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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 "llvm/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;
}
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 const BinaryOperator *getLogicalOperatorInChain(const CFGBlock *block) {
if (block->empty())
return 0;
const CFGStmt *cstmt = block->front().getAs<CFGStmt>();
if (!cstmt)
return 0;
const BinaryOperator *b = 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);
}
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];
}
#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';
}
static void printVector(const char *name, ValueVector const &bv) {
llvm::errs() << name << " : ";
for (unsigned i = 0; i < bv.size(); ++i) {
llvm::errs() << ' ' << bv[i];
}
llvm::errs() << "\n";
}
#endif
void CFGBlockValues::mergeIntoScratch(ValueVector const &source,
bool isFirst) {
if (isFirst)
scratch = source;
else
scratch |= source;
}
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 {
SmallVector<const CFGBlock *, 20> worklist;
llvm::BitVector enqueuedBlocks;
public:
DataflowWorklist(const CFG &cfg) : enqueuedBlocks(cfg.getNumBlockIDs()) {}
void enqueueSuccessors(const CFGBlock *block);
const CFGBlock *dequeue();
};
}
void DataflowWorklist::enqueueSuccessors(const clang::CFGBlock *block) {
unsigned OldWorklistSize = worklist.size();
for (CFGBlock::const_succ_iterator I = block->succ_begin(),
E = block->succ_end(); I != E; ++I) {
const CFGBlock *Successor = *I;
if (!Successor || enqueuedBlocks[Successor->getBlockID()])
continue;
worklist.push_back(Successor);
enqueuedBlocks[Successor->getBlockID()] = true;
}
if (OldWorklistSize == 0 || OldWorklistSize == worklist.size())
return;
// Rotate the newly added blocks to the start of the worklist so that it forms
// a proper queue when we pop off the end of the worklist.
std::rotate(worklist.begin(), worklist.begin() + OldWorklistSize,
worklist.end());
}
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 StmtVisitor<TransferFunctions> {
CFGBlockValues &vals;
const CFG &cfg;
AnalysisDeclContext &ac;
UninitVariablesHandler *handler;
/// The last DeclRefExpr seen when analyzing a block. Used to
/// cheat when detecting cases when the address of a variable is taken.
DeclRefExpr *lastDR;
/// The last lvalue-to-rvalue conversion of a variable whose value
/// was uninitialized. Normally this results in a warning, but it is
/// possible to either silence the warning in some cases, or we
/// propagate the uninitialized value.
CastExpr *lastLoad;
/// For some expressions, we want to ignore any post-processing after
/// visitation.
bool skipProcessUses;
public:
TransferFunctions(CFGBlockValues &vals, const CFG &cfg,
AnalysisDeclContext &ac,
UninitVariablesHandler *handler)
: vals(vals), cfg(cfg), ac(ac), handler(handler),
lastDR(0), lastLoad(0),
skipProcessUses(false) {}
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 VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs);
void Visit(Stmt *s);
bool isTrackedVar(const VarDecl *vd) {
return ::isTrackedVar(vd, cast<DeclContext>(ac.getDecl()));
}
FindVarResult findBlockVarDecl(Expr *ex);
void ProcessUses(Stmt *s = 0);
};
}
static const Expr *stripCasts(ASTContext &C, const Expr *Ex) {
while (Ex) {
Ex = Ex->IgnoreParenNoopCasts(C);
if (const CastExpr *CE = dyn_cast<CastExpr>(Ex)) {
if (CE->getCastKind() == CK_LValueBitCast) {
Ex = CE->getSubExpr();
continue;
}
}
break;
}
return 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::VisitObjCForCollectionStmt(ObjCForCollectionStmt *fs) {
// 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)
vals[vd] = Initialized;
}
void TransferFunctions::VisitBlockExpr(BlockExpr *be) {
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 (!isTrackedVar(vd))
continue;
if (i->isByRef()) {
vals[vd] = Initialized;
continue;
}
Value v = vals[vd];
if (handler && isUninitialized(v))
handler->handleUseOfUninitVariable(be, vd, isAlwaysUninit(v));
}
}
void TransferFunctions::VisitDeclRefExpr(DeclRefExpr *dr) {
// Record the last DeclRefExpr seen. This is an lvalue computation.
// We use this value to later detect if a variable "escapes" the analysis.
if (const VarDecl *vd = dyn_cast<VarDecl>(dr->getDecl()))
if (isTrackedVar(vd)) {
ProcessUses();
lastDR = dr;
}
}
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()) {
// 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.
if (init == lastLoad) {
const DeclRefExpr *DR
= cast<DeclRefExpr>(stripCasts(ac.getASTContext(),
lastLoad->getSubExpr()));
if (DR->getDecl() == vd) {
// int x = x;
// Propagate uninitialized value, but don't immediately report
// a problem.
vals[vd] = Uninitialized;
lastLoad = 0;
lastDR = 0;
if (handler)
handler->handleSelfInit(vd);
return;
}
}
// All other cases: treat the new variable as initialized.
