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

- In Sema, when encountering Decls with function effects needing
verification, add them to a vector, DeclsWithEffectsToVerify.
- Update AST serialization to include DeclsWithEffectsToVerify.
- In AnalysisBasedWarnings, use DeclsWithEffectsToVerify as a work
queue, verifying functions with declared effects, and inferring (when
permitted and necessary) whether their callees have effects.

---------

Co-authored-by: Doug Wyatt <[email protected]>
Co-authored-by: Sirraide <[email protected]>
Co-authored-by: Erich Keane <[email protected]>

Author: 4 people

clang/docs/ReleaseNotes.rst

@@ -632,6 +632,11 @@ New features
   if class of allocation and deallocation function mismatches.
   `Documentation <https://clang.llvm.org/docs/analyzer/checkers.html#unix-mismatcheddeallocator-c-c>`__.
 
+- Function effects, e.g. the ``nonblocking`` and ``nonallocating`` "performance constraint" 
+  attributes, are now verified. For example, for functions declared with the ``nonblocking`` 
+  attribute, the compiler can generate warnings about the use of any language features, or calls to
+  other functions, which may block.
+
 Crash and bug fixes
 ^^^^^^^^^^^^^^^^^^^
 

clang/include/clang/AST/Type.h

@@ -49,6 +49,7 @@
 #include "llvm/Support/PointerLikeTypeTraits.h"
 #include "llvm/Support/TrailingObjects.h"
 #include "llvm/Support/type_traits.h"
+#include <bitset>
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
@@ -119,6 +120,8 @@ class EnumDecl;
 class Expr;
 class ExtQualsTypeCommonBase;
 class FunctionDecl;
+class FunctionEffectsRef;
+class FunctionEffectKindSet;
 class FunctionEffectSet;
 class IdentifierInfo;
 class NamedDecl;
@@ -4712,12 +4715,13 @@ class FunctionEffect {
 public:
   /// Identifies the particular effect.
   enum class Kind : uint8_t {
-    None = 0,
-    NonBlocking = 1,
-    NonAllocating = 2,
-    Blocking = 3,
-    Allocating = 4
+    NonBlocking,
+    NonAllocating,
+    Blocking,
+    Allocating,
+    Last = Allocating
   };
+  constexpr static size_t KindCount = static_cast<size_t>(Kind::Last) + 1;
 
   /// Flags describing some behaviors of the effect.
   using Flags = unsigned;
@@ -4743,8 +4747,6 @@ class FunctionEffect {
   // be considered for uniqueness.
 
 public:
-  FunctionEffect() : FKind(Kind::None) {}
-
   explicit FunctionEffect(Kind K) : FKind(K) {}
 
   /// The kind of the effect.
@@ -4773,35 +4775,43 @@ class FunctionEffect {
     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.
+  friend raw_ostream &operator<<(raw_ostream &OS,
+                                 const FunctionEffect &Effect) {
+    OS << Effect.name();
+    return OS;
+  }
+
+  /// Determine whether the effect is allowed to be inferred on the callee,
+  /// which is either a FunctionDecl or BlockDecl. If the returned optional
+  /// is empty, inference is permitted; otherwise it holds the effect which
+  /// blocked inference.
   /// Example: This allows nonblocking(false) to prevent inference for the
   /// function.
-  bool canInferOnFunction(const Decl &Callee) const;
+  std::optional<FunctionEffect>
+  effectProhibitingInference(const Decl &Callee,
+                             FunctionEffectKindSet CalleeFX) 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;
+                                  FunctionEffectKindSet CalleeFX) const;
 
-  friend bool operator==(const FunctionEffect &LHS, const FunctionEffect &RHS) {
+  friend bool operator==(FunctionEffect LHS, FunctionEffect RHS) {
     return LHS.FKind == RHS.FKind;
   }
-  friend bool operator!=(const FunctionEffect &LHS, const FunctionEffect &RHS) {
+  friend bool operator!=(FunctionEffect LHS, FunctionEffect RHS) {
     return !(LHS == RHS);
   }
-  friend bool operator<(const FunctionEffect &LHS, const FunctionEffect &RHS) {
+  friend bool operator<(FunctionEffect LHS, FunctionEffect RHS) {
     return LHS.FKind < RHS.FKind;
   }
 };
@@ -4829,13 +4839,14 @@ struct FunctionEffectWithCondition {
   FunctionEffect Effect;
   EffectConditionExpr Cond;
 
-  FunctionEffectWithCondition() = default;
-  FunctionEffectWithCondition(const FunctionEffect &E,
-                              const EffectConditionExpr &C)
+  FunctionEffectWithCondition(FunctionEffect E, const EffectConditionExpr &C)
       : Effect(E), Cond(C) {}
 
   /// Return a textual description of the effect, and its condition, if any.
   std::string description() const;
+
+  friend raw_ostream &operator<<(raw_ostream &OS,
+                                 const FunctionEffectWithCondition &CFE);
 };
 
