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llvm-project/clang/lib/Analysis/UninitializedValues.cpp

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//==- UninitializedValues.cpp - Find Uninitialized Values -------*- 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 uninitialized values analysis for source-level CFGs.
//
//===----------------------------------------------------------------------===//
#include <utility>
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/PackedVector.h"
#include "llvm/ADT/DenseMap.h"
#include "clang/AST/Decl.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/AnalysisContext.h"
#include "clang/Analysis/Visitors/CFGRecStmtDeclVisitor.h"
#include "clang/Analysis/Analyses/UninitializedValues.h"
#include "clang/Analysis/Support/SaveAndRestore.h"
using namespace clang;
static bool isTrackedVar(const VarDecl *vd, const DeclContext *dc) {
if (vd->isLocalVarDecl() && !vd->hasGlobalStorage() &&
!vd->isExceptionVariable() &&
vd->getDeclContext() == dc) {
QualType ty = vd->getType();
return ty->isScalarType() || ty->isVectorType();
}
return false;
}
//------------------------------------------------------------------------====//
// DeclToIndex: a mapping from Decls we track to value indices.
//====------------------------------------------------------------------------//
namespace {
class DeclToIndex {
llvm::DenseMap<const VarDecl *, unsigned> map;
public:
DeclToIndex() {}
/// Compute the actual mapping from declarations to bits.
void computeMap(const DeclContext &dc);
/// Return the number of declarations in the map.
unsigned size() const { return map.size(); }
/// Returns the bit vector index for a given declaration.
llvm::Optional<unsigned> getValueIndex(const VarDecl *d) const;
};
}
void DeclToIndex::computeMap(const DeclContext &dc) {
unsigned count = 0;
DeclContext::specific_decl_iterator<VarDecl> I(dc.decls_begin()),
E(dc.decls_end());
for ( ; I != E; ++I) {
const VarDecl *vd = *I;
if (isTrackedVar(vd, &dc))
map[vd] = count++;
}
}
llvm::Optional<unsigned> DeclToIndex::getValueIndex(const VarDecl *d) const {
llvm::DenseMap<const VarDecl *, unsigned>::const_iterator I = map.find(d);
if (I == map.end())
return llvm::Optional<unsigned>();
return I->second;
}
//------------------------------------------------------------------------====//
// CFGBlockValues: dataflow values for CFG blocks.
//====------------------------------------------------------------------------//
// These values are defined in such a way that a merge can be done using
// a bitwise OR.
enum Value { Unknown = 0x0, /* 00 */
Initialized = 0x1, /* 01 */
Uninitialized = 0x2, /* 10 */
MayUninitialized = 0x3 /* 11 */ };
static bool isUninitialized(const Value v) {
return v >= Uninitialized;
}
static bool isAlwaysUninit(const Value v) {
return v == Uninitialized;
}
namespace {
typedef llvm::PackedVector<Value, 2> ValueVector;
typedef std::pair<ValueVector *, ValueVector *> BVPair;
class CFGBlockValues {
const CFG &cfg;
BVPair *vals;
ValueVector scratch;
DeclToIndex declToIndex;
ValueVector &lazyCreate(ValueVector *&bv);
public:
CFGBlockValues(const CFG &cfg);
~CFGBlockValues();
unsigned getNumEntries() const { return declToIndex.size(); }
void computeSetOfDeclarations(const DeclContext &dc);
ValueVector &getValueVector(const CFGBlock *block,
const CFGBlock *dstBlock);
BVPair &getValueVectors(const CFGBlock *block, bool shouldLazyCreate);
void mergeIntoScratch(ValueVector const &source, bool isFirst);
bool updateValueVectorWithScratch(const CFGBlock *block);
bool updateValueVectors(const CFGBlock *block, const BVPair &newVals);
bool hasNoDeclarations() const {
return declToIndex.size() == 0;
}
bool hasEntry(const VarDecl *vd) const {
