[SILOptimizer] Use BitfieldRef, not invalidate.

`SSAPrunedLiveness::invalidate` is used as though it reset the state of
the instance it is called on.  Clients then reuse the instance with the
expectation that it has been reset.  But since it has not been reset,
this results in unexpected liveness results.

rdar://108627366

Author: nate-chandler

lib/SILOptimizer/Mandatory/DiagnoseLifetimeIssues.cpp

@@ -66,7 +66,7 @@ class DiagnoseLifetimeIssues {
   SILFunction *function = nullptr;
 
   /// The liveness of the object in question, computed in visitUses.
-  SSAPrunedLiveness liveness;
+  BitfieldRef<SSAPrunedLiveness> liveness;
 
   /// All weak stores of the object, which are found in visitUses.
   llvm::SmallVector<SILInstruction *, 8> weakStores;
@@ -86,8 +86,7 @@ class DiagnoseLifetimeIssues {
   void reportDeadStore(SILInstruction *allocationInst);
 
 public:
-  DiagnoseLifetimeIssues(SILFunction *function)
-    : function(function), liveness(function) {}
+  DiagnoseLifetimeIssues(SILFunction *function) : function(function) {}
 
   void diagnose();
 };
@@ -215,7 +214,7 @@ visitUses(SILValue def, bool updateLivenessAndWeakStores, int callDepth) {
       case OperandOwnership::UnownedInstantaneousUse:
       case OperandOwnership::BitwiseEscape:
         if (updateLivenessAndWeakStores)
-          liveness.updateForUse(user, /*lifetimeEnding*/ false);
+          liveness->updateForUse(user, /*lifetimeEnding*/ false);
         break;
       case OperandOwnership::GuaranteedForwarding:
       case OperandOwnership::ForwardingConsume:
@@ -241,9 +240,9 @@ visitUses(SILValue def, bool updateLivenessAndWeakStores, int callDepth) {
           return CanEscape;
         break;
       case OperandOwnership::Borrow: {
-        if (updateLivenessAndWeakStores
-            && (liveness.updateForBorrowingOperand(use)
-                != InnerBorrowKind::Contained)) {
+        if (updateLivenessAndWeakStores &&
+            (liveness->updateForBorrowingOperand(use) !=
+             InnerBorrowKind::Contained)) {
           return CanEscape;
         }
         BorrowingOperand borrowOper(use);
@@ -326,11 +325,12 @@ static bool isOutOfLifetime(SILInstruction *inst, SSAPrunedLiveness &liveness) {
 /// Reports a warning if the stored object \p storedObj is never loaded within
 /// the lifetime of the stored object.
 void DiagnoseLifetimeIssues::reportDeadStore(SILInstruction *allocationInst) {
-  liveness.invalidate();
+  BitfieldRef<SSAPrunedLiveness>::StackState livenessBitfieldContainer(
+      liveness, allocationInst->getFunction());
   weakStores.clear();
 
   SILValue storedDef = cast<SingleValueInstruction>(allocationInst);
-  liveness.initializeDef(storedDef);
+  liveness->initializeDef(storedDef);
 
   // Compute the canonical lifetime of storedDef, like the copy-propagation pass
   // would do.
@@ -346,7 +346,7 @@ void DiagnoseLifetimeIssues::reportDeadStore(SILInstruction *allocationInst) {
   assert((state == IsStoredWeakly) == !weakStores.empty());
 
   for (SILInstruction *storeInst : weakStores) {
-    if (isOutOfLifetime(storeInst, liveness)) {
+    if (isOutOfLifetime(storeInst, *liveness)) {
       // Issue the warning.
       storeInst->getModule().getASTContext().Diags.diagnose(
         storeInst->getLoc().getSourceLoc(), diag::warn_dead_weak_store);

lib/SILOptimizer/Mandatory/MoveOnlyAddressCheckerUtils.cpp

@@ -1359,14 +1359,17 @@ struct GatherUsesVisitor final : public TransitiveAddressWalker {
 
   // Pruned liveness used to validate that load [take]/load [copy] can be
   // converted to load_borrow without violating exclusivity.
-  SSAPrunedLiveness &liveness;
+  BitfieldRef<SSAPrunedLiveness> liveness;
 
-  GatherUsesVisitor(MoveOnlyAddressCheckerPImpl &moveChecker,
-                    UseState &useState, MarkMustCheckInst *markedValue,
-                    DiagnosticEmitter &diagnosticEmitter,
-                    SSAPrunedLiveness &gatherUsesLiveness)
+  SmallVectorImpl<SILBasicBlock *> &gatherUsesDiscoveredBlocks;
+
+  GatherUsesVisitor(
+      MoveOnlyAddressCheckerPImpl &moveChecker, UseState &useState,
+      MarkMustCheckInst *markedValue, DiagnosticEmitter &diagnosticEmitter,
+      SmallVectorImpl<SILBasicBlock *> &gatherUsesDiscoveredBlocks)
       : moveChecker(moveChecker), useState(useState), markedValue(markedValue),
-        diagnosticEmitter(diagnosticEmitter), liveness(gatherUsesLiveness) {}
+        diagnosticEmitter(diagnosticEmitter),
+        gatherUsesDiscoveredBlocks(gatherUsesDiscoveredBlocks) {}
 
   bool visitUse(Operand *op) override;
   void reset(MarkMustCheckInst *address) { useState.address = address; }
@@ -1383,7 +1386,8 @@ struct GatherUsesVisitor final : public TransitiveAddressWalker {
 
   /// Returns true if we emitted an error.
   bool checkForExclusivityHazards(LoadInst *li) {
-    SWIFT_DEFER { liveness.invalidate(); };
+    BitfieldRef<SSAPrunedLiveness>::StackState state(
+        liveness, li->getFunction(), &gatherUsesDiscoveredBlocks);
 
     LLVM_DEBUG(llvm::dbgs() << "Checking for exclusivity hazards for: " << *li);
 
@@ -1404,10 +1408,10 @@ struct GatherUsesVisitor final : public TransitiveAddressWalker {
     }
 
     bool emittedError = false;
-    liveness.initializeDef(bai);
-    liveness.computeSimple();
+    liveness->initializeDef(bai);
+    liveness->computeSimple();
     for (auto *consumingUse : li->getConsumingUses()) {
-      if (!liveness.isWithinBoundary(consumingUse->getUser())) {
+      if (!liveness->isWithinBoundary(consumingUse->getUser())) {
         diagnosticEmitter.emitAddressExclusivityHazardDiagnostic(
             markedValue, consumingUse->getUser());
         emittedError = true;
@@ -2416,9 +2420,8 @@ bool MoveOnlyAddressCheckerPImpl::performSingleCheck(
   // to categorize the uses of this address into their ownership behavior (e.x.:
   // init, reinit, take, destroy, etc.).
   SmallVector<SILBasicBlock *, 32> gatherUsesDiscoveredBlocks;
-  SSAPrunedLiveness gatherUsesLiveness(fn, &gatherUsesDiscoveredBlocks);
   GatherUsesVisitor visitor(*this, addressUseState, markedAddress,
-                            diagnosticEmitter, gatherUsesLiveness);
+                            diagnosticEmitter, gatherUsesDiscoveredBlocks);
   SWIFT_DEFER { visitor.clear(); };
   visitor.reset(markedAddress);
   if (AddressUseKind::Unknown == std::move(visitor).walk(markedAddress)) {