TF.Visit(const_cast<Stmt*>(term));
521 // Apply the transfer function for all Stmts in the block.
522 for (CFGBlock::const_reverse_iterator it = block->rbegin(),
523 ei = block->rend(); it != ei; ++it) {
524 const CFGElement &elem = *it;
525 if (!isa<CFGStmt>(elem))
528 const Stmt *S = cast<CFGStmt>(elem).getStmt();
529 TF.Visit(const_cast<Stmt*>(S));
530 stmtsToLiveness[S] = val;
535 void LiveVariables::runOnAllBlocks(LiveVariables::Observer &obs) {
536 const CFG *cfg = getImpl(impl).analysisContext.getCFG();
537 for (CFG::const_iterator it = cfg->begin(), ei = cfg->end(); it != ei; ++it)
538 getImpl(impl).runOnBlock(*it, getImpl(impl).blocksEndToLiveness[*it], &obs);
541 LiveVariables::LiveVariables(void *im) : impl(im) {}
543 LiveVariables::~LiveVariables() {
544 delete (LiveVariablesImpl*) impl;
548 LiveVariables::computeLiveness(AnalysisContext &AC,
552 CFG *cfg = AC.getCFG();
556 LiveVariablesImpl *LV = new LiveVariablesImpl(AC, killAtAssign);
558 // Construct the dataflow worklist. Enqueue the exit block as the
559 // start of the analysis.
560 DataflowWorklist worklist(*cfg);
561 llvm::BitVector everAnalyzedBlock(cfg->getNumBlockIDs());
563 // FIXME: we should enqueue using post order.
564 for (CFG::const_iterator it = cfg->begin(), ei = cfg->end(); it != ei; ++it) {
565 const CFGBlock *block = *it;
566 worklist.enqueueBlock(block);
568 // FIXME: Scan for DeclRefExprs using in the LHS of an assignment.
569 // We need to do this because we lack context in the reverse analysis
570 // to determine if a DeclRefExpr appears in such a context, and thus
571 // doesn't constitute a "use".
573 for (CFGBlock::const_iterator bi = block->begin(), be = block->end();
575 if (const CFGStmt *cs = bi->getAs<CFGStmt>()) {
576 if (const BinaryOperator *BO = dyn_cast<BinaryOperator>(cs->getStmt())) {
577 if (BO->getOpcode() == BO_Assign) {
578 if (const DeclRefExpr *DR =
579 dyn_cast<DeclRefExpr>(BO->getLHS()->IgnoreParens())) {
580 LV->inAssignment[DR] = 1;
588 worklist.sortWorklist();
590 while (const CFGBlock *block = worklist.dequeue()) {
591 // Determine if the block's end value has changed. If not, we
592 // have nothing left to do for this block.
593 LivenessValues &prevVal = LV->blocksEndToLiveness[block];
595 // Merge the values of all successor blocks.
597 for (CFGBlock::const_succ_iterator it = block->succ_begin(),
598 ei = block->succ_end(); it != ei; ++it) {
599 if (const CFGBlock *succ = *it) {
600 val = LV->merge(val, LV->blocksBeginToLiveness[succ]);
604 if (!everAnalyzedBlock[block->getBlockID()])
605 everAnalyzedBlock[block->getBlockID()] = true;
606 else if (prevVal.equals(val))
611 // Update the dataflow value for the start of this block.
612 LV->blocksBeginToLiveness[block] = LV->runOnBlock(block, val);
614 // Enqueue the value to the predecessors.
615 worklist.enqueuePredecessors(block);
618 return new LiveVariables(LV);
621 static bool compare_entries(const CFGBlock *A, const CFGBlock *B) {
622 return A->getBlockID() < B->getBlockID();
625 static bool compare_vd_entries(const Decl *A, const Decl *B) {
626 SourceLocation ALoc = A->getLocStart();
627 SourceLocation BLoc = B->getLocStart();
628 return ALoc.getRawEncoding() < BLoc.getRawEncoding();
631 void LiveVariables::dumpBlockLiveness(const SourceManager &M) {
632 getImpl(impl).dumpBlockLiveness(M);
635 void LiveVariablesImpl::dumpBlockLiveness(const SourceManager &M) {
636 std::vector<const CFGBlock *> vec;
637 for (llvm::DenseMap<const CFGBlock *, LiveVariables::LivenessValues>::iterator
638 it = blocksEndToLiveness.begin(), ei = blocksEndToLiveness.end();
640 vec.push_back(it->first);
642 std::sort(vec.begin(), vec.end(), compare_entries);
644 std::vector<const VarDecl*> declVec;
646 for (std::vector<const CFGBlock *>::iterator
647 it = vec.begin(), ei = vec.end(); it != ei; ++it) {
648 llvm::errs() << "\n[ B" << (*it)->getBlockID()
649 << " (live variables at block exit) ]\n";
651 LiveVariables::LivenessValues vals = blocksEndToLiveness[*it];
654 for (llvm::ImmutableSet<const VarDecl *>::iterator si =
655 vals.liveDecls.begin(),
656 se = vals.liveDecls.end(); si != se; ++si) {
657 declVec.push_back(*si);
660 std::sort(declVec.begin(), declVec.end(), compare_vd_entries);
662 for (std::vector<const VarDecl*>::iterator di = declVec.begin(),
663 de = declVec.end(); di != de; ++di) {
664 llvm::errs() << " " << (*di)->getDeclName().getAsString()
666 (*di)->getLocation().dump(M);
667 llvm::errs() << ">\n";
670 llvm::errs() << "\n";
673 const void *LiveVariables::getTag() { static int x; return &x; }
674 const void *RelaxedLiveVariables::getTag() { static int x; return &x; }