[Modules] Record side effect info in EvaluatedStmt (#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

6 files changed, 16 insertions, 34 deletions

diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index 5cdf75d..e036224 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/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 {
diff --git a/clang/lib/Sema/MultiplexExternalSemaSource.cpp b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
index 9f19f13..fbfb242 100644
--- a/clang/lib/Sema/MultiplexExternalSemaSource.cpp
+++ b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
@@ -115,14 +115,6 @@ bool MultiplexExternalSemaSource::wasThisDeclarationADefinition(
   return false;
 }
 
-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,
     const DeclContext *OriginalDC) {
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index d42847a..d380afd 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -9733,10 +9733,6 @@ bool ASTReader::wasThisDeclarationADefinition(const FunctionDecl *FD) {
   return ThisDeclarationWasADefinitionSet.contains(FD);
 }
 
-bool ASTReader::hasInitializerWithSideEffects(const VarDecl *VD) const {
-  return InitSideEffectVars.count(VD);
-}
-
 Selector ASTReader::getLocalSelector(ModuleFile &M, unsigned LocalID) {
   return DecodeSelector(getGlobalSelectorID(M, LocalID));
 }
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 0ffd784..8bde213 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -1628,9 +1628,6 @@ 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 =
@@ -1701,6 +1698,8 @@ 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())
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 874b24b..2bd9ae5 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -7320,6 +7320,10 @@ 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();
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 7f1b39c..a4474bb 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1305,7 +1305,6 @@ 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();