Merge pull request swiftlang#68608 from nate-chandler/rdar115468707

nate-chandler · web-flow · commit 397a25c377ee · 2023-09-21T20:25:46.000-07:00
[CanonicalizeOSSALifetime] Extend lexical lifetimes to unreachables.
diff --git a/include/swift/SIL/OSSALifetimeCompletion.h b/include/swift/SIL/OSSALifetimeCompletion.h
@@ -85,6 +85,10 @@ class OSSALifetimeCompletion {
                : LifetimeCompletion::AlreadyComplete;
   }
 
+  static void visitUnreachableLifetimeEnds(
+      SILValue value, const SSAPrunedLiveness &liveness,
+      llvm::function_ref<void(UnreachableInst *)> visit);
+
 protected:
   bool analyzeAndUpdateLifetime(SILValue value, bool forceBoundaryCompletion);
 };
diff --git a/include/swift/SIL/PrunedLiveness.h b/include/swift/SIL/PrunedLiveness.h
@@ -154,8 +154,6 @@ class DeadEndBlocks;
 /// blocks to the blocks that occur on or after the def block. If any uses is
 /// not dominated by a def block, then liveness will include the entry block,
 /// as if defined by a function argument
-///
-/// TODO: For efficiency, use BasicBlockBitfield rather than SmallDenseMap.
 class PrunedLiveBlocks {
 public:
   /// Per-block liveness state computed during backward dataflow propagation.
@@ -200,6 +198,17 @@ class PrunedLiveBlocks {
     assert(!discoveredBlocks || discoveredBlocks->empty());
   }
 
+  PrunedLiveBlocks(PrunedLiveBlocks const &other,
+                   SmallVectorImpl<SILBasicBlock *> *discoveredBlocks = nullptr)
+      : liveBlocks(other.liveBlocks.getFunction(), 2),
+        discoveredBlocks(discoveredBlocks) {
+    assert(!discoveredBlocks || other.discoveredBlocks);
+    for (auto &block : *other.liveBlocks.getFunction()) {
+      liveBlocks.set(&block, other.liveBlocks.get(&block));
+    }
+    initializedFlag = other.initializedFlag;
+  }
+
   bool isInitialized() const { return initializedFlag; }
 
   void initializeDiscoveredBlocks(
@@ -363,6 +372,10 @@ class PrunedLiveness {
                  SmallVectorImpl<SILBasicBlock *> *discoveredBlocks = nullptr)
       : liveBlocks(function, discoveredBlocks) {}
 
+  PrunedLiveness(PrunedLiveness const &other,
+                 SmallVectorImpl<SILBasicBlock *> *discoveredBlocks = nullptr)
+      : liveBlocks(other.liveBlocks, discoveredBlocks), users(other.users) {}
+
   bool isInitialized() const { return liveBlocks.isInitialized(); }
 
   bool empty() const { return users.empty(); }
@@ -531,6 +544,10 @@ class PrunedLiveRange : public PrunedLiveness {
                   SmallVectorImpl<SILBasicBlock *> *discoveredBlocks = nullptr)
       : PrunedLiveness(function, discoveredBlocks) {}
 
+  PrunedLiveRange(PrunedLiveRange const &other,
+                  SmallVectorImpl<SILBasicBlock *> *discoveredBlocks = nullptr)
+      : PrunedLiveness(other, discoveredBlocks) {}
+
   LiveRangeSummary recursivelyUpdateForDef(SILValue initialDef,
                                            ValueSet &visited,
                                            SILValue value);
@@ -628,6 +645,14 @@ class SSAPrunedLiveness : public PrunedLiveRange<SSAPrunedLiveness> {
       SmallVectorImpl<SILBasicBlock *> *discoveredBlocks = nullptr)
       : PrunedLiveRange(function, discoveredBlocks) {}
 
+  SSAPrunedLiveness(
+      SSAPrunedLiveness const &other,
+      SmallVectorImpl<SILBasicBlock *> *discoveredBlocks = nullptr)
+      : PrunedLiveRange(other, discoveredBlocks) {
+    def = other.def;
+    defInst = other.defInst;
+  }
+
   SILValue getDef() const { return def; }
 
   void initializeDef(SILValue def) {
diff --git a/include/swift/SILOptimizer/Utils/CanonicalizeOSSALifetime.h b/include/swift/SILOptimizer/Utils/CanonicalizeOSSALifetime.h
@@ -319,7 +319,7 @@ class CanonicalizeOSSALifetime final {
 
     currentDef = def;
 
