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bazel / crubit / c9e3a054c64ece906d02100fa03f848df89d0e7f / . / nullability / pointer_nullability_analysis.cc
blob: 4c042cf787324ad87546cd7bc8bbd8ce5ecdb3cf [file] [log] [blame]
// Part of the Crubit project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "nullability/pointer_nullability_analysis.h"
#include <cassert>
#include <deque>
#include <functional>
#include <optional>
#include <utility>
#include <vector>
#include "absl/base/nullability.h"
#include "absl/log/check.h"
#include "nullability/ast_helpers.h"
#include "nullability/macro_arg_capture.h"
#include "nullability/pointer_nullability.h"
#include "nullability/pointer_nullability_lattice.h"
#include "nullability/pointer_nullability_matchers.h"
#include "nullability/pragma.h"
#include "nullability/type_nullability.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/OperationKinds.h"
#include "clang/AST/Stmt.h"
#include "clang/AST/Type.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/ASTMatchers/ASTMatchers.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/FlowSensitive/Arena.h"
#include "clang/Analysis/FlowSensitive/CFGMatchSwitch.h"
#include "clang/Analysis/FlowSensitive/DataflowAnalysis.h"
#include "clang/Analysis/FlowSensitive/DataflowAnalysisContext.h"
#include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
#include "clang/Analysis/FlowSensitive/DataflowLattice.h"
#include "clang/Analysis/FlowSensitive/Formula.h"
#include "clang/Analysis/FlowSensitive/RecordOps.h"
#include "clang/Analysis/FlowSensitive/StorageLocation.h"
#include "clang/Analysis/FlowSensitive/Value.h"
#include "clang/Basic/Builtins.h"
#include "clang/Basic/IdentifierTable.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/OperatorKinds.h"
#include "clang/Basic/Specifiers.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
namespace clang::tidy::nullability {
using ast_matchers::anyOf;
using ast_matchers::MatchFinder;
using dataflow::Arena;
using dataflow::BoolValue;
using dataflow::CFGMatchSwitchBuilder;
using dataflow::ComparisonResult;
using dataflow::DataflowAnalysisContext;
using dataflow::Environment;
using dataflow::Formula;
using dataflow::LatticeEffect;
using dataflow::PointerValue;
using dataflow::RecordStorageLocation;
using dataflow::StorageLocation;
using dataflow::TransferState;
using dataflow::Value;
using dataflow::WidenResult;
#define DEBUG_TYPE "pointer_nullability_analysis.cc"
namespace {
TypeNullability prepend(NullabilityKind Head, const TypeNullability &Tail) {
TypeNullability Result = {Head};
Result.insert(Result.end(), Tail.begin(), Tail.end());
return Result;
}
// If `E` is already associated with a `PointerValue`, returns it.
// Otherwise, associates a newly created `PointerValue` with `E` and returns it.
// Returns null iff `E` is not a raw pointer expression.
absl::Nullable<PointerValue *> ensureRawPointerHasValue(
absl::Nonnull<const Expr *> E, Environment &Env) {
if (!isSupportedRawPointerType(E->getType())) return nullptr;
if (E->isPRValue()) {
if (auto *Val = Env.get<PointerValue>(*E)) return Val;
auto *Val = cast<PointerValue>(Env.createValue(E->getType()));
Env.setValue(*E, *Val);
return Val;
}
StorageLocation *Loc = Env.getStorageLocation(*E);
if (Loc == nullptr) {
Loc = &Env.createStorageLocation(*E);
Env.setStorageLocation(*E, *Loc);
}
if (auto *Val = Env.get<PointerValue>(*Loc)) return Val;
auto *Val = cast<PointerValue>(Env.createValue(E->getType()));
Env.setValue(*Loc, *Val);
return Val;
}
// If `Elt` is an expression of raw pointer type, ensures that it has a
// `PointerValue` associated with it.
void ensureRawPointerHasValue(const CFGElement &Elt, Environment &Env) {
auto S = Elt.getAs<CFGStmt>();
if (!S) return;
const Expr *E = dyn_cast<Expr>(S->getStmt());
if (!E) return;
ensureRawPointerHasValue(E, Env);
}
void computeNullability(absl::Nonnull<const Expr *> E,
TransferState<PointerNullabilityLattice> &State,
std::function<TypeNullability()> Compute) {
(void)State.Lattice.insertExprNullabilityIfAbsent(E, [&] {
auto Nullability = Compute();
if (unsigned ExpectedSize = countPointersInType(E);
ExpectedSize != Nullability.size()) {
// A nullability vector must have one entry per pointer in the type.
// If this is violated, we probably failed to handle some AST node.
LLVM_DEBUG({
llvm::dbgs()
<< "=== Nullability vector has wrong number of entries: ===\n";
llvm::dbgs() << "Expression: \n";
dump(E, llvm::dbgs());
llvm::dbgs() << "\nNullability (" << Nullability.size()
<< " pointers): " << nullabilityToString(Nullability)
<< "\n";
llvm::dbgs() << "\nType (" << ExpectedSize << " pointers): \n";
dump(exprType(E), llvm::dbgs());
llvm::dbgs() << "=================================\n";
});
// We can't meaningfully interpret the vector, so discard it.
// TODO: fix all broken cases and upgrade to CHECK or DCHECK or so.
Nullability.assign(ExpectedSize, NullabilityKind::Unspecified);
}
return Nullability;
});
}
// Returns the computed nullability for a subexpr of the current expression.
// This is always available as we compute bottom-up.
const TypeNullability &getNullabilityForChild(
absl::Nonnull<const Expr *> E,
TransferState<PointerNullabilityLattice> &State) {
return State.Lattice.insertExprNullabilityIfAbsent(E, [&] {
// Since we process child nodes before parents, we should already have
// computed the child nullability. However, this is not true in all test
// cases. So, we return unspecified nullability annotations.
// TODO: fix this issue, and CHECK() instead.
LLVM_DEBUG({
llvm::dbgs() << "=== Missing child nullability: ===\n";
dump(E, llvm::dbgs());
llvm::dbgs() << "==================================\n";
});
return unspecifiedNullability(E);
});
}
// The Resugarer describes the nullability of template arguments within types we
// query using getTypeNullability().
//
// When the template arguments are bound within the queried type, e.g.
// getTypeNullability( vector<Nonnull<int*>>::value_type )
// then getTypeNullability() will record the sugar and resolve the
// SubstTemplateTypeParmType within `value_type` itself.
//
// However when the template arguments are bound elsewhere in the code, e.g.
// vector<Nonnull<int*>> a;
// getTypeNullability( a.front() )
// then we must provide the nullability vector, via the callback passed
// to getTypeNullability().
//
// This class implements that callback interface, based on the common patterns
// where template arguments can be determined from surrounding code.
struct Resugarer {
using SubstTy = SubstTemplateTypeParmType;
const TypeNullabilityDefaults &Defaults;
Resugarer(const TypeNullabilityDefaults &Defaults) : Defaults(Defaults) {}
// The entity referenced is nested within a class template, e.g. `a.front()`
// where a is a vector<Nonnull<int*>>.
// We have a nullability vector [Nonnull] for the specialization vector<int*>.
struct FromEnclosingClassNullability {
ClassTemplateSpecializationDecl *Specialization;
const ArrayRef<PointerTypeNullability> SpecializationNullability;
std::optional<TypeNullability> operator()(const SubstTy *ST) const {
if (Specialization != ST->getAssociatedDecl()) return std::nullopt;
// TODO: The code below does not deal correctly with partial
// specializations. We should eventually handle these, but for now, just
// bail out.
if (isa<ClassTemplatePartialSpecializationDecl>(
ST->getReplacedParameter()->getDeclContext()))
return std::nullopt;
unsigned ArgIndex = ST->getIndex();
auto TemplateArgs = Specialization->getTemplateArgs().asArray();
// TODO: If the type was substituted from a pack template argument,
// we must find the slice that pertains to this particular type.
// For now, just give up on resugaring this type.
if (ST->getPackIndex().has_value()) return std::nullopt;
unsigned PointerCount =
countPointersInType(Specialization->getDeclContext());
for (auto TA : TemplateArgs.take_front(ArgIndex)) {
PointerCount += countPointersInType(TA);
}
unsigned SliceSize = countPointersInType(TemplateArgs[ArgIndex]);
return SpecializationNullability.slice(PointerCount, SliceSize).vec();
}
};
llvm::SmallVector<FromEnclosingClassNullability> Enclosing;
// The entity is referenced using template arguments, e.g.
// `make_unique<Nonnull<int*>>`. We have the template arguments.
struct FromTemplateArgs {
TemplateDecl *Template;
ArrayRef<TemplateArgumentLoc> Args;
std::optional<TypeNullability> operator()(
const SubstTy *ST, const TypeNullabilityDefaults &Defaults) const {
if (Template != ST->getAssociatedDecl()) return std::nullopt;
// Some or all of the template arguments may be deduced, and we won't
// see those on the `DeclRefExpr`. If the template argument was deduced,
// we don't have any sugar for it.
// TODO(b/268348533): Can we somehow obtain it from e.g. the function
// param it was deduced from?
