Merge pull request #41113 from nate-chandler/lexical_lifetimes/destroy_folding/add

[CopyPropagation] Added lexical destroy folding.

Author: nate-chandler

include/swift/SIL/PrunedLiveness.h

@@ -338,6 +338,10 @@ class PrunedLiveness {
   bool areUsesWithinBoundary(ArrayRef<Operand *> uses,
                              DeadEndBlocks *deadEndBlocks) const;
 
+  /// \p deadEndBlocks is optional.
+  bool areUsesOutsideBoundary(ArrayRef<Operand *> uses,
+                              DeadEndBlocks *deadEndBlocks) const;
+
   /// Compute liveness for a single SSA definition.
   void computeSSALiveness(SILValue def);
 };

include/swift/SILOptimizer/Analysis/Reachability.h

@@ -43,7 +43,7 @@ namespace swift {
 ///
 ///   // Mark the beginning of a block reachable. Only called once per block.
 ///   // Typically a BasicBlockSet wrapper.
-///   boid markReachableBegin(SILBasicBlock *block);
+///   void markReachableBegin(SILBasicBlock *block);
 /// 
 ///   // Mark the end of a block reachable. Only called once per block.
 ///   // Typically a BasicBlockSet wrapper.

include/swift/SILOptimizer/Utils/CanonicalOSSALifetime.h

@@ -313,6 +313,23 @@ class CanonicalizeOSSALifetime {
   CanonicalOSSAConsumeInfo consumes;
 
 public:
+  /// When rewriting destroys, is this an instruction which destroys should not
+  /// be hoisted over to avoid churn and infinite looping.
+  static bool ignoredByDestroyHoisting(SILInstructionKind kind) {
+    switch (kind) {
+    case SILInstructionKind::DestroyValueInst:
+    case SILInstructionKind::CopyValueInst:
+    case SILInstructionKind::BeginBorrowInst:
+    case SILInstructionKind::EndBorrowInst:
+    case SILInstructionKind::FunctionRefInst:
+    case SILInstructionKind::EnumInst:
+    case SILInstructionKind::StructInst:
+      return true;
+    default:
+      return false;
+    }
+  }
+
   void maybeNotifyMoveOnlyCopy(Operand *use) {
     if (!moveOnlyCopyValueNotification)
       return;

include/swift/SILOptimizer/Utils/CanonicalizeBorrowScope.h

@@ -151,6 +151,10 @@ bool shrinkBorrowScope(
     BeginBorrowInst *bbi, InstructionDeleter &deleter,
     SmallVectorImpl<CopyValueInst *> &modifiedCopyValueInsts);
 
+bool foldDestroysOfCopiedLexicalBorrow(BeginBorrowInst *bbi,
+                                       DominanceInfo &dominanceTree,
+                                       InstructionDeleter &deleter);
+
 } // namespace swift
 
 #endif // SWIFT_SILOPTIMIZER_UTILS_CANONICALIZEBORROWSCOPES_H

lib/SIL/Utils/PrunedLiveness.cpp

@@ -167,6 +167,20 @@ bool PrunedLiveness::areUsesWithinBoundary(ArrayRef<Operand *> uses,
   return true;
 }
 
+bool PrunedLiveness::areUsesOutsideBoundary(
+    ArrayRef<Operand *> uses, DeadEndBlocks *deadEndBlocks) const {
+  auto checkDeadEnd = [deadEndBlocks](SILInstruction *inst) {
+    return deadEndBlocks && deadEndBlocks->isDeadEnd(inst->getParent());
+  };
+
+  for (auto *use : uses) {
+    auto *user = use->getUser();
+    if (isWithinBoundary(user) || checkDeadEnd(user))
+      return false;
+  }
+  return true;
+}
+
 // An SSA def meets all the criteria for pruned liveness--def dominates all uses
 // with no holes in the liverange. The lifetime-ending uses are also
 // recorded--destroy_value or end_borrow. However destroy_values may not

