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bazel / crubit / 51b749b38539718a4a755874fe4bf6f28da2c1fc / . / nullability / inference / collect_evidence.cc
blob: 1bbf5e989aaf5a0edb263d202f098307fcf91792 [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/inference/collect_evidence.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <memory>
#include <optional>
#include <string>
#include <string_view>
#include <utility>
#include <vector>
#include "absl/base/nullability.h"
#include "absl/container/flat_hash_map.h"
#include "absl/log/check.h"
#include "nullability/ast_helpers.h"
#include "nullability/inference/inferable.h"
#include "nullability/inference/inference.proto.h"
#include "nullability/inference/slot_fingerprint.h"
#include "nullability/macro_arg_capture.h"
#include "nullability/pointer_nullability.h"
#include "nullability/pointer_nullability_analysis.h"
#include "nullability/pointer_nullability_lattice.h"
#include "nullability/pragma.h"
#include "nullability/type_nullability.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Attr.h"
#include "clang/AST/Attrs.inc"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclBase.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclGroup.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/OperationKinds.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/AST/Stmt.h"
#include "clang/AST/Type.h"
#include "clang/AST/TypeLoc.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/FlowSensitive/ASTOps.h"
#include "clang/Analysis/FlowSensitive/AdornedCFG.h"
#include "clang/Analysis/FlowSensitive/Arena.h"
#include "clang/Analysis/FlowSensitive/DataflowAnalysis.h"
#include "clang/Analysis/FlowSensitive/DataflowAnalysisContext.h"
#include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
#include "clang/Analysis/FlowSensitive/Formula.h"
#include "clang/Analysis/FlowSensitive/Solver.h"
#include "clang/Analysis/FlowSensitive/StorageLocation.h"
#include "clang/Analysis/FlowSensitive/Value.h"
#include "clang/Analysis/FlowSensitive/WatchedLiteralsSolver.h"
#include "clang/Basic/Builtins.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/OperatorKinds.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/Specifiers.h"
#include "clang/Index/USRGeneration.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/FunctionExtras.h"
#include "llvm/ADT/STLFunctionalExtras.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
namespace clang::tidy::nullability {
using ::clang::dataflow::DataflowAnalysisContext;
using ::clang::dataflow::Environment;
using ::clang::dataflow::Formula;
using ::clang::dataflow::RecordInitListHelper;
using ::clang::dataflow::WatchedLiteralsSolver;
using ConcreteNullabilityCache =
absl::flat_hash_map<const Decl *,
std::optional<const PointerTypeNullability>>;
std::string_view getOrGenerateUSR(USRCache &Cache, const Decl &Decl) {
auto [It, Inserted] = Cache.try_emplace(&Decl);
if (Inserted) {
llvm::SmallString<128> USR;
if (!index::generateUSRForDecl(&Decl, USR)) It->second = USR.str();
}
return It->second;
}
static llvm::DenseSet<const CXXMethodDecl *> getOverridden(
const CXXMethodDecl *Derived) {
llvm::DenseSet<const CXXMethodDecl *> Overridden;
for (const CXXMethodDecl *Base : Derived->overridden_methods()) {
Overridden.insert(Base);
for (const CXXMethodDecl *BaseOverridden : getOverridden(Base)) {
Overridden.insert(BaseOverridden);
}
}
return Overridden;
}
/// Shared base class for visitors that walk the AST for evidence collection
/// purposes, to ensure they see the same nodes.
template <typename Derived>
struct EvidenceLocationsWalker : public RecursiveASTVisitor<Derived> {
// We do want to see concrete code, including function instantiations.
bool shouldVisitTemplateInstantiations() const { return true; }
// In order to collect from more default member initializers, we do want to
// see defaulted default constructors, which are implicitly-defined
// functions whether the declaration is implicit or explicit. We also want
// to see lambda bodies in the form of operator() definitions that are not
// themselves implicit but show up in an implicit context.
bool shouldVisitImplicitCode() const { return true; }
};
using VirtualMethodOverridesMap =
absl::flat_hash_map<const CXXMethodDecl *,
llvm::DenseSet<const CXXMethodDecl *>>;
/// Collect a map from virtual methods to a set of their overrides.
static VirtualMethodOverridesMap getVirtualMethodOverrides(ASTContext &Ctx) {
struct Walker : public EvidenceLocationsWalker<Walker> {
VirtualMethodOverridesMap Out;
bool VisitCXXMethodDecl(const CXXMethodDecl *MD) {
if (MD->isVirtual()) {
for (const auto *O : getOverridden(MD)) {
Out[O].insert(MD);
}
}
return true;
}
};
Walker W;
W.TraverseAST(Ctx);
return std::move(W.Out);
}
namespace {
enum VirtualMethodEvidenceFlowDirection {
kFromBaseToDerived,
kFromDerivedToBase,
kBoth,
};
} // namespace
static VirtualMethodEvidenceFlowDirection getFlowDirection(Evidence::Kind Kind,
bool ForReturnSlot) {
switch (Kind) {
case Evidence::ANNOTATED_NONNULL:
case Evidence::UNCHECKED_DEREFERENCE:
case Evidence::NONNULL_ARGUMENT:
case Evidence::NONNULL_RETURN:
case Evidence::ASSIGNED_TO_NONNULL:
case Evidence::ABORT_IF_NULL:
case Evidence::ARITHMETIC:
case Evidence::GCC_NONNULL_ATTRIBUTE:
// Evidence pointing toward Unknown is only used to prevent Nonnull
// inferences; it cannot override Nullable. So propagate it in the same
// direction we do for Nonnull-pointing evidence.
case Evidence::ANNOTATED_UNKNOWN:
case Evidence::UNKNOWN_ARGUMENT:
case Evidence::UNKNOWN_RETURN:
return ForReturnSlot ? kFromBaseToDerived : kFromDerivedToBase;
case Evidence::ANNOTATED_NULLABLE:
case Evidence::NULLABLE_ARGUMENT:
case Evidence::NULLABLE_RETURN:
case Evidence::ASSIGNED_TO_MUTABLE_NULLABLE:
case Evidence::ASSIGNED_FROM_NULLABLE:
case Evidence::NULLPTR_DEFAULT_MEMBER_INITIALIZER:
return ForReturnSlot ? kFromDerivedToBase : kFromBaseToDerived;
case Evidence::NULLABLE_REFERENCE_RETURN:
case Evidence::NONNULL_REFERENCE_RETURN:
case Evidence::UNKNOWN_REFERENCE_RETURN:
case Evidence::NULLABLE_REFERENCE_ARGUMENT:
case Evidence::NONNULL_REFERENCE_ARGUMENT:
case Evidence::UNKNOWN_REFERENCE_ARGUMENT:
return kBoth;
}
}
static llvm::DenseSet<const CXXMethodDecl *>
getAdditionalTargetsForVirtualMethod(
const CXXMethodDecl *MD, Evidence::Kind Kind, bool ForReturnSlot,
const VirtualMethodOverridesMap &OverridesMap) {
VirtualMethodEvidenceFlowDirection FlowDirection =
getFlowDirection(Kind, ForReturnSlot);
switch (FlowDirection) {
case kFromBaseToDerived:
if (auto It = OverridesMap.find(MD); It != OverridesMap.end())
return It->second;
return {};
case kFromDerivedToBase:
return getOverridden(MD);
case kBoth:
llvm::DenseSet<const CXXMethodDecl *> Results = getOverridden(MD);
if (auto It = OverridesMap.find(MD); It != OverridesMap.end())
Results.insert(It->second.begin(), It->second.end());
return Results;
}
}
llvm::unique_function<EvidenceEmitter> evidenceEmitter(
llvm::unique_function<void(const Evidence &) const> Emit,
USRCache &USRCache, ASTContext &Ctx) {
class EvidenceEmitterImpl {
public:
EvidenceEmitterImpl(
llvm::unique_function<void(const Evidence &) const> Emit,
nullability::USRCache &USRCache, ASTContext &Ctx)
: Emit(std::move(Emit)),
USRCache(USRCache),
OverridesMap(getVirtualMethodOverrides(Ctx)) {}
void operator()(const Decl &Target, Slot S, Evidence::Kind Kind,
SourceLocation Loc) const {
CHECK(isInferenceTarget(Target))
<< "Evidence emitted for a Target which is not an inference target: "
<< (dyn_cast<NamedDecl>(&Target)
? dyn_cast<NamedDecl>(&Target)->getQualifiedNameAsString()
: "not a named decl");
Evidence E;
E.set_slot(S);
E.set_kind(Kind);
std::string_view USR = getOrGenerateUSR(USRCache, Target);
if (USR.empty()) return; // Can't emit without a USR
E.mutable_symbol()->set_usr(USR);
// TODO: make collecting and propagating location information optional?
auto &SM =
Target.getDeclContext()->getParentASTContext().getSourceManager();
// TODO: are macro locations actually useful enough for debugging?
