[SILGenCleanup] Complete lifetimes of defs backwards reachable from dead-end blocks.

include/swift/SIL/BasicBlockDatastructures.h

@@ -83,6 +83,9 @@ class BasicBlockWorklist {
     push(initialBlock);
   }
 
+  /// Whether there are any remaining blocks to process.
+  bool empty() { return worklist.empty(); }
+
   /// Pops the last added element from the worklist or returns null, if the
   /// worklist is empty.
   SILBasicBlock *pop() {

include/swift/SIL/SILFunction.h

@@ -1565,6 +1565,17 @@ class SILFunction
     }
   }
 
+  /// Populate \p output with every block terminated by an unreachable
+  /// instruction.
+  void visitUnreachableTerminatedBlocks(
+      llvm::function_ref<void(SILBasicBlock &)> visitor) const {
+    for (auto &block : const_cast<SILFunction &>(*this)) {
+      if (isa<UnreachableInst>(block.getTerminator())) {
+        visitor(block);
+      }
+    }
+  }
+
   //===--------------------------------------------------------------------===//
   // Argument Helper Methods
   //===--------------------------------------------------------------------===//

include/swift/SILOptimizer/Utils/BasicBlockOptUtils.h

@@ -38,10 +38,32 @@ class SILLoopInfo;
 /// Compute the set of reachable blocks.
 class ReachableBlocks {
   BasicBlockSet visited;
+  bool isComputed;
 
 public:
-  ReachableBlocks(SILFunction *function) : visited(function) {}
+  ReachableBlocks(SILFunction *function)
+      : visited(function), isComputed(false) {}
 
+  /// Populate `visited` with the blocks reachable in the function.
+  void compute();
+
+  /// Whether `block` is reachable from the entry block.
+  bool isReachable(SILBasicBlock *block) const {
+    assert(isComputed);
+    return visited.contains(block);
+  }
+
+  bool hasUnreachableBlocks() const {
+    assert(isComputed);
+    for (auto &block : *visited.getFunction()) {
+      if (!isReachable(&block)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+private:
   /// Invoke \p visitor for each reachable block in \p f in worklist order (at
   /// least one predecessor has been visited--defs are always visited before
   /// uses except for phi-type block args). The \p visitor takes a block
@@ -50,9 +72,6 @@ class ReachableBlocks {
   ///
   /// Returns true if all reachable blocks were visited.
   bool visit(function_ref<bool(SILBasicBlock *)> visitor);
-
-  /// Return true if \p bb has been visited.
-  bool isVisited(SILBasicBlock *bb) const { return visited.contains(bb); }
 };
 
 /// Computes the set of blocks from which a path to the return-block exists.

lib/SILOptimizer/Mandatory/ClosureLifetimeFixup.cpp

@@ -587,8 +587,7 @@ static SILValue tryRewriteToPartialApplyStack(
     ConvertEscapeToNoEscapeInst *cvt, SILInstruction *closureUser,
     DominanceAnalysis *dominanceAnalysis, InstructionDeleter &deleter,
     llvm::DenseMap<SILInstruction *, SILInstruction *> &memoized,
-    llvm::DenseSet<SILBasicBlock *> &unreachableBlocks,
-    const bool &modifiedCFG) {
+    ReachableBlocks const &reachableBlocks, const bool &modifiedCFG) {
 
   auto *origPA = dyn_cast<PartialApplyInst>(skipConvert(cvt->getOperand()));
   if (!origPA)
@@ -972,8 +971,8 @@ static SILValue tryRewriteToPartialApplyStack(
 
   // Don't run insertDeallocOfCapturedArguments if newPA is in an unreachable
   // block insertDeallocOfCapturedArguments will run code that computes the DF
-  // for newPA that will loop infinetly.
-  if (unreachableBlocks.count(newPA->getParent()))
+  // for newPA that will loop infinitely.
+  if (!reachableBlocks.isReachable(newPA->getParent()))
     return closureOp;
 
   auto getAddressToDealloc = [&](SILValue argAddress) -> SILValue {
@@ -995,8 +994,8 @@ static bool tryExtendLifetimeToLastUse(
     ConvertEscapeToNoEscapeInst *cvt, DominanceAnalysis *dominanceAnalysis,
     DeadEndBlocksAnalysis *deadEndBlocksAnalysis,
     llvm::DenseMap<SILInstruction *, SILInstruction *> &memoized,
-    llvm::DenseSet<SILBasicBlock *> &unreachableBlocks,
-    InstructionDeleter &deleter, const bool &modifiedCFG) {
+    ReachableBlocks const &reachableBlocks, InstructionDeleter &deleter,
+    const bool &modifiedCFG) {
   // If there is a single user, this is simple: extend the
   // lifetime of the operand until the use ends.
   auto *singleUser = lookThroughRebastractionUsers(cvt, memoized);
@@ -1019,7 +1018,7 @@ static bool tryExtendLifetimeToLastUse(
 
   if (SILValue closureOp = tryRewriteToPartialApplyStack(
           cvt, singleUser, dominanceAnalysis, deleter, memoized,
-          unreachableBlocks, /*const*/ modifiedCFG)) {
+          reachableBlocks, /*const*/ modifiedCFG)) {
     if (endAsyncLet) {
       // Add the closure as a second operand to the endAsyncLet builtin.
       // This ensures that the closure arguments are kept alive until the
@@ -1428,22 +1427,6 @@ static bool fixupCopyBlockWithoutEscaping(CopyBlockWithoutEscapingInst *cb,
   return true;
 }
 
-static void computeUnreachableBlocks(
-  llvm::DenseSet<SILBasicBlock*> &unreachableBlocks,
-  SILFunction &fn) {
-
-  ReachableBlocks isReachable(&fn);
-  llvm::DenseSet<SILBasicBlock *> reachable;
-  isReachable.visit([&] (SILBasicBlock *block) -> bool {
-                    reachable.insert(block);
-                    return true;
-                   });
-  for (auto &block : fn) {
-    if (!reachable.count(&block))
-      unreachableBlocks.insert(&block);
-  }
-}
-
 static bool fixupClosureLifetimes(SILFunction &fn,
                                   DominanceAnalysis *dominanceAnalysis,
                                   DeadEndBlocksAnalysis *deadEndBlocksAnalysis,
@@ -1454,8 +1437,8 @@ static bool fixupClosureLifetimes(SILFunction &fn,
   // queries.
   llvm::DenseMap<SILInstruction *, SILInstruction *> memoizedQueries;
 
-  llvm::DenseSet<SILBasicBlock *> unreachableBlocks;
-  computeUnreachableBlocks(unreachableBlocks, fn);
+  ReachableBlocks reachableBlocks(&fn);
+  reachableBlocks.compute();
 
   for (auto &block : fn) {
     SILSSAUpdater updater;
@@ -1485,7 +1468,7 @@ static bool fixupClosureLifetimes(SILFunction &fn,
 
       if (tryExtendLifetimeToLastUse(cvt, dominanceAnalysis,
                                      deadEndBlocksAnalysis, memoizedQueries,
-                                     unreachableBlocks, updater.getDeleter(),
+                                     reachableBlocks, updater.getDeleter(),
                                      /*const*/ modifiedCFG)) {
         changed = true;
         checkStackNesting = true;