[MoveValueChecker] Complete lifetimes first.

Before move-checking values, complete the lifetimes of all the values
derived from them via copy, borrow, and move.

Collect all such values and their derived transitive values and then
complete the lifetimes of each, visiting the instructions which produce
them in post-order.

Once OSSALifetimeCommpletion runs as part of SILGenCleanup, this code
can be deleted.

Author: nate-chandler

lib/SILOptimizer/Mandatory/MoveOnlyChecker.cpp

@@ -30,6 +30,7 @@
 #include "swift/SIL/FieldSensitivePrunedLiveness.h"
 #include "swift/SIL/InstructionUtils.h"
 #include "swift/SIL/MemAccessUtils.h"
+#include "swift/SIL/OSSALifetimeCompletion.h"
 #include "swift/SIL/OwnershipUtils.h"
 #include "swift/SIL/PrunedLiveness.h"
 #include "swift/SIL/SILArgument.h"
@@ -86,6 +87,7 @@ struct MoveOnlyChecker {
   }
 
   void checkObjects();
+  void completeObjectLifetimes(ArrayRef<MarkUnresolvedNonCopyableValueInst *>);
   void checkAddresses();
 };
 
@@ -110,10 +112,75 @@ void MoveOnlyChecker::checkObjects() {
     return;
   }
 
+  completeObjectLifetimes(moveIntroducersToProcess.getArrayRef());
+
   MoveOnlyObjectChecker checker{diagnosticEmitter, domTree, poa, allocator};
   madeChange |= checker.check(moveIntroducersToProcess);
 }
 
+void MoveOnlyChecker::completeObjectLifetimes(
+    ArrayRef<MarkUnresolvedNonCopyableValueInst *> insts) {
+// TODO: Delete once OSSALifetimeCompletion is run as part of SILGenCleanup.
+  OSSALifetimeCompletion completion(fn, domTree);
+
+  // Collect all values derived from each mark_unresolved_non_copyable_value
+  // instruction via ownership instructions and phis.
+  ValueWorklist transitiveValues(fn);
+  for (auto *inst : insts) {
+    transitiveValues.push(inst);
+  }
+  while (auto value = transitiveValues.pop()) {
+    for (auto *use : value->getUses()) {
+      auto *user = use->getUser();
+      switch (user->getKind()) {
+      case SILInstructionKind::BeginBorrowInst:
+      case SILInstructionKind::CopyValueInst:
+      case SILInstructionKind::MoveValueInst:
+        transitiveValues.pushIfNotVisited(cast<SingleValueInstruction>(user));
+        break;
+      case SILInstructionKind::BranchInst: {
+        PhiOperand po(use);
+        transitiveValues.pushIfNotVisited(po.getValue());
+        break;
+      }
+      default: {
+        auto forward = ForwardingOperation(user);
+        if (!forward)
+          continue;
+        forward.visitForwardedValues([&transitiveValues](auto forwarded) {
+          transitiveValues.pushIfNotVisited(forwarded);
+          return true;
+        });
+        break;
+      }
+      }
+    }
+  }
+  // Complete the lifetime of each collected value.  This is a subset of the
+  // work that SILGenCleanup will do.
+  for (auto *block : poa->get(fn)->getPostOrder()) {
+    for (SILInstruction &inst : reverse(*block)) {
+      for (auto result : inst.getResults()) {
+        if (!transitiveValues.isVisited(result))
+          continue;
+        if (completion.completeOSSALifetime(result) ==
+            LifetimeCompletion::WasCompleted) {
+          madeChange = true;
+        }
+      }
+    }
+    for (SILArgument *arg : block->getArguments()) {
+      assert(!arg->isReborrow() && "reborrows not legal at this SIL stage");
+      if (!transitiveValues.isVisited(arg))
+        continue;
+      if (completion.completeOSSALifetime(arg) ==
+          LifetimeCompletion::WasCompleted) {
+        madeChange = true;
+      }
+    }
+  }
+}
+
 void MoveOnlyChecker::checkAddresses() {
   unsigned diagCount = diagnosticEmitter.getDiagnosticCount();
   SmallSetVector<MarkUnresolvedNonCopyableValueInst *, 32>

validation-test/SILOptimizer/gh68328.swift

@@ -0,0 +1,16 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift %s -o %t/bin 
+// RUN: %target-run %t/bin 2> %t/out.txt || true
+// RUN: %FileCheck %s < %t/out.txt
+
+struct Example: ~Copyable {
+    private var failureString: String { "Goodbye." }
+    deinit { fatalError("FATAL ERROR: \(failureString)") }
+}
+
+func doit() {
+  let e = Example()
+  // CHECK: FATAL ERROR: Goodbye.
+}
+
+doit()