microsoft
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clang-1
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clang-1/lib/Analysis/ReachableCode.cpp

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