Fix BorrowingOperand::getBorrowIntroducingUserResult()

To handle borrowing operands that produce a dependence value but do not create a
nested borrow scope. This includes non-reborrow borrowed-from and guaranteed
mark_dependence [nonescaping].

Author: atrick

include/swift/SIL/OwnershipUtils.h

@@ -428,7 +428,7 @@ struct BorrowingOperand {
   /// cannot be reborrowed.
   ///
   /// If true, getBorrowIntroducingUserResult() can be called to acquire the
-  /// BorrowedValue that introduces a new borrow scope.
+  /// SILValue that introduces a new borrow scope.
   bool hasBorrowIntroducingUser() const {
     // TODO: Can we derive this by running a borrow introducer check ourselves?
     switch (kind) {
@@ -451,9 +451,11 @@ struct BorrowingOperand {
     llvm_unreachable("Covered switch isn't covered?!");
   }
 
-  /// If this operand's user has a borrowed value result return a valid
-  /// BorrowedValue instance.
-  BorrowedValue getBorrowIntroducingUserResult() const;
+  /// If this operand's user has a single result that introduces the borrow
+  /// scope, return the result value. If the result is scoped (begin_borrow)
+  /// then it can be used to initialize a BorrowedValue. Some results, like
+  /// guaranteed forwarding phis, are not scoped.
+  SILValue getBorrowIntroducingUserResult() const;
 
   /// Return the borrowing operand's value.
   SILValue getScopeIntroducingUserResult();

include/swift/SIL/SILInstruction.h

@@ -4769,7 +4769,7 @@ class BorrowedFromInst final : public InstructionBaseWithTrailingOperands<
 
 public:
 
-  SILValue getBorrowedValue() {
+  SILValue getBorrowedValue() const {
     return getAllOperands()[0].get();
   }
 

lib/SIL/Utils/OwnershipLiveness.cpp

@@ -159,8 +159,7 @@ struct InteriorLivenessVisitor :
   /// Handles begin_borrow, load_borrow, store_borrow, begin_apply.
   bool handleInnerBorrow(BorrowingOperand borrowingOperand) {
     if (handleInnerScopeCallback) {
-      auto value = borrowingOperand.getScopeIntroducingUserResult();
-      if (value) {
+      if (auto value = borrowingOperand.getScopeIntroducingUserResult()) {
         handleInnerScopeCallback(value);
       }
     }

lib/SIL/Utils/OwnershipUtils.cpp

@@ -60,8 +60,8 @@ bool swift::findPointerEscape(SILValue original) {
       }
       case OperandOwnership::Borrow: {
         auto borrowOp = BorrowingOperand(use);
-        if (auto borrowValue = borrowOp.getBorrowIntroducingUserResult()) {
-          worklist.pushIfNotVisited(borrowValue.value);
+        if (auto result = borrowOp.getBorrowIntroducingUserResult()) {
+          worklist.pushIfNotVisited(result);
         }
         break;
       }
@@ -548,7 +548,7 @@ findExtendedTransitiveGuaranteedUses(SILValue guaranteedValue,
     usePoints.pop_back();
     auto borrowedPhi =
       BorrowingOperand(reborrow).getBorrowIntroducingUserResult();
-    reborrows.insert(borrowedPhi.value);
+    reborrows.insert(borrowedPhi);
   };
   if (!findTransitiveGuaranteedUses(guaranteedValue, usePoints, visitReborrow))
     return false;
@@ -768,13 +768,15 @@ bool BorrowingOperand::visitExtendedScopeEndingUses(
   function_ref<bool(Operand *)> visitUnknownUse) const {
 
   if (hasBorrowIntroducingUser()) {
-    auto borrowedValue = getBorrowIntroducingUserResult();
-    return borrowedValue.visitExtendedScopeEndingUses(visitor);
+    auto result = getBorrowIntroducingUserResult();
+    if (auto borrowedValue = BorrowedValue(result)) {
+      return borrowedValue.visitExtendedScopeEndingUses(visitor);
+    }
   }
   return visitScopeEndingUses(visitor, visitUnknownUse);
 }
 
