[DI] InitAccessors: Handle assign_or_init without initializations

Introduce a placeholder "init" use anchored on `assign_or_init`
instruction to make sure that `handleStoreUse` gets a called and
sets the kind.

Author: xedin

lib/SILOptimizer/Mandatory/DIMemoryUseCollector.cpp

@@ -1209,8 +1209,16 @@ ElementUseCollector::collectAssignOrInitUses(PartialApplyInst *pai,
                      useKind);
     };
 
-    for (auto *property : inst->getInitializedProperties())
-      addUse(property, DIUseKind::InitOrAssign);
+    auto initializedElts = inst->getInitializedProperties();
+    if (initializedElts.empty()) {
+      // Add a placeholder use that doesn't touch elements to make sure that
+      // the `assign_or_init` instruction gets the kind set when `initializes`
+      // list is empty.
+      trackUse(DIMemoryUse(User, DIUseKind::InitOrAssign, BaseEltNo, 0));
+    } else {
+      for (auto *property : initializedElts)
+        addUse(property, DIUseKind::InitOrAssign);
+    }
 
     for (auto *property : inst->getAccessedProperties())
       addUse(property, DIUseKind::Load);

lib/SILOptimizer/Mandatory/DefiniteInitialization.cpp

@@ -1436,7 +1436,18 @@ void LifetimeChecker::handleStoreUse(unsigned UseID) {
   // If this is an initialization or a normal assignment, upgrade the store to
   // an initialization or assign in the uses list so that clients know about it.
   if (isFullyUninitialized) {
-    Use.Kind = DIUseKind::Initialization;
+    // If this is a placeholder use of `assign_or_init` instruction,
+    // check whether all of the fields are initialized - if so, call a setter,
+    // otherwise call init accessor.
+    if (isa<AssignOrInitInst>(Use.Inst) && Use.NumElements == 0) {
+      auto allFieldsInitialized =
+          getAnyUninitializedMemberAtInst(Use.Inst, 0,
+                                          TheMemory.getNumElements()) == -1;
+      Use.Kind =
+          allFieldsInitialized ? DIUseKind::Set : DIUseKind::Initialization;
+    } else {
+      Use.Kind = DIUseKind::Initialization;
+    }
   } else if (isFullyInitialized && isa<AssignByWrapperInst>(Use.Inst)) {
     // If some fields are uninitialized, re-write assign_by_wrapper to assignment
     // of the backing wrapper. If all fields are initialized, assign to the wrapped