lib/SILOptimizer/Transforms/CopyPropagation.cpp

@@ -434,21 +434,50 @@ void CopyPropagation::run() {
     }
   }
 
+  // canonicalizer performs all modifications through deleter's callbacks, so we
+  // don't need to explicitly check for changes.
+  CanonicalizeOSSALifetime canonicalizer(pruneDebug, poisonRefs,
+                                         accessBlockAnalysis, domTree, deleter);
+
   // NOTE: We assume that the function is in reverse post order so visiting the
   //       blocks and pushing begin_borrows as we see them and then popping them
   //       off the end will result in shrinking inner borrow scopes first.
   while (auto *bbi = beginBorrowsToShrink.pop()) {
-    SmallVector<CopyValueInst *, 4> modifiedCopyValueInsts;
-    changed |= shrinkBorrowScope(bbi, deleter, modifiedCopyValueInsts);
-    for (auto *cvi : modifiedCopyValueInsts)
-      defWorklist.updateForCopy(cvi);
+    bool firstRun = true;
+    // Run the sequence of utilities:
+    // - ShrinkBorrowScope
+    // - CanonicalizeOSSALifetime
+    // - LexicalDestroyFolder
+    // at least once and then until each stops making changes.
+    while (true) {
+      SmallVector<CopyValueInst *, 4> modifiedCopyValueInsts;
+      auto shrunk = shrinkBorrowScope(bbi, deleter, modifiedCopyValueInsts);
+      for (auto *cvi : modifiedCopyValueInsts)
+        defWorklist.updateForCopy(cvi);
+      changed |= shrunk;
+      if (!shrunk && !firstRun)
+        break;
+
+      // If borrowed value is not owned, neither CanonicalizeOSSALifetime nor
+      // LexicalDestroyFolding will do anything with it.  Just bail out now.
+      auto borrowee = bbi->getOperand();
+      if (borrowee.getOwnershipKind() != OwnershipKind::Owned)
+        break;
+
+      auto canonicalized = canonicalizer.canonicalizeValueLifetime(borrowee);
+      if (!canonicalized && !firstRun)
+        break;
+
+      auto folded = foldDestroysOfCopiedLexicalBorrow(bbi, *domTree, deleter);
+      if (!folded)
+        break;
+      // We don't add the produced move_value instruction to the worklist
+      // because it can't handle propagation.
+      firstRun = false;
+    }
   }
   deleter.cleanupDeadInstructions();
 
-  // canonicalizer performs all modifications through deleter's callbacks, so we
-  // don't need to explicitly check for changes.
-  CanonicalizeOSSALifetime canonicalizer(pruneDebug, poisonRefs,
-                                         accessBlockAnalysis, domTree, deleter);
   // For now, only modify forwarding instructions
   // At -Onone, we do nothing but rewrite copies of owned values.
   if (canonicalizeBorrows) {

lib/SILOptimizer/Utils/CMakeLists.txt

@@ -18,6 +18,7 @@ target_sources(swiftSILOptimizer PRIVATE
   InstructionDeleter.cpp
   InstOptUtils.cpp
   KeyPathProjector.cpp
+  LexicalDestroyFolding.cpp
   LoadStoreOptUtils.cpp
   LoopUtils.cpp
   OptimizerStatsUtils.cpp

lib/SILOptimizer/Utils/CanonicalOSSALifetime.cpp

@@ -492,9 +492,10 @@ void CanonicalizeOSSALifetime::findOrInsertDestroyInBlock(SILBasicBlock *bb) {
       return;
     }
     // This is not a potential last user. Keep scanning.
-    // Allow lifetimes to be artificially extended up to the next call. The goal
-    // is to prevent repeated destroy rewriting without inhibiting optimization.
-    if (ApplySite::isa(inst)) {
+    // Allow lifetimes to be artificially extended up to the next non-ignored
+    // instruction. The goal is to prevent repeated destroy rewriting without
+    // inhibiting optimization.
+    if (!ignoredByDestroyHoisting(inst->getKind())) {
       existingDestroy = nullptr;
     } else if (!existingDestroy) {
       if (auto *destroy = dyn_cast<DestroyValueInst>(inst)) {