[Modules] Record side effect info in EvaluatedStmt (llvm#146468)

All deserialized VarDecl initializers are EvaluatedStmt, but not all
EvaluatedStmt initializers are from a PCH. Calling
`VarDecl::hasInitWithSideEffects` can trigger constant evaluation, but
it's hard to know ahead of time whether that will trigger
deserialization - even if the initializer is fully deserialized, it may
contain a call to a constructor whose body is not deserialized. By
caching the result of `VarDecl::hasInitWithSideEffects` and populating
that cache during deserialization we can guarantee that calling it won't
trigger deserialization regardless of the state of the initializer.
This also reduces memory usage by removing the `InitSideEffectVars` set
in `ASTReader`.

rdar://154717930
(cherry picked from commit 2910c24)

Author: hnrklssn

clang/include/clang/AST/Decl.h

@@ -874,13 +874,17 @@ struct EvaluatedStmt {
   bool HasICEInit : 1;
   bool CheckedForICEInit : 1;
 
+  bool HasSideEffects : 1;
+  bool CheckedForSideEffects : 1;
+
   LazyDeclStmtPtr Value;
   APValue Evaluated;
 
   EvaluatedStmt()
       : WasEvaluated(false), IsEvaluating(false),
         HasConstantInitialization(false), HasConstantDestruction(false),
-        HasICEInit(false), CheckedForICEInit(false) {}
+        HasICEInit(false), CheckedForICEInit(false), HasSideEffects(false),
+        CheckedForSideEffects(false) {}
 };
 
 /// Represents a variable declaration or definition.
@@ -1339,9 +1343,11 @@ class VarDecl : public DeclaratorDecl, public Redeclarable<VarDecl> {
     return const_cast<VarDecl *>(this)->getInitializingDeclaration();
   }
 
-  /// Checks whether this declaration has an initializer with side effects,
-  /// without triggering deserialization if the initializer is not yet
-  /// deserialized.
+  /// Checks whether this declaration has an initializer with side effects.
+  /// The result is cached. If the result hasn't been computed this can trigger
+  /// deserialization and constant evaluation. By running this during
+  /// serialization and serializing the result all clients can safely call this
+  /// without triggering further deserialization.
   bool hasInitWithSideEffects() const;
 
   /// Determine whether this variable's value might be usable in a

clang/include/clang/AST/ExternalASTSource.h

@@ -174,10 +174,6 @@ class ExternalASTSource : public RefCountedBase<ExternalASTSource> {
 
   virtual ExtKind hasExternalDefinitions(const Decl *D);
 
-  virtual bool hasInitializerWithSideEffects(const VarDecl *VD) const {
-    return false;
-  }
-
   /// Finds all declarations lexically contained within the given
   /// DeclContext, after applying an optional filter predicate.
   ///
@@ -412,17 +408,6 @@ struct LazyOffsetPtr {
     return GetPtr();
   }
 
-  /// Retrieve the pointer to the AST node that this lazy pointer points to,
-  /// if it can be done without triggering deserialization.
-  ///
-  /// \returns a pointer to the AST node, or null if not yet deserialized.
-  T *getWithoutDeserializing() const {
-    if (isOffset()) {
-      return nullptr;
-    }
-    return GetPtr();
-  }
-
   /// Retrieve the address of the AST node pointer. Deserializes the pointee if
   /// necessary.
   T **getAddressOfPointer(ExternalASTSource *Source) const {

clang/include/clang/Sema/MultiplexExternalSemaSource.h

@@ -92,8 +92,6 @@ class MultiplexExternalSemaSource : public ExternalSemaSource {
 
   ExtKind hasExternalDefinitions(const Decl *D) override;
 
-  bool hasInitializerWithSideEffects(const VarDecl *VD) const override;
-
   /// Find all declarations with the given name in the
   /// given context.
   bool FindExternalVisibleDeclsByName(const DeclContext *DC,

clang/include/clang/Serialization/ASTReader.h

@@ -1348,12 +1348,6 @@ class ASTReader
     const StringRef &operator*() && = delete;
   };
 
-  /// VarDecls with initializers containing side effects must be emitted,
-  /// but DeclMustBeEmitted is not allowed to deserialize the intializer.
-  /// FIXME: Lower memory usage by removing VarDecls once the initializer
-  /// is deserialized.
-  llvm::SmallPtrSet<Decl *, 16> InitSideEffectVars;
-
 public:
   /// Get the buffer for resolving paths.
   SmallString<0> &getPathBuf() { return PathBuf; }
@@ -2269,8 +2263,6 @@ class ASTReader
 
   ExtKind hasExternalDefinitions(const Decl *D) override;
 
-  bool hasInitializerWithSideEffects(const VarDecl *VD) const override;
-
   /// Retrieve a selector from the given module with its local ID
   /// number.
   Selector getLocalSelector(ModuleFile &M, unsigned LocalID);

clang/lib/AST/Decl.cpp

@@ -2444,24 +2444,16 @@ bool VarDecl::hasInitWithSideEffects() const {
   if (!hasInit())
     return false;
 
