[clang] nonblocking/nonallocating attributes: 2nd pass caller/callee analysis (PR #99656)
via cfe-commits
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Tue Aug 13 23:05:09 PDT 2024
================
@@ -0,0 +1,1199 @@
+//=== EffectAnalysis.cpp - Sema warnings for function effects -------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements caller/callee analysis for function effects.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/AST/Decl.h"
+#include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/AST/Stmt.h"
+#include "clang/AST/Type.h"
+#include "clang/Basic/SourceManager.h"
+#include "clang/Sema/SemaInternal.h"
+
+#define DEBUG_TYPE "fxanalysis"
+
+using namespace clang;
+
+namespace {
+
+enum class ViolationID : uint8_t {
+ None = 0, // sentinel for an empty Violation
+ Throws,
+ Catches,
+ CallsObjC,
+ AllocatesMemory,
+ HasStaticLocal,
+ AccessesThreadLocal,
+
+ // These only apply to callees, where the analysis stops at the Decl
+ DeclDisallowsInference,
+
+ CallsDeclWithoutEffect,
+ CallsExprWithoutEffect,
+};
+
+// Represents a violation of the rules, potentially for the entire duration of
+// the analysis phase, in order to refer to it when explaining why a caller has
+// been made unsafe by a callee. Can be transformed into either a Diagnostic
+// (warning or a note), depending on whether the violation pertains to a
+// function failing to be verifed as holding an effect vs. a function failing to
+// be inferred as holding that effect.
+struct Violation {
+ FunctionEffect Effect;
+ FunctionEffect CalleeEffectPreventingInference; // only for certain IDs
+ ViolationID ID = ViolationID::None;
+ SourceLocation Loc;
+ const Decl *Callee = nullptr; // only valid for Calls*
+
+ Violation() = default;
+
+ Violation(const FunctionEffect &Effect, ViolationID ID, SourceLocation Loc,
+ const Decl *Callee = nullptr,
+ const FunctionEffect *CalleeEffect = nullptr)
+ : Effect(Effect), ID(ID), Loc(Loc), Callee(Callee) {
+ if (CalleeEffect != nullptr)
+ CalleeEffectPreventingInference = *CalleeEffect;
+ }
+};
+
+enum class SpecialFuncType : uint8_t { None, OperatorNew, OperatorDelete };
+enum class CallableType {
+ // unknown: probably function pointer
+ Unknown,
+ Function,
+ Virtual,
+ Block
+};
+
+// Return whether a function's effects CAN be verified.
+// The question of whether it SHOULD be verified is independent.
+static bool functionIsVerifiable(const FunctionDecl *FD) {
+ if (FD->isTrivial()) {
+ // Otherwise `struct x { int a; };` would have an unverifiable default
+ // constructor.
+ return true;
+ }
+ return FD->hasBody();
+}
+
+static bool isNoexcept(const FunctionDecl *FD) {
+ const auto *FPT = FD->getType()->castAs<FunctionProtoType>();
+ if (FPT->isNothrow() || FD->hasAttr<NoThrowAttr>())
+ return true;
+ return false;
+}
+
+// Transitory, more extended information about a callable, which can be a
+// function, block, or function pointer.
+struct CallableInfo {
+ // CDecl holds the function's definition, if any.
+ // FunctionDecl if CallableType::Function or Virtual
+ // BlockDecl if CallableType::Block
+ const Decl *CDecl;
+
+ // Remember whether the callable is a function, block, virtual method,
+ // or (presumed) function pointer.
+ CallableType CType = CallableType::Unknown;
+
+ // Remember whether the callable is an operator new or delete function,
+ // so that calls to them are reported more meaningfully, as memory
+ // allocations.
+ SpecialFuncType FuncType = SpecialFuncType::None;
+
+ // We inevitably want to know the callable's declared effects, so cache them.
