335 lines
10 KiB
C++
335 lines
10 KiB
C++
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//=- ReachableCodePathInsensitive.cpp ---------------------------*- C++ --*-==//
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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 a flow-sensitive, path-insensitive analysis of
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// determining reachable blocks within a CFG.
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//
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//===----------------------------------------------------------------------===//
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#include "clang/Analysis/Analyses/ReachableCode.h"
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#include "clang/AST/Expr.h"
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#include "clang/AST/ExprCXX.h"
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#include "clang/AST/ExprObjC.h"
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#include "clang/AST/StmtCXX.h"
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#include "clang/Analysis/AnalysisContext.h"
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#include "clang/Analysis/CFG.h"
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#include "clang/Basic/SourceManager.h"
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#include "llvm/ADT/BitVector.h"
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#include "llvm/ADT/SmallVector.h"
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using namespace clang;
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namespace {
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class DeadCodeScan {
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llvm::BitVector Visited;
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llvm::BitVector &Reachable;
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SmallVector<const CFGBlock *, 10> WorkList;
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typedef SmallVector<std::pair<const CFGBlock *, const Stmt *>, 12>
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DeferredLocsTy;
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DeferredLocsTy DeferredLocs;
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public:
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DeadCodeScan(llvm::BitVector &reachable)
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: Visited(reachable.size()),
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Reachable(reachable) {}
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void enqueue(const CFGBlock *block);
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unsigned scanBackwards(const CFGBlock *Start,
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clang::reachable_code::Callback &CB);
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bool isDeadCodeRoot(const CFGBlock *Block);
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const Stmt *findDeadCode(const CFGBlock *Block);
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void reportDeadCode(const Stmt *S,
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clang::reachable_code::Callback &CB);
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};
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}
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void DeadCodeScan::enqueue(const CFGBlock *block) {
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unsigned blockID = block->getBlockID();
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if (Reachable[blockID] || Visited[blockID])
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return;
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Visited[blockID] = true;
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WorkList.push_back(block);
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}
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bool DeadCodeScan::isDeadCodeRoot(const clang::CFGBlock *Block) {
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bool isDeadRoot = true;
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for (CFGBlock::const_pred_iterator I = Block->pred_begin(),
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E = Block->pred_end(); I != E; ++I) {
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if (const CFGBlock *PredBlock = *I) {
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unsigned blockID = PredBlock->getBlockID();
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if (Visited[blockID]) {
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isDeadRoot = false;
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continue;
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}
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if (!Reachable[blockID]) {
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isDeadRoot = false;
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Visited[blockID] = true;
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WorkList.push_back(PredBlock);
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continue;
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}
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}
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}
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return isDeadRoot;
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}
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static bool isValidDeadStmt(const Stmt *S) {
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if (S->getLocStart().isInvalid())
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return false;
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if (const BinaryOperator *BO = dyn_cast<BinaryOperator>(S))
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return BO->getOpcode() != BO_Comma;
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return true;
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}
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const Stmt *DeadCodeScan::findDeadCode(const clang::CFGBlock *Block) {
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for (CFGBlock::const_iterator I = Block->begin(), E = Block->end(); I!=E; ++I)
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if (Optional<CFGStmt> CS = I->getAs<CFGStmt>()) {
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const Stmt *S = CS->getStmt();
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if (isValidDeadStmt(S))
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return S;
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}
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if (CFGTerminator T = Block->getTerminator()) {
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const Stmt *S = T.getStmt();
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if (isValidDeadStmt(S))
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return S;
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}
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return 0;
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}
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static int SrcCmp(const std::pair<const CFGBlock *, const Stmt *> *p1,
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const std::pair<const CFGBlock *, const Stmt *> *p2) {
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if (p1->second->getLocStart() < p2->second->getLocStart())
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return -1;
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if (p2->second->getLocStart() < p1->second->getLocStart())
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return 1;
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return 0;
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}
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unsigned DeadCodeScan::scanBackwards(const clang::CFGBlock *Start,
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clang::reachable_code::Callback &CB) {
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unsigned count = 0;
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enqueue(Start);
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while (!WorkList.empty()) {
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const CFGBlock *Block = WorkList.pop_back_val();
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// It is possible that this block has been marked reachable after
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// it was enqueued.
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if (Reachable[Block->getBlockID()])
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continue;
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// Look for any dead code within the block.
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const Stmt *S = findDeadCode(Block);
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if (!S) {
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// No dead code. Possibly an empty block. Look at dead predecessors.
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for (CFGBlock::const_pred_iterator I = Block->pred_begin(),
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E = Block->pred_end(); I != E; ++I) {
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if (const CFGBlock *predBlock = *I)
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enqueue(predBlock);
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}
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continue;
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}
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// Specially handle macro-expanded code.
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if (S->getLocStart().isMacroID()) {
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count += clang::reachable_code::ScanReachableFromBlock(Block, Reachable);
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continue;
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}
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if (isDeadCodeRoot(Block)) {
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reportDeadCode(S, CB);
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count += clang::reachable_code::ScanReachableFromBlock(Block, Reachable);
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}
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else {
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// Record this statement as the possibly best location in a
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// strongly-connected component of dead code for emitting a
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// warning.
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DeferredLocs.push_back(std::make_pair(Block, S));
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}
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}
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// If we didn't find a dead root, then report the dead code with the
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// earliest location.
