RawSILInstLowering: delete dead load instructions when lowering assign_by_wrapper

If only the init-closure is used and the setter-closure is dead, the argument to the setter partial_apply also needs to be delete - in case it's a load.
Otherwise it would cause a memory lifetime failure.

Author: eeckstein

lib/SILOptimizer/Mandatory/RawSILInstLowering.cpp

@@ -210,6 +210,12 @@ static void lowerAssignByWrapperInstruction(SILBuilderWithScope &b,
       // is an inout. Therefore we cannot keep it as a dead closure to be
       // cleaned up later. We have to delete it in this pass.
       toDelete.insert(inst->getSetter());
+      
+      // Also the argument of the closure (which usually is a "load") has to be
+      // deleted to avoid memory lifetime violations.
+      auto *setterPA = dyn_cast<PartialApplyInst>(inst->getSetter());
+      if (setterPA && setterPA->getNumArguments() == 1)
+        toDelete.insert(setterPA->getArgument(0));
       break;
     }
     case AssignByWrapperInst::AssignWrappedValue: {
@@ -251,6 +257,22 @@ static void deleteDeadAccessMarker(BeginAccessInst *BA) {
   BA->eraseFromParent();
 }
 
+/// Delete a dead load for a dead setter-closure.
+static void deleteDeadClosureArg(LoadInst *load) {
+  if (load->getOwnershipQualifier() != LoadOwnershipQualifier::Trivial &&
+      load->getOwnershipQualifier() != LoadOwnershipQualifier::Copy)
+    return;
+    
+  for (Operand *use : load->getUses()) {
+    if (!isa<DestroyValueInst>(use->getUser()))
+      return;
+  }
+  while (!load->use_empty()) {
+    load->use_begin()->getUser()->eraseFromParent();
+  }
+  load->eraseFromParent();
+}
+
 /// lowerRawSILOperations - There are a variety of raw-sil instructions like
 /// 'assign' that are only used by this pass.  Now that definite initialization
 /// checking is done, remove them.
@@ -311,6 +333,8 @@ static bool lowerRawSILOperations(SILFunction &fn) {
     for (SILValue deadVal : toDelete) {
       if (auto *beginAccess = dyn_cast<BeginAccessInst>(deadVal)) {
         deleteDeadAccessMarker(beginAccess);
+      } else if (auto *load = dyn_cast<LoadInst>(deadVal)) {
+        deleteDeadClosureArg(load);
       } else if (auto *svi = dyn_cast<SingleValueInstruction>(deadVal)) {
         tryDeleteDeadClosure(svi);
       }

test/SILOptimizer/di_property_wrappers.swift

@@ -558,6 +558,14 @@ struct NonMutatingWrapperTestStruct {
   }
 }
 
+// Check if a non-trivial value passes the memory lifetime verifier.
+struct NonMutatingWrapperTestStructString {
+  @NonMutatingSetterWrapper var SomeProp: String
+  init(val: String) {
+    SomeProp = val
+  }
+}
+
 func testNonMutatingSetterStruct() {
   // CHECK: ## NonMutatingSetterWrapper
   print("\n## NonMutatingSetterWrapper")