+ FunctionEffectKindSet Effects;
+
+ CallableInfo(const Decl &CD, SpecialFuncType FT = SpecialFuncType::None)
+ : CDecl(&CD), FuncType(FT) {
+ FunctionEffectsRef DeclEffects;
+ if (auto *FD = dyn_cast<FunctionDecl>(CDecl)) {
+ // Use the function's definition, if any.
+ if (const FunctionDecl *Def = FD->getDefinition())
+ CDecl = FD = Def;
+ CType = CallableType::Function;
+ if (auto *Method = dyn_cast<CXXMethodDecl>(FD);
+ Method && Method->isVirtual())
+ CType = CallableType::Virtual;
+ DeclEffects = FD->getFunctionEffects();
+ } else if (auto *BD = dyn_cast<BlockDecl>(CDecl)) {
+ CType = CallableType::Block;
+ DeclEffects = BD->getFunctionEffects();
+ } else if (auto *VD = dyn_cast<ValueDecl>(CDecl)) {
+ // ValueDecl is function, enum, or variable, so just look at its type.
+ DeclEffects = FunctionEffectsRef::get(VD->getType());
+ }
+ Effects = FunctionEffectKindSet(DeclEffects);
+ }
+
+ CallableType type() const { return CType; }
+
+ bool isCalledDirectly() const {
+ return CType == CallableType::Function || CType == CallableType::Block;
+ }
+
+ bool isVerifiable() const {
+ switch (CType) {
+ case CallableType::Unknown:
+ case CallableType::Virtual:
+ return false;
+ case CallableType::Block:
+ return true;
+ case CallableType::Function:
+ return functionIsVerifiable(dyn_cast<FunctionDecl>(CDecl));
+ }
+ llvm_unreachable("undefined CallableType");
+ }
+
+ /// Generate a name for logging and diagnostics.
+ std::string name(Sema &Sem) const {
+ std::string Name;
+ llvm::raw_string_ostream OS(Name);
+
+ if (auto *FD = dyn_cast<FunctionDecl>(CDecl))
+ FD->getNameForDiagnostic(OS, Sem.getPrintingPolicy(),
+ /*Qualified=*/true);
+ else if (auto *BD = dyn_cast<BlockDecl>(CDecl))
+ OS << "(block " << BD->getBlockManglingNumber() << ")";
+ else if (auto *VD = dyn_cast<NamedDecl>(CDecl))
+ VD->printQualifiedName(OS);
+ return Name;
+ }
+};
+
+// ----------
+// Map effects to single Violations, to hold the first (of potentially many)
+// violations pertaining to an effect, per function.
+class EffectToViolationMap {
+ // Since we currently only have a tiny number of effects (typically no more
+ // than 1), use a sorted SmallVector with an inline capacity of 1. Since it
+ // is often empty, use a unique_ptr to the SmallVector.
+ // Note that Violation itself contains a FunctionEffect which is the key.
+ using ImplVec = llvm::SmallVector<Violation, 1>;
+ std::unique_ptr<ImplVec> Impl;
+
+public:
+ // Insert a new Violation if we do not already have one for its effect.
+ void maybeInsert(const Violation &Viol) {
+ if (Impl == nullptr)
+ Impl = std::make_unique<ImplVec>();
+ auto *Iter = _find(Viol.Effect);
+ if (Iter != Impl->end() && Iter->Effect == Viol.Effect)
+ return;
+
+ Impl->insert(Iter, Viol);
+ }
+
+ const Violation *lookup(FunctionEffect Key) {
+ if (Impl == nullptr)
+ return nullptr;
+
+ auto *Iter = _find(Key);
+ if (Iter != Impl->end() && Iter->Effect == Key)
+ return &*Iter;
+
+ return nullptr;
+ }
+
+ size_t size() const { return Impl ? Impl->size() : 0; }
+
+private:
+ ImplVec::iterator _find(const FunctionEffect &key) {
+ // A linear search suffices for a tiny number of possible effects.
