Implement InteriorLivenessVisitor::handleInnerBorrow for all BorrowingOperand kinds

Not all BorrowingOperand introduce a BorrowedValue. Add a new api to get the defining value
for use in InteriorLivenessVisitor::handleInnerBorrow.

Author: meg-gupta

include/swift/SIL/OwnershipUtils.h

@@ -475,6 +475,9 @@ struct BorrowingOperand {
   /// valid BorrowedValue instance.
   BorrowedValue getBorrowIntroducingUserResult();
 
+  /// Return the borrowing operand's value.
+  SILValue getScopeIntroducingUserResult();
+
   /// Compute the implicit uses that this borrowing operand "injects" into the
   /// set of its operands uses.
   ///

lib/SIL/Utils/OwnershipLiveness.cpp

@@ -140,8 +140,10 @@ struct InteriorLivenessVisitor :
   /// Handles begin_borrow, load_borrow, store_borrow, begin_apply.
   bool handleInnerBorrow(BorrowingOperand borrowingOperand) {
     if (handleInnerScopeCallback) {
-      handleInnerScopeCallback(
-        borrowingOperand.getBorrowIntroducingUserResult().value);
+      auto value = borrowingOperand.getScopeIntroducingUserResult();
+      if (value) {
+        handleInnerScopeCallback(value);
+      }
     }
     return true;
   }

lib/SIL/Utils/OwnershipUtils.cpp

@@ -751,6 +751,30 @@ BorrowedValue BorrowingOperand::getBorrowIntroducingUserResult() {
   llvm_unreachable("covered switch");
 }
 
+SILValue BorrowingOperand::getScopeIntroducingUserResult() {
+  switch (kind) {
+  case BorrowingOperandKind::Invalid:
+  case BorrowingOperandKind::Yield:
+  case BorrowingOperandKind::Apply:
+  case BorrowingOperandKind::TryApply:
+    return SILValue();
+
+  case BorrowingOperandKind::BeginAsyncLet:
+  case BorrowingOperandKind::PartialApplyStack:
+  case BorrowingOperandKind::BeginBorrow:
+    return cast<SingleValueInstruction>(op->getUser());
+
+  case BorrowingOperandKind::BeginApply:
+    return cast<BeginApplyInst>(op->getUser())->getTokenResult();
+
+  case BorrowingOperandKind::Branch: {
+    PhiOperand phiOp(op);
+    return phiOp.getValue();
+  }
+  }
+  llvm_unreachable("covered switch");
+}
+
 void BorrowingOperand::getImplicitUses(
     SmallVectorImpl<Operand *> &foundUses) const {
   // FIXME: this visitScopeEndingUses should never return false once dead