 /// Support iteration in parallel through a pair of FunctionEffect and
@@ -4940,6 +4951,85 @@ class FunctionEffectsRef {
   void dump(llvm::raw_ostream &OS) const;
 };
 
+/// A mutable set of FunctionEffect::Kind.
+class FunctionEffectKindSet {
+  // For now this only needs to be a bitmap.
+  constexpr static size_t EndBitPos = FunctionEffect::KindCount;
+  using KindBitsT = std::bitset<EndBitPos>;
+
+  KindBitsT KindBits{};
+
+  explicit FunctionEffectKindSet(KindBitsT KB) : KindBits(KB) {}
+
+  // Functions to translate between an effect kind, starting at 1, and a
+  // position in the bitset.
+
+  constexpr static size_t kindToPos(FunctionEffect::Kind K) {
+    return static_cast<size_t>(K);
+  }
+
+  constexpr static FunctionEffect::Kind posToKind(size_t Pos) {
+    return static_cast<FunctionEffect::Kind>(Pos);
+  }
+
+  // Iterates through the bits which are set.
+  class iterator {
+    const FunctionEffectKindSet *Outer = nullptr;
+    size_t Idx = 0;
+
+    // If Idx does not reference a set bit, advance it until it does,
+    // or until it reaches EndBitPos.
+    void advanceToNextSetBit() {
+      while (Idx < EndBitPos && !Outer->KindBits.test(Idx))
+        ++Idx;
+    }
+
+  public:
+    iterator();
+    iterator(const FunctionEffectKindSet &O, size_t I) : Outer(&O), Idx(I) {
+      advanceToNextSetBit();
+    }
+    bool operator==(const iterator &Other) const { return Idx == Other.Idx; }
+    bool operator!=(const iterator &Other) const { return Idx != Other.Idx; }
+
+    iterator operator++() {
+      ++Idx;
+      advanceToNextSetBit();
+      return *this;
+    }
+
+    FunctionEffect operator*() const {
+      assert(Idx < EndBitPos && "Dereference of end iterator");
+      return FunctionEffect(posToKind(Idx));
+    }
+  };
+
+public:
+  FunctionEffectKindSet() = default;
+  explicit FunctionEffectKindSet(FunctionEffectsRef FX) { insert(FX); }
+
+  iterator begin() const { return iterator(*this, 0); }
+  iterator end() const { return iterator(*this, EndBitPos); }
+
+  void insert(FunctionEffect Effect) { KindBits.set(kindToPos(Effect.kind())); }
+  void insert(FunctionEffectsRef FX) {
+    for (FunctionEffect Item : FX.effects())
+      insert(Item);
+  }
+  void insert(FunctionEffectKindSet Set) { KindBits |= Set.KindBits; }
+
+  bool empty() const { return KindBits.none(); }
+  bool contains(const FunctionEffect::Kind EK) const {
+    return KindBits.test(kindToPos(EK));
+  }
+  void dump(llvm::raw_ostream &OS) const;
+
+  static FunctionEffectKindSet difference(FunctionEffectKindSet LHS,
+                                          FunctionEffectKindSet RHS) {
+    return FunctionEffectKindSet(LHS.KindBits & ~RHS.KindBits);
+  }
+};
+
 /// A mutable set of FunctionEffects and possibly conditions attached to them.
 /// Used to compare and merge effects on declarations.
 ///

clang/include/clang/Basic/AttrDocs.td

@@ -8482,9 +8482,9 @@ compiler warnings:
 - A redeclaration of a ``nonblocking`` or ``nonallocating`` function must also be declared with
   the same attribute (or a stronger one). A redeclaration may add an attribute.
 
-The warnings are controlled by ``-Wfunction-effects``, which is enabled by default.
+The warnings are controlled by ``-Wfunction-effects``, which is disabled by default.
 
-In a future commit, the compiler will diagnose function calls from ``nonblocking`` and ``nonallocating``
+The compiler also diagnoses function calls from ``nonblocking`` and ``nonallocating``
 functions to other functions which lack the appropriate attribute.
   }];
 }

clang/include/clang/Basic/DiagnosticGroups.td

@@ -1125,6 +1125,11 @@ def ThreadSafety : DiagGroup<"thread-safety",
 def ThreadSafetyVerbose : DiagGroup<"thread-safety-verbose">;
 def ThreadSafetyBeta : DiagGroup<"thread-safety-beta">;
 
+// Warnings and notes related to the function effects system which underlies
+// the nonblocking and nonallocating attributes.
+def FunctionEffects : DiagGroup<"function-effects">;
+def PerfConstraintImpliesNoexcept : DiagGroup<"perf-constraint-implies-noexcept">;
+
 // Uniqueness Analysis warnings
 def Consumed       : DiagGroup<"consumed">;
 
@@ -1133,7 +1138,7 @@ def Consumed       : DiagGroup<"consumed">;
 // DefaultIgnore in addition to putting it here.
 def All : DiagGroup<"all", [Most, Parentheses, Switch, SwitchBool,
                             MisleadingIndentation, PackedNonPod,
-                            VLACxxExtension]>;
+                            VLACxxExtension, PerfConstraintImpliesNoexcept]>;
 
