[SIL] Add BorrowedValueKind::BeginApplyToken.

The token is a guaranteed value introduced by the begin_apply and
consumed by its end_apply, abort_apply, and end_borrow users.

Author: nate-chandler

include/swift/SIL/OwnershipUtils.h

@@ -490,6 +490,7 @@ class BorrowedValueKind {
     BeginBorrow,
     SILFunctionArgument,
     Phi,
+    BeginApplyToken,
   };
 
 private:
@@ -520,6 +521,13 @@ class BorrowedValueKind {
       }
       return Kind::Phi;
     }
+    case ValueKind::MultipleValueInstructionResult:
+      if (!isaResultOf<BeginApplyInst>(value))
+        return Kind::Invalid;
+      if (value->isBeginApplyToken()) {
+        return Kind::BeginApplyToken;
+      }
+      return Kind::Invalid;
     }
   }
 
@@ -540,6 +548,7 @@ class BorrowedValueKind {
     case BorrowedValueKind::BeginBorrow:
     case BorrowedValueKind::LoadBorrow:
     case BorrowedValueKind::Phi:
+    case BorrowedValueKind::BeginApplyToken:
       return true;
     case BorrowedValueKind::SILFunctionArgument:
       return false;

lib/SIL/Utils/OwnershipUtils.cpp

@@ -913,6 +913,9 @@ void BorrowedValueKind::print(llvm::raw_ostream &os) const {
   case BorrowedValueKind::Phi:
     os << "Phi";
     return;
+  case BorrowedValueKind::BeginApplyToken:
+    os << "BeginApply";
+    return;
   }
   llvm_unreachable("Covered switch isn't covered?!");
 }
@@ -945,6 +948,7 @@ bool BorrowedValue::visitLocalScopeEndingUses(
   case BorrowedValueKind::LoadBorrow:
   case BorrowedValueKind::BeginBorrow:
   case BorrowedValueKind::Phi:
+  case BorrowedValueKind::BeginApplyToken:
     for (auto *use : lookThroughBorrowedFromUser(value)->getUses()) {
       if (use->isLifetimeEnding()) {
         if (!visitor(use))
@@ -1819,6 +1823,7 @@ class FindEnclosingDefs {
 
       case BorrowedValueKind::LoadBorrow:
       case BorrowedValueKind::SILFunctionArgument:
+      case BorrowedValueKind::BeginApplyToken:
         // There is no enclosing def on this path.
         return true;
       }
@@ -2037,6 +2042,7 @@ class FindEnclosingDefs {
     }
     case BorrowedValueKind::LoadBorrow:
     case BorrowedValueKind::SILFunctionArgument:
+    case BorrowedValueKind::BeginApplyToken:
       // There is no enclosing def on this path.
       break;
     }

lib/SILOptimizer/Utils/CanonicalizeBorrowScope.cpp

@@ -140,6 +140,7 @@ SILValue CanonicalizeBorrowScope::getCanonicalBorrowedDef(SILValue def) {
 
       case BorrowedValueKind::LoadBorrow:
       case BorrowedValueKind::Phi:
+      case BorrowedValueKind::BeginApplyToken:
         break;
       }
     }
@@ -170,6 +171,7 @@ bool CanonicalizeBorrowScope::computeBorrowLiveness() {
     // can handle persistentCopies.
     return false;
   case BorrowedValueKind::BeginBorrow:
+  case BorrowedValueKind::BeginApplyToken:
     break;
   }
   // Note that there is no need to look through any reborrows. The reborrowed

test/SILOptimizer/ossa_lifetime_completion.sil

@@ -513,3 +513,27 @@ entry(%instance : @owned $C):
   store %instance to [init] %addr : $*C
   unreachable
 }
+
+// CHECK-LABEL: sil [ossa] @begin_apply : {{.*}} {
+// CHECK:         ({{%[^,]+}}, [[TOKEN:%[^,]+]]) = begin_apply undef()
+// CHECK:         cond_br undef, [[LEFT:bb[0-9]+]], [[RIGHT:bb[0-9]+]]
+// CHECK:       [[LEFT]]:
+// CHECK:         end_apply [[TOKEN]]
+// CHECK:       [[RIGHT]]:
+// CHECK:         end_borrow [[TOKEN]]
+// CHECK:         unreachable
+// CHECK-LABEL: } // end sil function 'begin_apply'
+sil [ossa] @begin_apply : $@convention(thin) () -> () {
+entry:
+  (%_, %token) = begin_apply undef() : $@yield_once @convention(thin) () -> (@yields @in_guaranteed ())
+  specify_test "ossa-lifetime-completion %token"
+  cond_br undef, left, right
+
+left:
+  end_apply %token as $()
+  %retval = tuple ()
+  return %retval : $()
+
+right:
+  unreachable
+}