// we could leave them out, and make room for non-macro samples.
if (Loc = SM.getFileLoc(Loc); Loc.isValid())
E.set_location(Loc.printToString(SM));
Emit(E);
// Virtual methods and their overrides constrain each other's
// nullabilities, so propagate evidence in the appropriate direction based
// on the evidence kind and whether the evidence is for the return type or
// a parameter type.
if (auto *MD = dyn_cast<CXXMethodDecl>(&Target); MD && MD->isVirtual()) {
for (const auto *O : getAdditionalTargetsForVirtualMethod(
MD, Kind, S == SLOT_RETURN_TYPE, OverridesMap)) {
USR = getOrGenerateUSR(USRCache, *O);
if (USR.empty()) return; // Can't emit without a USR
E.mutable_symbol()->set_usr(USR);
Emit(E);
}
}
}
private:
llvm::unique_function<void(const Evidence &) const> Emit;
nullability::USRCache &USRCache;
const VirtualMethodOverridesMap OverridesMap;
};
return EvidenceEmitterImpl(std::move(Emit), USRCache, Ctx);
}
namespace {
class InferableSlot {
public:
InferableSlot(PointerTypeNullability Nullability, Slot Slot, const Decl &Decl)
: SymbolicNullability(Nullability),
TargetSlot(Slot),
InferenceTarget(Decl) {}
const PointerTypeNullability &getSymbolicNullability() const {
return SymbolicNullability;
}
Slot getTargetSlot() const { return TargetSlot; }
const Decl &getInferenceTarget() const { return InferenceTarget; }
private:
const PointerTypeNullability SymbolicNullability;
const Slot TargetSlot;
const Decl &InferenceTarget;
};
} // namespace
/// If Stmt is a dereference, returns its target and location.
static std::pair<const Expr *, SourceLocation> describeDereference(
const Stmt &Stmt) {
if (auto *Op = dyn_cast<UnaryOperator>(&Stmt);
Op && Op->getOpcode() == UO_Deref) {
return {Op->getSubExpr(), Op->getOperatorLoc()};
}
if (auto *ME = dyn_cast<MemberExpr>(&Stmt); ME && ME->isArrow()) {
return {ME->getBase(), ME->getOperatorLoc()};
}
// pointers to members; at the time of writing, they aren't a supported
// pointer type, so this is a no-op.
if (const auto *BO = dyn_cast<BinaryOperator>(&Stmt);
BO && (BO->getOpcode() == clang::BinaryOperatorKind::BO_PtrMemD ||
BO->getOpcode() == clang::BinaryOperatorKind::BO_PtrMemI)) {
return {BO->getRHS(), BO->getOperatorLoc()};
}
if (const auto *OCE = dyn_cast<CXXOperatorCallExpr>(&Stmt);
OCE && OCE->getOperator() == clang::OO_Star &&
isSupportedSmartPointerType(OCE->getArg(0)->getType())) {
return {OCE->getArg(0), OCE->getOperatorLoc()};
}
return {nullptr, SourceLocation()};
}
/// Inferable slots are nullability slots not explicitly annotated in source
/// code that we are currently capable of handling. This returns a boolean
/// constraint representing these slots having a) the nullability inferred from
/// the previous round for this slot or b) Unknown nullability if no inference
/// was made in the previous round or there was no previous round.
static const Formula &getInferableSlotsAsInferredOrUnknownConstraint(
const std::vector<InferableSlot> &InferableSlots, USRCache &USRCache,
const PreviousInferences &PreviousInferences, dataflow::Arena &A) {
const Formula *Constraint = &A.makeLiteral(true);
for (auto &IS : InferableSlots) {
std::string_view USR = getOrGenerateUSR(USRCache, IS.getInferenceTarget());
SlotFingerprint Fingerprint = fingerprint(USR, IS.getTargetSlot());
auto Nullability = IS.getSymbolicNullability();
const Formula &Nullable = PreviousInferences.Nullable.contains(Fingerprint)
? Nullability.isNullable(A)
: A.makeNot(Nullability.isNullable(A));
const Formula &Nonnull = PreviousInferences.Nonnull.contains(Fingerprint)
? Nullability.isNonnull(A)
: A.makeNot(Nullability.isNonnull(A));
Constraint = &A.makeAnd(*Constraint, A.makeAnd(Nullable, Nonnull));
}
return *Constraint;
}
static void overrideNullability(const ValueDecl &D,
const PointerNullabilityLattice &Lattice,
TypeNullability &N) {
if (N.empty()) {
// We expect this not to be the case, but not to a crash-worthy level, so
// just log if it is.
llvm::errs() << "Nullability for type " << D.getType().getAsString();
if (auto *ND = dyn_cast<clang::NamedDecl>(&D)) {
llvm::errs() << " for Decl named " << ND->getQualifiedNameAsString();
}
llvm::errs() << " requested with overrides, but is an empty vector.\n";
} else {
Lattice.overrideNullabilityFromDecl(&D, N);
}
}
static TypeNullability getNullabilityAnnotationsFromDeclAndOverrides(
const ValueDecl &D, const PointerNullabilityLattice &Lattice) {
TypeNullability N = getTypeNullability(D, Lattice.defaults());
overrideNullability(D, Lattice, N);
return N;
}
static TypeNullability getReturnTypeNullabilityAnnotations(
const FunctionDecl &D, const TypeNullabilityDefaults &Defaults) {
// Use the QualType, FileID overload of getTypeNullability for return types,
// because of complexity around the following cases:
//
// The return TypeLoc for `auto`-returning functions contains an undeduced
// `auto` type, even if the `auto` has been deduced. See
// https://github.com/llvm/llvm-project/issues/42259 for more.
//
// FunctionDecls with top-level TypeLocs that are not simple
// FunctionTypeLoc, such as those with attributes, would need excavation of
// the function's FunctionTypeLoc before being able to retrieve the return
// TypeLoc.
return getTypeNullability(D.getReturnType(), getGoverningFile(&D), Defaults);
}
static TypeNullability getReturnTypeNullabilityAnnotationsWithOverrides(
const FunctionDecl &D, const PointerNullabilityLattice &Lattice) {
TypeNullability N =
getReturnTypeNullabilityAnnotations(D, Lattice.defaults());
// The FunctionDecl is the key used for overrides for the return
// type. To look up overrides for parameters, we would pass a
// ParmVarDecl to `overrideNullability`.
overrideNullability(D, Lattice, N);
return N;
}
static Evidence::Kind getArgEvidenceKindFromNullability(
NullabilityKind Nullability, bool IsReference) {
switch (Nullability) {
case NullabilityKind::Nullable:
return IsReference ? Evidence::NULLABLE_REFERENCE_ARGUMENT
: Evidence::NULLABLE_ARGUMENT;
case NullabilityKind::NonNull:
return IsReference ? Evidence::NONNULL_REFERENCE_ARGUMENT
: Evidence::NONNULL_ARGUMENT;
default:
return IsReference ? Evidence::UNKNOWN_REFERENCE_ARGUMENT
: Evidence::UNKNOWN_ARGUMENT;
}
}
static std::optional<Evidence::Kind> evidenceKindFromDeclaredNullability(
const TypeNullability &Nullability) {
switch (Nullability.front().concrete()) {
default:
return std::nullopt;
case NullabilityKind::NonNull:
return Evidence::ANNOTATED_NONNULL;
case NullabilityKind::Nullable:
return Evidence::ANNOTATED_NULLABLE;
}
}
static std::optional<Evidence::Kind> evidenceKindFromDeclaredTypeLoc(
TypeLoc Loc, const TypeNullabilityDefaults &Defaults) {
if (!isSupportedPointerType(Loc.getType().getNonReferenceType()))
return std::nullopt;
auto Nullability = getTypeNullability(Loc, Defaults);
return evidenceKindFromDeclaredNullability(Nullability);
}
static std::optional<Evidence::Kind> evidenceKindFromDeclaredReturnType(
const FunctionDecl &D, const TypeNullabilityDefaults &Defaults) {
if (!isSupportedPointerType(D.getReturnType().getNonReferenceType()))
return std::nullopt;
return evidenceKindFromDeclaredNullability(
getReturnTypeNullabilityAnnotations(D, Defaults));
}
static bool isOrIsConstructedFromNullPointerConstant(
absl::Nonnull<const Expr *> E, ASTContext &Ctx) {
if (E->isNullPointerConstant(Ctx, Expr::NPC_ValueDependentIsNotNull) !=
Expr::NPCK_NotNull) {
return true;
}
if (auto *DefaultInit = dyn_cast<CXXDefaultInitExpr>(E)) {
E = DefaultInit->getExpr();
}
const Expr *SubExpr = &dataflow::ignoreCFGOmittedNodes(*E);
if (auto *MaterializeTempExpr = dyn_cast<MaterializeTemporaryExpr>(SubExpr)) {
SubExpr = MaterializeTempExpr->getSubExpr();
}
if (auto *BindTemp = dyn_cast<CXXBindTemporaryExpr>(SubExpr)) {
SubExpr = BindTemp->getSubExpr();
}
auto *CE = dyn_cast<CXXConstructExpr>(SubExpr->IgnoreImpCasts());
if (!CE) return false;
return CE != nullptr && CE->getNumArgs() == 1 &&
CE->getArg(0)->isNullPointerConstant(
Ctx, Expr::NPC_ValueDependentIsNotNull) != Expr::NPCK_NotNull;
}
namespace {
class DefinitionEvidenceCollector {
public:
// Instantiate the class only in this static function, to restrict the
// lifetime of the object, which holds reference parameters.