+ auto *End = Impl->end();
+ for (auto *Iter = Impl->begin(); Iter != End; ++Iter)
+ if (!(Iter->Effect < key))
+ return Iter;
+ return End;
+ }
+};
+
+// ----------
+// State pertaining to a function whose AST is walked and whose effect analysis
+// is dependent on a subsequent analysis of other functions.
+class PendingFunctionAnalysis {
+ friend class CompleteFunctionAnalysis;
+
+public:
+ struct DirectCall {
+ const Decl *Callee;
+ SourceLocation CallLoc;
+ // Not all recursive calls are detected, just enough
+ // to break cycles.
+ bool Recursed = false;
+
+ DirectCall(const Decl *D, SourceLocation CallLoc)
+ : Callee(D), CallLoc(CallLoc) {}
+ };
+
+ // We always have two disjoint sets of effects to verify:
+ // 1. Effects declared explicitly by this function.
+ // 2. All other inferrable effects needing verification.
+ FunctionEffectKindSet DeclaredVerifiableEffects;
+ FunctionEffectKindSet FXToInfer;
+
+private:
+ // Violations pertaining to the function's explicit effects.
+ SmallVector<Violation, 0> ViolationsForExplicitFX;
+
+ // Violations pertaining to other, non-explicit, inferrable effects.
+ EffectToViolationMap InferrableEffectToFirstViolation;
+
+ // These unverified direct calls are what keeps the analysis "pending",
+ // until the callees can be verified.
+ SmallVector<DirectCall, 0> UnverifiedDirectCalls;
+
+public:
+ PendingFunctionAnalysis(
+ Sema &Sem, const CallableInfo &CInfo,
+ const FunctionEffectKindSet &AllInferrableEffectsToVerify)
+ : DeclaredVerifiableEffects(CInfo.Effects) {
+ // Check for effects we are not allowed to infer
+ FunctionEffectKindSet InferrableFX;
+
+ for (const FunctionEffect &effect : AllInferrableEffectsToVerify) {
+ std::optional<FunctionEffect> ProblemCalleeEffect =
+ effect.effectProhibitingInference(*CInfo.CDecl, CInfo.Effects);
+ if (!ProblemCalleeEffect)
+ InferrableFX.insert(effect);
+ else {
+ // Add a Violation for this effect if a caller were to
+ // try to infer it.
+ InferrableEffectToFirstViolation.maybeInsert(Violation(
+ effect, ViolationID::DeclDisallowsInference,
+ CInfo.CDecl->getLocation(), nullptr, &*ProblemCalleeEffect));
+ }
+ }
+ // InferrableFX is now the set of inferrable effects which are not
+ // prohibited
+ FXToInfer = FunctionEffectKindSet::difference(InferrableFX,
+ DeclaredVerifiableEffects);
+ }
+
+ // Hide the way that Violations for explicitly required effects vs. inferred
+ // ones are handled differently.
+ void checkAddViolation(bool Inferring, const Violation &NewViol) {
+ if (!Inferring)
+ ViolationsForExplicitFX.push_back(NewViol);
+ else
+ InferrableEffectToFirstViolation.maybeInsert(NewViol);
+ }
+
+ void addUnverifiedDirectCall(const Decl *D, SourceLocation CallLoc) {
+ UnverifiedDirectCalls.emplace_back(D, CallLoc);
+ }
+
+ // Analysis is complete when there are no unverified direct calls.