// This is a minor optimization to reduce the propagation
// of the analysis, since we will have already reported
// the use of the uninitialized value (which visiting the
// initializer).
vals[vd] = Initialized;
}
}
}
}
}
void TransferFunctions::VisitBinaryOperator(clang::BinaryOperator *bo) {
if (bo->isAssignmentOp()) {
const FindVarResult &res = findBlockVarDecl(bo->getLHS());
if (const VarDecl *vd = res.getDecl()) {
ValueVector::reference val = vals[vd];
if (isUninitialized(val)) {
if (bo->getOpcode() != BO_Assign)
reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
else
val = Initialized;
}
}
}
}
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()) {
assert(res.getDeclRefExpr() == lastDR);
// We null out lastDR to indicate we have fully processed it
// and we don't want the auto-value setting in Visit().
lastDR = 0;
ValueVector::reference val = vals[vd];
if (isUninitialized(val))
reportUninit(res.getDeclRefExpr(), vd, isAlwaysUninit(val));
}
break;
}
default:
break;
}
}
void TransferFunctions::VisitCastExpr(clang::CastExpr *ce) {
if (ce->getCastKind() == CK_LValueToRValue) {
const FindVarResult &res = findBlockVarDecl(ce->getSubExpr());
if (res.getDecl()) {
assert(res.getDeclRefExpr() == lastDR);
lastLoad = ce;
}
}
else if (ce->getCastKind() == CK_NoOp ||
ce->getCastKind() == CK_LValueBitCast) {
skipProcessUses = true;
}
else if (CStyleCastExpr *cse = dyn_cast<CStyleCastExpr>(ce)) {
if (cse->getType()->isVoidType()) {
// e.g. (void) x;
if (lastLoad == cse->getSubExpr()) {
// Squelch any detected load of an uninitialized value if
// we cast it to void.
lastLoad = 0;
lastDR = 0;
}
}
}
}
void TransferFunctions::Visit(clang::Stmt *s) {
skipProcessUses = false;
StmtVisitor<TransferFunctions>::Visit(s);
if (!skipProcessUses)
ProcessUses(s);
}
void TransferFunctions::ProcessUses(Stmt *s) {
// This method is typically called after visiting a CFGElement statement
// in the CFG. We delay processing of reporting many loads of uninitialized
// values until here.
if (lastLoad) {
// If we just visited the lvalue-to-rvalue cast, there is nothing
// left to do.
if (lastLoad == s)
return;
const DeclRefExpr *DR =
cast<DeclRefExpr>(stripCasts(ac.getASTContext(),
lastLoad->getSubExpr()));
const VarDecl *VD = cast<VarDecl>(DR->getDecl());
// If we reach here, we may have seen a load of an uninitialized value
// and it hasn't been casted to void or otherwise handled. In this
// situation, report the incident.
if (isUninitialized(vals[VD]))
reportUninit(DR, VD, isAlwaysUninit(vals[VD]));
lastLoad = 0;
if (DR == lastDR) {
lastDR = 0;
return;
}
}
// Any other uses of 'lastDR' involve taking an lvalue of variable.
// In this case, it "escapes" the analysis.
if (lastDR && lastDR != s) {
vals[cast<VarDecl>(lastDR->getDecl())] = Initialized;
lastDR = 0;
}
}
//------------------------------------------------------------------------====//
// High-level "driver" logic for uninitialized values analysis.
//====------------------------------------------------------------------------//
static bool runOnBlock(const CFGBlock *block, const CFG &cfg,
AnalysisDeclContext &ac, CFGBlockValues &vals,
llvm::BitVector &wasAnalyzed,
UninitVariablesHandler *handler = 0) {
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) {
const CFGBlock *pred = *I;
if (wasAnalyzed[pred->getBlockID()]) {
vals.mergeIntoScratch(vals.getValueVector(pred, block), isFirst);
isFirst = false;
}
}
// Apply the transfer function.
TransferFunctions tf(vals, cfg, ac, handler);
for (CFGBlock::const_iterator I = block->begin(), E = block->end();
I != E; ++I) {
if (const CFGStmt *cs = dyn_cast<CFGStmt>(&*I)) {
tf.Visit(const_cast<Stmt*>(cs->getStmt()));
}
}
tf.ProcessUses();
return vals.updateValueVectorWithScratch(block);
}
void clang::runUninitializedVariablesAnalysis(
const DeclContext &dc,
const CFG &cfg,
AnalysisDeclContext &ac,
UninitVariablesHandler &handler,
UninitVariablesAnalysisStats &stats) {
CFGBlockValues vals(cfg);
vals.computeSetOfDeclarations(dc);
if (vals.hasNoDeclarations())
return;
stats.NumVariablesAnalyzed = vals.getNumEntries();
// 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);
wasAnalyzed[cfg.getEntry().getBlockID()] = true;
while (const CFGBlock *block = worklist.dequeue()) {
// Did the block change?
bool changed = runOnBlock(block, cfg, ac, vals, wasAnalyzed);
++stats.NumBlockVisits;
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) {
const CFGBlock *block = *BI;
if (wasAnalyzed[block->getBlockID()]) {
runOnBlock(block, cfg, ac, vals, wasAnalyzed, &handler);
++stats.NumBlockVisits;
}
}
}
UninitVariablesHandler::~UninitVariablesHandler() {}
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