// TODO(b/268345783): This check, as well as the index into
// `template_arguments` below, may be incorrect in the presence of
// parameters packs. In function templates, parameter packs may appear
// anywhere in the parameter list. The index may therefore refer to one
// of the pack arguments, but we might incorrectly interpret it as
// referring to an argument that follows the pack.
if (ST->getIndex() >= Args.size()) return std::nullopt;
TypeSourceInfo *TSI = Args[ST->getIndex()].getTypeSourceInfo();
if (TSI == nullptr) return std::nullopt;
return getTypeNullability(TSI->getTypeLoc(), Defaults);
}
};
llvm::SmallVector<FromTemplateArgs> Template;
// Add a FromTemplateArgs context reflecting that the specialization
// `ResolvedTo` was chosen using the provided template arguments.
void addTemplateArgs(const ValueDecl *ResolvedTo,
ArrayRef<TemplateArgumentLoc> UsingArgs) {
if (const auto *VD = llvm::dyn_cast<VarDecl>(ResolvedTo)) {
Template.push_back(
{cast<VarTemplateSpecializationDecl>(VD)->getSpecializedTemplate(),
UsingArgs});
} else if (auto *FD = llvm::dyn_cast<FunctionDecl>(ResolvedTo)) {
// TODO(b/268345783): We don't currently handle template arguments for
// function templates with template parameter packs correctly when looking
// up arguments later. For function templates, other template parameters
// can follow a template parameter pack and we may report incorrect
// information for those, so we go out of our way here to avoid that and
// skip resugaring any arguments for function template specializations
// with template parameter packs followed by other template parameters.
auto TemplateArgs = FD->getTemplateSpecializationArgs()->asArray();
bool SeenPack = false;
for (const auto &TA : TemplateArgs) {
if (SeenPack) return;
if (TA.getKind() == TemplateArgument::Pack) SeenPack = true;
}
Template.push_back(
{FD->getTemplateSpecializationInfo()->getTemplate(), UsingArgs});
}
}
// Implement the getTypeNullability() callback interface by searching
// all our contexts for a match.
std::optional<TypeNullability> operator()(const SubstTy *ST) const {
for (const auto &R : Enclosing)
if (auto Ret = R(ST)) return Ret;
for (const auto &R : Template)
if (auto Ret = R(ST, Defaults)) return Ret;
return std::nullopt;
}
};
PointerTypeNullability getPointerTypeNullability(
absl::Nonnull<const Expr *> E, PointerNullabilityAnalysis::Lattice &L) {
// TODO: handle this in non-flow-sensitive transfer instead
if (auto FromClang = E->getType()->getNullability();
FromClang && *FromClang != NullabilityKind::Unspecified)
return *FromClang;
if (const auto *TyNullability = L.getTypeNullability(E)) {
if (!TyNullability->empty())
// Return the nullability of the topmost pointer in the type.
return TyNullability->front();
}
return NullabilityKind::Unspecified;
}
void initPointerFromTypeNullability(
PointerValue &PointerVal, absl::Nonnull<const Expr *> E,
TransferState<PointerNullabilityLattice> &State) {
initPointerNullState(PointerVal, State.Env.getDataflowAnalysisContext(),
getPointerTypeNullability(E, State.Lattice));
}
/// If the pointer value stored at `PointerLoc` has any "top" nullability
/// properties, creates a new pointer value referencing the same location with
/// the "top" properties unpacked into fresh atoms. Returns:
/// - The unpacked pointer value if unpacking took place.
/// - The original pointer value if no unpacking took place.
/// - Null if `PointerLoc` is not associated with a value.
/// This is analogous to the unpacking done on `TopBoolValue`s in the framework.
absl::Nullable<PointerValue *> unpackPointerValue(StorageLocation &PointerLoc,
Environment &Env) {
auto *PointerVal = Env.get<PointerValue>(PointerLoc);
if (!PointerVal) return nullptr;
PointerNullState NullState = getPointerNullState(*PointerVal);
if (NullState.FromNullable && NullState.IsNull) return PointerVal;
auto &A = Env.getDataflowAnalysisContext().arena();
if (NullState.FromNullable == nullptr)
NullState.FromNullable = &A.makeAtomRef(A.makeAtom());
if (NullState.IsNull == nullptr)
NullState.IsNull = &A.makeAtomRef(A.makeAtom());
auto &NewPointerVal = Env.create<PointerValue>(PointerVal->getPointeeLoc());
initPointerNullState(NewPointerVal, Env.getDataflowAnalysisContext(),
NullState);
Env.setValue(PointerLoc, NewPointerVal);
return &NewPointerVal;
}
void setToPointerWithNullability(StorageLocation &PtrLoc, NullabilityKind NK,
Environment &Env) {
auto &Val = *cast<PointerValue>(Env.createValue(PtrLoc.getType()));
initPointerNullState(Val, Env.getDataflowAnalysisContext(), NK);
Env.setValue(PtrLoc, Val);
}
void initSmartPointerForExpr(const Expr *E,
TransferState<PointerNullabilityLattice> &State) {
RecordStorageLocation *Loc = nullptr;
if (E->isPRValue()) {
Loc = &State.Env.getResultObjectLocation(*E);
} else {
Loc = State.Env.get<RecordStorageLocation>(*E);
if (Loc == nullptr) {
Loc = &cast<RecordStorageLocation>(State.Env.createStorageLocation(*E));
State.Env.setStorageLocation(*E, *Loc);
}
}
StorageLocation &PtrLoc = Loc->getSyntheticField(PtrField);
auto *Val = State.Env.get<PointerValue>(PtrLoc);
if (Val == nullptr) {
Val = cast<PointerValue>(State.Env.createValue(PtrLoc.getType()));
State.Env.setValue(PtrLoc, *Val);
}
initPointerFromTypeNullability(*Val, E, State);
}
void transferValue_NullPointer(
absl::Nonnull<const Expr *> NullPointer, const MatchFinder::MatchResult &,
TransferState<PointerNullabilityLattice> &State) {
if (auto *PointerVal = ensureRawPointerHasValue(NullPointer, State.Env)) {
initNullPointer(*PointerVal, State.Env.getDataflowAnalysisContext());
}
}
void transferValue_NotNullPointer(
absl::Nonnull<const Expr *> NotNullPointer,
const MatchFinder::MatchResult &,
TransferState<PointerNullabilityLattice> &State) {
if (auto *PointerVal = ensureRawPointerHasValue(NotNullPointer, State.Env)) {
initPointerNullState(*PointerVal, State.Env.getDataflowAnalysisContext(),
NullabilityKind::NonNull);
}
}
bool isStdWeakPtrType(QualType Ty) {
const CXXRecordDecl *RD = Ty.getCanonicalType()->getAsCXXRecordDecl();
if (RD == nullptr) return false;
if (!RD->getDeclContext()->isStdNamespace()) return false;
const IdentifierInfo *ID = RD->getIdentifier();
if (ID == nullptr) return false;
return ID->getName() == "weak_ptr";
}
bool isPointerTypeConvertible(QualType From, QualType To) {
assert(isSupportedRawPointerType(From));
assert(isSupportedRawPointerType(To));
if (From == To) return true;
auto *FromDecl = From->getPointeeType()->getAsCXXRecordDecl();
auto *ToDecl = To->getPointeeType()->getAsCXXRecordDecl();
// If these aren't pointers to records, then just assume they're convertible.
if (FromDecl == nullptr || ToDecl == nullptr) return true;
return FromDecl == ToDecl || FromDecl->isDerivedFrom(ToDecl);
}
void transferValue_SmartPointerConstructor(
const CXXConstructExpr *Ctor, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
RecordStorageLocation &Loc = State.Env.getResultObjectLocation(*Ctor);
// Default and `nullptr_t` constructor.
if (Ctor->getConstructor()->isDefaultConstructor() ||
(Ctor->getNumArgs() >= 1 &&
Ctor->getArg(0)->getType()->isNullPtrType())) {
setSmartPointerToNull(Loc, State.Env);
return;
}
// Construct from raw pointer.
if (Ctor->getNumArgs() >= 1 &&
isSupportedRawPointerType(Ctor->getArg(0)->getType()) &&
isPointerTypeConvertible(Ctor->getArg(0)->getType(),
Loc.getSyntheticField(PtrField).getType())) {
setSmartPointerValue(Loc, getRawPointerValue(Ctor->getArg(0), State.Env),
State.Env);
return;
}
// Copy or move from an existing smart pointer.
if (Ctor->getNumArgs() >= 1 &&
isSupportedSmartPointerType(Ctor->getArg(0)->getType())) {
auto *SrcLoc = Ctor->getArg(0)->isGLValue()
? State.Env.get<RecordStorageLocation>(*Ctor->getArg(0))
: &State.Env.getResultObjectLocation(*Ctor->getArg(0));
if (Ctor->getNumArgs() == 2 &&
isSupportedRawPointerType(Ctor->getArg(1)->getType())) {
// `shared_ptr` aliasing constructor.
setSmartPointerValue(Loc, getRawPointerValue(Ctor->getArg(1), State.Env),
State.Env);
} else {
setSmartPointerValue(
Loc, getPointerValueFromSmartPointer(SrcLoc, State.Env), State.Env);
}
if (Ctor->getConstructor()
->getParamDecl(0)
->getType()
->isRValueReferenceType() &&
SrcLoc != nullptr) {
setSmartPointerToNull(*SrcLoc, State.Env);
}
return;
}
// Construct from `weak_ptr`. This throws if the `weak_ptr` is empty, so we
// can assume the `shared_ptr` is non-null if the constructor returns.
if (Ctor->getNumArgs() == 1 && isStdWeakPtrType(Ctor->getArg(0)->getType()))
setToPointerWithNullability(Loc.getSyntheticField(PtrField),
NullabilityKind::NonNull, State.Env);
}
void transferValue_SmartPointerAssignment(
const CXXOperatorCallExpr *OpCall, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
auto *Loc = State.Env.get<RecordStorageLocation>(*OpCall->getArg(0));
if (Loc == nullptr) return;
if (OpCall->getArg(1)->getType()->isNullPtrType()) {
setSmartPointerToNull(*Loc, State.Env);
return;
}
auto *SrcLoc = State.Env.get<RecordStorageLocation>(*OpCall->getArg(1));
setSmartPointerValue(*Loc, getPointerValueFromSmartPointer(SrcLoc, State.Env),
State.Env);
// If this is the move assignment operator, set the source to null.