static void collect(std::vector<InferableSlot> &InferableSlots,
const Formula &InferableSlotsConstraint,
llvm::function_ref<EvidenceEmitter> Emit,
const CFGElement &CFGElem,
const PointerNullabilityLattice &Lattice,
const Environment &Env) {
DefinitionEvidenceCollector Collector(
InferableSlots, InferableSlotsConstraint, Emit, Lattice, Env);
if (auto CFGStmt = CFGElem.getAs<clang::CFGStmt>()) {
const Stmt *S = CFGStmt->getStmt();
if (!S) return;
Collector.fromDereference(*S);
Collector.fromCallExpr(*S);
Collector.fromConstructExpr(*S);
Collector.fromReturn(*S);
Collector.fromAssignment(*S);
Collector.fromArithmetic(*S);
Collector.fromAggregateInitialization(*S);
} else if (auto CFGInit = CFGElem.getAs<clang::CFGInitializer>()) {
Collector.fromCFGInitializer(*CFGInit);
}
}
private:
DefinitionEvidenceCollector(std::vector<InferableSlot> &InferableSlots,
const Formula &InferableSlotsConstraint,
llvm::function_ref<EvidenceEmitter> Emit,
const PointerNullabilityLattice &Lattice,
const Environment &Env)
: InferableSlots(InferableSlots),
InferableSlotsConstraint(InferableSlotsConstraint),
Emit(Emit),
Lattice(Lattice),
Env(Env) {}
/// Records evidence derived from the necessity that `Value` is nonnull.
/// It may be dereferenced, passed as a nonnull param, etc, per
/// `EvidenceKind`.
void mustBeNonnull(const dataflow::PointerValue &Value, SourceLocation Loc,
Evidence::Kind EvidenceKind) {
CHECK(hasPointerNullState(Value))
<< "Value should be the value of an expression. Cannot collect "
"evidence for nonnull-ness if there is no null state.";
auto *IsNull = getPointerNullState(Value).IsNull;
// If `IsNull` is top, we can't infer anything about it.
if (IsNull == nullptr) return;
auto &A = Env.arena();
mustBeTrue(A.makeNot(*IsNull), Loc, EvidenceKind);
}
/// Records evidence for Nonnull-ness derived from the necessity that
/// `MustBeTrue` must be true.
///
/// Does not consider the possibility that the formula can only be proven true
/// by marking a slot Nullable, as this is is not a pattern we have yet seen
/// in practice. This function could easily be extended to do so, though.
void mustBeTrue(const Formula &MustBeTrue, SourceLocation Loc,
Evidence::Kind EvidenceKind) {
auto &A = Env.arena();
// If `Value` is already proven true or false (or both, which indicates
// unsatisfiable flow conditions), collect no evidence.
if (Env.proves(MustBeTrue) || Env.proves(A.makeNot(MustBeTrue))) return;
for (auto &IS : InferableSlots) {
auto &SlotNonnull = IS.getSymbolicNullability().isNonnull(A);
auto &SlotNonnullImpliesFormulaTrue =
A.makeImplies(SlotNonnull, MustBeTrue);
// Don't collect evidence if the implication is true by virtue of
// `SlotNonnull` being false.
//
// In practice, `SlotNonnull` can be made false by a flow condition, and
// marking the slot Nonnull would make that conditioned block dead code.
// Technically, this does make a dereference, etc. "safe", but we'd prefer
// to mark a different slot Nonnull that has a more direct relationship
// with `MustBeTrue`.
//
// e.g. We'd prefer to mark `q` Nonnull rather than `p` in the following:
// ```
// void target(int* p, int* q) {
// if (!p) {
// *q;
// }
// }
// ```
if (Env.allows(SlotNonnull) &&
Env.proves(SlotNonnullImpliesFormulaTrue)) {
Emit(IS.getInferenceTarget(), IS.getTargetSlot(), EvidenceKind, Loc);
return;
}
}
}
void fromDereference(const Stmt &S) {
auto [Target, Loc] = describeDereference(S);
if (!Target || !isSupportedPointerType(Target->getType())) return;
// It is a dereference of a pointer. Now gather evidence from it.
dataflow::PointerValue *DereferencedValue = getPointerValue(Target, Env);
if (!DereferencedValue) return;
mustBeNonnull(*DereferencedValue, Loc, Evidence::UNCHECKED_DEREFERENCE);
}
/// Collect evidence for each of `InferableSlots` if that slot being marked
/// Nullable would imply `Value`'s FromNullable property.
///
/// This function is called when we have reason to believe that `Value` must
/// be Nullable. As we can't directly retrieve the combination of Decl and
/// Slot that corresponds to `Value`'s nullability, we consider each inferable
/// slot and emit evidence for all inferable slots that, if marked Nullable,
/// cause `Value` to be considered explicitly Nullable.
void mustBeMarkedNullable(const dataflow::PointerValue &Value,
SourceLocation Loc, Evidence::Kind EvidenceKind) {
CHECK(hasPointerNullState(Value))
<< "Value should be the value of an expression. Cannot collect "
"evidence for nonnull-ness if there is no null state.";
auto *FromNullable = getPointerNullState(Value).FromNullable;
// If `FromNullable` is top, we can't infer anything about it.
if (FromNullable == nullptr) return;
// If the flow conditions already imply that `Value` is from a Nullable,
// then we don't have any new evidence of a necessary annotation.
if (Env.proves(*FromNullable)) return;
auto &A = Env.arena();
// Otherwise, if an inferable slot being annotated Nullable would imply that
// `Value` is from a Nullable, then we have evidence suggesting that slot
// should be annotated. We collect this evidence for every slot that
// connects in this way to `Value`.
//
// e.g. We should mark both `p` and `q` Nullable in the following:
// ```
// void target(int* p, int* q, bool b) {
// Nullable<int*>& x = b ? p : q;
// ...
// }
// ```
// because at runtime, either `p` or `q` could be taken as a mutable
// reference and later set to nullptr.
for (auto &IS : InferableSlots) {
auto &SlotNullableImpliesValueFromNullable = A.makeImplies(
IS.getSymbolicNullability().isNullable(A), *FromNullable);
if (Env.proves(SlotNullableImpliesValueFromNullable))
Emit(IS.getInferenceTarget(), IS.getTargetSlot(), EvidenceKind, Loc);
}
}
void fromAssignmentToType(QualType Type,
const TypeNullability &TypeNullability,
const dataflow::PointerValue &PointerValue,
SourceLocation ValueLoc) {
// TODO: Account for variance and each layer of nullability when we handle
// more than top-level pointers.
if (TypeNullability.empty()) return;
const PointerTypeNullability &TopLevel = TypeNullability[0];
dataflow::Arena &A = Env.arena();
if (TopLevel.concrete() == NullabilityKind::NonNull ||
(TopLevel.isSymbolic() &&
Env.proves(
A.makeImplies(InferableSlotsConstraint, TopLevel.isNonnull(A))))) {
mustBeNonnull(PointerValue, ValueLoc, Evidence::ASSIGNED_TO_NONNULL);
} else if (!Type.isConstQualified() && Type->isReferenceType() &&
(TopLevel.concrete() == NullabilityKind::Nullable ||
(TopLevel.isSymbolic() &&
Env.proves(A.makeImplies(InferableSlotsConstraint,
TopLevel.isNullable(A)))))) {
mustBeMarkedNullable(PointerValue, ValueLoc,
Evidence::ASSIGNED_TO_MUTABLE_NULLABLE);
}
}
template <typename CallOrConstructExpr>
void fromArgsAndParams(const FunctionDecl &CalleeDecl,
const CallOrConstructExpr &Expr) {
bool CollectEvidenceForCallee = isInferenceTarget(CalleeDecl);
bool CollectEvidenceForCaller = !InferableSlots.empty();
for (ParamAndArgIterator<CallOrConstructExpr> Iter(CalleeDecl, Expr); Iter;
++Iter) {
const auto ParamType = Iter.param().getType().getNonReferenceType();
if (!isSupportedPointerType(ParamType)) continue;
if (!isSupportedPointerType(Iter.arg().getType())) {
// These builtins are declared with pointer type parameters even when
// given a valid argument of type uintptr_t. In this case, there's
// nothing to infer, but also nothing unexpected to crash over.
auto BuiltinID = CalleeDecl.getBuiltinID();
if (BuiltinID == Builtin::BI__builtin_is_aligned ||
BuiltinID == Builtin::BI__builtin_align_up ||
BuiltinID == Builtin::BI__builtin_align_down) {
continue;
}
}
// the corresponding argument should also be a pointer.