return declToIndex.getValueIndex(vd).hasValue();
}
bool hasValues(const CFGBlock *block);
void resetScratch();
ValueVector &getScratch() { return scratch; }
ValueVector::reference operator[](const VarDecl *vd);
};
} // end anonymous namespace
CFGBlockValues::CFGBlockValues(const CFG &c) : cfg(c), vals(0) {
unsigned n = cfg.getNumBlockIDs();
if (!n)
return;
vals = new std::pair<ValueVector*, ValueVector*>[n];
memset((void*)vals, 0, sizeof(*vals) * n);
}
CFGBlockValues::~CFGBlockValues() {
unsigned n = cfg.getNumBlockIDs();
if (n == 0)
return;
for (unsigned i = 0; i < n; ++i) {
delete vals[i].first;
delete vals[i].second;
}
delete [] vals;
}
void CFGBlockValues::computeSetOfDeclarations(const DeclContext &dc) {
declToIndex.computeMap(dc);
scratch.resize(declToIndex.size());
}
ValueVector &CFGBlockValues::lazyCreate(ValueVector *&bv) {
if (!bv)
bv = new ValueVector(declToIndex.size());
return *bv;
}
/// This function pattern matches for a '&&' or '||' that appears at
/// the beginning of a CFGBlock that also (1) has a terminator and
/// (2) has no other elements. If such an expression is found, it is returned.
static BinaryOperator *getLogicalOperatorInChain(const CFGBlock *block) {
if (block->empty())
return 0;
const CFGStmt *cstmt = block->front().getAs<CFGStmt>();
if (!cstmt)
return 0;
BinaryOperator *b = llvm::dyn_cast_or_null<BinaryOperator>(cstmt->getStmt());
if (!b || !b->isLogicalOp())
return 0;
if (block->pred_size() == 2) {
if (block->getTerminatorCondition() == b) {
if (block->succ_size() == 2)
return b;
}
else if (block->size() == 1)
return b;
}
return 0;
}
ValueVector &CFGBlockValues::getValueVector(const CFGBlock *block,
const CFGBlock *dstBlock) {
unsigned idx = block->getBlockID();
if (dstBlock && getLogicalOperatorInChain(block)) {
if (*block->succ_begin() == dstBlock)
return lazyCreate(vals[idx].first);
assert(*(block->succ_begin()+1) == dstBlock);
return lazyCreate(vals[idx].second);
}
assert(vals[idx].second == 0);
return lazyCreate(vals[idx].first);
}
bool CFGBlockValues::hasValues(const CFGBlock *block) {
unsigned idx = block->getBlockID();
return vals[idx].second != 0;
}
BVPair &CFGBlockValues::getValueVectors(const clang::CFGBlock *block,
bool shouldLazyCreate) {
unsigned idx = block->getBlockID();
lazyCreate(vals[idx].first);
if (shouldLazyCreate)
lazyCreate(vals[idx].second);
return vals[idx];
}
void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
bool isFirst) {
if (isFirst)
scratch = source;
else
scratch |= source;
}
#if 0
static void printVector(const CFGBlock *block, ValueVector &bv,
unsigned num) {
llvm::errs() << block->getBlockID() << " :";
for (unsigned i = 0; i < bv.size(); ++i) {
llvm::errs() << ' ' << bv[i];
}
llvm::errs() << " : " << num << '\n';
}
#endif
bool CFGBlockValues::updateValueVectorWithScratch(const CFGBlock *block) {
ValueVector &dst = getValueVector(block, 0);
bool changed = (dst != scratch);
if (changed)
dst = scratch;
#if 0
printVector(block, scratch, 0);
#endif
return changed;
}
bool CFGBlockValues::updateValueVectors(const CFGBlock *block,
const BVPair &newVals) {
BVPair &vals = getValueVectors(block, true);
bool changed = *newVals.first != *vals.first ||
*newVals.second != *vals.second;
*vals.first = *newVals.first;
*vals.second = *newVals.second;
#if 0
printVector(block, *vals.first, 1);
printVector(block, *vals.second, 2);
#endif
return changed;
}
void CFGBlockValues::resetScratch() {
scratch.reset();
}
ValueVector::reference CFGBlockValues::operator[](const VarDecl *vd) {
const llvm::Optional<unsigned> &idx = declToIndex.getValueIndex(vd);
assert(idx.hasValue());
return scratch[idx.getValue()];
}
//------------------------------------------------------------------------====//
// Worklist: worklist for dataflow analysis.