-    if (maximizeLifetime) {
+    if (maximizeLifetime || respectsDeinitBarriers()) {
       liveness->initializeDiscoveredBlocks(&discoveredBlocks);
     }
     liveness->initializeDef(getCurrentDef());
@@ -396,10 +396,18 @@ class CanonicalizeOSSALifetime final {
   UserRange getUsers() const { return liveness->getAllUsers(); }
 
 private:
+  bool respectsDeinitBarriers() const {
+    if (!currentDef->isLexical())
+      return false;
+    auto &module = currentDef->getFunction()->getModule();
+    return module.getASTContext().SILOpts.supportsLexicalLifetimes(module);
+  }
+
   void recordDebugValue(DebugValueInst *dvi) { debugValues.insert(dvi); }
 
-  void recordConsumingUse(Operand *use) {
-    consumingBlocks.insert(use->getUser()->getParent());
+  void recordConsumingUse(Operand *use) { recordConsumingUser(use->getUser()); }
+  void recordConsumingUser(SILInstruction *user) {
+    consumingBlocks.insert(user->getParent());
   }
   bool computeCanonicalLiveness();
 
diff --git a/lib/SIL/Utils/OSSALifetimeCompletion.cpp b/lib/SIL/Utils/OSSALifetimeCompletion.cpp
@@ -99,8 +99,9 @@ static bool endLifetimeAtBoundary(SILValue value,
   return changed;
 }
 
-static bool endLifetimeAtUnreachableBlocks(SILValue value,
-                                           const SSAPrunedLiveness &liveness) {
+void OSSALifetimeCompletion::visitUnreachableLifetimeEnds(
+    SILValue value, const SSAPrunedLiveness &liveness,
+    llvm::function_ref<void(UnreachableInst *)> visit) {
   PrunedLivenessBoundary boundary;
   liveness.computeBoundary(boundary);
 
@@ -119,20 +120,28 @@ static bool endLifetimeAtUnreachableBlocks(SILValue value,
   }
   // Forward CFG walk from the non-lifetime-ending boundary to the unreachable
   // instructions.
-  bool changed = false;
   while (auto *block = deadEndBlocks.pop()) {
     if (block->succ_empty()) {
       // This assert will fail unless there are already lifetime-ending
       // instruction on all paths to normal function exits.
       auto *unreachable = cast<UnreachableInst>(block->getTerminator());
-      SILBuilderWithScope builder(unreachable);
-      endOSSALifetime(value, builder);
-      changed = true;
+      visit(unreachable);
     }
     for (auto *successor : block->getSuccessorBlocks()) {
       deadEndBlocks.pushIfNotVisited(successor);
     }
   }
+}
+
+static bool endLifetimeAtUnreachableBlocks(SILValue value,
+                                           const SSAPrunedLiveness &liveness) {
+  bool changed = false;
+  OSSALifetimeCompletion::visitUnreachableLifetimeEnds(
+      value, liveness, [&](auto *unreachable) {
+        SILBuilderWithScope builder(unreachable);
+        endOSSALifetime(value, builder);
+        changed = true;
+      });
   return changed;
 }
 
diff --git a/lib/SILOptimizer/SILCombiner/SILCombinerMiscVisitors.cpp b/lib/SILOptimizer/SILCombiner/SILCombinerMiscVisitors.cpp
@@ -810,17 +810,47 @@ SILInstruction *SILCombiner::visitCondFailInst(CondFailInst *CFI) {
   if (!I->getValue().getBoolValue())
     return eraseInstFromFunction(*CFI);
 
-  // Remove any code that follows a (cond_fail 1) and set the block's
-  // terminator to unreachable.
+  // Remove non-lifetime-ending code that follows a (cond_fail 1) and set the
+  // block's terminator to unreachable.
 
-  // Nothing more to do here
+  // Are there instructions after this point to delete?
+
+  // First check if the next instruction is unreachable.
   if (isa<UnreachableInst>(std::next(SILBasicBlock::iterator(CFI))))
     return nullptr;
 
-  // Collect together all the instructions after this point
+  // Otherwise, check if the only instructions are unreachables and destroys of
+  // lexical values.
+
+  // Collect all instructions and, in OSSA, the values they define.
   llvm::SmallVector<SILInstruction *, 32> ToRemove;
-  for (auto Inst = CFI->getParent()->rbegin(); &*Inst != CFI; ++Inst)
-    ToRemove.push_back(&*Inst);
+  ValueSet DefinedValues(CFI->getFunction());
+  for (auto Iter = std::next(CFI->getIterator());
+       Iter != CFI->getParent()->end(); ++Iter) {
+    if (!CFI->getFunction()->hasOwnership()) {
+      ToRemove.push_back(&*Iter);
+      continue;
+    }
+
+    for (auto result : Iter->getResults()) {
+      DefinedValues.insert(result);
+    }
+    // Look for destroys of lexical values whose def isn't after the cond_fail.
+    if (auto *dvi = dyn_cast<DestroyValueInst>(&*Iter)) {
+      auto value = dvi->getOperand();
+      if (!DefinedValues.contains(value) && value->isLexical())
+        continue;
+    }
+    ToRemove.push_back(&*Iter);
+  }
+
+  unsigned instructionsToDelete = ToRemove.size();
+  // If the last instruction is an unreachable already, it needn't be deleted.
+  if (isa<UnreachableInst>(ToRemove.back())) {
+    --instructionsToDelete;
+  }
+  if (instructionsToDelete == 0)
+    return nullptr;
 