CHECK(isSupportedPointerType(Iter.arg().getType()))
<< "Unsupported argument " << Iter.argIdx()
<< " type: " << Iter.arg().getType().getAsString();
if (isa<clang::CXXDefaultArgExpr>(Iter.arg())) {
// Evidence collection for the callee from default argument values is
// handled when collecting from declarations, and there's no useful
// evidence available to collect for the caller.
return;
}
dataflow::PointerValue *PV = getPointerValue(&Iter.arg(), Env);
if (!PV) continue;
SourceLocation ArgLoc = Iter.arg().getExprLoc();
if (CollectEvidenceForCaller) {
auto ParamNullability = getNullabilityAnnotationsFromDeclAndOverrides(
Iter.param(), Lattice);
// Collect evidence from constraints that the parameter's nullability
// places on the argument's nullability.
fromAssignmentToType(Iter.param().getType(), ParamNullability, *PV,
ArgLoc);
}
if (CollectEvidenceForCallee) {
// Emit evidence of the parameter's nullability. First, calculate that
// nullability based on InferableSlots for the caller being assigned to
// Unknown or their previously-inferred value, to reflect the current
// annotations and not all possible annotations for them.
NullabilityKind ArgNullability =
getNullability(*PV, Env, &InferableSlotsConstraint);
Emit(CalleeDecl, paramSlot(Iter.paramIdx()),
getArgEvidenceKindFromNullability(
ArgNullability, Iter.param().getType()->isReferenceType()),
ArgLoc);
}
}
}
/// Collects evidence from the assignment of function arguments to the types
/// of the corresponding parameter, used when we have a FunctionProtoType but
/// no FunctionDecl.
/// TODO: When we collect evidence for more complex slots than just top-level
/// pointers, emit evidence of the function parameter's nullability as a slot
/// in the appropriate declaration.
void fromFunctionProtoTypeCall(const FunctionProtoType &CalleeType,
const CallExpr &Expr) {
// For each pointer parameter of the function, ...
for (unsigned I = 0; I < CalleeType.getNumParams(); ++I) {
const auto ParamType = CalleeType.getParamType(I);
if (!isSupportedPointerType(ParamType.getNonReferenceType())) continue;
// the corresponding argument should also be a pointer.
CHECK(isSupportedPointerType(Expr.getArg(I)->getType()))
<< "Unsupported argument " << I
<< " type: " << Expr.getArg(I)->getType().getAsString();
dataflow::PointerValue *PV = getPointerValue(Expr.getArg(I), Env);
if (!PV) continue;
// TODO: when we infer function pointer/reference parameters'
// nullabilities, check for overrides from previous inference iterations.
auto ParamNullability = getNullabilityAnnotationsFromType(ParamType);
// Collect evidence from constraints that the parameter's nullability
// places on the argument's nullability.
fromAssignmentToType(ParamType, ParamNullability, *PV,
Expr.getArg(I)->getExprLoc());
}
}
/// Collect evidence that the function pointer was dereferenced and from the
/// matching up of parameter/argument nullabilities.
void fromFunctionPointerCallExpr(const Type &CalleeFunctionType,
const CallExpr &Expr) {
if (InferableSlots.empty()) return;
if (const auto *Callee = Expr.getCallee()) {
// Function pointers are only ever raw pointers.
if (const auto *PV = getRawPointerValue(Callee, Env)) {
mustBeNonnull(*PV, Expr.getExprLoc(), Evidence::UNCHECKED_DEREFERENCE);
}
}
auto *CalleeFunctionProtoType =
CalleeFunctionType.getAs<FunctionProtoType>();
CHECK(CalleeFunctionProtoType);
fromFunctionProtoTypeCall(*CalleeFunctionProtoType, Expr);
}
/// Handles the case of a call to a function without a FunctionDecl, e.g. that
/// is provided as a parameter or another decl, e.g. a field or local
/// variable.
///
/// Example: We can collect evidence for the nullability of `p` and (when we
/// handle more than top-level pointer slots) `j` in the following, based on
/// the call to `callee`:
/// ```
/// void target(int* p, void (*callee)(Nonnull<int*> i, int* j)) {
/// callee(p, nullptr);
/// }
/// ```
///
/// With `CalleeDecl` in this case not being a FunctionDecl as in most
/// CallExpr cases, distinct handling is needed.
void fromCallExprWithoutFunctionCalleeDecl(const Decl &CalleeDecl,
const CallExpr &Expr) {
if (CalleeDecl.isFunctionPointerType()) {
if (auto *FuncType = CalleeDecl.getFunctionType()) {
fromFunctionPointerCallExpr(*FuncType, Expr);
} else if (const auto *BD = dyn_cast<BindingDecl>(&CalleeDecl)) {
// TODO(b/352043668): This is a workaround for the unexplained returning
// of nullptr from `getFunctionType()` for BindingDecls.
fromFunctionPointerCallExpr(*BD->getType()->getPointeeType(), Expr);
} else {
llvm::errs() << "Unsupported case of a function pointer type, for "
"which we aren't retrieving a valid FunctionType. \n";
CalleeDecl.dump();
}
return;
}
// Ignore calls of pointers to members. The dereferencing of the pointer is
// handled as a dereference at the BinaryOperator node, which additionally
// captures pointers to fields.
// TODO(b/309625642) Consider collecting evidence for the arguments being
// passed as parameters to the pointed-to member.
if (const auto *BinaryOpCallee = dyn_cast_or_null<BinaryOperator>(
Expr.getCallee()->IgnoreParenImpCasts());
BinaryOpCallee &&
(BinaryOpCallee->getOpcode() == clang::BinaryOperatorKind::BO_PtrMemD ||
BinaryOpCallee->getOpcode() ==
clang::BinaryOperatorKind::BO_PtrMemI)) {
return;
}
// Function references are a rare case, but similar to function pointers, we
// can collect evidence from arguments assigned to parameter types.
if (auto *FuncType = CalleeDecl.getFunctionType()) {
if (auto *FuncProtoType = FuncType->getAs<FunctionProtoType>()) {
fromFunctionProtoTypeCall(*FuncProtoType, Expr);
return;
}
}
// A reference to a function pointer is another rare case, but we can
// collect the same evidence we would for a function pointer.
if (const auto *CalleeAsValueDecl =
dyn_cast<clang::ValueDecl>(&CalleeDecl)) {
if (QualType CalleeType = CalleeAsValueDecl->getType();
CalleeType.getNonReferenceType()->isFunctionPointerType()) {
fromFunctionPointerCallExpr(
*(CalleeType.getNonReferenceType()->getPointeeType()), Expr);
return;
}
}
// If we run into other cases meeting this criterion, skip them, but log
// first so we can potentially add support later.
llvm::errs() << "Unsupported case of a CallExpr without a FunctionDecl. "
"Not collecting any evidence from this CallExpr:\n";
Expr.getBeginLoc().dump(CalleeDecl.getASTContext().getSourceManager());
Expr.dump();
llvm::errs() << "Which is a call to:\n";
CalleeDecl.dump();
}
/// Given a `CallExpr` for a call to our special macro single-argument capture
/// function, collect evidence for a slot that can prevent the abort condition
/// from being true if it is annotated Nonnull.
///
/// e.g. From `CHECK(x)`, we collect evidence for a slot that can cause `x` to
/// not be null.
void fromAbortIfFalseMacroCall(const CallExpr &CallExpr) {
CHECK_EQ(CallExpr.getNumArgs(), 1);
const Expr *Arg = CallExpr.getArg(0);
if (!Arg) return;
QualType ArgType = Arg->getType();
if (isSupportedPointerType(ArgType)) {
const dataflow::PointerValue *PV = getPointerValue(Arg, Env);
if (!PV) return;
mustBeNonnull(*PV, Arg->getExprLoc(), Evidence::ABORT_IF_NULL);
} else if (ArgType->isBooleanType()) {
const dataflow::BoolValue *BV = Env.get<dataflow::BoolValue>(*Arg);
if (!BV || BV->getKind() == dataflow::BoolValue::Kind::TopBool) return;
mustBeTrue(BV->formula(), Arg->getExprLoc(), Evidence::ABORT_IF_NULL);
}
}
/// Given a `CallExpr` for a call to our special macro two-argument capture
/// function for not-equal checks, if one of the arguments is a nullptr
/// constant or provably null, collect evidence for a slot that can prevent
/// the other argument from being null.