 // Warnings that should be in clang-cl /w4.
 def : DiagGroup<"CL4", [All, Extra]>;
@@ -1566,10 +1571,6 @@ def UnsafeBufferUsageInContainer : DiagGroup<"unsafe-buffer-usage-in-container">
 def UnsafeBufferUsageInLibcCall : DiagGroup<"unsafe-buffer-usage-in-libc-call">;
 def UnsafeBufferUsage : DiagGroup<"unsafe-buffer-usage", [UnsafeBufferUsageInContainer, UnsafeBufferUsageInLibcCall]>;
 
-// Warnings and notes related to the function effects system underlying
-// the nonblocking and nonallocating attributes.
-def FunctionEffects : DiagGroup<"function-effects">;
-
 // Warnings and notes InstallAPI verification.
 def InstallAPIViolation : DiagGroup<"installapi-violation">;
 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10972,19 +10972,68 @@ def warn_imp_cast_drops_unaligned : Warning<
   InGroup<DiagGroup<"unaligned-qualifier-implicit-cast">>;
 
 // Function effects
+def warn_func_effect_violation : Warning<
+  "%select{function|constructor|destructor|lambda|block|member initializer of constructor}0 "
+  "with '%1' attribute "
+  "must not %select{allocate or deallocate memory|throw or catch exceptions|"
+  "have static local variables|use thread-local variables|access ObjC methods or properties}2">,
+  InGroup<FunctionEffects>, DefaultIgnore;
+def note_func_effect_violation : Note<
+  "%select{function|constructor|destructor|lambda|block|member initializer}0 "
+  "cannot be inferred '%1' because it "
+  "%select{allocates or deallocates memory|throws or catches exceptions|"
+  "has a static local variable|uses a thread-local variable|"
+  "accesses an ObjC method or property}2">;
+def warn_func_effect_calls_func_without_effect : Warning<
+  "%select{function|constructor|destructor|lambda|block|member initializer of constructor}0 "
+  "with '%1' attribute "
+  "must not call non-'%1' "
+  "%select{function|constructor|destructor|lambda|block}2 "
+  "'%3'">,
+  InGroup<FunctionEffects>, DefaultIgnore;
+def note_func_effect_calls_func_without_effect : Note<
+  "%select{function|constructor|destructor|lambda|block|member initializer}0 "
+  "cannot be inferred '%1' because it calls non-'%1' "
+  "%select{function|constructor|destructor|lambda|block}2 "
+  "'%3'">;
+def warn_func_effect_calls_expr_without_effect : Warning<
+  "%select{function|constructor|destructor|lambda|block|member initializer of constructor}0 "
+  "with '%1' attribute "
+  "must not call non-'%1' expression">,
+  InGroup<FunctionEffects>, DefaultIgnore;
+def note_func_effect_call_extern : Note<
+  "declaration cannot be inferred '%0' because it has no definition in this translation unit">;
+def note_func_effect_call_disallows_inference : Note<
+  "%select{function|constructor|destructor|lambda|block}0 "
+  "does not permit inference of '%1' because it is declared '%2'">;
+def note_func_effect_call_indirect : Note<
+  "%select{virtual method|function pointer}0 cannot be inferred '%1'">;
+def warn_perf_constraint_implies_noexcept : Warning<
+  "%select{function|constructor|destructor|lambda|block}0 "
+  "with '%1' attribute should be declared noexcept">,
+  InGroup<PerfConstraintImpliesNoexcept>, DefaultIgnore;
+
+// FIXME: It would be nice if we could provide fuller template expansion notes.
+def note_func_effect_from_template : Note<
+  "in template expansion here">;
+def note_func_effect_in_constructor : Note<
+  "in%select{| implicit}0 constructor here">;
+def note_in_evaluating_default_argument : Note<
+  "in evaluating default argument here">;
+
 // spoofing nonblocking/nonallocating
 def warn_invalid_add_func_effects : Warning<
   "attribute '%0' should not be added via type conversion">,
-  InGroup<FunctionEffects>;
+  InGroup<FunctionEffects>, DefaultIgnore;
 def warn_mismatched_func_effect_override : Warning<
   "attribute '%0' on overriding function does not match base declaration">,
-  InGroup<FunctionEffects>;
+  InGroup<FunctionEffects>, DefaultIgnore;
 def warn_mismatched_func_effect_redeclaration : Warning<
   "attribute '%0' on function does not match previous declaration">,
-  InGroup<FunctionEffects>;
+  InGroup<FunctionEffects>, DefaultIgnore;
 def warn_conflicting_func_effects : Warning<
   "effects conflict when merging declarations; kept '%0', discarded '%1'">,
-  InGroup<FunctionEffects>;
+  InGroup<FunctionEffects>, DefaultIgnore;
 def err_func_with_effects_no_prototype : Error<
   "'%0' function must have a prototype">;