auto *Method = dyn_cast_or_null<CXXMethodDecl>(OpCall->getCalleeDecl());
if (Method != nullptr &&
Method->getParamDecl(0)->getType()->isRValueReferenceType()) {
setSmartPointerToNull(*SrcLoc, State.Env);
}
}
void transferValue_SmartPointerReleaseCall(
const CXXMemberCallExpr *MCE, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
RecordStorageLocation *Loc = getImplicitObjectLocation(*MCE, State.Env);
if (Loc == nullptr) return;
StorageLocation &PtrLoc = Loc->getSyntheticField(PtrField);
if (auto *Val = State.Env.get<PointerValue>(PtrLoc))
State.Env.setValue(*MCE, *Val);
State.Env.setValue(
PtrLoc, createNullPointer(PtrLoc.getType()->getPointeeType(), State.Env));
}
void transferValue_SmartPointerResetCall(
const CXXMemberCallExpr *MCE, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
RecordStorageLocation *Loc = getImplicitObjectLocation(*MCE, State.Env);
if (Loc == nullptr) return;
// Zero-arg and `nullptr_t` overloads, as well as single-argument constructor
// with default argument.
if (MCE->getNumArgs() == 0 ||
(MCE->getNumArgs() == 1 && MCE->getArg(0)->getType()->isNullPtrType()) ||
(MCE->getNumArgs() == 1 && MCE->getArg(0)->isDefaultArgument())) {
setSmartPointerToNull(*Loc, State.Env);
return;
}
setSmartPointerValue(*Loc, getRawPointerValue(MCE->getArg(0), State.Env),
State.Env);
}
void swapSmartPointers(RecordStorageLocation *Loc1, RecordStorageLocation *Loc2,
Environment &Env) {
PointerValue *Val1 = getPointerValueFromSmartPointer(Loc1, Env);
PointerValue *Val2 = getPointerValueFromSmartPointer(Loc2, Env);
if (Loc1) setSmartPointerValue(*Loc1, Val2, Env);
if (Loc2) setSmartPointerValue(*Loc2, Val1, Env);
}
void transferValue_SmartPointerMemberSwapCall(
const CXXMemberCallExpr *MCE, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
swapSmartPointers(getImplicitObjectLocation(*MCE, State.Env),
State.Env.get<RecordStorageLocation>(*MCE->getArg(0)),
State.Env);
}
void transferValue_SmartPointerFreeSwapCall(
const CallExpr *CE, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
swapSmartPointers(State.Env.get<RecordStorageLocation>(*CE->getArg(0)),
State.Env.get<RecordStorageLocation>(*CE->getArg(1)),
State.Env);
}
void transferValue_SmartPointerGetCall(
const CXXMemberCallExpr *MCE, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
if (Value *Val = getPointerValueFromSmartPointer(
getImplicitObjectLocation(*MCE, State.Env), State.Env))
State.Env.setValue(*MCE, *Val);
}
void transferValue_SmartPointerBoolConversionCall(
const CXXMemberCallExpr *MCE, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
if (PointerValue *Val = getPointerValueFromSmartPointer(
getImplicitObjectLocation(*MCE, State.Env), State.Env)) {
if (const Formula *IsNull = getPointerNullState(*Val).IsNull)
State.Env.setValue(
*MCE, State.Env.makeNot(State.Env.arena().makeBoolValue(*IsNull)));
}
}
void transferValue_SmartPointerOperatorStar(
const CXXOperatorCallExpr *OpCall, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
if (PointerValue *Val = getSmartPointerValue(OpCall->getArg(0), State.Env)) {
State.Env.setStorageLocation(*OpCall, Val->getPointeeLoc());
}
}
void transferValue_SmartPointerOperatorArrow(
const CXXOperatorCallExpr *OpCall, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
if (PointerValue *Val = getSmartPointerValue(OpCall->getArg(0), State.Env)) {
State.Env.setValue(*OpCall, *Val);
}
}
void transferValue_SmartPointerFactoryCall(
const CallExpr *CE, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
RecordStorageLocation &Loc = State.Env.getResultObjectLocation(*CE);
StorageLocation &PtrLoc = Loc.getSyntheticField(PtrField);
setToPointerWithNullability(PtrLoc, NullabilityKind::NonNull, State.Env);
}
void transferValue_SmartPointerComparisonOpCall(
const CXXOperatorCallExpr *OpCall, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
// Formula representing an equality (`==`) comparison of the two operands.
// If the operator is `!=`, this will need to be negated below.
const Formula *EqualityFormula = nullptr;
bool NullPtr1 = OpCall->getArg(0)->getType()->isNullPtrType();
bool NullPtr2 = OpCall->getArg(1)->getType()->isNullPtrType();
assert(!NullPtr1 || !NullPtr2);
PointerValue *Val1 = nullptr;
if (!NullPtr1) Val1 = getSmartPointerValue(OpCall->getArg(0), State.Env);
PointerValue *Val2 = nullptr;
if (!NullPtr2) Val2 = getSmartPointerValue(OpCall->getArg(1), State.Env);
if (NullPtr1) {
if (Val2 == nullptr) return;
EqualityFormula = getPointerNullState(*Val2).IsNull;
} else if (NullPtr2) {
if (Val1 == nullptr) return;
EqualityFormula = getPointerNullState(*Val1).IsNull;
} else {
if (Val1 == nullptr || Val2 == nullptr) return;
EqualityFormula = &State.Env.arena().makeLiteral(&Val1->getPointeeLoc() ==
&Val2->getPointeeLoc());
}
if (EqualityFormula == nullptr) return;
BoolValue &EqualityValue = State.Env.arena().makeBoolValue(*EqualityFormula);
if (OpCall->getOperator() == OO_EqualEqual)
State.Env.setValue(*OpCall, EqualityValue);
else
State.Env.setValue(*OpCall, State.Env.makeNot(EqualityValue));
}
void transferValue_SharedPtrCastCall(
const CallExpr *CE, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
if (!smartPointersEnabled()) return;
Environment &Env = State.Env;
DataflowAnalysisContext &Ctx = Env.getDataflowAnalysisContext();
Arena &A = Env.arena();
auto *Callee = dyn_cast_or_null<FunctionDecl>(CE->getCalleeDecl());
if (Callee == nullptr) return;
auto *SrcLoc = Env.get<RecordStorageLocation>(*CE->getArg(0));
if (SrcLoc == nullptr) return;
StorageLocation &SrcPtrLoc = SrcLoc->getSyntheticField(PtrField);
auto *SrcPtrVal = Env.get<PointerValue>(SrcPtrLoc);
if (SrcPtrVal == nullptr) return;
RecordStorageLocation &DestLoc = Env.getResultObjectLocation(*CE);
StorageLocation &DestPtrLoc = DestLoc.getSyntheticField(PtrField);
if (Callee->getName() == "const_pointer_cast") {
// A `const_pointer_cast` will definitely produce a pointer with the same
// storage location as the source, so we can simply copy the underlying
// pointer value.
Env.setValue(DestPtrLoc, *SrcPtrVal);
} else {
auto &DestPtrVal =
*cast<PointerValue>(Env.createValue(DestPtrLoc.getType()));
initPointerNullState(DestPtrVal, Ctx);
State.Env.setValue(DestPtrLoc, DestPtrVal);
PointerNullState SrcNullability = getPointerNullState(*SrcPtrVal);
PointerNullState DestNullability = getPointerNullState(DestPtrVal);
assert(DestNullability.IsNull != nullptr);
assert(DestNullability.FromNullable != nullptr);
if (Callee->getName() == "dynamic_pointer_cast") {
// A `dynamic_pointer_cast` may fail. So source `IsNull` implies
// destination `IsNull` (but not the other way around), and the result is
// always nullable.
if (SrcNullability.IsNull != nullptr)
Env.assume(
A.makeImplies(*SrcNullability.IsNull, *DestNullability.IsNull));
Env.assume(*DestNullability.FromNullable);
} else {
if (SrcNullability.IsNull != nullptr)
Env.assume(
A.makeEquals(*SrcNullability.IsNull, *DestNullability.IsNull));
if (SrcNullability.FromNullable != nullptr)
Env.assume(A.makeEquals(*SrcNullability.FromNullable,
*DestNullability.FromNullable));
}
}
// Is this an overload taking an rvalue reference?
if (Callee->getParamDecl(0)->getType()->isRValueReferenceType()) {
if (Callee->getName() == "dynamic_pointer_cast") {
// `dynamic_pointer_cast` sets its argument to null only if the cast
// succeeded. So if the argument wasn't yet nullable, replace it with a
// new nullable pointer.
PointerNullState SrcNullability = getPointerNullState(*SrcPtrVal);
if (SrcNullability.FromNullable == nullptr ||
!Env.proves(*SrcNullability.FromNullable))
setToPointerWithNullability(SrcPtrLoc, NullabilityKind::Nullable,
State.Env);
} else {
setSmartPointerToNull(*SrcLoc, State.Env);
}
}
}
void transferValue_WeakPtrLockCall(
const CXXMemberCallExpr *MCE, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
if (!smartPointersEnabled()) return;
RecordStorageLocation &Loc = State.Env.getResultObjectLocation(*MCE);
StorageLocation &PtrLoc = Loc.getSyntheticField(PtrField);
setToPointerWithNullability(PtrLoc, NullabilityKind::Nullable, State.Env);
}
void transferValue_SmartPointerArrowMemberExpr(
const MemberExpr *ME, const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
// Most accesses of a smart pointer involve a glvalue of smart pointer type,
// and `transferValue_SmartPointer` will ensure in this case that the
// nullability properties of the underlying raw pointer are initialized.