-BorrowedValue BorrowingOperand::getBorrowIntroducingUserResult() const {
+SILValue BorrowingOperand::getBorrowIntroducingUserResult() const {
   switch (kind) {
   case BorrowingOperandKind::Invalid:
   case BorrowingOperandKind::Apply:
@@ -785,20 +787,15 @@ BorrowedValue BorrowingOperand::getBorrowIntroducingUserResult() const {
   case BorrowingOperandKind::MarkDependenceNonEscaping:
   case BorrowingOperandKind::BeginAsyncLet:
   case BorrowingOperandKind::StoreBorrow:
-    return BorrowedValue();
+    return SILValue();
 
   case BorrowingOperandKind::BeginBorrow:
   case BorrowingOperandKind::BorrowedFrom: {
-    auto value = BorrowedValue(cast<SingleValueInstruction>(op->getUser()));
-    assert(value);
-    return value;
+    return cast<SingleValueInstruction>(op->getUser());
   }
   case BorrowingOperandKind::Branch: {
     auto *bi = cast<BranchInst>(op->getUser());
-    auto value =
-        BorrowedValue(bi->getDestBB()->getArgument(op->getOperandNumber()));
-    assert(value && "guaranteed-to-unowned conversion not allowed on branches");
-    return value;
+    return bi->getDestBB()->getArgument(op->getOperandNumber());
   }
   }
   llvm_unreachable("covered switch");
@@ -970,9 +967,9 @@ bool BorrowedValue::visitExtendedScopeEndingUses(
 
   auto visitEnd = [&](Operand *scopeEndingUse) {
     if (scopeEndingUse->getOperandOwnership() == OperandOwnership::Reborrow) {
-      auto borrowedValue =
+      auto result =
           BorrowingOperand(scopeEndingUse).getBorrowIntroducingUserResult();
-      reborrows.insert(borrowedValue.value);
+      reborrows.insert(result);
       return true;
     }
     return visitor(scopeEndingUse);
@@ -997,9 +994,9 @@ bool BorrowedValue::visitTransitiveLifetimeEndingUses(
 
   auto visitEnd = [&](Operand *scopeEndingUse) {
     if (scopeEndingUse->getOperandOwnership() == OperandOwnership::Reborrow) {
-      auto borrowedValue =
+      auto result =
           BorrowingOperand(scopeEndingUse).getBorrowIntroducingUserResult();
-      reborrows.insert(borrowedValue.value);
+      reborrows.insert(result);
       // visitor on the reborrow
       return visitor(scopeEndingUse);
     }
@@ -1050,8 +1047,8 @@ bool BorrowedValue::visitInteriorPointerOperandHelper(
         break;
       }
 
-      auto bv = borrowingOperand.getBorrowIntroducingUserResult();
-      for (auto *use : bv->getUses()) {
+      auto result = borrowingOperand.getBorrowIntroducingUserResult();
+      for (auto *use : result->getUses()) {
         if (auto intPtrOperand = InteriorPointerOperand(use)) {
           func(intPtrOperand);
           continue;

lib/SILOptimizer/SILCombiner/SILCombinerBuiltinVisitors.cpp

@@ -119,8 +119,10 @@ SILCombiner::optimizeBuiltinCOWBufferForReadingOSSA(BuiltinInst *bi) {
     if (auto operand = BorrowingOperand(use)) {
       if (operand.isReborrow())
         return nullptr;
-      auto bv = operand.getBorrowIntroducingUserResult();
-      accumulatedBorrowedValues.push_back(bv);
+      auto result = operand.getBorrowIntroducingUserResult();
+      if (auto bv = BorrowedValue(result)) {
+        accumulatedBorrowedValues.push_back(bv);
+      }
       continue;
     }
 

lib/SILOptimizer/Utils/OwnershipOptUtils.cpp

@@ -618,7 +618,7 @@ void BorrowedLifetimeExtender::analyzeExtendedScope() {
       SWIFT_ASSERT_ONLY(reborrowedOperands.insert(endScope));
 
       // TODO: if non-phi reborrows are added, handle multiple results.
-      discoverReborrow(borrowingOper.getBorrowIntroducingUserResult().value);
+      discoverReborrow(borrowingOper.getBorrowIntroducingUserResult());
     }
     return true;
   };