[clang] nonblocking/nonallocating attributes: 2nd pass caller/callee analysis (PR #99656)

[Doug Wyatt via cfe-commits]

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+//=== 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).
----------------
dougsonos wrote:

Done

https://github.com/llvm/llvm-project/pull/99656