// An exception to this is if we access members of a smart pointer using
// arrow syntax; in this case, there is no glvalue of smart pointer type,
// and this function handles initialization of the underlying raw pointer
// in this case.
const Expr &Base = *ME->getBase();
auto *BasePtrVal = State.Env.get<PointerValue>(Base);
if (BasePtrVal == nullptr) {
BasePtrVal = cast<PointerValue>(State.Env.createValue(Base.getType()));
State.Env.setValue(Base, *BasePtrVal);
}
auto &SmartPtrLoc = cast<RecordStorageLocation>(BasePtrVal->getPointeeLoc());
StorageLocation &PtrLoc = SmartPtrLoc.getSyntheticField(PtrField);
auto *PtrVal = State.Env.get<PointerValue>(PtrLoc);
if (PtrVal == nullptr) {
PtrVal = cast<PointerValue>(State.Env.createValue(PtrLoc.getType()));
State.Env.setValue(PtrLoc, *PtrVal);
}
PointerTypeNullability Nullability = NullabilityKind::Unspecified;
if (const auto *TyNullability =
State.Lattice.getTypeNullability(ME->getBase())) {
if (TyNullability->size() >= 2) Nullability = (*TyNullability)[1];
}
initPointerNullState(*PtrVal, State.Env.getDataflowAnalysisContext(),
Nullability);
}
void transferValue_Pointer(absl::Nonnull<const Expr *> PointerExpr,
const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
auto *PointerVal = ensureRawPointerHasValue(PointerExpr, State.Env);
if (!PointerVal) return;
initPointerFromTypeNullability(*PointerVal, PointerExpr, State);
if (const auto *Cast = dyn_cast<CastExpr>(PointerExpr);
Cast && Cast->getCastKind() == CK_LValueToRValue) {
if (StorageLocation *Loc =
State.Env.getStorageLocation(*Cast->getSubExpr())) {
if (PointerValue *Val = unpackPointerValue(*Loc, State.Env)) {
State.Env.setValue(*PointerExpr, *Val);
}
}
}
}
// `ComparisonFormula` represents the comparison between the two pointer values.
//
// `LHSNull` and `RHSNull` represent the nullability of the left- and right-hand
// expresssions, respectively. A nullptr value is interpreted as Top.
absl::Nullable<BoolValue *> processPointerComparison(
const Formula &ComparisonFormula, absl::Nullable<const Formula *> LHSNull,
absl::Nullable<const Formula *> RHSNull, BinaryOperatorKind Opcode,
Environment &Env) {
auto &A = Env.arena();
// If the null state of either pointer is "top", the result of the comparison
// is a top bool, and we don't have any knowledge we can add to the flow
// condition.
if (LHSNull == nullptr || RHSNull == nullptr) {
return &A.makeTopValue();
}
// Special case: Are we comparing against `nullptr`?
// We can avoid modifying the flow condition in this case and simply propagate
// the nullability of the other operand (potentially with a negation).
if (LHSNull->isLiteral(true))
return &A.makeBoolValue(Opcode == BO_EQ ? *RHSNull : A.makeNot(*RHSNull));
if (RHSNull->isLiteral(true))
return &A.makeBoolValue(Opcode == BO_EQ ? *LHSNull : A.makeNot(*LHSNull));
CHECK(Opcode == BO_EQ || Opcode == BO_NE);
auto &PointerEQ =
Opcode == BO_EQ ? ComparisonFormula : A.makeNot(ComparisonFormula);
auto &PointerNE =
Opcode == BO_EQ ? A.makeNot(ComparisonFormula) : ComparisonFormula;
// nullptr == nullptr
Env.assume(A.makeImplies(A.makeAnd(*LHSNull, *RHSNull), PointerEQ));
// nullptr != notnull
Env.assume(
A.makeImplies(A.makeAnd(*LHSNull, A.makeNot(*RHSNull)), PointerNE));
// notnull != nullptr
Env.assume(
A.makeImplies(A.makeAnd(A.makeNot(*LHSNull), *RHSNull), PointerNE));
// We used the pre-existing formula, so nothing to return.
return nullptr;
}
// TODO(b/233582219): Implement promotion of nullability for initially
// unknown pointers when there is evidence that it is nullable, for example
// when the pointer is compared to nullptr, or cast to boolean.
void transferValue_NullCheckComparison(
absl::Nonnull<const BinaryOperator *> BinaryOp,
const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
auto *LHS = BinaryOp->getLHS();
auto *RHS = BinaryOp->getRHS();
assert(LHS != nullptr && RHS != nullptr);
// Boolean representing the comparison between the two pointer values.
// We can rely on the dataflow framework to have produced a value for this.
auto *ComparisonVal = State.Env.get<BoolValue>(*BinaryOp);
assert(ComparisonVal != nullptr);
auto &ComparisonFormula = ComparisonVal->formula();
auto *LHSVal = getRawPointerValue(LHS, State.Env);
if (!LHSVal || !hasPointerNullState(*LHSVal)) return;
auto *RHSVal = getRawPointerValue(RHS, State.Env);
if (!RHSVal || !hasPointerNullState(*RHSVal)) return;
if (auto *Val = processPointerComparison(ComparisonFormula,
getPointerNullState(*LHSVal).IsNull,
getPointerNullState(*RHSVal).IsNull,
BinaryOp->getOpcode(), State.Env))
State.Env.setValue(*BinaryOp, *Val);
}
void transferValue_NullCheckImplicitCastPtrToBool(
absl::Nonnull<const Expr *> CastExpr, const MatchFinder::MatchResult &,
TransferState<PointerNullabilityLattice> &State) {
auto &A = State.Env.arena();
auto *PointerVal = getRawPointerValue(CastExpr->IgnoreImplicit(), State.Env);
if (!PointerVal) return;
auto Nullability = getPointerNullState(*PointerVal);
if (Nullability.IsNull != nullptr)
State.Env.setValue(*CastExpr,
A.makeBoolValue(A.makeNot(*Nullability.IsNull)));
else
State.Env.setValue(*CastExpr, A.makeTopValue());
}
void initializeOutputParameter(absl::Nonnull<const Expr *> Arg,
TransferState<PointerNullabilityLattice> &State,
const VarDecl &Param) {
// When a function has an "output parameter" - a non-const pointer or
// reference to a pointer of unknown nullability - assume that the function
// may set the pointer to non-null.
//
// For example, in the following code sequence we assume that the function may
// modify the pointer in a way that makes a subsequent dereference safe:
//
// void maybeModify(int ** _Nonnull);
//
// int *p = nullptr;
// initializePointer(&p);
// *p; // safe
QualType ParamTy = Param.getType();
if (ParamTy.isNull()) return;
if (!ParamTy->isPointerType() && !ParamTy->isReferenceType()) return;
if (!isSupportedPointerType(ParamTy->getPointeeType())) return;
if (ParamTy->getPointeeType().isConstQualified()) return;
// TODO: if the called function was instantiated from a template, examining
// the instantiated param decl may miss nullability from template params.
// TODO(b/298200521): This should extend support to annotations that suggest
// different in/out state
TypeNullability OuterNullability =
getTypeNullability(Param, State.Lattice.defaults());
auto InnerNullability = ParamTy->getAs<ReferenceType>()
? ArrayRef(OuterNullability)
: ArrayRef(OuterNullability).drop_front();
if (InnerNullability.front().concrete() != NullabilityKind::Unspecified)
return;
StorageLocation *Loc = nullptr;
if (ParamTy->isPointerType()) {
if (PointerValue *OuterPointer = getRawPointerValue(Arg, State.Env))
Loc = &OuterPointer->getPointeeLoc();
} else if (ParamTy->isReferenceType()) {
Loc = State.Env.getStorageLocation(*Arg);
}
if (Loc == nullptr) return;
if (isSupportedRawPointerType(ParamTy->getPointeeType())) {
auto *InnerPointer =
cast<PointerValue>(State.Env.createValue(ParamTy->getPointeeType()));
initPointerNullState(*InnerPointer, State.Env.getDataflowAnalysisContext(),
NullabilityKind::Unspecified);
State.Env.setValue(*Loc, *InnerPointer);
} else {
auto &SmartPointerLoc = *cast<RecordStorageLocation>(Loc);
setToPointerWithNullability(SmartPointerLoc.getSyntheticField(PtrField),
NullabilityKind::Unspecified, State.Env);
}
}
// `D` is declared somewhere in `absl` or `util`, either directly or nested.
bool isDeclaredInAbseilOrUtil(const Decl &D) {
const auto *DC = D.getDeclContext();
if (DC == nullptr || DC->isTranslationUnit()) return false;
// Find the topmost, non-TU DeclContext.
const DeclContext *Parent = DC->getParent();
while (Parent != nullptr && !Parent->isTranslationUnit()) {
DC = Parent;
Parent = DC->getParent();
}
// Check if it is the `absl` namespace.
const auto *NS = dyn_cast_or_null<NamespaceDecl>(DC);
return NS != nullptr && NS->getDeclName().isIdentifier() &&
(NS->getName() == "absl" || NS->getName() == "util");
}
// Models the `GetReferenceableValue` functions used in Abseil logging and
// elsewhere.
void modelGetReferenceableValue(const CallExpr &CE, Environment &Env) {
// We only model the `GetReferenceableValue` overload that takes and returns a
// reference.
if (!CE.isGLValue()) return;
assert(CE.getNumArgs() == 1);
assert(CE.getArg(0) != nullptr);
if (StorageLocation *Loc = Env.getStorageLocation(*CE.getArg(0)))
Env.setStorageLocation(CE, *Loc);
}
// Models the Abseil-logging `CheckNE_Impl` function. Essentially, associates
// the `IsNull` of the call result with the comparison `arg0 != arg1`.
void modelCheckNE(const CallExpr &CE, Environment &Env) {
assert(isSupportedRawPointerType(CE.getType()));
auto *PointerVal = getRawPointerValue(&CE, Env);
if (!PointerVal)
PointerVal = cast<PointerValue>(Env.createValue(CE.getType()));
// Force the pointer state to `Nullable`, which we will then potentially
// refine below.