+ bool isComplete() const { return UnverifiedDirectCalls.empty(); }
+
+ const Violation *violationForInferrableEffect(FunctionEffect effect) {
+ return InferrableEffectToFirstViolation.lookup(effect);
+ }
+
+ SmallVector<DirectCall, 0> &unverifiedCalls() {
+ assert(!isComplete());
+ return UnverifiedDirectCalls;
+ }
+
+ SmallVector<Violation, 0> &getViolationsForExplicitFX() {
+ return ViolationsForExplicitFX;
+ }
+
+ void dump(Sema &SemaRef, llvm::raw_ostream &OS) const {
+ OS << "Pending: Declared ";
+ DeclaredVerifiableEffects.dump(OS);
+ OS << ", " << ViolationsForExplicitFX.size() << " violations; ";
+ OS << " Infer ";
+ FXToInfer.dump(OS);
+ OS << ", " << InferrableEffectToFirstViolation.size() << " violations";
+ if (!UnverifiedDirectCalls.empty()) {
+ OS << "; Calls: ";
+ for (const DirectCall &Call : UnverifiedDirectCalls) {
+ CallableInfo CI(*Call.Callee);
+ OS << " " << CI.name(SemaRef);
+ }
+ }
+ OS << "\n";
+ }
+};
+
+// ----------
+class CompleteFunctionAnalysis {
+ // Current size: 2 pointers
+public:
+ // Has effects which are both the declared ones -- not to be inferred -- plus
+ // ones which have been successfully inferred. These are all considered
+ // "verified" for the purposes of callers; any issue with verifying declared
+ // effects has already been reported and is not the problem of any caller.
+ FunctionEffectKindSet VerifiedEffects;
+
+private:
+ // This is used to generate notes about failed inference.
+ EffectToViolationMap InferrableEffectToFirstViolation;
+
+public:
+ // The incoming Pending analysis is consumed (member(s) are moved-from).
+ CompleteFunctionAnalysis(
+ ASTContext &Ctx, PendingFunctionAnalysis &Pending,
+ const FunctionEffectKindSet &DeclaredEffects,
+ const FunctionEffectKindSet &AllInferrableEffectsToVerify)
+ : VerifiedEffects(DeclaredEffects) {
+ for (const FunctionEffect &effect : AllInferrableEffectsToVerify)
+ if (Pending.violationForInferrableEffect(effect) == nullptr)
+ VerifiedEffects.insert(effect);
+
+ InferrableEffectToFirstViolation =
+ std::move(Pending.InferrableEffectToFirstViolation);
+ }
+
+ const Violation *firstViolationForEffect(const FunctionEffect &Effect) {
+ return InferrableEffectToFirstViolation.lookup(Effect);
+ }
+
+ void dump(llvm::raw_ostream &OS) const {
+ OS << "Complete: Verified ";
+ VerifiedEffects.dump(OS);
+ OS << "; Infer ";
+ OS << InferrableEffectToFirstViolation.size() << " violations\n";
+ }
+};
+
+const Decl *CanonicalFunctionDecl(const Decl *D) {
+ if (auto *FD = dyn_cast<FunctionDecl>(D)) {
+ FD = FD->getCanonicalDecl();
+ assert(FD != nullptr);
+ return FD;
+ }
+ return D;
+}
+
+// ==========
+class Analyzer {
+ Sema &Sem;
+
+ // Subset of Sema.AllEffectsToVerify
+ FunctionEffectKindSet AllInferrableEffectsToVerify;
+
+ using FuncAnalysisPtr =
+ llvm::PointerUnion<PendingFunctionAnalysis *, CompleteFunctionAnalysis *>;
+
+ // Map all Decls analyzed to FuncAnalysisPtr. Pending state is larger
+ // than complete state, so use different objects to represent them.
+ // The state pointers are owned by the container.
+ class AnalysisMap : protected llvm::DenseMap<const Decl *, FuncAnalysisPtr> {
+ using Base = llvm::DenseMap<const Decl *, FuncAnalysisPtr>;
+
+ public:
+ ~AnalysisMap();
+
+ // Use non-public inheritance in order to maintain the invariant
+ // that lookups and insertions are via the canonical Decls.
+
+ FuncAnalysisPtr lookup(const Decl *Key) const {
+ return Base::lookup(CanonicalFunctionDecl(Key));
+ }
+
+ FuncAnalysisPtr &operator[](const Decl *Key) {
+ return Base::operator[](CanonicalFunctionDecl(Key));
+ }
+
+ /// Shortcut for the case where we only care about completed analysis.