//====------------------------------------------------------------------------//
namespace {
class DataflowWorklist {
llvm::SmallVector<const CFGBlock *, 20> worklist;
llvm::BitVector enqueuedBlocks;
public:
DataflowWorklist(const CFG &cfg) : enqueuedBlocks(cfg.getNumBlockIDs()) {}
void enqueue(const CFGBlock *block);
void enqueueSuccessors(const CFGBlock *block);
const CFGBlock *dequeue();
};
}
void DataflowWorklist::enqueue(const CFGBlock *block) {
if (!block)
return;
unsigned idx = block->getBlockID();
if (enqueuedBlocks[idx])
return;
worklist.push_back(block);
enqueuedBlocks[idx] = true;
}
void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) {
for (CFGBlock::const_succ_iterator I = block->succ_begin(),
E = block->succ_end(); I != E; ++I) {
enqueue(*I);
}
}
const CFGBlock *DataflowWorklist::dequeue() {
if (worklist.empty())
return 0;
const CFGBlock *b = worklist.back();
worklist.pop_back();
enqueuedBlocks[b->getBlockID()] = false;
return b;
}
//------------------------------------------------------------------------====//
// Transfer function for uninitialized values analysis.
//====------------------------------------------------------------------------//
namespace {
class FindVarResult {
const VarDecl *vd;
const DeclRefExpr *dr;
public:
FindVarResult(VarDecl *vd, DeclRefExpr *dr) : vd(vd), dr(dr) {}
const DeclRefExpr *getDeclRefExpr() const { return dr; }
const VarDecl *getDecl() const { return vd; }
};
class TransferFunctions : public CFGRecStmtVisitor<TransferFunctions> {
CFGBlockValues &vals;
const CFG &cfg;
AnalysisContext &ac;
UninitVariablesHandler *handler;
const DeclRefExpr *currentDR;
const Expr *currentVoidCast;
const bool flagBlockUses;
public:
TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
AnalysisContext &ac,
UninitVariablesHandler *handler,
bool flagBlockUses)
: vals(vals), cfg(cfg), ac(ac), handler(handler), currentDR(0),
currentVoidCast(0), flagBlockUses(flagBlockUses) {}
const CFG &getCFG() { return cfg; }
void reportUninit(const DeclRefExpr *ex, const VarDecl *vd,
bool isAlwaysUninit);
void VisitBlockExpr(BlockExpr *be);
void VisitDeclStmt(DeclStmt *ds);
void VisitDeclRefExpr(DeclRefExpr *dr);
void VisitUnaryOperator(UnaryOperator *uo);
void VisitBinaryOperator(BinaryOperator *bo);
void VisitCastExpr(CastExpr *ce);
void VisitUnaryExprOrTypeTraitExpr(UnaryExprOrTypeTraitExpr *se);
void VisitCXXTypeidExpr(CXXTypeidExpr *E);
void BlockStmt_VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs);
bool isTrackedVar(const VarDecl *vd) {
return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
}
FindVarResult findBlockVarDecl(Expr *ex);
};
}
void TransferFunctions::reportUninit(const DeclRefExpr *ex,
const VarDecl *vd, bool isAlwaysUnit) {
if (handler) handler->handleUseOfUninitVariable(ex, vd, isAlwaysUnit);
}
FindVarResult TransferFunctions::findBlockVarDecl(Expr* ex) {
if (DeclRefExpr* dr = dyn_cast<DeclRefExpr>(ex->IgnoreParenCasts()))
if (VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
if (isTrackedVar(vd))
return FindVarResult(vd, dr);
return FindVarResult(0, 0);
}
void TransferFunctions::BlockStmt_VisitObjCForCollectionStmt(
ObjCForCollectionStmt *fs) {
Visit(fs->getCollection());
// This represents an initialization of the 'element' value.