// TODO Add the annotation in the logging library so that we don't have
// to hard-code this here.
initPointerNullState(*PointerVal, Env.getDataflowAnalysisContext(),
NullabilityKind::Nullable);
Env.setValue(CE, *PointerVal);
const Formula *IsNull = getPointerNullState(*PointerVal).IsNull;
assert(IsNull != nullptr && "`IsNull` can never be 'Top' here");
auto *LHS = CE.getArg(0);
auto *RHS = CE.getArg(1);
assert(LHS != nullptr && RHS != nullptr);
auto LTy = LHS->getType();
auto RTy = RHS->getType();
if (!isSupportedPointerType(LTy) && !LTy->isNullPtrType()) return;
if (!isSupportedPointerType(RTy) && !RTy->isNullPtrType()) return;
const Formula *LHSNull = nullptr;
if (LTy->isNullPtrType()) {
// Values of nullptr type are not themselves pointers and so not
// modeled directly. They are only modeled if and when they are cast
// to pointers. So, we need to supply a formula directly.
LHSNull = &Env.arena().makeLiteral(true);
} else {
auto *V = getPointerValue(LHS, Env);
if (!V) return;
assert(hasPointerNullState(*V));
LHSNull = getPointerNullState(*V).IsNull;
}
const Formula *RHSNull = nullptr;
if (RTy->isNullPtrType()) {
RHSNull = &Env.arena().makeLiteral(true);
} else {
auto *V = getPointerValue(RHS, Env);
if (!V) return;
assert(hasPointerNullState(*V));
RHSNull = getPointerNullState(*V).IsNull;
}
if (auto *Val =
processPointerComparison(*IsNull, LHSNull, RHSNull, BO_NE, Env))
Env.assume(Env.arena().makeEquals(Val->formula(), *IsNull));
}
void transferValue_CallExpr(absl::Nonnull<const CallExpr *> CE,
const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
// The dataflow framework itself generally does not model `CallExpr`s
// (including creating values for the results). We model some specific
// function calls and handle value creation for certain types.
const auto *FuncDecl = CE->getDirectCallee();
if (FuncDecl != nullptr) {
if (const IdentifierInfo *FunII =
FuncDecl->getDeclName().getAsIdentifierInfo()) {
if (FunII->isStr("__assert_nullability")) return;
// This is part of the implementation of `CHECK_NE`.
if (FunII->isStr("GetReferenceableValue") &&
isDeclaredInAbseilOrUtil(*FuncDecl)) {
modelGetReferenceableValue(*CE, State.Env);
return;
}
if (FunII->isStr("Check_NEImpl") && isDeclaredInAbseilOrUtil(*FuncDecl)) {
modelCheckNE(*CE, State.Env);
return;
}
}
}
StorageLocation *Loc = nullptr;
if (CE->isGLValue()) {
// The function returned a reference. Create a storage location for the
// expression so that if code creates a pointer from the reference, we will
// produce a `PointerValue`.
Loc = State.Env.getStorageLocation(*CE);
if (!Loc) {
// This is subtle: We call `createStorageLocation(QualType)`, not
// `createStorageLocation(const Expr &)`, so that we create a new
// storage location every time.
Loc = &State.Env.createStorageLocation(CE->getType());
State.Env.setStorageLocation(*CE, *Loc);
}
}
if (isSupportedRawPointerType(CE->getType())) {
// Create a pointer so that we can attach nullability to it and have the
// nullability propagate with the pointer.
auto *PointerVal = getRawPointerValue(CE, State.Env);
if (!PointerVal) {
PointerVal = cast<PointerValue>(State.Env.createValue(CE->getType()));
}
initPointerFromTypeNullability(*PointerVal, CE, State);
if (Loc != nullptr)
State.Env.setValue(*Loc, *PointerVal);
else
// `Loc` is set iff `CE` is a glvalue, so we know here that it must
// be a prvalue.
State.Env.setValue(*CE, *PointerVal);
}
if (CE->isCallToStdMove() || FuncDecl == nullptr) return;
// Don't treat parameters of our macro replacement argument-capture functions
// as output parameters.
if (const IdentifierInfo *FunII =
FuncDecl->getDeclName().getAsIdentifierInfo();
FunII && (FunII->isStr(ArgCaptureAbortIfFalse) ||
FunII->isStr(ArgCaptureAbortIfEqual)))
return;
// Make output parameters (with unknown nullability) initialized to unknown.
for (ParamAndArgIterator<CallExpr> Iter(*FuncDecl, *CE); Iter; ++Iter)
initializeOutputParameter(&Iter.arg(), State, Iter.param());
}
void transferValue_AccessorCall(
absl::Nonnull<const CXXMemberCallExpr *> MCE,
const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
auto *member = Result.Nodes.getNodeAs<clang::ValueDecl>("member-decl");
PointerValue *PointerVal = nullptr;
if (dataflow::RecordStorageLocation *RecordLoc =
dataflow::getImplicitObjectLocation(*MCE, State.Env)) {
StorageLocation *Loc = RecordLoc->getChild(*member);
PointerVal = dyn_cast_or_null<PointerValue>(State.Env.getValue(*Loc));
}
if (!PointerVal) {
PointerVal = ensureRawPointerHasValue(MCE, State.Env);
}
if (PointerVal) {
State.Env.setValue(*MCE, *PointerVal);
initPointerFromTypeNullability(*PointerVal, MCE, State);
}
}
void handleConstMemberCall(
absl::Nonnull<const CallExpr *> CE,
absl::Nullable<dataflow::RecordStorageLocation *> RecordLoc,
const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
// If the const method returns a smart pointer, handle it separately.
// Smart pointers are represented as RecordStorangeLocations, so their
// treatment is different from booleans or raw pointers, which are
// represented as Values.
if (RecordLoc != nullptr && isSupportedSmartPointerType(CE->getType())) {
StorageLocation *Loc = State.Lattice.getConstMethodReturnStorageLocation(
*RecordLoc, CE, State.Env);
if (Loc == nullptr) return;
if (CE->isGLValue()) {
// If the call to the const method returns a reference to a smart pointer,
// we can use link the call expression to the smart pointer via
// setStorageLocation.
State.Env.setStorageLocation(*CE, *Loc);
} else {
// If the call to the const method returns a smart pointer by value, we
// need to use CopyRecord to link the smart pointer to the result object
// of the call expression.
copyRecord(*cast<RecordStorageLocation>(Loc),
State.Env.getResultObjectLocation(*CE), State.Env);
}
return;
}
// If the const method returns a raw pointer or boolean (represented as
// Values) handle them appropriately.
if (RecordLoc != nullptr && CE->isPRValue() &&
(isSupportedRawPointerType(CE->getType()) ||
CE->getType()->isBooleanType())) {
Value *Val =
State.Lattice.getConstMethodReturnValue(*RecordLoc, CE, State.Env);
if (Val == nullptr) return;
State.Env.setValue(*CE, *Val);
if (auto *PointerVal = dyn_cast<PointerValue>(Val))
initPointerFromTypeNullability(*PointerVal, CE, State);
return;
}
// Perform default handling for remaining return types
transferValue_CallExpr(CE, Result, State);
}
void transferValue_ConstMemberCall(
absl::Nonnull<const CXXMemberCallExpr *> MCE,
const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
handleConstMemberCall(
MCE, dataflow::getImplicitObjectLocation(*MCE, State.Env), Result, State);
}
void transferValue_OptionalOperatorArrowCall(
absl::Nonnull<const CXXOperatorCallExpr *> OCE,
const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
auto *RecordLoc = cast_or_null<dataflow::RecordStorageLocation>(
State.Env.getStorageLocation(*OCE->getArg(0)));
// `optional::operator->` isn't necessarily const, but it behaves the way we
// model "const member calls": It always returns the same pointer if the
// optional wasn't mutated in the meantime.
handleConstMemberCall(OCE, RecordLoc, Result, State);
}
void handleNonConstMemberCall(absl::Nonnull<const CallExpr *> CE,
dataflow::RecordStorageLocation *RecordLoc,
const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
// When a non-const member function is called, clear all pointer-type fields
// of the receiver.
if (RecordLoc != nullptr) {
for (const auto [Field, FieldLoc] : RecordLoc->children()) {
// We can't produce a new `PointerValue` here because we don't necessarily
// know what to initialize its nullability properties with. The record may
// be a `ClassTemplateSpecializationDecl`, which uses canonical types for
// its type arguments (there only be one specialization for the same
// canonical type arguments), so the `FieldDecl` doesn't contain
// nullability annotations. The best thing we can do, therefore, is to
// clear the value.
if (isSupportedRawPointerType(Field->getType()))
State.Env.clearValue(*FieldLoc);
}
State.Lattice.clearConstMethodReturnValues(*RecordLoc);
State.Lattice.clearConstMethodReturnStorageLocations(*RecordLoc);
}
// Perform default handling.