+ CompleteFunctionAnalysis *completedAnalysisForDecl(const Decl *D) const {
+ if (FuncAnalysisPtr AP = lookup(D);
+ isa_and_nonnull<CompleteFunctionAnalysis *>(AP))
+ return AP.get<CompleteFunctionAnalysis *>();
+ return nullptr;
+ }
+
+ void dump(Sema &SemaRef, llvm::raw_ostream &OS) {
+ OS << "\nAnalysisMap:\n";
+ for (const auto &item : *this) {
+ CallableInfo CI(*item.first);
+ const auto AP = item.second;
+ OS << item.first << " " << CI.name(SemaRef) << " : ";
+ if (AP.isNull())
+ OS << "null\n";
+ else if (isa<CompleteFunctionAnalysis *>(AP)) {
+ auto *CFA = AP.get<CompleteFunctionAnalysis *>();
+ OS << CFA << " ";
+ CFA->dump(OS);
+ } else if (isa<PendingFunctionAnalysis *>(AP)) {
+ auto *PFA = AP.get<PendingFunctionAnalysis *>();
+ OS << PFA << " ";
+ PFA->dump(SemaRef, OS);
+ } else
+ llvm_unreachable("never");
+ }
+ OS << "---\n";
+ }
+ };
+ AnalysisMap DeclAnalysis;
+
+public:
+ Analyzer(Sema &S) : Sem(S) {}
+
+ void run(const TranslationUnitDecl &TU) {
+ // Gather all of the effects to be verified to see what operations need to
+ // be checked, and to see which ones are inferrable.
+ for (const FunctionEffect &Effect : Sem.AllEffectsToVerify) {
+ const FunctionEffect::Flags Flags = Effect.flags();
+ if (Flags & FunctionEffect::FE_InferrableOnCallees)
+ AllInferrableEffectsToVerify.insert(Effect);
+ }
+ LLVM_DEBUG(llvm::dbgs() << "AllInferrableEffectsToVerify: ";
+ AllInferrableEffectsToVerify.dump(llvm::dbgs());
+ llvm::dbgs() << "\n";);
+
+ // We can use DeclsWithEffectsToVerify as a stack for a
+ // depth-first traversal; there's no need for a second container. But first,
+ // reverse it, so when working from the end, Decls are verified in the order
+ // they are declared.
+ SmallVector<const Decl *> &VerificationQueue = Sem.DeclsWithEffectsToVerify;
+ std::reverse(VerificationQueue.begin(), VerificationQueue.end());
+
+ while (!VerificationQueue.empty()) {
+ const Decl *D = VerificationQueue.back();
+ if (FuncAnalysisPtr AP = DeclAnalysis.lookup(D)) {
+ if (isa<CompleteFunctionAnalysis *>(AP)) {
+ // already done
+ VerificationQueue.pop_back();
+ continue;
+ }
+ if (isa<PendingFunctionAnalysis *>(AP)) {
+ // All children have been traversed; finish analysis.
+ auto *Pending = AP.get<PendingFunctionAnalysis *>();
+ finishPendingAnalysis(D, Pending);
+ VerificationQueue.pop_back();
+ continue;
+ }
+ llvm_unreachable("unexpected DeclAnalysis item");
+ }
+
+ // Not previously visited; begin a new analysis for this Decl.
+ PendingFunctionAnalysis *Pending = verifyDecl(D);
+ if (Pending == nullptr) {
+ // completed now
+ VerificationQueue.pop_back();
+ continue;
+ }
+
+ // Analysis remains pending because there are direct callees to be
+ // verified first. Push them onto the queue.
