Add an option to force boundary completion of lexical values

Author: meg-gupta

include/swift/SIL/OSSALifetimeCompletion.h

@@ -53,12 +53,19 @@ class OSSALifetimeCompletion {
   /// Insert a lifetime-ending instruction on every path to complete the OSSA
   /// lifetime of \p value. Lifetime completion is only relevant for owned
   /// values or borrow introducers.
-  ///
+  /// For lexical values lifetime is completed at unreachable instructions.
+  /// For non-lexical values lifetime is completed at the lifetime boundary.
+  /// When \p forceBoundaryCompletion is true, the client is able to guarantee
+  /// that lifetime completion of lexical values at the lifetime boundary is
+  /// sufficient.
+  /// Currently \p forceBoundaryCompletion is used by mem2reg and temprvalueopt
+  /// to complete lexical enum values on trivial paths.
   /// Returns true if any new instructions were created to complete the
   /// lifetime.
   ///
   /// TODO: We also need to complete scoped addresses (e.g. store_borrow)!
-  LifetimeCompletion completeOSSALifetime(SILValue value) {
+  LifetimeCompletion
+  completeOSSALifetime(SILValue value, bool forceBoundaryCompletion = false) {
     if (value->getOwnershipKind() == OwnershipKind::None)
       return LifetimeCompletion::NoLifetime;
 
@@ -73,13 +80,13 @@ class OSSALifetimeCompletion {
     if (!completedValues.insert(value))
       return LifetimeCompletion::AlreadyComplete;
 
-    return analyzeAndUpdateLifetime(value)
-      ? LifetimeCompletion::WasCompleted
-      : LifetimeCompletion::AlreadyComplete;
+    return analyzeAndUpdateLifetime(value, forceBoundaryCompletion)
+               ? LifetimeCompletion::WasCompleted
+               : LifetimeCompletion::AlreadyComplete;
   }
 
 protected:
-  bool analyzeAndUpdateLifetime(SILValue value);
+  bool analyzeAndUpdateLifetime(SILValue value, bool forceBoundaryCompletion);
 };
 
 //===----------------------------------------------------------------------===//

lib/SIL/Utils/OSSALifetimeCompletion.cpp

@@ -142,7 +142,8 @@ static bool endLifetimeAtUnreachableBlocks(SILValue value,
 /// This is only meant to cleanup lifetimes that lead to dead-end blocks. After
 /// recursively completing all nested scopes, it then simply ends the lifetime
 /// at the Unreachable instruction.
-bool OSSALifetimeCompletion::analyzeAndUpdateLifetime(SILValue value) {
+bool OSSALifetimeCompletion::analyzeAndUpdateLifetime(
+    SILValue value, bool forceBoundaryCompletion) {
   // Called for inner borrows, inner adjacent reborrows, inner reborrows, and
   // scoped addresses.
   auto handleInnerScope = [this](SILValue innerBorrowedValue) {
@@ -152,7 +153,7 @@ bool OSSALifetimeCompletion::analyzeAndUpdateLifetime(SILValue value) {
   liveness.compute(domInfo, handleInnerScope);
 
   bool changed = false;
-  if (value->isLexical()) {
+  if (value->isLexical() && !forceBoundaryCompletion) {
     changed |= endLifetimeAtUnreachableBlocks(value, liveness.getLiveness());
   } else {
     changed |= endLifetimeAtBoundary(value, liveness.getLiveness());