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

[Henrik G. Olsson via cfe-commits]

================
@@ -2434,6 +2434,31 @@ VarDecl *VarDecl::getInitializingDeclaration() {
   return Def;
 }
 
+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 {
+    auto *Eval = getEvaluatedStmt();
+    if (!Eval->Value.isOffset())
+      E = cast<Expr>(Eval->Value.get(nullptr));
+  }
+
+  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
+  return getASTContext().getExternalSource()->hasInitializerWithSideEffects(
----------------
hnrklssn wrote:

I'm fine with this change, but I'm curious if you know of any case when `hasInit() && !isa<Stmt>(Init) && !getASTContext().getExternalSource()` would be true? 

https://github.com/llvm/llvm-project/pull/143739