transferValue_CallExpr(CE, Result, State);
}
void transferValue_NonConstMemberCall(
absl::Nonnull<const CXXMemberCallExpr *> MCE,
const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
handleNonConstMemberCall(
MCE, dataflow::getImplicitObjectLocation(*MCE, State.Env), Result, State);
}
void transferValue_NonConstMemberOperatorCall(
absl::Nonnull<const CXXOperatorCallExpr *> OCE,
const MatchFinder::MatchResult &Result,
TransferState<PointerNullabilityLattice> &State) {
auto *RecordLoc = cast_or_null<dataflow::RecordStorageLocation>(
State.Env.getStorageLocation(*OCE->getArg(0)));
handleNonConstMemberCall(OCE, RecordLoc, Result, State);
}
void transferType_DeclRefExpr(absl::Nonnull<const DeclRefExpr *> DRE,
const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(DRE, State, [&] {
Resugarer Resugar(State.Lattice.defaults());
if (DRE->hasExplicitTemplateArgs())
Resugar.addTemplateArgs(DRE->getDecl(), DRE->template_arguments());
std::deque<TypeNullability> ScopeNullabilityStorage;
for (auto NNS = DRE->getQualifierLoc(); NNS; NNS = NNS.getPrefix()) {
if (auto *CTSD = llvm::dyn_cast_or_null<ClassTemplateSpecializationDecl>(
NNS.getNestedNameSpecifier()->getAsRecordDecl())) {
ScopeNullabilityStorage.push_back(
getTypeNullability(NNS.getTypeLoc(), State.Lattice.defaults()));
Resugar.Enclosing.push_back({CTSD, ScopeNullabilityStorage.back()});
}
}
auto Nullability =
getTypeNullability(*DRE->getDecl(), State.Lattice.defaults(), Resugar);
State.Lattice.overrideNullabilityFromDecl(DRE->getDecl(), Nullability);
return Nullability;
});
}
void transferType_MemberExpr(absl::Nonnull<const MemberExpr *> ME,
const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(ME, State, [&]() {
auto *Member = ME->getMemberDecl();
auto BaseType = ME->getBase()->getType();
auto BaseNullability =
ArrayRef(getNullabilityForChild(ME->getBase(), State));
if (ME->isArrow() && BaseType->isPointerType()) {
BaseType = BaseType->getPointeeType();
BaseNullability = BaseNullability.drop_front();
}
Resugarer Resugar(State.Lattice.defaults());
if (const auto *RT = BaseType->getAs<RecordType>()) {
if (auto *CTSpec =
dyn_cast<ClassTemplateSpecializationDecl>(RT->getDecl())) {
Resugar.Enclosing.push_back({CTSpec, BaseNullability});
}
}
if (ME->hasExplicitTemplateArgs())
Resugar.addTemplateArgs(ME->getMemberDecl(), ME->template_arguments());
auto Nullability =
getTypeNullability(*Member, State.Lattice.defaults(), Resugar);
State.Lattice.overrideNullabilityFromDecl(ME->getMemberDecl(), Nullability);
return Nullability;
});
}
void transferType_CastExpr(absl::Nonnull<const CastExpr *> CE,
const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(CE, State, [&]() -> TypeNullability {
// Most casts that can convert ~unrelated types drop nullability in general.
// As a special case, preserve nullability of outer pointer types.
// For example, int* p; (void*)p; is a BitCast, but preserves nullability.
auto PreserveTopLevelPointers = [&](TypeNullability V) {
auto ArgNullability = getNullabilityForChild(CE->getSubExpr(), State);
const PointerType *ArgType = dyn_cast<PointerType>(
CE->getSubExpr()->getType().getCanonicalType().getTypePtr());
const PointerType *CastType =
dyn_cast<PointerType>(CE->getType().getCanonicalType().getTypePtr());
for (int I = 0; ArgType && CastType; ++I) {
V[I] = ArgNullability[I];
ArgType = dyn_cast<PointerType>(ArgType->getPointeeType().getTypePtr());
CastType =
dyn_cast<PointerType>(CastType->getPointeeType().getTypePtr());
}
return V;
};
switch (CE->getCastKind()) {
// Casts between unrelated types: we can't say anything about nullability.
case CK_LValueBitCast:
case CK_BitCast:
case CK_LValueToRValueBitCast:
return PreserveTopLevelPointers(unspecifiedNullability(CE));
// Casts between equivalent types.
case CK_LValueToRValue:
case CK_NoOp:
case CK_AtomicToNonAtomic:
case CK_NonAtomicToAtomic:
case CK_AddressSpaceConversion:
return getNullabilityForChild(CE->getSubExpr(), State);
// Controlled conversions between types
// TODO: these should be doable somehow
case CK_BaseToDerived:
case CK_DerivedToBase:
case CK_UncheckedDerivedToBase:
return PreserveTopLevelPointers(unspecifiedNullability(CE));
case CK_UserDefinedConversion:
return unspecifiedNullability(CE);
case CK_ConstructorConversion:
if (auto *CCE = llvm::dyn_cast<CXXConstructExpr>(CE->getSubExpr())) {
// This node is syntactic only.
return getNullabilityForChild(CE->getSubExpr(), State);
}
return unspecifiedNullability(CE);
case CK_Dynamic: {
auto Result = unspecifiedNullability(CE);
// A dynamic_cast to pointer is null if the runtime check fails.
if (isa<PointerType>(CE->getType().getCanonicalType()))
Result.front() = NullabilityKind::Nullable;
return Result;
}
// Primitive values have no nullability.
case CK_ToVoid:
case CK_MemberPointerToBoolean:
case CK_PointerToBoolean:
case CK_PointerToIntegral:
case CK_IntegralCast:
case CK_IntegralToBoolean:
case CK_IntegralToFloating:
case CK_FloatingToFixedPoint:
case CK_FixedPointToFloating:
case CK_FixedPointCast:
case CK_FixedPointToIntegral:
case CK_IntegralToFixedPoint:
case CK_FixedPointToBoolean:
case CK_FloatingToIntegral:
case CK_FloatingToBoolean:
case CK_BooleanToSignedIntegral:
case CK_FloatingCast:
case CK_FloatingRealToComplex:
case CK_FloatingComplexToReal:
case CK_FloatingComplexToBoolean:
case CK_FloatingComplexCast:
case CK_FloatingComplexToIntegralComplex:
case CK_IntegralRealToComplex:
case CK_IntegralComplexToReal:
case CK_IntegralComplexToBoolean:
case CK_IntegralComplexCast:
case CK_IntegralComplexToFloatingComplex:
return {};
// This can definitely be null!
case CK_NullToPointer: {
TypeNullability Nullability;
// Explicit casts get the inner of the written type.
if (const auto *ECE = dyn_cast<ExplicitCastExpr>(CE))
Nullability =
getTypeNullability(ECE->getTypeInfoAsWritten()->getTypeLoc(),
State.Lattice.defaults());
else
Nullability = unspecifiedNullability(CE);
// Despite the name `NullToPointer`, the destination type of the cast
// may be `nullptr_t` (which is, itself, not a pointer type).
if (!CE->getType()->isNullPtrType())
Nullability.front() = NullabilityKind::Nullable;
return Nullability;
}
// Pointers out of thin air, who knows?
case CK_IntegralToPointer:
return unspecifiedNullability(CE);
// Decayed objects are never null.
case CK_ArrayToPointerDecay:
case CK_FunctionToPointerDecay:
return prepend(NullabilityKind::NonNull,
getNullabilityForChild(CE->getSubExpr(), State));
// Despite its name, the result type of `BuiltinFnToFnPtr` is a function,
// not a function pointer, so nullability doesn't change.
case CK_BuiltinFnToFnPtr:
return getNullabilityForChild(CE->getSubExpr(), State);
// TODO: what is our model of member pointers?
case CK_BaseToDerivedMemberPointer:
case CK_DerivedToBaseMemberPointer:
case CK_NullToMemberPointer:
case CK_ReinterpretMemberPointer:
case CK_ToUnion: // and unions?
return unspecifiedNullability(CE);
// TODO: Non-C/C++ constructs, do we care about these?
case CK_CPointerToObjCPointerCast:
case CK_ObjCObjectLValueCast:
case CK_MatrixCast:
case CK_VectorSplat:
case CK_BlockPointerToObjCPointerCast:
case CK_AnyPointerToBlockPointerCast:
case CK_ARCProduceObject:
case CK_ARCConsumeObject:
case CK_ARCReclaimReturnedObject:
case CK_ARCExtendBlockObject:
case CK_CopyAndAutoreleaseBlockObject:
case CK_ZeroToOCLOpaqueType:
case CK_IntToOCLSampler:
case CK_HLSLVectorTruncation:
case CK_HLSLArrayRValue:
return unspecifiedNullability(CE);
case CK_Dependent:
CHECK(false) << "Shouldn't see dependent casts here?";
}
});
}
void transferType_MaterializeTemporaryExpr(
absl::Nonnull<const MaterializeTemporaryExpr *> MTE,
const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(MTE, State, [&]() {
return getNullabilityForChild(MTE->getSubExpr(), State);
});
}
void transferType_CXXBindTemporaryExpr(
const CXXBindTemporaryExpr *BTE, const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(BTE, State, [&]() {
return getNullabilityForChild(BTE->getSubExpr(), State);
});
}
void transferType_CopyOrMoveConstruct(
const CXXConstructExpr *CCE, const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(CCE, State, [&]() {
return getNullabilityForChild(CCE->getArg(0), State);
});
}
void transferType_CallExpr(absl::Nonnull<const CallExpr *> CE,
const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(CE, State, [&]() {
if (auto ID = CE->getBuiltinCallee();
(ID == Builtin::BIforward || ID == Builtin::BImove) &&
CE->getNumArgs() == 1) {
return getNullabilityForChild(CE->getArg(0), State);
}
TypeNullability CalleeNullability =
getNullabilityForChild(CE->getCallee(), State);
ArrayRef ResultNullability = CalleeNullability;
if (CE->getCallee()->getType()->isPointerType()) // Callee is usually fptr.
ResultNullability = ResultNullability.drop_front();
// Return value nullability is at the front of the function type.