+ for (PendingFunctionAnalysis::DirectCall &Call :
+ Pending->unverifiedCalls()) {
+ FuncAnalysisPtr AP = DeclAnalysis.lookup(Call.Callee);
+ if (AP.isNull()) {
+ VerificationQueue.push_back(Call.Callee);
+ continue;
+ }
+ if (isa<PendingFunctionAnalysis *>(AP)) {
+ // This indicates recursion (not necessarily direct). For the
+ // purposes of effect analysis, we can just ignore it since
+ // no effects forbid recursion.
+ Call.Recursed = true;
+ continue;
+ }
+ llvm_unreachable("unexpected DeclAnalysis item");
+ }
+ }
+ }
+
+private:
+ // Verify a single Decl. Return the pending structure if that was the result,
+ // else null. This method must not recurse.
+ PendingFunctionAnalysis *verifyDecl(const Decl *D) {
+ CallableInfo CInfo(*D);
+ bool isExternC = false;
+
+ if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
+ assert(FD->getBuiltinID() == 0);
+ isExternC = FD->getCanonicalDecl()->isExternCContext();
+ }
+
+ // For C++, with non-extern "C" linkage only - if any of the Decl's declared
+ // effects forbid throwing (e.g. nonblocking) then the function should also
+ // be declared noexcept.
+ if (Sem.getLangOpts().CPlusPlus && !isExternC) {
+ for (const FunctionEffect &Effect : CInfo.Effects) {
+ if (!(Effect.flags() & FunctionEffect::FE_ExcludeThrow))
+ continue;
+
+ bool IsNoexcept = false;
+ if (auto *FD = D->getAsFunction()) {
+ IsNoexcept = isNoexcept(FD);
+ } else if (auto *BD = dyn_cast<BlockDecl>(D)) {
+ if (auto *TSI = BD->getSignatureAsWritten()) {
+ auto *FPT = TSI->getType()->getAs<FunctionProtoType>();
+ IsNoexcept = FPT->isNothrow() || BD->hasAttr<NoThrowAttr>();
+ }
+ }
+ if (!IsNoexcept)
+ Sem.Diag(D->getBeginLoc(),
+ diag::warn_perf_constraint_implies_noexcept)
+ << Effect.name();
+ break;
+ }
+ }
+
+ // Build a PendingFunctionAnalysis on the stack. If it turns out to be
+ // complete, we'll have avoided a heap allocation; if it's incomplete, it's
+ // a fairly trivial move to a heap-allocated object.
+ PendingFunctionAnalysis FAnalysis(Sem, CInfo, AllInferrableEffectsToVerify);
+
+ LLVM_DEBUG(llvm::dbgs() << "\nVerifying " << CInfo.name(Sem) << " ";
+ FAnalysis.dump(Sem, llvm::dbgs()););
+
+ FunctionBodyASTVisitor Visitor(*this, FAnalysis, CInfo);
+
+ Visitor.run();
+ if (FAnalysis.isComplete()) {
+ completeAnalysis(CInfo, FAnalysis);
+ return nullptr;
+ }
+ // Move the pending analysis to the heap and save it in the map.
+ PendingFunctionAnalysis *PendingPtr =
+ new PendingFunctionAnalysis(std::move(FAnalysis));
+ DeclAnalysis[D] = PendingPtr;
+ LLVM_DEBUG(llvm::dbgs() << "inserted pending " << PendingPtr << "\n";
+ DeclAnalysis.dump(Sem, llvm::dbgs()););
+ return PendingPtr;
+ }
+
+ // Consume PendingFunctionAnalysis, create with it a CompleteFunctionAnalysis,
+ // inserted in the container.
+ void completeAnalysis(const CallableInfo &CInfo,
+ PendingFunctionAnalysis &Pending) {
+ if (SmallVector<Violation, 0> &Viols = Pending.getViolationsForExplicitFX();
----------------
Sirraide wrote:
```suggestion
if (ArrayRef<Violation> Viols = Pending.getViolationsForExplicitFX();
```
https://github.com/llvm/llvm-project/pull/99656
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