Stmt *element = fs->getElement();
const VarDecl* vd = 0;
if (DeclStmt* ds = dyn_cast<DeclStmt>(element)) {
vd = cast<VarDecl>(ds->getSingleDecl());
if (!isTrackedVar(vd))
vd = 0;
}
else {
// Initialize the value of the reference variable.
const FindVarResult &res = findBlockVarDecl(cast<Expr>(element));
vd = res.getDecl();
if (!vd) {
Visit(element);
return;
}
}
if (vd)
vals[vd] = Initialized;
}
void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
if (!flagBlockUses || !handler)
return;
const BlockDecl *bd = be->getBlockDecl();
for (BlockDecl::capture_const_iterator i = bd->capture_begin(),
e = bd->capture_end() ; i != e; ++i) {
const VarDecl *vd = i->getVariable();
if (!vd->hasLocalStorage())
continue;
if (!isTrackedVar(vd))
continue;
if (i->isByRef()) {
vals[vd] = Initialized;
continue;
}
Value v = vals[vd];
if (isUninitialized(v))
handler->handleUseOfUninitVariable(be, vd, isAlwaysUninit(v));
}
}
void TransferFunctions::VisitDeclStmt(DeclStmt *ds) {
for (DeclStmt::decl_iterator DI = ds->decl_begin(), DE = ds->decl_end();
DI != DE; ++DI) {
if (VarDecl *vd = dyn_cast<VarDecl>(*DI)) {
if (isTrackedVar(vd)) {
if (Expr *init = vd->getInit()) {
Visit(init);
// If the initializer consists solely of a reference to itself, we
// explicitly mark the variable as uninitialized. This allows code
// like the following:
//
// int x = x;
//
// to deliberately leave a variable uninitialized. Different analysis
// clients can detect this pattern and adjust their reporting
// appropriately, but we need to continue to analyze subsequent uses
// of the variable.
DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(init->IgnoreParenImpCasts());
vals[vd] = (DRE && DRE->getDecl() == vd) ? Uninitialized
: Initialized;
}
} else if (Stmt *init = vd->getInit()) {
Visit(init);
}
}
}
}
void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
// We assume that DeclRefExprs wrapped in an lvalue-to-rvalue cast
// cannot be block-level expressions. Therefore, we determine if
// a DeclRefExpr is involved in a "load" by comparing it to the current
// DeclRefExpr found when analyzing the last lvalue-to-rvalue CastExpr.
// If a DeclRefExpr is not involved in a load, we are essentially computing
// its address, either for assignment to a reference or via the '&' operator.
// In such cases, treat the variable as being initialized, since this
// analysis isn't powerful enough to do alias tracking.
if (dr != currentDR)
if (const VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
if (isTrackedVar(vd))
vals[vd] = Initialized;
}
void TransferFunctions::VisitBinaryOperator(clang::BinaryOperator *bo) {
if (bo->isAssignmentOp()) {
const FindVarResult &res = findBlockVarDecl(bo->getLHS());
if (const VarDecl* vd = res.getDecl()) {
// We assume that DeclRefExprs wrapped in a BinaryOperator "assignment"
// cannot be block-level expressions. Therefore, we determine if
// a DeclRefExpr is involved in a "load" by comparing it to the current
// DeclRefExpr found when analyzing the last lvalue-to-rvalue CastExpr.