///
/// e.g. From `CHECK_NE(x, nullptr)`, we collect evidence for a slot that can
/// cause `x` to not be null.
void fromAbortIfEqualMacroCall(const CallExpr &CallExpr) {
CHECK_EQ(CallExpr.getNumArgs(), 2);
const Expr *First = CallExpr.getArg(0);
const Expr *Second = CallExpr.getArg(1);
bool FirstSupported = isSupportedPointerType(First->getType());
bool SecondSupported = isSupportedPointerType(Second->getType());
if (!FirstSupported && !SecondSupported) return;
ASTContext &Context = CallExpr.getCalleeDecl()->getASTContext();
const dataflow::PointerValue *ValueComparedToNull = nullptr;
SourceLocation EvidenceLoc;
if (First->isNullPointerConstant(Context,
Expr::NPC_ValueDependentIsNotNull)) {
if (!isSupportedPointerType(Second->getType())) return;
ValueComparedToNull = getPointerValue(Second, Env);
if (!ValueComparedToNull) return;
EvidenceLoc = Second->getExprLoc();
} else if (Second->isNullPointerConstant(
Context, Expr::NPC_ValueDependentIsNotNull)) {
if (!isSupportedPointerType(First->getType())) return;
ValueComparedToNull = getPointerValue(First, Env);
if (!ValueComparedToNull) return;
EvidenceLoc = First->getExprLoc();
} else {
if (!FirstSupported || !SecondSupported) {
// If this happens outside of the nullptr literal case, we'd like to
// know about it.
llvm::errs() << "Value of a supported pointer type compared to a value "
"of a type that is not a supported pointer type.: \n";
CallExpr.dump();
CallExpr.getExprLoc().dump(
CallExpr.getCalleeDecl()->getASTContext().getSourceManager());
return;
}
const dataflow::PointerValue *FirstPV = getPointerValue(First, Env);
if (!FirstPV) return;
const dataflow::PointerValue *SecondPV = getPointerValue(Second, Env);
if (!SecondPV) return;
PointerNullState FirstNullState = getPointerNullState(*FirstPV);
if (!FirstNullState.IsNull) return;
PointerNullState SecondNullState = getPointerNullState(*SecondPV);
if (!SecondNullState.IsNull) return;
if (Env.proves(*FirstNullState.IsNull)) {
ValueComparedToNull = SecondPV;
EvidenceLoc = Second->getExprLoc();
} else if (Env.proves(*SecondNullState.IsNull)) {
ValueComparedToNull = FirstPV;
EvidenceLoc = First->getExprLoc();
} else {
return;
}
}
mustBeNonnull(*ValueComparedToNull, EvidenceLoc, Evidence::ABORT_IF_NULL);
}
void fromCallExpr(const Stmt &S) {
auto *CallExpr = dyn_cast<clang::CallExpr>(&S);
if (!CallExpr) return;
auto *CalleeDecl = CallExpr->getCalleeDecl();
if (!CalleeDecl) return;
if (auto *CalleeFunctionDecl = dyn_cast<clang::FunctionDecl>(CalleeDecl)) {
if (CalleeFunctionDecl->getDeclName().isIdentifier()) {
llvm::StringRef Name = CalleeFunctionDecl->getName();
if (Name == ArgCaptureAbortIfFalse) {
fromAbortIfFalseMacroCall(*CallExpr);
return;
}
if (Name == ArgCaptureAbortIfEqual) {
fromAbortIfEqualMacroCall(*CallExpr);
return;
}
}
fromArgsAndParams(*CalleeFunctionDecl, *CallExpr);
} else {
fromCallExprWithoutFunctionCalleeDecl(*CalleeDecl, *CallExpr);
}
}
void fromConstructExpr(const Stmt &S) {
auto *ConstructExpr = dyn_cast<clang::CXXConstructExpr>(&S);
if (!ConstructExpr) return;
auto *ConstructorDecl = dyn_cast_or_null<clang::CXXConstructorDecl>(
ConstructExpr->getConstructor());
if (!ConstructorDecl) return;
fromArgsAndParams(*ConstructorDecl, *ConstructExpr);
}
void fromReturn(const Stmt &S) {
// Is this CFGElement a return statement?
auto *ReturnStmt = dyn_cast<clang::ReturnStmt>(&S);
if (!ReturnStmt) return;
auto *ReturnExpr = ReturnStmt->getRetValue();
if (!ReturnExpr || !isSupportedPointerType(ReturnExpr->getType())) return;
const FunctionDecl *CurrentFunc = Env.getCurrentFunc();
CHECK(CurrentFunc) << "A return statement outside of a function?";
// Skip gathering evidence about the current function's return type if
// the current function is not an inference target or the return type
// already includes an annotation.
if (isInferenceTarget(*CurrentFunc) &&
!evidenceKindFromDeclaredReturnType(*CurrentFunc, Lattice.defaults())) {
NullabilityKind ReturnNullability =
getNullability(ReturnExpr, Env, &InferableSlotsConstraint);
bool ReturnTypeIsReference =
CurrentFunc->getReturnType()->isReferenceType();
Evidence::Kind ReturnEvidenceKind;
switch (ReturnNullability) {
case NullabilityKind::Nullable:
ReturnEvidenceKind = ReturnTypeIsReference
? Evidence::NULLABLE_REFERENCE_RETURN
: Evidence::NULLABLE_RETURN;
break;
case NullabilityKind::NonNull:
ReturnEvidenceKind = ReturnTypeIsReference
? Evidence::NONNULL_REFERENCE_RETURN
: Evidence::NONNULL_RETURN;
break;
default:
ReturnEvidenceKind = ReturnTypeIsReference
? Evidence::UNKNOWN_REFERENCE_RETURN
: Evidence::UNKNOWN_RETURN;
}
Emit(*CurrentFunc, SLOT_RETURN_TYPE, ReturnEvidenceKind,
ReturnExpr->getExprLoc());
}
const dataflow::PointerValue *PV = getPointerValue(ReturnExpr, Env);
if (!PV) return;
TypeNullability ReturnTypeNullability =
getReturnTypeNullabilityAnnotationsWithOverrides(*CurrentFunc, Lattice);
fromAssignmentToType(Env.getCurrentFunc()->getReturnType(),
ReturnTypeNullability, *PV, ReturnExpr->getExprLoc());
}
/// Checks whether PointerValue is null or nullable and if so, collects
/// evidence for a slot that would, if marked Nullable, cause
/// TypeNullability's first-layer nullability to be Nullable.
///
/// e.g. This is used for example to collect from the following:
/// ```
/// void target(int* p, int* q, NullabilityUnknown<int*> r) {
/// p = nullptr;
/// if (!r) {
/// q = r;
/// }
/// }
/// ```
/// evidence for each of the assignments of `p` and `q` that they were
/// ASSIGNED_FROM_NULLABLE.
void fromAssignmentFromNullable(const TypeNullability &TypeNullability,
const dataflow::PointerValue &PointerValue,
SourceLocation ValueLoc,
Evidence::Kind EvidenceKind) {
if (TypeNullability.empty() || !hasPointerNullState(PointerValue)) return;
dataflow::Arena &A = Env.arena();
if (getNullability(PointerValue, Env, &InferableSlotsConstraint) ==
NullabilityKind::Nullable) {
const Formula &TypeIsNullable = TypeNullability[0].isNullable(A);
// If the flow conditions already imply that the type is nullable, or
// that the type is not nullable, we can skip collecting evidence.
if (Env.proves(TypeIsNullable) || !Env.allows(TypeIsNullable)) return;
for (auto &IS : InferableSlots) {
auto &Implication = A.makeImplies(
IS.getSymbolicNullability().isNullable(A), TypeIsNullable);
// It's not expected that a slot's isNullable formula could be proven
// false by the environment alone (without the
// InferableSlotsConstraint), but SAT calls are relatively expensive, so
// only DCHECK.