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if (!DeferredLocs.empty()) {
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llvm::array_pod_sort(DeferredLocs.begin(), DeferredLocs.end(), SrcCmp);
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for (DeferredLocsTy::iterator I = DeferredLocs.begin(),
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E = DeferredLocs.end(); I != E; ++I) {
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const CFGBlock *block = I->first;
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if (Reachable[block->getBlockID()])
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continue;
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reportDeadCode(I->second, CB);
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count += clang::reachable_code::ScanReachableFromBlock(block, Reachable);
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}
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}
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return count;
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}
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static SourceLocation GetUnreachableLoc(const Stmt *S,
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SourceRange &R1,
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SourceRange &R2) {
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R1 = R2 = SourceRange();
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if (const Expr *Ex = dyn_cast<Expr>(S))
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S = Ex->IgnoreParenImpCasts();
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switch (S->getStmtClass()) {
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case Expr::BinaryOperatorClass: {
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const BinaryOperator *BO = cast<BinaryOperator>(S);
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return BO->getOperatorLoc();
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}
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case Expr::UnaryOperatorClass: {
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const UnaryOperator *UO = cast<UnaryOperator>(S);
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R1 = UO->getSubExpr()->getSourceRange();
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return UO->getOperatorLoc();
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}
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case Expr::CompoundAssignOperatorClass: {
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const CompoundAssignOperator *CAO = cast<CompoundAssignOperator>(S);
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R1 = CAO->getLHS()->getSourceRange();
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R2 = CAO->getRHS()->getSourceRange();
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return CAO->getOperatorLoc();
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}
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case Expr::BinaryConditionalOperatorClass:
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case Expr::ConditionalOperatorClass: {
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const AbstractConditionalOperator *CO =
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cast<AbstractConditionalOperator>(S);
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return CO->getQuestionLoc();
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}
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case Expr::MemberExprClass: {
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const MemberExpr *ME = cast<MemberExpr>(S);
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R1 = ME->getSourceRange();
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return ME->getMemberLoc();
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}
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case Expr::ArraySubscriptExprClass: {
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const ArraySubscriptExpr *ASE = cast<ArraySubscriptExpr>(S);
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R1 = ASE->getLHS()->getSourceRange();
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R2 = ASE->getRHS()->getSourceRange();
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return ASE->getRBracketLoc();
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}
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case Expr::CStyleCastExprClass: {
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const CStyleCastExpr *CSC = cast<CStyleCastExpr>(S);
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R1 = CSC->getSubExpr()->getSourceRange();
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return CSC->getLParenLoc();
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}
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case Expr::CXXFunctionalCastExprClass: {
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const CXXFunctionalCastExpr *CE = cast <CXXFunctionalCastExpr>(S);
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R1 = CE->getSubExpr()->getSourceRange();
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return CE->getLocStart();
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}
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case Stmt::CXXTryStmtClass: {
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return cast<CXXTryStmt>(S)->getHandler(0)->getCatchLoc();
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}
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case Expr::ObjCBridgedCastExprClass: {
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const ObjCBridgedCastExpr *CSC = cast<ObjCBridgedCastExpr>(S);
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R1 = CSC->getSubExpr()->getSourceRange();
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return CSC->getLParenLoc();
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}
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default: ;
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}
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R1 = S->getSourceRange();
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return S->getLocStart();
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}
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void DeadCodeScan::reportDeadCode(const Stmt *S,
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clang::reachable_code::Callback &CB) {
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SourceRange R1, R2;
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SourceLocation Loc = GetUnreachableLoc(S, R1, R2);
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CB.HandleUnreachable(Loc, R1, R2);
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}
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namespace clang { namespace reachable_code {
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void Callback::anchor() { }
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unsigned ScanReachableFromBlock(const CFGBlock *Start,
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llvm::BitVector &Reachable) {
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unsigned count = 0;
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// Prep work queue
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SmallVector<const CFGBlock*, 32> WL;
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// The entry block may have already been marked reachable
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// by the caller.
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if (!Reachable[Start->getBlockID()]) {
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++count;
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Reachable[Start->getBlockID()] = true;
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}
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WL.push_back(Start);
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// Find the reachable blocks from 'Start'.
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while (!WL.empty()) {
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const CFGBlock *item = WL.pop_back_val();
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// Look at the successors and mark then reachable.
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for (CFGBlock::const_succ_iterator I = item->succ_begin(),
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E = item->succ_end(); I != E; ++I)
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if (const CFGBlock *B = *I) {
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unsigned blockID = B->getBlockID();
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if (!Reachable[blockID]) {
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Reachable.set(blockID);
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WL.push_back(B);
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++count;
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}
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}
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}
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return count;
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}
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void FindUnreachableCode(AnalysisDeclContext &AC, Callback &CB) {
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CFG *cfg = AC.getCFG();
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if (!cfg)
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return;
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// Scan for reachable blocks from the entrance of the CFG.
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// If there are no unreachable blocks, we're done.
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llvm::BitVector reachable(cfg->getNumBlockIDs());
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unsigned numReachable = ScanReachableFromBlock(&cfg->getEntry(), reachable);
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if (numReachable == cfg->getNumBlockIDs())
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return;
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// If there aren't explicit EH edges, we should include the 'try' dispatch
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// blocks as roots.
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if (!AC.getCFGBuildOptions().AddEHEdges) {
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for (CFG::try_block_iterator I = cfg->try_blocks_begin(),
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E = cfg->try_blocks_end() ; I != E; ++I) {
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numReachable += ScanReachableFromBlock(*I, reachable);
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}
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if (numReachable == cfg->getNumBlockIDs())
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return;
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}
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// There are some unreachable blocks. We need to find the root blocks that
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// contain code that should be considered unreachable.
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for (CFG::iterator I = cfg->begin(), E = cfg->end(); I != E; ++I) {
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const CFGBlock *block = *I;
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// A block may have been marked reachable during this loop.
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if (reachable[block->getBlockID()])
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continue;
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DeadCodeScan DS(reachable);
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numReachable += DS.scanBackwards(block, CB);
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if (numReachable == cfg->getNumBlockIDs())
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return;
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}
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}
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}} // end namespace clang::reachable_code
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