   for (auto *Inst : ToRemove) {
     // Replace any still-remaining uses with undef and erase.
diff --git a/lib/SILOptimizer/Utils/CanonicalizeOSSALifetime.cpp b/lib/SILOptimizer/Utils/CanonicalizeOSSALifetime.cpp
@@ -68,6 +68,7 @@
 #include "swift/SILOptimizer/Utils/CanonicalizeOSSALifetime.h"
 #include "swift/SIL/InstructionUtils.h"
 #include "swift/SIL/NodeDatastructures.h"
+#include "swift/SIL/OSSALifetimeCompletion.h"
 #include "swift/SIL/OwnershipUtils.h"
 #include "swift/SIL/PrunedLiveness.h"
 #include "swift/SIL/Test.h"
@@ -249,6 +250,35 @@ void CanonicalizeOSSALifetime::extendLivenessToDeinitBarriers() {
   SmallVector<SILInstruction *, 4> outsideDestroys;
   findDestroysOutsideBoundary(outsideDestroys);
 
+  // OSSALifetimeCompletion: With complete lifetimes, creating completeLiveness
+  // and using it to visiti unreachable lifetime ends should be deleted.
+  SmallVector<SILBasicBlock *, 32> discoveredBlocks(this->discoveredBlocks);
+  SSAPrunedLiveness completeLiveness(*liveness, &discoveredBlocks);
+
+  for (auto *end : outsideDestroys) {
+    completeLiveness.updateForUse(end, /*lifetimeEnding*/ true);
+  }
+
+  OSSALifetimeCompletion::visitUnreachableLifetimeEnds(
+      getCurrentDef(), completeLiveness, [&](auto *unreachable) {
+        recordConsumingUser(unreachable);
+        if (auto *previous = unreachable->getPreviousInstruction()) {
+          if (liveness->isInterestingUser(previous) ==
+              PrunedLiveness::IsInterestingUser::NonUser) {
+            liveness->updateForUse(previous, /*lifetimeEnding=*/false);
+          }
+          return;
+        }
+        for (auto *predecessor :
+             unreachable->getParent()->getPredecessorBlocks()) {
+          auto *previous = &predecessor->back();
+          if (liveness->isInterestingUser(previous) ==
+              PrunedLiveness::IsInterestingUser::NonUser) {
+            liveness->updateForUse(previous, /*lifetimeEnding=*/false);
+          }
+        }
+      });
+
   auto *def = getCurrentDef()->getDefiningInstruction();
   using InitialBlocks = ArrayRef<SILBasicBlock *>;
   auto *defBlock = getCurrentDef()->getParentBlock();
@@ -890,6 +920,27 @@ static void insertDestroyBeforeInstruction(SILInstruction *nextInstruction,
                                            SILValue currentDef,
                                            CanonicalOSSAConsumeInfo &consumes,
                                            InstModCallbacks &callbacks) {
+  // OSSALifetimeCompletion: This conditional clause can be deleted with
+  // complete lifetimes.
+  if (isa<UnreachableInst>(nextInstruction)) {
+    // Don't create a destroy_value if the next instruction is an unreachable.
+    // If there was a destroy here already, it would be reused.  Avoids
+    // creating an explicit destroy of a value which might have an unclosed
+    // borrow scope.  Doing so would result in
+    //
+    //     somewhere:
+    //       %def
+    //       %borrow = begin_borrow ...
+    //
+    //     die:
+    //       destroy_value %def
+    //       unreachable
+    //
+    // which is invalid (although the verifier doesn't catch
+    // it--rdar://115850528) because there must be an `end_borrow %borrow`
+    // before the destroy_value.
+    return;
+  }
   SILBuilderWithScope builder(nextInstruction);
   auto loc =
       RegularLocation::getAutoGeneratedLocation(nextInstruction->getLoc());
@@ -1124,7 +1175,7 @@ bool CanonicalizeOSSALifetime::computeLiveness() {
     clear();
     return false;
   }
-  if (currentDef->isLexical()) {
+  if (respectsDeinitBarriers()) {
     extendLivenessToDeinitBarriers();
   }
   if (accessBlockAnalysis) {
diff --git a/test/SILOptimizer/canonicalize_ossa_lifetime_unit.sil b/test/SILOptimizer/canonicalize_ossa_lifetime_unit.sil
diff --git a/test/SILOptimizer/mem2reg_lifetime.sil b/test/SILOptimizer/mem2reg_lifetime.sil