ResultNullability =
ResultNullability.take_front(countPointersInType(CE->getType()));
return ResultNullability.vec();
});
}
void transferType_UnaryOperator(
absl::Nonnull<const UnaryOperator *> UO, const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(UO, State, [&]() -> TypeNullability {
switch (UO->getOpcode()) {
case UO_AddrOf:
return prepend(NullabilityKind::NonNull,
getNullabilityForChild(UO->getSubExpr(), State));
case UO_Deref:
return ArrayRef(getNullabilityForChild(UO->getSubExpr(), State))
.drop_front()
.vec();
case UO_PostInc:
case UO_PostDec:
case UO_PreInc:
case UO_PreDec:
case UO_Plus:
case UO_Minus:
case UO_Not:
case UO_LNot:
case UO_Real:
case UO_Imag:
case UO_Extension:
return getNullabilityForChild(UO->getSubExpr(), State);
case UO_Coawait:
// TODO: work out what to do here!
return unspecifiedNullability(UO);
}
});
}
void transferType_BinaryOperator(
absl::Nonnull<const BinaryOperator *> BO,
const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(BO, State, [&]() -> TypeNullability {
switch (BO->getOpcode()) {
case BO_PtrMemD:
case BO_PtrMemI:
// TODO: pointers-to-member should really have nullability vectors
return unspecifiedNullability(BO);
case BO_Assign:
case BO_Comma:
return getNullabilityForChild(BO->getRHS(), State);
default:
// No other built-in binary operators can be pointer-valued
return unspecifiedNullability(BO);
}
});
}
void transferType_NewExpr(absl::Nonnull<const CXXNewExpr *> NE,
const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(NE, State, [&]() {
TypeNullability ObjectNullability =
getTypeNullability(NE->getAllocatedTypeSourceInfo()->getTypeLoc(),
State.Lattice.defaults());
return prepend(NE->shouldNullCheckAllocation() ? NullabilityKind::Nullable
: NullabilityKind::NonNull,
ObjectNullability);
});
}
void transferType_ArraySubscriptExpr(
absl::Nonnull<const ArraySubscriptExpr *> ASE,
const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(ASE, State, [&]() {
auto &BaseNullability = getNullabilityForChild(ASE->getBase(), State);
QualType BaseType = ASE->getBase()->getType();
CHECK(isSupportedRawPointerType(BaseType) || BaseType->isVectorType());
return isSupportedRawPointerType(BaseType)
? ArrayRef(BaseNullability).slice(1).vec()
: BaseNullability;
});
}
void transferType_ThisExpr(absl::Nonnull<const CXXThisExpr *> TE,
const MatchFinder::MatchResult &MR,
TransferState<PointerNullabilityLattice> &State) {
computeNullability(TE, State, [&]() {
// If the current class is an instantiation, we can't assume any particular
// nullability of its arguments.
TypeNullability Result = unspecifiedNullability(TE);
Result.front() = NullabilityKind::NonNull;
return Result;
});
}
auto buildTypeTransferer() {
return CFGMatchSwitchBuilder<TransferState<PointerNullabilityLattice>>()
.CaseOfCFGStmt<DeclRefExpr>(ast_matchers::declRefExpr(),
transferType_DeclRefExpr)
.CaseOfCFGStmt<MemberExpr>(ast_matchers::memberExpr(),
transferType_MemberExpr)
.CaseOfCFGStmt<CastExpr>(ast_matchers::castExpr(), transferType_CastExpr)
.CaseOfCFGStmt<MaterializeTemporaryExpr>(
ast_matchers::materializeTemporaryExpr(),
transferType_MaterializeTemporaryExpr)
.CaseOfCFGStmt<CXXBindTemporaryExpr>(ast_matchers::cxxBindTemporaryExpr(),
transferType_CXXBindTemporaryExpr)
.CaseOfCFGStmt<CallExpr>(ast_matchers::callExpr(), transferType_CallExpr)
.CaseOfCFGStmt<UnaryOperator>(ast_matchers::unaryOperator(),
transferType_UnaryOperator)
.CaseOfCFGStmt<BinaryOperator>(ast_matchers::binaryOperator(),
transferType_BinaryOperator)
.CaseOfCFGStmt<CXXNewExpr>(ast_matchers::cxxNewExpr(),
transferType_NewExpr)
.CaseOfCFGStmt<ArraySubscriptExpr>(ast_matchers::arraySubscriptExpr(),
transferType_ArraySubscriptExpr)
.CaseOfCFGStmt<CXXThisExpr>(ast_matchers::cxxThisExpr(),
transferType_ThisExpr)
.CaseOfCFGStmt<CXXConstructExpr>(
ast_matchers::cxxConstructExpr(
ast_matchers::argumentCountIs(1),
ast_matchers::hasDeclaration(ast_matchers::cxxConstructorDecl(
anyOf(ast_matchers::isCopyConstructor(),
ast_matchers::isMoveConstructor())))),
transferType_CopyOrMoveConstruct)
.Build();
}
auto buildValueTransferer() {
// The value transfer functions must establish:
// - if we're transferring over an Expr
// - and the Expr has a supported pointer type
// - and the Expr's value is modeled by the framework (or this analysis)
// - then the PointerValue has nullability properties (is_null/from_nullable)
return CFGMatchSwitchBuilder<TransferState<PointerNullabilityLattice>>()
// Handles initialization of the null states of pointers.
.CaseOfCFGStmt<Expr>(isAddrOf(), transferValue_NotNullPointer)
// TODO(mboehme): I believe we should be able to move handling of null
// pointers to the non-flow-sensitive part of the analysis.
.CaseOfCFGStmt<Expr>(isNullPointerLiteral(), transferValue_NullPointer)
.CaseOfCFGStmt<CXXScalarValueInitExpr>(isRawPointerValueInit(),
transferValue_NullPointer)
.CaseOfCFGStmt<CXXConstructExpr>(isSmartPointerConstructor(),
transferValue_SmartPointerConstructor)
.CaseOfCFGStmt<CXXOperatorCallExpr>(isSmartPointerOperatorCall("="),
transferValue_SmartPointerAssignment)
.CaseOfCFGStmt<CXXMemberCallExpr>(isSmartPointerMethodCall("release"),
transferValue_SmartPointerReleaseCall)
.CaseOfCFGStmt<CXXMemberCallExpr>(isSmartPointerMethodCall("reset"),
transferValue_SmartPointerResetCall)
.CaseOfCFGStmt<CXXMemberCallExpr>(
isSmartPointerMethodCall("swap"),
transferValue_SmartPointerMemberSwapCall)
.CaseOfCFGStmt<CallExpr>(isSmartPointerFreeSwapCall(),
transferValue_SmartPointerFreeSwapCall)
.CaseOfCFGStmt<CXXMemberCallExpr>(isSmartPointerMethodCall("get"),
transferValue_SmartPointerGetCall)
.CaseOfCFGStmt<CXXMemberCallExpr>(
isSmartPointerBoolConversionCall(),
transferValue_SmartPointerBoolConversionCall)
.CaseOfCFGStmt<CXXOperatorCallExpr>(
isSmartPointerOperatorCall("*"),
transferValue_SmartPointerOperatorStar)
.CaseOfCFGStmt<CXXOperatorCallExpr>(
isSmartPointerOperatorCall("->"),
transferValue_SmartPointerOperatorArrow)
.CaseOfCFGStmt<CallExpr>(isSmartPointerFactoryCall(),
transferValue_SmartPointerFactoryCall)
.CaseOfCFGStmt<CXXOperatorCallExpr>(
isSmartPointerComparisonOpCall(),
transferValue_SmartPointerComparisonOpCall)
.CaseOfCFGStmt<CallExpr>(isSharedPtrCastCall(),
transferValue_SharedPtrCastCall)
.CaseOfCFGStmt<CXXMemberCallExpr>(isWeakPtrLockCall(),
transferValue_WeakPtrLockCall)
.CaseOfCFGStmt<CXXMemberCallExpr>(isSupportedPointerAccessorCall(),
transferValue_AccessorCall)
.CaseOfCFGStmt<CXXMemberCallExpr>(isZeroParamConstMemberCall(),
transferValue_ConstMemberCall)
.CaseOfCFGStmt<CXXOperatorCallExpr>(
isOptionalOperatorArrowCall(),
transferValue_OptionalOperatorArrowCall)
.CaseOfCFGStmt<CXXMemberCallExpr>(isNonConstMemberCall(),
transferValue_NonConstMemberCall)
.CaseOfCFGStmt<CXXOperatorCallExpr>(
isNonConstMemberOperatorCall(),
transferValue_NonConstMemberOperatorCall)
.CaseOfCFGStmt<CallExpr>(ast_matchers::callExpr(), transferValue_CallExpr)
.CaseOfCFGStmt<MemberExpr>(isSmartPointerArrowMemberExpr(),
transferValue_SmartPointerArrowMemberExpr)
.CaseOfCFGStmt<Expr>(isPointerExpr(), transferValue_Pointer)
// Handles comparison between 2 pointers.
.CaseOfCFGStmt<BinaryOperator>(isPointerCheckBinOp(),
transferValue_NullCheckComparison)
// Handles checking of pointer as boolean.