DCHECK(Env.allows(IS.getSymbolicNullability().isNullable(A)));
if (Env.proves(Implication)) {
Emit(IS.getInferenceTarget(), IS.getTargetSlot(), EvidenceKind,
ValueLoc);
return;
}
}
}
}
/// Collects evidence based on an assignment of RHS to LHSDecl, through a
/// direct assignment statement, aggregate initialization, etc.
void fromAssignmentLike(const ValueDecl &LHSDecl, const Expr &RHS,
SourceLocation Loc,
Evidence::Kind EvidenceKindForAssignmentFromNullable =
Evidence::ASSIGNED_FROM_NULLABLE) {
fromAssignmentLike(
LHSDecl.getType(),
getNullabilityAnnotationsFromDeclAndOverrides(LHSDecl, Lattice), RHS,
Loc, EvidenceKindForAssignmentFromNullable);
}
/// Collects evidence based on an assignment of RHS to an expression with type
/// LHSType and nullability LHSNullability, through a direct assignment
/// statement, aggregate initialization, etc.
void fromAssignmentLike(QualType LHSType,
const TypeNullability &LHSNullability,
const Expr &RHS, SourceLocation Loc,
Evidence::Kind EvidenceKindForAssignmentFromNullable =
Evidence::ASSIGNED_FROM_NULLABLE) {
const dataflow::PointerValue *PV = getPointerValue(&RHS, Env);
if (!PV) return;
fromAssignmentToType(LHSType, LHSNullability, *PV, Loc);
fromAssignmentFromNullable(LHSNullability, *PV, Loc,
EvidenceKindForAssignmentFromNullable);
}
/// Collects evidence from direct assignment statements, e.g. `p = nullptr`,
/// whether initializing a new declaration or re-assigning to an existing
/// declaration.
void fromAssignment(const Stmt &S) {
if (InferableSlots.empty()) return;
// Initialization of new decl.
if (auto *DeclStmt = dyn_cast<clang::DeclStmt>(&S)) {
for (auto *Decl : DeclStmt->decls()) {
if (auto *VarDecl = dyn_cast<clang::VarDecl>(Decl);
VarDecl && VarDecl->hasInit()) {
bool DeclTypeSupported =
isSupportedPointerType(VarDecl->getType().getNonReferenceType());
bool InitTypeSupported = isSupportedPointerType(
VarDecl->getInit()->getType().getNonReferenceType());
if (!DeclTypeSupported) return;
if (!InitTypeSupported) {
llvm::errs() << "Unsupported init type for pointer decl: "
<< VarDecl->getInit()->getType() << "\n";
return;
}
fromAssignmentLike(*VarDecl, *VarDecl->getInit(),
VarDecl->getInit()->getExprLoc());
}
}
return;
}
// Assignment to existing decl.
const Expr *LHS = nullptr;
const Expr *RHS = nullptr;
std::optional<SourceLocation> Loc = std::nullopt;
// Raw pointers.
if (auto *BinaryOp = dyn_cast<clang::BinaryOperator>(&S);
BinaryOp &&
BinaryOp->getOpcode() == clang::BinaryOperatorKind::BO_Assign) {
LHS = BinaryOp->getLHS();
RHS = BinaryOp->getRHS();
Loc = BinaryOp->getOperatorLoc();
} else if (
// Smart pointers.
auto *CXXOpCall = dyn_cast<clang::CXXOperatorCallExpr>(&S);
CXXOpCall && CXXOpCall->getOperator() == clang::OO_Equal) {
LHS = CXXOpCall->getArg(0);
RHS = CXXOpCall->getArg(1);
Loc = CXXOpCall->getOperatorLoc();
} else {
return;
}
const QualType LHSType = LHS->getType();
if (!isSupportedPointerType(LHSType)) return;
if (!isSupportedPointerType(RHS->getType())) return;
const TypeNullability *TypeNullability = Lattice.getTypeNullability(LHS);
CHECK(TypeNullability);
fromAssignmentLike(LHSType, *TypeNullability, *RHS, *Loc);
}
void fromArithmeticArg(const Expr *Arg, SourceLocation Loc) {
// No support needed for smart pointers, which do not support arithmetic
// operations.
if (!Arg || !isSupportedRawPointerType(Arg->getType())) return;
if (auto *PV = getPointerValue(Arg, Env))
mustBeNonnull(*PV, Loc, Evidence::ARITHMETIC);
}
void fromArithmetic(const Stmt &S) {
// A nullptr can be added to 0 and nullptr can be subtracted from nullptr
// without hitting UB. But for now, we skip handling these special cases and
// assume all pointers involved in these operations must be nonnull.
switch (S.getStmtClass()) {
default:
return;
case Stmt::CompoundAssignOperatorClass: {
auto *Op = cast<clang::CompoundAssignOperator>(&S);
switch (Op->getOpcode()) {
default:
return;
case BO_AddAssign:
case BO_SubAssign:
fromArithmeticArg(Op->getLHS(), Op->getExprLoc());
}
break;
}
case Stmt::BinaryOperatorClass: {
auto *Op = cast<clang::BinaryOperator>(&S);
switch (Op->getOpcode()) {
default:
return;
case BO_Add:
case BO_Sub:
fromArithmeticArg(Op->getLHS(), Op->getExprLoc());
fromArithmeticArg(Op->getRHS(), Op->getExprLoc());
}
break;
}
case Stmt::UnaryOperatorClass: {
auto *Op = cast<clang::UnaryOperator>(&S);
switch (Op->getOpcode()) {
default:
return;
case UO_PostInc:
case UO_PreInc:
case UO_PostDec:
case UO_PreDec:
fromArithmeticArg(Op->getSubExpr(), Op->getExprLoc());
}
break;
}
}
}
void fromCFGInitializer(const CFGInitializer &CFGInit) {
const CXXCtorInitializer *Initializer = CFGInit.getInitializer();
if (!Initializer) {
// We expect this not to be the case, but not to a production-crash-worthy
// level, so assert instead of CHECK.
llvm::errs() << "CFGInitializer with null CXXCtorInitializer.\n";
CFGInit.dump();
assert(Initializer);
}
// Base and delegating initializers are collected from when we see the
// underlying CXXConstructExpr, so we don't need to handle those, only the
// member initializers.
const FieldDecl *Field = Initializer->getAnyMember();
if (Field == nullptr || InferableSlots.empty() ||
!isSupportedPointerType(Field->getType()))
return;
bool IsDefaultInitializer = Initializer->isInClassMemberInitializer();
if (isSupportedSmartPointerType(Field->getType()) &&
!IsDefaultInitializer && !Initializer->isWritten()) {
// We skip unwritten non-default member initializers for smart pointer
// fields because we check the end block of the constructor for the
// fields' nullability later. This allows us to avoid inferring Nullable
// for smart pointers without default initializers that are only ever (and
// always) assigned to a Nonnull value in constructor bodies.
return;
}
const Expr *InitExpr = Initializer->getInit();
bool NullptrDefaultInit =
IsDefaultInitializer && isOrIsConstructedFromNullPointerConstant(
InitExpr, Field->getASTContext());
fromAssignmentLike(*Field, *InitExpr, InitExpr->getExprLoc(),
NullptrDefaultInit
? Evidence::NULLPTR_DEFAULT_MEMBER_INITIALIZER
: Evidence::ASSIGNED_FROM_NULLABLE);
}
void fromFieldInits(const RecordInitListHelper &Helper) {
// Any initialization of base classes/fields will be collected from the
// InitListExpr for the base initialization, so we only need to collect here
// from the field inits.
for (auto [Field, InitExpr] : Helper.field_inits()) {
if (!isSupportedPointerType(Field->getType())) return;
fromAssignmentLike(*Field, *InitExpr, InitExpr->getExprLoc());
}
}
void fromAggregateInitialization(const Stmt &S) {
if (auto *InitList = dyn_cast<clang::InitListExpr>(&S);
InitList && InitList->getType()->isRecordType() &&
!(InitList->isSemanticForm() && InitList->isTransparent())) {
fromFieldInits(RecordInitListHelper(InitList));
return;
}
if (auto *ParenListInit = dyn_cast<clang::CXXParenListInitExpr>(&S);
ParenListInit && ParenListInit->getType()->isRecordType()) {
fromFieldInits(RecordInitListHelper(ParenListInit));
}
}
const std::vector<InferableSlot> &InferableSlots;
const Formula &InferableSlotsConstraint;
llvm::function_ref<EvidenceEmitter> Emit;
const PointerNullabilityLattice &Lattice;
const Environment &Env;
};
} // namespace
/// Returns a function that the analysis can use to override Decl nullability
/// values from the source code being analyzed with previously inferred
/// nullabilities.
