[Modules] Record whether VarDecl initializers contain side effects (#143739)

Calling `DeclMustBeEmitted` should not lead to more deserialization, as
it may occur before previous deserialization has finished.
When passed a `VarDecl` with an initializer however, `DeclMustBeEmitted`
needs to know whether that initializer contains side effects. When the
`VarDecl` is deserialized but the initializer is not, this triggers
deserialization of the initializer. To avoid this we add a bit to the
serialization format for `VarDecl`s, indicating whether its initializer
contains side effects or not, so that the `ASTReader` can query this
information directly without deserializing the initializer.

rdar://153085264

1 files changed, 8 insertions, 6 deletions

diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 2d93832..2e390db 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1306,6 +1306,7 @@ 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();
@@ -1355,10 +1356,11 @@ void ASTDeclWriter::VisitVarDecl(VarDecl *D) {
       !D->hasExtInfo() && D->getFirstDecl() == D->getMostRecentDecl() &&
       D->getKind() == Decl::Var && !D->isInline() && !D->isConstexpr() &&
       !D->isInitCapture() && !D->isPreviousDeclInSameBlockScope() &&
-      !D->isEscapingByref() && !HasDeducedType &&
-      D->getStorageDuration() != SD_Static && !D->getDescribedVarTemplate() &&
-      !D->getMemberSpecializationInfo() && !D->isObjCForDecl() &&
-      !isa<ImplicitParamDecl>(D) && !D->isEscapingByref())
+      !D->hasInitWithSideEffects() && !D->isEscapingByref() &&
+      !HasDeducedType && D->getStorageDuration() != SD_Static &&
+      !D->getDescribedVarTemplate() && !D->getMemberSpecializationInfo() &&
+      !D->isObjCForDecl() && !isa<ImplicitParamDecl>(D) &&
+      !D->isEscapingByref())
     AbbrevToUse = Writer.getDeclVarAbbrev();
 
   Code = serialization::DECL_VAR;
@@ -2731,12 +2733,12 @@ void ASTWriter::WriteDeclAbbrevs() {
   // VarDecl
   Abv->Add(BitCodeAbbrevOp(
       BitCodeAbbrevOp::Fixed,
-      21)); // Packed Var Decl bits:  Linkage, ModulesCodegen,
+      22)); // Packed Var Decl bits:  Linkage, ModulesCodegen,
             // SClass, TSCSpec, InitStyle,
             // isARCPseudoStrong, IsThisDeclarationADemotedDefinition,
             // isExceptionVariable, isNRVOVariable, isCXXForRangeDecl,
             // isInline, isInlineSpecified, isConstexpr,
-            // isInitCapture, isPrevDeclInSameScope,
+            // isInitCapture, isPrevDeclInSameScope, hasInitWithSideEffects,
             // EscapingByref, HasDeducedType, ImplicitParamKind, isObjCForDecl
   Abv->Add(BitCodeAbbrevOp(0));                         // VarKind (local enum)
   // Type Source Info