.CaseOfCFGStmt<Expr>(isImplicitCastPointerToBool(),
transferValue_NullCheckImplicitCastPtrToBool)
.Build();
}
// Ensure that all expressions of smart pointer type have an underlying
// raw pointer initialized from the type nullability.
void ensureSmartPointerInitialized(
const CFGElement &Elt, TransferState<PointerNullabilityLattice> &State) {
auto S = Elt.getAs<CFGStmt>();
if (!S) return;
auto *E = dyn_cast<Expr>(S->getStmt());
if (E == nullptr || !isSupportedSmartPointerType(E->getType())) return;
initSmartPointerForExpr(E, State);
auto *SmartPtrLoc = E->isGLValue() ? State.Env.get<RecordStorageLocation>(*E)
: &State.Env.getResultObjectLocation(*E);
if (SmartPtrLoc == nullptr) return;
StorageLocation &PtrLoc = SmartPtrLoc->getSyntheticField(PtrField);
unpackPointerValue(PtrLoc, State.Env);
}
} // namespace
PointerNullabilityAnalysis::PointerNullabilityAnalysis(
ASTContext &Context, Environment &Env, const NullabilityPragmas &Pragmas)
: DataflowAnalysis<PointerNullabilityAnalysis, PointerNullabilityLattice>(
Context),
TypeTransferer(buildTypeTransferer()),
ValueTransferer(buildValueTransferer()) {
Env.getDataflowAnalysisContext().setSyntheticFieldCallback(
[](QualType Ty) -> llvm::StringMap<QualType> {
QualType RawPointerTy = underlyingRawPointerType(Ty, AS_private);
if (RawPointerTy.isNull()) return {};
return {{PtrField, RawPointerTy}};
});
NFS.Defaults = TypeNullabilityDefaults(Context, Pragmas);
}
PointerTypeNullability PointerNullabilityAnalysis::assignNullabilityVariable(
absl::Nonnull<const ValueDecl *> D, dataflow::Arena &A) {
auto [It, Inserted] = NFS.DeclTopLevelNullability.try_emplace(
cast<ValueDecl>(D->getCanonicalDecl()));
if (Inserted) It->second = PointerTypeNullability::createSymbolic(A);
return It->second;
}
void PointerNullabilityAnalysis::transfer(const CFGElement &Elt,
PointerNullabilityLattice &Lattice,
Environment &Env) {
TransferState<PointerNullabilityLattice> State(Lattice, Env);
TypeTransferer(Elt, getASTContext(), State);
ValueTransferer(Elt, getASTContext(), State);
ensureRawPointerHasValue(Elt, Env);
ensureSmartPointerInitialized(Elt, State);
}
static absl::Nullable<const Formula *> mergeFormulas(
absl::Nullable<const Formula *> Bool1, const Environment &Env1,
absl::Nullable<const Formula *> Bool2, const Environment &Env2,
Environment &MergedEnv) {
if (Bool1 == Bool2) {
return Bool1;
}
if (Bool1 == nullptr || Bool2 == nullptr) return nullptr;
auto &A = MergedEnv.arena();
// If `Bool1` and `Bool2` is constrained to the same true / false value, that
// can serve as the return value - this simplifies the flow condition tracked
// in `MergedEnv`. Otherwise, information about which path was taken is used
// to associate the return value with `Bool1` and `Bool2`.
if (Env1.proves(*Bool1)) {
if (Env2.proves(*Bool2)) {
return &A.makeLiteral(true);
}
} else if (Env1.proves(A.makeNot(*Bool1)) && Env2.proves(A.makeNot(*Bool2))) {
return &A.makeLiteral(false);
}
auto &MergedBool = A.makeAtomRef(A.makeAtom());
// TODO(b/233582219): Flow conditions are not necessarily mutually
// exclusive, a fix is in order: https://reviews.llvm.org/D130270. Update
// this section when the patch is commited.
auto FC1 = Env1.getFlowConditionToken();
auto FC2 = Env2.getFlowConditionToken();
MergedEnv.assume(A.makeOr(
A.makeAnd(A.makeAtomRef(FC1), A.makeEquals(MergedBool, *Bool1)),
A.makeAnd(A.makeAtomRef(FC2), A.makeEquals(MergedBool, *Bool2))));
return &MergedBool;
}
void PointerNullabilityAnalysis::join(QualType Type, const Value &Val1,
const Environment &Env1,
const Value &Val2,
const Environment &Env2, Value &MergedVal,
Environment &MergedEnv) {
if (!isSupportedRawPointerType(Type)) return;
if (!hasPointerNullState(cast<PointerValue>(Val1)) ||
!hasPointerNullState(cast<PointerValue>(Val2))) {
// It can happen that we merge pointers without null state, if either or
// both of the pointers has not appeared in an expression (and has not
// otherwise been initialized with nullability properties) before the merge.
// We return true to keep the `MergedVal` produced by the framework. When
// the merged value appears in an expression, `tranferValue_Pointer` will
// take care of initializing it with nullability properties.
return;
}
auto Nullability1 = getPointerNullState(cast<PointerValue>(Val1));
auto Nullability2 = getPointerNullState(cast<PointerValue>(Val2));
auto *FromNullable =
mergeFormulas(Nullability1.FromNullable, Env1, Nullability2.FromNullable,
Env2, MergedEnv);
auto *Null = mergeFormulas(Nullability1.IsNull, Env1, Nullability2.IsNull,
Env2, MergedEnv);
initPointerNullState(cast<PointerValue>(MergedVal),
MergedEnv.getDataflowAnalysisContext(),
{FromNullable, Null});
}
ComparisonResult PointerNullabilityAnalysis::compare(QualType Type,
const Value &Val1,
const Environment &Env1,
const Value &Val2,
const Environment &Env2) {
if (const auto *PointerVal1 = dyn_cast<PointerValue>(&Val1)) {
const auto &PointerVal2 = cast<PointerValue>(Val2);
if (&PointerVal1->getPointeeLoc() != &PointerVal2.getPointeeLoc())
return ComparisonResult::Different;
if (hasPointerNullState(*PointerVal1) != hasPointerNullState(PointerVal2))
return ComparisonResult::Different;
if (!hasPointerNullState(*PointerVal1)) return ComparisonResult::Same;
auto Nullability1 = getPointerNullState(*PointerVal1);
auto Nullability2 = getPointerNullState(PointerVal2);
// Ideally, we would be checking for equivalence of formulas, but that's
// expensive, so we simply check for identity instead.
return Nullability1.FromNullable == Nullability2.FromNullable &&
Nullability1.IsNull == Nullability2.IsNull
? ComparisonResult::Same
: ComparisonResult::Different;
}
return ComparisonResult::Unknown;
}
// Returns the result of widening a nullability property.
// `Prev` is the formula in the previous iteration, `Cur` is the formula in the
// current iteration.
// Returns `nullptr` (Top), if `Prev` is already Top or `Prev` and `Cur` cannot
// be proven equivalent. Otherwise, (`Prev` and `Cur` are provably equivalent),
// returns `Cur`. Returns `Cur`, if `Prev` is equivalent to `Cur`. Otherwise,
// returns `Top`.
static std::pair<absl::Nullable<const Formula *>, LatticeEffect>
widenNullabilityProperty(absl::Nullable<const Formula *> Prev,
const Environment &PrevEnv,
absl::Nullable<const Formula *> Cur,
Environment &CurEnv) {
if (Prev == Cur) return {Cur, LatticeEffect::Unchanged};
if (Prev == nullptr) return {nullptr, LatticeEffect::Unchanged};
if (Cur == nullptr) return {nullptr, LatticeEffect::Changed};
Arena &A = CurEnv.arena();
// Note that either of `PrevEnv` or `CurEnv` may be self-contradictory
// (unsatisfiable). So, we're careful to check only that both are consistent
// in their conclusions. We do not draw conclusions from them independently.
// For example, if PrevEnv => Prev`, we do *not* conclude that
// `PrevEnv => !Prev` is false, and use that to optimize the branches below.
if ((PrevEnv.proves(*Prev) && CurEnv.proves(*Cur)) ||
(PrevEnv.proves(A.makeNot(*Prev)) && CurEnv.proves(A.makeNot(*Cur))))
return {Cur, LatticeEffect::Unchanged};
return {nullptr, LatticeEffect::Changed};
}
std::optional<WidenResult> PointerNullabilityAnalysis::widen(
QualType Type, Value &Prev, const Environment &PrevEnv, Value &Current,
Environment &CurrentEnv) {
auto *PrevPtr = dyn_cast<PointerValue>(&Prev);
if (PrevPtr == nullptr) return std::nullopt;
// Widen pointers (when different) to a pointer with a "top" storage location.
auto &CurPtr = cast<PointerValue>(Current);
DataflowAnalysisContext &DACtx = CurrentEnv.getDataflowAnalysisContext();
assert(&PrevEnv.getDataflowAnalysisContext() == &DACtx);
bool LocUnchanged = &PrevPtr->getPointeeLoc() == &CurPtr.getPointeeLoc();
// If either `PrevPtr` or `CurPtr` lack null state, we consider the modeled
// value to be outside the scope. TODO: we should consider all pointers in
// scope and handle this case accordingly. We will widen the pointer location,
// but (always) return a pointer value with no null state.
if (!hasPointerNullState(*PrevPtr) || !hasPointerNullState(CurPtr))
return std::nullopt;
auto [FromNullablePrev, NullPrev] = getPointerNullState(*PrevPtr);
auto [FromNullableCur, NullCur] = getPointerNullState(CurPtr);
auto [FromNullableWidened, FNWEffect] = widenNullabilityProperty(
FromNullablePrev, PrevEnv, FromNullableCur, CurrentEnv);
auto [NullWidened, NWEffect] =
widenNullabilityProperty(NullPrev, PrevEnv, NullCur, CurrentEnv);
if (LocUnchanged && FNWEffect == LatticeEffect::Unchanged &&
NWEffect == LatticeEffect::Unchanged)
return WidenResult{&CurPtr, LatticeEffect::Unchanged};
// Widen the loc if needed.
StorageLocation *WidenedLoc =
LocUnchanged
? &CurPtr.getPointeeLoc()
: &getTopStorageLocation(DACtx, CurPtr.getPointeeLoc().getType());
// Construct the new, widened value.
auto &WidenedPtr = CurrentEnv.create<PointerValue>(*WidenedLoc);
initPointerNullState(WidenedPtr, CurrentEnv.getDataflowAnalysisContext(),
{FromNullableWidened, NullWidened});
LatticeEffect Effect = (WidenedLoc == &PrevPtr->getPointeeLoc() &&
FNWEffect == LatticeEffect::Unchanged &&
NWEffect == LatticeEffect::Unchanged)
? LatticeEffect::Unchanged
: LatticeEffect::Changed;
return WidenResult{&WidenedPtr, Effect};
}
StorageLocation &PointerNullabilityAnalysis::getTopStorageLocation(
DataflowAnalysisContext &DACtx, QualType Ty) {
auto [It, Inserted] = TopStorageLocations.try_emplace(Ty, nullptr);
if (Inserted) It->second = &DACtx.createStorageLocation(Ty);
return *It->second;
}
} // namespace clang::tidy::nullability