///
/// In practice, this should only override the default nullability for Decls
/// that do not spell out a nullability in source code, because we only pass in
/// inferences from the previous round which are non-trivial and annotations
/// "inferred" by reading an annotation from source code in the previous round
/// were marked trivial.
static auto getConcreteNullabilityOverrideFromPreviousInferences(
ConcreteNullabilityCache &Cache, USRCache &USRCache,
const PreviousInferences &PreviousInferences) {
return [&](const Decl &D) -> std::optional<const PointerTypeNullability *> {
auto [It, Inserted] = Cache.try_emplace(&D);
if (Inserted) {
std::optional<const Decl *> FingerprintedDecl;
Slot Slot;
if (auto *FD = dyn_cast<FunctionDecl>(&D)) {
FingerprintedDecl = FD;
Slot = SLOT_RETURN_TYPE;
} else if (auto *PD = dyn_cast<ParmVarDecl>(&D)) {
if (auto *Parent = dyn_cast_or_null<FunctionDecl>(
PD->getParentFunctionOrMethod())) {
FingerprintedDecl = Parent;
Slot = paramSlot(PD->getFunctionScopeIndex());
}
}
if (!FingerprintedDecl) return std::nullopt;
auto Fingerprint =
fingerprint(getOrGenerateUSR(USRCache, **FingerprintedDecl), Slot);
if (PreviousInferences.Nullable.contains(Fingerprint)) {
It->second.emplace(NullabilityKind::Nullable);
} else if (PreviousInferences.Nonnull.contains(Fingerprint)) {
It->second.emplace(NullabilityKind::NonNull);
} else {
It->second = std::nullopt;
}
}
if (!It->second) return std::nullopt;
return &*It->second;
};
}
template <typename ContainerT>
static bool hasAnyInferenceTargets(const ContainerT &Decls) {
return std::any_of(Decls.begin(), Decls.end(),
[](const Decl *D) { return D && isInferenceTarget(*D); });
}
static bool hasAnyInferenceTargets(dataflow::ReferencedDecls &RD) {
return hasAnyInferenceTargets(RD.Fields) ||
hasAnyInferenceTargets(RD.Globals) ||
hasAnyInferenceTargets(RD.Functions);
}
std::unique_ptr<dataflow::Solver> makeDefaultSolverForInference() {
constexpr std::int64_t MaxSATIterations = 200'000;
return std::make_unique<dataflow::WatchedLiteralsSolver>(MaxSATIterations);
}
// If D is a constructor definition, collect ASSIGNED_FROM_NULLABLE evidence for
// smart pointer fields implicitly default-initialized and left nullable in the
// exit block of the constructor body.
static void collectEvidenceFromConstructorExitBlock(
const clang::Decl &MaybeConstructor, const Environment &ExitEnv,
llvm::function_ref<EvidenceEmitter> Emit) {
auto *Ctor = dyn_cast<CXXConstructorDecl>(&MaybeConstructor);
if (!Ctor) return;
for (auto *Initializer : Ctor->inits()) {
if (Initializer->isWritten() || Initializer->isInClassMemberInitializer()) {
// We collect evidence from explicitly-written member initializers and
// default member initializers elsewhere, when analyzing the
// constructor's CFGInitializers.
continue;
}
const FieldDecl *Field = Initializer->getAnyMember();
if (Field == nullptr || !isSupportedSmartPointerType(Field->getType()) ||
!isInferenceTarget(*Field))
continue;
// `Field` is a smart pointer field that was not explicitly
// initialized in the constructor member initializer list and does not
// have a default member initializer, so it was default constructed
// (and null) at the beginning of the constructor body.
// If it is still nullable in the constructor's exit block
// environment, we collect evidence that it was assigned from a
// nullable value.
const dataflow::PointerValue *PV = getPointerValueFromSmartPointer(
cast<dataflow::RecordStorageLocation>(
ExitEnv.getThisPointeeStorageLocation()->getChild(*Field)),
ExitEnv);
if (PV == nullptr) continue;
// We have seen copy/move constructors that leave smart pointer fields
// without null state, because the field of the copied/moved-from value is
// not modeled or referenced and so has no null state.
// We don't get useful evidence from these cases anyway, because whether the
// field has been initialized with a non-null value is determined by some
// other form of construction for the same type, and we'll collect the
// relevant evidence there.
// In these cases, return early without emitting evidence.
if (!hasPointerNullState(*PV) && Ctor->isCopyOrMoveConstructor()) return;
// Otherwise, we should always have null state for smart pointer fields. If
// not, we should fail loudly so we find out about it and can better handle
// those specific cases.
CHECK(hasPointerNullState(*PV));
if (isNullable(*PV, ExitEnv)) {
Emit(*Field, Slot(0), Evidence::ASSIGNED_FROM_NULLABLE,
Ctor->isImplicit() ? Field->getBeginLoc() : Ctor->getBeginLoc());
}
}
}
llvm::Error collectEvidenceFromDefinition(
const Decl &Definition, llvm::function_ref<EvidenceEmitter> Emit,
USRCache &USRCache, const NullabilityPragmas &Pragmas,
const PreviousInferences PreviousInferences,
const SolverFactory &MakeSolver) {
ASTContext &Ctx = Definition.getASTContext();
dataflow::ReferencedDecls ReferencedDecls;
Stmt *TargetStmt = nullptr;
std::optional<DeclStmt> DeclStmtForVarDecl;
const auto *TargetAsFunc = dyn_cast<FunctionDecl>(&Definition);
if (TargetAsFunc != nullptr) {
if (!TargetAsFunc->doesThisDeclarationHaveABody()) {
return llvm::createStringError(llvm::inconvertibleErrorCode(),
"Function definitions must have a body.");
}
TargetStmt = TargetAsFunc->getBody();
ReferencedDecls = dataflow::getReferencedDecls(*TargetAsFunc);
} else if (auto *Var = dyn_cast<VarDecl>(&Definition)) {
if (!Var->hasInit()) {
return llvm::createStringError(
llvm::inconvertibleErrorCode(),
"Variable definitions must have an initializer.");
}
// Synthesize a temporary DeclStmt for the assignment of the variable to
// its initializing expression. This is an unusual pattern that does not
// perfectly reflect the CFG or AST for declaration or assignment of a
// global variable, and it is possible that this may cause unexpected
// behavior in clang tools/utilities.
TargetStmt =
&DeclStmtForVarDecl.emplace(DeclGroupRef(const_cast<VarDecl *>(Var)),
Var->getBeginLoc(), Var->getEndLoc());
ReferencedDecls = dataflow::getReferencedDecls(*TargetStmt);
if (!isInferenceTarget(*Var) && !hasAnyInferenceTargets(ReferencedDecls)) {
// If this variable is not an inference target and the initializer does
// not reference any inference targets, we won't be able to collect any
// useful evidence from the initializer.
return llvm::Error::success();
}
} else {
std::string Msg =
"Unable to find a valid target definition from Definition:\n";
llvm::raw_string_ostream Stream(Msg);
Definition.dump(Stream);
return llvm::createStringError(llvm::inconvertibleErrorCode(), Msg);
}
CHECK(TargetStmt) << "TargetStmt should have been assigned a non-null value.";
llvm::Expected<dataflow::AdornedCFG> ACFG =
dataflow::AdornedCFG::build(Definition, *TargetStmt, Ctx);
if (!ACFG) return ACFG.takeError();
std::unique_ptr<dataflow::Solver> Solver = MakeSolver();
DataflowAnalysisContext AnalysisContext(*Solver);
Environment Env = TargetAsFunc ? Environment(AnalysisContext, *TargetAsFunc)
: Environment(AnalysisContext, *TargetStmt);
PointerNullabilityAnalysis Analysis(Ctx, Env, Pragmas);
TypeNullabilityDefaults Defaults = TypeNullabilityDefaults(Ctx, Pragmas);
std::vector<InferableSlot> InferableSlots;
if (TargetAsFunc && isInferenceTarget(*TargetAsFunc)) {
auto Parameters = TargetAsFunc->parameters();
for (auto I = 0; I < Parameters.size(); ++I) {
if (hasInferable(Parameters[I]->getType().getNonReferenceType()) &&
!evidenceKindFromDeclaredTypeLoc(
Parameters[I]->getTypeSourceInfo()->getTypeLoc(), Defaults)) {
InferableSlots.emplace_back(Analysis.assignNullabilityVariable(
Parameters[I], AnalysisContext.arena()),
paramSlot(I), *TargetAsFunc);
}
}
}
for (const FieldDecl *Field : ReferencedDecls.Fields) {
if (isInferenceTarget(*Field) &&
!evidenceKindFromDeclaredTypeLoc(
Field->getTypeSourceInfo()->getTypeLoc(), Defaults)) {
InferableSlots.emplace_back(
Analysis.assignNullabilityVariable(Field, AnalysisContext.arena()),
Slot(0), *Field);
}
}
for (const VarDecl *Global : ReferencedDecls.Globals) {
if (isInferenceTarget(*Global) &&
!evidenceKindFromDeclaredTypeLoc(
Global->getTypeSourceInfo()->getTypeLoc(), Defaults)) {
InferableSlots.emplace_back(
Analysis.assignNullabilityVariable(Global, AnalysisContext.arena()),
Slot(0), *Global);
}
}
for (const FunctionDecl *Function : ReferencedDecls.Functions) {
if (isInferenceTarget(*Function) &&
hasInferable(Function->getReturnType()) &&
!evidenceKindFromDeclaredReturnType(*Function, Defaults)) {
InferableSlots.emplace_back(
Analysis.assignNullabilityVariable(Function, AnalysisContext.arena()),
SLOT_RETURN_TYPE, *Function);
}
}
const auto &InferableSlotsConstraint =
getInferableSlotsAsInferredOrUnknownConstraint(InferableSlots, USRCache,
PreviousInferences,
AnalysisContext.arena());
ConcreteNullabilityCache ConcreteNullabilityCache;
Analysis.assignNullabilityOverride(
getConcreteNullabilityOverrideFromPreviousInferences(
ConcreteNullabilityCache, USRCache, PreviousInferences));
std::vector<
std::optional<dataflow::DataflowAnalysisState<PointerNullabilityLattice>>>
Results;
dataflow::CFGEltCallbacks<PointerNullabilityAnalysis> PostAnalysisCallbacks;
PostAnalysisCallbacks.Before =
[&](const CFGElement &Element,
const dataflow::DataflowAnalysisState<PointerNullabilityLattice>
&State) {
DefinitionEvidenceCollector::collect(InferableSlots,
InferableSlotsConstraint, Emit,
Element, State.Lattice, State.Env);
};
if (llvm::Error Error = dataflow::runDataflowAnalysis(*ACFG, Analysis, Env,
PostAnalysisCallbacks)
.moveInto(Results))
return Error;
if (Solver->reachedLimit()) {
return llvm::createStringError(llvm::errc::interrupted,
"SAT solver reached iteration limit");
}
if (Results.empty()) return llvm::Error::success();
if (std::optional<dataflow::DataflowAnalysisState<PointerNullabilityLattice>>
&ExitBlockResult = Results[ACFG->getCFG().getExit().getBlockID()]) {
collectEvidenceFromConstructorExitBlock(Definition, ExitBlockResult->Env,
Emit);
}
return llvm::Error::success();
}
static void collectEvidenceFromDefaultArgument(
const clang::FunctionDecl &Fn, const clang::ParmVarDecl &ParamDecl,
Slot ParamSlot, llvm::function_ref<EvidenceEmitter> Emit) {
// We don't handle all cases of default arguments, because the expressions
// used for the argument are not available in any CFG, because the AST nodes
// are once-per-decl children of the ParmVarDecl, not once-per-call children
// of the CallExpr. Including them in the callsite CFG would be a
// significant undertaking, so for now, only handle nullptr literals (and 0)
// and expressions whose types already include an annotation, which we can
// handle just from declarations instead of call sites and should handle the
// majority of cases.