-  // Check if we can get the initializer without deserializing
-  const Expr *E = nullptr;
-  if (auto *S = dyn_cast<Stmt *>(Init)) {
-    E = cast<Expr>(S);
-  } else {
-    E = cast_or_null<Expr>(getEvaluatedStmt()->Value.getWithoutDeserializing());
-  }
-
-  if (E)
-    return E->HasSideEffects(getASTContext()) &&
-           // We can get a value-dependent initializer during error recovery.
-           (E->isValueDependent() || !evaluateValue());
-
-  assert(getEvaluatedStmt()->Value.isOffset());
-  // ASTReader tracks this without having to deserialize the initializer
-  if (auto Source = getASTContext().getExternalSource())
-    return Source->hasInitializerWithSideEffects(this);
-  return false;
+  EvaluatedStmt *ES = ensureEvaluatedStmt();
+  if (!ES->CheckedForSideEffects) {
+    const Expr *E = getInit();
+    ES->HasSideEffects =
+        E->HasSideEffects(getASTContext()) &&
+        // We can get a value-dependent initializer during error recovery.
+        (E->isValueDependent() || !evaluateValue());
+    ES->CheckedForSideEffects = true;
+  }
+  return ES->HasSideEffects;
 }
 
 bool VarDecl::isOutOfLine() const {

clang/lib/Sema/MultiplexExternalSemaSource.cpp

@@ -107,14 +107,6 @@ MultiplexExternalSemaSource::hasExternalDefinitions(const Decl *D) {
   return EK_ReplyHazy;
 }
 
-bool MultiplexExternalSemaSource::hasInitializerWithSideEffects(
-    const VarDecl *VD) const {
-  for (const auto &S : Sources)
-    if (S->hasInitializerWithSideEffects(VD))
-      return true;
-  return false;
-}
-
 bool MultiplexExternalSemaSource::
 FindExternalVisibleDeclsByName(const DeclContext *DC, DeclarationName Name) {
   bool AnyDeclsFound = false;

clang/lib/Serialization/ASTReader.cpp

@@ -9268,10 +9268,6 @@ ExternalASTSource::ExtKind ASTReader::hasExternalDefinitions(const Decl *FD) {
   return I->second ? EK_Never : EK_Always;
 }
 
-bool ASTReader::hasInitializerWithSideEffects(const VarDecl *VD) const {
-  return InitSideEffectVars.count(VD);
-}
-
 Selector ASTReader::getLocalSelector(ModuleFile &M, unsigned LocalID) {
   return DecodeSelector(getGlobalSelectorID(M, LocalID));
 }

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -1622,9 +1622,6 @@ ASTDeclReader::RedeclarableResult ASTDeclReader::VisitVarDeclImpl(VarDecl *VD) {
     VD->NonParmVarDeclBits.PreviousDeclInSameBlockScope =
         VarDeclBits.getNextBit();
 
-    if (VarDeclBits.getNextBit())
-      Reader.InitSideEffectVars.insert(VD);
-
     VD->NonParmVarDeclBits.EscapingByref = VarDeclBits.getNextBit();
     HasDeducedType = VarDeclBits.getNextBit();
     VD->NonParmVarDeclBits.ImplicitParamKind =
@@ -1695,6 +1692,8 @@ void ASTDeclReader::ReadVarDeclInit(VarDecl *VD) {
     Eval->HasConstantInitialization = (Val & 2) != 0;
     Eval->HasConstantDestruction = (Val & 4) != 0;
     Eval->WasEvaluated = (Val & 8) != 0;
+    Eval->HasSideEffects = (Val & 16) != 0;
+    Eval->CheckedForSideEffects = true;
     if (Eval->WasEvaluated) {
       Eval->Evaluated = Record.readAPValue();
       if (Eval->Evaluated.needsCleanup())

clang/lib/Serialization/ASTWriter.cpp

@@ -6834,6 +6834,10 @@ void ASTRecordWriter::AddVarDeclInit(const VarDecl *VD) {
 
   uint64_t Val = 1;
   if (EvaluatedStmt *ES = VD->getEvaluatedStmt()) {
+    // This may trigger evaluation, so run it first
+    if (VD->hasInitWithSideEffects())
+      Val |= 16;
+    assert(ES->CheckedForSideEffects);
     Val |= (ES->HasConstantInitialization ? 2 : 0);
     Val |= (ES->HasConstantDestruction ? 4 : 0);
     APValue *Evaluated = VD->getEvaluatedValue();

clang/lib/Serialization/ASTWriterDecl.cpp

@@ -1158,7 +1158,6 @@ void ASTDeclWriter::VisitVarDecl(VarDecl *D) {
     VarDeclBits.addBit(D->isConstexpr());
     VarDeclBits.addBit(D->isInitCapture());
     VarDeclBits.addBit(D->isPreviousDeclInSameBlockScope());
-    VarDeclBits.addBit(D->hasInitWithSideEffects());
 
     VarDeclBits.addBit(D->isEscapingByref());
     HasDeducedType = D->getType()->getContainedDeducedType();