SaveAndRestore<const DeclRefExpr*> lastDR(currentDR,
res.getDeclRefExpr());
Visit(bo->getRHS());
Visit(bo->getLHS());
ValueVector::reference val = vals[vd];
if (isUninitialized(val)) {
if (bo->getOpcode() != BO_Assign)
reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
val = Initialized;
}
return;
}
}
Visit(bo->getRHS());
Visit(bo->getLHS());
}
void TransferFunctions::VisitUnaryOperator(clang::UnaryOperator *uo) {
switch (uo->getOpcode()) {
case clang::UO_PostDec:
case clang::UO_PostInc:
case clang::UO_PreDec:
case clang::UO_PreInc: {
const FindVarResult &res = findBlockVarDecl(uo->getSubExpr());
if (const VarDecl *vd = res.getDecl()) {
// We assume that DeclRefExprs wrapped in a unary operator ++/--
// cannot be block-level expressions. Therefore, we determine if
// a DeclRefExpr is involved in a "load" by comparing it to the current
// DeclRefExpr found when analyzing the last lvalue-to-rvalue CastExpr.
SaveAndRestore<const DeclRefExpr*> lastDR(currentDR,
res.getDeclRefExpr());
Visit(uo->getSubExpr());
ValueVector::reference val = vals[vd];
if (isUninitialized(val)) {
reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
// Don't cascade warnings.
val = Initialized;
}
return;
}
break;
}
default:
break;
}
Visit(uo->getSubExpr());
}
void TransferFunctions::VisitCastExpr(clang::CastExpr *ce) {
if (ce->getCastKind() == CK_LValueToRValue) {
const FindVarResult &res = findBlockVarDecl(ce->getSubExpr());
if (const VarDecl *vd = res.getDecl()) {
// We assume that DeclRefExprs wrapped in an lvalue-to-rvalue cast
// cannot be block-level expressions. Therefore, we determine if
// a DeclRefExpr is involved in a "load" by comparing it to the current
// DeclRefExpr found when analyzing the last lvalue-to-rvalue CastExpr.
// Here we update 'currentDR' to be the one associated with this
// lvalue-to-rvalue cast. Then, when we analyze the DeclRefExpr, we
// will know that we are not computing its lvalue for other purposes
// than to perform a load.
SaveAndRestore<const DeclRefExpr*> lastDR(currentDR,
res.getDeclRefExpr());
Visit(ce->getSubExpr());
if (currentVoidCast != ce) {
Value val = vals[vd];
if (isUninitialized(val)) {
reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
// Don't cascade warnings.
vals[vd] = Initialized;
}
}
return;
}
}
else if (CStyleCastExpr *cse = dyn_cast<CStyleCastExpr>(ce)) {
if (cse->getType()->isVoidType()) {
// e.g. (void) x;
SaveAndRestore<const Expr *>
lastVoidCast(currentVoidCast, cse->getSubExpr()->IgnoreParens());
Visit(cse->getSubExpr());
return;
}
}
Visit(ce->getSubExpr());
}
void TransferFunctions::VisitUnaryExprOrTypeTraitExpr(
UnaryExprOrTypeTraitExpr *se) {
if (se->getKind() == UETT_SizeOf) {
if (se->getType()->isConstantSizeType())
return;
// Handle VLAs.
Visit(se->getArgumentExpr());
}
}
void TransferFunctions::VisitCXXTypeidExpr(CXXTypeidExpr *E) {
// typeid(expression) is potentially evaluated when the argument is
// a glvalue of polymorphic type. (C++ 5.2.8p2-3)
if (!E->isTypeOperand() && E->Classify(ac.getASTContext()).isGLValue()) {
QualType SubExprTy = E->getExprOperand()->getType();
if (const RecordType *Record = SubExprTy->getAs<RecordType>())
if (cast<CXXRecordDecl>(Record->getDecl())->isPolymorphic())
Visit(E->getExprOperand());
}
}
//------------------------------------------------------------------------====//
// High-level "driver" logic for uninitialized values analysis.
