[clang] nonblocking/nonallocating attributes (was: nolock/noalloc) (PR #84983)

[via cfe-commits]

================
@@ -4639,6 +4644,312 @@ class FunctionNoProtoType : public FunctionType, public llvm::FoldingSetNode {
   }
 };
 
+// ------------------------------------------------------------------------------
+
+class Decl;
+class CXXMethodDecl;
+struct FunctionEffectDiff;
+class FunctionEffectsRef;
+class FunctionEffectSet;
+
+/// Represents an abstract function effect, using just an enumeration describing
+/// its kind.
+class FunctionEffect {
+public:
+  /// Identifies the particular effect.
+  enum class Kind : uint8_t {
+    None = 0,
+    NonBlocking = 1,
+    NonAllocating = 2,
+    Blocking = 3,
+    Allocating = 4
+  };
+
+  /// Flags describing some behaviors of the effect.
+  using Flags = unsigned;
+  enum FlagBit : Flags {
+    // Can verification inspect callees' implementations? (e.g. nonblocking:
+    // yes, tcb+types: no). This also implies the need for 2nd-pass
+    // verification.
+    FE_InferrableOnCallees = 0x1,
+
+    // Language constructs which effects can diagnose as disallowed.
+    FE_ExcludeThrow = 0x2,
+    FE_ExcludeCatch = 0x4,
+    FE_ExcludeObjCMessageSend = 0x8,
+    FE_ExcludeStaticLocalVars = 0x10,
+    FE_ExcludeThreadLocalVars = 0x20
+  };
+
+private:
+  LLVM_PREFERRED_TYPE(Kind)
+  unsigned FKind : 3;
+
+  // Expansion: for hypothetical TCB+types, there could be one Kind for TCB,
+  // then ~16(?) bits "SubKind" to map to a specific named TCB. SubKind would
+  // be considered for uniqueness.
+
+public:
+  FunctionEffect() : FKind(unsigned(Kind::None)) {}
+
+  explicit FunctionEffect(Kind K) : FKind(unsigned(K)) {}
+
+  /// The kind of the effect.
+  Kind kind() const { return Kind(FKind); }
+
+  /// Return the opposite kind, for effects which have opposites.
+  Kind oppositeKind() const;
+
+  /// For serialization.
+  uint32_t toOpaqueInt32() const { return FKind; }
+  static FunctionEffect fromOpaqueInt32(uint32_t Value) {
+    return FunctionEffect(Kind(Value));
+  }
+
+  /// Flags describing some behaviors of the effect.
+  Flags flags() const {
+    switch (kind()) {
+    case Kind::NonBlocking:
+      return FE_InferrableOnCallees | FE_ExcludeThrow | FE_ExcludeCatch |
+             FE_ExcludeObjCMessageSend | FE_ExcludeStaticLocalVars |
+             FE_ExcludeThreadLocalVars;
+    case Kind::NonAllocating:
+      // Same as NonBlocking, except without FE_ExcludeStaticLocalVars
+      return FE_InferrableOnCallees | FE_ExcludeThrow | FE_ExcludeCatch |
+             FE_ExcludeObjCMessageSend | FE_ExcludeThreadLocalVars;
+    case Kind::Blocking:
+    case Kind::Allocating:
+      return 0;
+    case Kind::None:
+      break;
+    }
+    llvm_unreachable("unknown effect kind");
+  }
+
+  /// The description printed in diagnostics, e.g. 'nonblocking'.
+  StringRef name() const;
+
+  /// Return true if the effect is allowed to be inferred on the callee,
+  /// which is either a FunctionDecl or BlockDecl.
+  /// This is only used if the effect has FE_InferrableOnCallees flag set.
+  /// Example: This allows nonblocking(false) to prevent inference for the
+  /// function.
+  bool canInferOnFunction(const Decl &Callee) const;
+
+  // Return false for success. When true is returned for a direct call, then the
+  // FE_InferrableOnCallees flag may trigger inference rather than an immediate
+  // diagnostic. Caller should be assumed to have the effect (it may not have it
+  // explicitly when inferring).
+  bool shouldDiagnoseFunctionCall(bool Direct,
+                                  ArrayRef<FunctionEffect> CalleeFX) const;
+
+  friend bool operator==(const FunctionEffect &LHS, const FunctionEffect &RHS) {
+    return LHS.FKind == RHS.FKind;
+  }
+  friend bool operator!=(const FunctionEffect &LHS, const FunctionEffect &RHS) {
+    return !(LHS == RHS);
+  }
+  friend bool operator<(const FunctionEffect &LHS, const FunctionEffect &RHS) {
+    return LHS.FKind < RHS.FKind;
+  }
+};
+
+/// Wrap a function effect's condition expression in another struct so
+/// that FunctionProtoType's TrailingObjects can treat it separately.
+class FunctionEffectCondition {
+  Expr *Cond = nullptr; // if null, unconditional
+
+public:
+  FunctionEffectCondition() = default;
+  FunctionEffectCondition(Expr *E) : Cond(E) {} // implicit OK
+
+  Expr *expr() const { return Cond; }
+
+  bool operator==(const FunctionEffectCondition &RHS) const {
+    return Cond == RHS.Cond;
+  }
+};
+
+/// A FunctionEffect plus a potential boolean expression determining whether