if (!isSupportedPointerType(ParamDecl.getType().getNonReferenceType()))
return;
if (!ParamDecl.hasDefaultArg()) return;
if (ParamDecl.hasUnparsedDefaultArg() ||
ParamDecl.hasUninstantiatedDefaultArg()) {
Emit(Fn, ParamSlot, Evidence::UNKNOWN_ARGUMENT, ParamDecl.getEndLoc());
return;
}
const Expr *DefaultArg = ParamDecl.getDefaultArg();
CHECK(DefaultArg);
if (isOrIsConstructedFromNullPointerConstant(DefaultArg,
Fn.getASTContext())) {
Emit(Fn, ParamSlot, Evidence::NULLABLE_ARGUMENT, DefaultArg->getExprLoc());
} else {
auto Nullability = getNullabilityAnnotationsFromType(DefaultArg->getType());
if (auto K = getArgEvidenceKindFromNullability(
Nullability.front().concrete(),
ParamDecl.getType()->isReferenceType())) {
Emit(Fn, ParamSlot, K, DefaultArg->getExprLoc());
} else {
Emit(Fn, ParamSlot, Evidence::UNKNOWN_ARGUMENT, DefaultArg->getExprLoc());
}
}
}
static void collectNonnullAttributeEvidence(
const clang::FunctionDecl &Fn, unsigned ParamIndex, SourceLocation Loc,
llvm::function_ref<EvidenceEmitter> Emit) {
const ParmVarDecl *ParamDecl = Fn.getParamDecl(ParamIndex);
// The attribute does not apply to references-to-pointers or nested pointers
// or smart pointers.
if (isSupportedRawPointerType(ParamDecl->getType())) {
Emit(Fn, paramSlot(ParamIndex), Evidence::GCC_NONNULL_ATTRIBUTE, Loc);
}
}
void collectEvidenceFromTargetDeclaration(
const clang::Decl &D, llvm::function_ref<EvidenceEmitter> Emit,
const NullabilityPragmas &Pragmas) {
TypeNullabilityDefaults Defaults(D.getASTContext(), Pragmas);
if (const auto *Fn = dyn_cast<clang::FunctionDecl>(&D)) {
if (auto K = evidenceKindFromDeclaredReturnType(*Fn, Defaults))
Emit(*Fn, SLOT_RETURN_TYPE, *K,
Fn->getReturnTypeSourceRange().getBegin());
if (const auto *RNNA = Fn->getAttr<ReturnsNonNullAttr>()) {
// The attribute does not apply to references-to-pointers or nested
// pointers or smart pointers.
if (isSupportedRawPointerType(Fn->getReturnType())) {
Emit(*Fn, SLOT_RETURN_TYPE, Evidence::GCC_NONNULL_ATTRIBUTE,
RNNA->getLocation());
}
}
for (unsigned I = 0; I < Fn->param_size(); ++I) {
const ParmVarDecl *ParamDecl = Fn->getParamDecl(I);
if (auto K = evidenceKindFromDeclaredTypeLoc(
ParamDecl->getTypeSourceInfo()->getTypeLoc(), Defaults)) {
Emit(*Fn, paramSlot(I), *K, ParamDecl->getTypeSpecStartLoc());
}
collectEvidenceFromDefaultArgument(*Fn, *ParamDecl, paramSlot(I), Emit);
if (const auto *NNA = ParamDecl->getAttr<NonNullAttr>())
collectNonnullAttributeEvidence(*Fn, I, NNA->getLocation(), Emit);
}
if (const auto *NNA = Fn->getAttr<NonNullAttr>()) {
// The attribute may have arguments indicating one or more parameters
// that are nonnull. If no arguments are present, all top-level,
// non-reference, raw pointer parameter types are nonnull. Return types
// are not affected.
if (NNA->args_size() > 0) {
for (const clang::ParamIdx &P : NNA->args()) {
// getASTIndex starts with 0 and does not count any implicit `this`
// parameter, matching FunctionDecl::getParamDecl indexing.
unsigned I = P.getASTIndex();
collectNonnullAttributeEvidence(*Fn, I, NNA->getLocation(), Emit);
}
} else {
for (unsigned I = 0; I < Fn->param_size(); ++I) {
collectNonnullAttributeEvidence(*Fn, I, NNA->getLocation(), Emit);
}
}
}
} else if (const auto *Field = dyn_cast<clang::FieldDecl>(&D)) {
if (auto K = evidenceKindFromDeclaredTypeLoc(
Field->getTypeSourceInfo()->getTypeLoc(), Defaults)) {
Emit(*Field, Slot(0), *K, Field->getTypeSpecStartLoc());
}
} else if (const auto *Var = dyn_cast<clang::VarDecl>(&D)) {
if (auto K = evidenceKindFromDeclaredTypeLoc(
Var->getTypeSourceInfo()->getTypeLoc(), Defaults)) {
Emit(*Var, Slot(0), *K, Var->getTypeSpecStartLoc());
}
}
}
EvidenceSites EvidenceSites::discover(ASTContext &Ctx) {
struct Walker : public EvidenceLocationsWalker<Walker> {
EvidenceSites Out;
bool VisitFunctionDecl(absl::Nonnull<const FunctionDecl *> FD) {
if (isInferenceTarget(*FD)) Out.Declarations.insert(FD);
// Visiting template instantiations is fine, these are valid functions!
// But we'll be limited in what we can infer.
bool IsUsefulDefinition =
FD->doesThisDeclarationHaveABody() &&
// We will not get anywhere with dependent code.
!FD->isDependentContext() &&
// Defaulted (aka implicitly-defined) default constructors give us a
// chance to analyze default member initializers more thoroughly, but
// otherwise implicit functions are not generally useful.
(!FD->isImplicit() ||
(isa<CXXConstructorDecl>(FD) &&
cast<CXXConstructorDecl>(FD)->isDefaultConstructor()));
if (IsUsefulDefinition) Out.Definitions.insert(FD);
return true;
}
bool VisitFieldDecl(absl::Nonnull<const FieldDecl *> FD) {
if (isInferenceTarget(*FD)) Out.Declarations.insert(FD);
return true;
}
bool VisitVarDecl(absl::Nonnull<const VarDecl *> VD) {
if (isInferenceTarget(*VD)) {
Out.Declarations.insert(VD);
}
// Variable initializers outside of function bodies may contain evidence
// we won't otherwise see, even if the variable is not an inference
// target.
if (VD->hasInit() && !VD->getDeclContext()->isFunctionOrMethod() &&
!VD->isTemplated())
Out.Definitions.insert(VD);
return true;
}
};
Walker W;
W.TraverseAST(Ctx);
return std::move(W.Out);
}
} // namespace clang::tidy::nullability