//====------------------------------------------------------------------------//
static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
AnalysisContext &ac, CFGBlockValues &vals,
llvm::BitVector &wasAnalyzed,
UninitVariablesHandler *handler = 0,
bool flagBlockUses = false) {
wasAnalyzed[block->getBlockID()] = true;
if (const BinaryOperator *b = getLogicalOperatorInChain(block)) {
CFGBlock::const_pred_iterator itr = block->pred_begin();
BVPair vA = vals.getValueVectors(*itr, false);
++itr;
BVPair vB = vals.getValueVectors(*itr, false);
BVPair valsAB;
if (b->getOpcode() == BO_LAnd) {
// Merge the 'F' bits from the first and second.
vals.mergeIntoScratch(*(vA.second ? vA.second : vA.first), true);
vals.mergeIntoScratch(*(vB.second ? vB.second : vB.first), false);
valsAB.first = vA.first;
valsAB.second = &vals.getScratch();
}
else {
// Merge the 'T' bits from the first and second.
assert(b->getOpcode() == BO_LOr);
vals.mergeIntoScratch(*vA.first, true);
vals.mergeIntoScratch(*vB.first, false);
valsAB.first = &vals.getScratch();
valsAB.second = vA.second ? vA.second : vA.first;
}
return vals.updateValueVectors(block, valsAB);
}
// Default behavior: merge in values of predecessor blocks.
vals.resetScratch();
bool isFirst = true;
for (CFGBlock::const_pred_iterator I = block->pred_begin(),
E = block->pred_end(); I != E; ++I) {
vals.mergeIntoScratch(vals.getValueVector(*I, block), isFirst);
isFirst = false;
}
// Apply the transfer function.
TransferFunctions tf(vals, cfg, ac, handler, flagBlockUses);
for (CFGBlock::const_iterator I = block->begin(), E = block->end();
I != E; ++I) {
if (const CFGStmt *cs = dyn_cast<CFGStmt>(&*I)) {
tf.BlockStmt_Visit(cs->getStmt());
}
}
return vals.updateValueVectorWithScratch(block);
}
void clang::runUninitializedVariablesAnalysis(const DeclContext &dc,
const CFG &cfg,
AnalysisContext &ac,
UninitVariablesHandler &handler) {
CFGBlockValues vals(cfg);
vals.computeSetOfDeclarations(dc);
if (vals.hasNoDeclarations())
return;
// Mark all variables uninitialized at the entry.
const CFGBlock &entry = cfg.getEntry();
for (CFGBlock::const_succ_iterator i = entry.succ_begin(),
e = entry.succ_end(); i != e; ++i) {
if (const CFGBlock *succ = *i) {
ValueVector &vec = vals.getValueVector(&entry, succ);
const unsigned n = vals.getNumEntries();
for (unsigned j = 0; j < n ; ++j) {
vec[j] = Uninitialized;
}
}
}
// Proceed with the workist.
DataflowWorklist worklist(cfg);
llvm::BitVector previouslyVisited(cfg.getNumBlockIDs());
worklist.enqueueSuccessors(&cfg.getEntry());
llvm::BitVector wasAnalyzed(cfg.getNumBlockIDs(), false);
while (const CFGBlock *block = worklist.dequeue()) {
// Did the block change?
bool changed = runOnBlock(block, cfg, ac, vals, wasAnalyzed);
if (changed || !previouslyVisited[block->getBlockID()])
worklist.enqueueSuccessors(block);
previouslyVisited[block->getBlockID()] = true;
}
// Run through the blocks one more time, and report uninitialized variabes.
for (CFG::const_iterator BI = cfg.begin(), BE = cfg.end(); BI != BE; ++BI) {
if (wasAnalyzed[(*BI)->getBlockID()])
runOnBlock(*BI, cfg, ac, vals, wasAnalyzed, &handler,
/* flagBlockUses */ true);
}
}
UninitVariablesHandler::~UninitVariablesHandler() {}
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