+/// the effect is declared (e.g. nonblocking(expr)). Generally the condition
+/// expression when present, is dependent.
+struct FunctionEffectWithCondition {
+  FunctionEffect Effect;
+  FunctionEffectCondition Cond;
+
+  /// Return a textual description of the effect, and its condition, if any.
+  std::string description() const;
+};
+
+struct FunctionEffectDiff {
+  enum class Kind { Added, Removed, ConditionMismatch };
+
+  FunctionEffect::Kind EffectKind;
+  Kind DiffKind;
+  FunctionEffectWithCondition Old; // invalid when Added
+  FunctionEffectWithCondition New; // invalid when Removed
+
+  StringRef effectName() const {
+    if (Old.Effect.kind() != FunctionEffect::Kind::None)
+      return Old.Effect.name();
+    return New.Effect.name();
+  }
+
+  /// Describes the result of effects differing between a base class's virtual
+  /// method and an overriding method in a subclass.
+  enum class OverrideResult {
+    NoAction,
+    Warn,
+    Merge // Merge missing effect from base to derived
+  };
+
+  /// Return true if adding or removing the effect as part of a type conversion
+  /// should generate a diagnostic.
+  bool shouldDiagnoseConversion(QualType SrcType,
+                                const FunctionEffectsRef &SrcFX,
+                                QualType DstType,
+                                const FunctionEffectsRef &DstFX) const;
+
+  /// Return true if adding or removing the effect in a redeclaration should
+  /// generate a diagnostic.
+  bool shouldDiagnoseRedeclaration(const FunctionDecl &OldFunction,
+                                   const FunctionEffectsRef &OldFX,
+                                   const FunctionDecl &NewFunction,
+                                   const FunctionEffectsRef &NewFX) const;
+
+  /// Return true if adding or removing the effect in a C++ virtual method
+  /// override should generate a diagnostic.
+  OverrideResult shouldDiagnoseMethodOverride(
+      const CXXMethodDecl &OldMethod, const FunctionEffectsRef &OldFX,
+      const CXXMethodDecl &NewMethod, const FunctionEffectsRef &NewFX) const;
+};
+
+/// Support iteration in parallel through a pair of FunctionEffect and
+/// FunctionEffectCondition containers.
+template <typename Container> class FunctionEffectIterator {
+  const Container &Outer;
+  size_t Idx;
+
+public:
+  FunctionEffectIterator(const Container &O, size_t I) : Outer(O), Idx(I) {}
+  bool operator==(const FunctionEffectIterator &Other) const {
+    return Idx == Other.Idx;
+  }
+  bool operator!=(const FunctionEffectIterator &Other) const {
+    return Idx != Other.Idx;
+  }
+
+  // prefix increment
+  FunctionEffectIterator operator++() {
+    ++Idx;
+    return *this;
+  }
+
+  FunctionEffectWithCondition operator*() const {
+    const bool HasConds = !Outer.Conditions.empty();
+    return FunctionEffectWithCondition{Outer.Effects[Idx],
+                                       HasConds ? Outer.Conditions[Idx]
+                                                : FunctionEffectCondition()};
+  }
+};
+
+/// An immutable set of FunctionEffects and possibly conditions attached to
+/// them. The effects and conditions reside in memory not managed by this object
+/// (typically, trailing objects in FunctionProtoType, or borrowed references
+/// from a FunctionEffectSet).
+///
+/// Invariant: there is never more than one instance of any given effect.
+class FunctionEffectsRef {
+  ArrayRef<FunctionEffect> Effects;
+
+  // The array of conditions is either empty or has the same size
+  // as the array of effects.
+  ArrayRef<FunctionEffectCondition> Conditions;
+
+public:
+  /// Extract the effects from a Type if it is a function, block, or member
+  /// function pointer, or a reference or pointer to one.
+  static FunctionEffectsRef get(QualType QT);
+
+  FunctionEffectsRef() = default;
+
+  // The arrays are expected to have been sorted by the caller.
----------------
Sirraide wrote:

> Asserting is easy with `std::is_sorted()`.

Ah yeah; I candidly forgot it existed because I almost never have a reason to use it.

> add FunctionProtoType and FunctionEffectSet as friends, making them both responsible for the invariant.

If that doesn’t make the rest of the code much more complicated then I’d go with that; I’m just worried about a function (in this case a constructor) that has invariants that are supposed to be checked by the caller, but which anyone can just call without checking them.



https://github.com/llvm/llvm-project/pull/84983