Merge pull request #68531 from nate-chandler/nfc/20230914/1/reachability-visitor-api

[Reachability] NFC: Distinguish initial blocks from barrier blocks.

Author: nate-chandler

include/swift/SILOptimizer/Analysis/Reachability.h

@@ -347,6 +347,7 @@ class IterativeBackwardReachability final {
   ///     void visitBarrierInstruction(SILInstruction *)
   ///     void visitBarrierPhi(SILBasicBlock *)
   ///     void visitBarrierBlock(SILBasicBlock *)
+  ///     void visitInitialBlock(SILBasicBlock *)
   /// }
   template <typename Visitor>
   void findBarriers(Visitor &visitor);
@@ -423,6 +424,7 @@ class IterativeBackwardReachability final {
   ///     void visitBarrierInstruction(SILInstruction *)
   ///     void visitBarrierPhi(SILBasicBlock *)
   ///     void visitBarrierBlock(SILBasicBlock *)
+  ///     void visitInitialBlock(SILBasicBlock *)
   /// }
   template <typename Visitor>
   bool findBarrier(SILInstruction *from, SILBasicBlock *block,
@@ -710,6 +712,10 @@ IterativeBackwardReachability<Effects>::meetOverSuccessors(
 ///     /// Additionally, this may be invoked with the effective def block if
 ///     /// no barriers are found between the gens and it.
 ///     void visitBarrierBlock(SILBasicBlock *)
+///
+///     /// Invoked with either the function entry block or one of the specified
+///     /// initial blocks.
+///     void visitInitialBlock(SILBasicBlock *)
 /// }
 template <typename Effects>
 template <typename Visitor>
@@ -765,6 +771,10 @@ void IterativeBackwardReachability<Effects>::findBarriers(Visitor &visitor) {
 ///     /// Additionally, this may be invoked with the effective def block if
 ///     /// no barriers are found between the gens and it.
 ///     void visitBarrierBlock(SILBasicBlock *)
+///
+///     /// Invoked with either the function entry block or one of the specified
+///     /// initial blocks.
+///     void visitInitialBlock(SILBasicBlock *)
 /// }
 template <typename Effects>
 template <typename Visitor>
@@ -793,7 +803,7 @@ bool IterativeBackwardReachability<Effects>::findBarrier(SILInstruction *from,
   }
   assert(result.getEffectForBlock(block) != Effect::Kill());
   if (stopAtBlock(block)) {
-    visitor.visitBarrierBlock(block);
+    visitor.visitInitialBlock(block);
     return true;
   }
   return false;
@@ -922,6 +932,12 @@ struct ReachableBarriers final {
   /// (2) at least one adjacent edge's target is not reachable-at-begin.
   llvm::SmallVector<SILBasicBlock *, 4> edges;
 
+  /// Terminal blocks that were reached; blocks such that
+  /// (1) the block is reachable-at-begin
+  /// (2) it is either the function's entry block or one of the blocks passed
+  /// to findBarriersBackward's \p initialBlocks parameter.
+  llvm::SmallVector<SILBasicBlock *, 2> initialBlocks;
+
   ReachableBarriers() {}
   ReachableBarriers(ReachableBarriers const &) = delete;
   ReachableBarriers &operator=(ReachableBarriers const &) = delete;

lib/SILOptimizer/Analysis/Reachability.cpp

@@ -70,6 +70,10 @@ class FindBarriersBackwardDataflow final {
   void visitBarrierBlock(SILBasicBlock *block) {
     barriers.edges.push_back(block);
   }
+
+  void visitInitialBlock(SILBasicBlock *block) {
+    barriers.initialBlocks.push_back(block);
+  }
 };
 
 FindBarriersBackwardDataflow::Effect

lib/SILOptimizer/Transforms/DestroyAddrHoisting.cpp

@@ -318,6 +318,10 @@ class DeinitBarriers final {
       result.barrierBlocks.insert(block);
     }
 
+    void visitInitialBlock(SILBasicBlock *block) {
+      result.barrierBlocks.insert(block);
+    }
+
     /// VisitBarrierAccessScopes::Visitor
 
     ArrayRef<SILBasicBlock *> roots();

lib/SILOptimizer/Utils/CanonicalizeOSSALifetime.cpp

@@ -287,16 +287,15 @@ void CanonicalizeOSSALifetime::extendLivenessToDeinitBarriers() {
     }
   }
   for (auto *edge : barriers.edges) {
-    if (edge == getCurrentDef()->getParentBlock()) {
-      // A destroy should be inserted at the begin of this block, but that does
-      // not require adding any instructions to liveness.
-      continue;
-    }
     auto *predecessor = edge->getSinglePredecessorBlock();
     assert(predecessor);
     liveness->updateForUse(&predecessor->back(),
                            /*lifetimeEnding*/ false);
   }
+  // Ignore barriers.initialBlocks.  If the collection is non-empty, it
+  // contains the def-block.  Its presence means that no barriers were found
+  // between lifetime ends and def.  In that case, no new instructions need to
+  // be added to liveness.
 }
 
 // Return true if \p inst is an end_access whose access scope overlaps the end

lib/SILOptimizer/Utils/LexicalDestroyHoisting.cpp

@@ -184,6 +184,10 @@ class Dataflow final {
   void visitBarrierBlock(SILBasicBlock *block) {
     barriers.blocks.push_back(block);
   }
+
+  void visitInitialBlock(SILBasicBlock *block) {
+    barriers.blocks.push_back(block);
+  }
 };
 
 Dataflow::Classification

lib/SILOptimizer/Utils/ShrinkBorrowScope.cpp

@@ -213,6 +213,10 @@ class Dataflow final {
   void visitBarrierBlock(SILBasicBlock *block) {
     barriers.blocks.push_back(block);
   }
+
+  void visitInitialBlock(SILBasicBlock *block) {
+    barriers.blocks.push_back(block);
+  }
 };
 
 /// Whether the specified value is %lifetime or its iterated copy_value.