[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, 0 deletions

diff --git a/clang/lib/Sema/MultiplexExternalSemaSource.cpp b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
index fbfb242..9f19f13 100644
--- a/clang/lib/Sema/MultiplexExternalSemaSource.cpp
+++ b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
@@ -115,6 +115,14 @@ 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) {