[DI] Fix check that ignores loads related to assign_or_init and assign_by_wrapper

For cases where init accessor field has a nonmutating set we need
ignore copies and borrows associated with load of "self" because
they are going to be erased together with the setter application
by DI.

(cherry picked from commit 24c4fcc)

Author: xedin

lib/SILOptimizer/Mandatory/DefiniteInitialization.cpp

@@ -662,14 +662,32 @@ bool LifetimeChecker::shouldEmitError(const SILInstruction *Inst) {
   // This is safe to ignore because assign_by_wrapper/assign_or_init will
   // only be re-written to use the setter if the value is fully initialized.
   if (auto *load = dyn_cast<SingleValueInstruction>(Inst)) {
-    if (auto Op = load->getSingleUse()) {
-      if (auto PAI = dyn_cast<PartialApplyInst>(Op->getUser())) {
-        if (std::find_if(PAI->use_begin(), PAI->use_end(), [](auto PAIUse) {
-              return isa<AssignByWrapperInst>(PAIUse->getUser()) ||
-                     isa<AssignOrInitInst>(PAIUse->getUser());
-            }) != PAI->use_end()) {
-          return false;
-        }
+    auto isOnlyUsedByPartialApply =
+        [&](const SingleValueInstruction *inst) -> PartialApplyInst * {
+      Operand *result = nullptr;
+      for (auto *op : inst->getUses()) {
+        auto *user = op->getUser();
+
+        // Ignore copies, destroys and borrows because they'd be
+        // erased together with the setter.
+        if (isa<DestroyValueInst>(user) || isa<CopyValueInst>(user) ||
+            isa<BeginBorrowInst>(user) || isa<EndBorrowInst>(user))
+          continue;
+
+        if (result)
+          return nullptr;
+
+        result = op;
+      }
+      return result ? dyn_cast<PartialApplyInst>(result->getUser()) : nullptr;
+    };
+
+    if (auto *PAI = isOnlyUsedByPartialApply(load)) {
+      if (std::find_if(PAI->use_begin(), PAI->use_end(), [](auto PAIUse) {
+            return isa<AssignByWrapperInst>(PAIUse->getUser()) ||
+                   isa<AssignOrInitInst>(PAIUse->getUser());
+          }) != PAI->use_end()) {
+        return false;
       }
     }
   }