Merge pull request #78830 from atrick/fix-lifedep-trivial-deadend

SILGenCleanup: extend to handle trivial local var scopes

Author: atrick

include/swift/SIL/OSSALifetimeCompletion.h

@@ -39,6 +39,10 @@ class DeadEndBlocks;
 enum class LifetimeCompletion { NoLifetime, AlreadyComplete, WasCompleted };
 
 class OSSALifetimeCompletion {
+public:
+  enum HandleTrivialVariable_t { IgnoreTrivialVariable, ExtendTrivialVariable };
+
+private:
   // If domInfo is nullptr, then InteriorLiveness never assumes dominance. As a
   // result it may report extra unenclosedPhis. In that case, any attempt to
   // create a new phi would result in an immediately redundant phi.
@@ -50,11 +54,15 @@ class OSSALifetimeCompletion {
   // recomputing their lifetimes.
   ValueSet completedValues;
 
+  // Extend trivial variables for lifetime diagnostics (only in SILGenCleanup).
+  HandleTrivialVariable_t handleTrivialVariable;
+
 public:
   OSSALifetimeCompletion(SILFunction *function, const DominanceInfo *domInfo,
-                         DeadEndBlocks &deadEndBlocks)
+                         DeadEndBlocks &deadEndBlocks,
+                         HandleTrivialVariable_t handleTrivialVariable = IgnoreTrivialVariable)
       : domInfo(domInfo), deadEndBlocks(deadEndBlocks),
-        completedValues(function) {}
+        completedValues(function), handleTrivialVariable(handleTrivialVariable) {}
 
   // The kind of boundary at which to complete the lifetime.
   //
@@ -93,10 +101,15 @@ class OSSALifetimeCompletion {
   LifetimeCompletion completeOSSALifetime(SILValue value, Boundary boundary) {
     switch (value->getOwnershipKind()) {
     case OwnershipKind::None: {
-      auto scopedAddress = ScopedAddressValue(value);
-      if (!scopedAddress)
-        return LifetimeCompletion::NoLifetime;
-      break;
+      if (auto scopedAddress = ScopedAddressValue(value)) {
+        break;
+      }
+      // During SILGenCleanup, extend move_value [var_decl].
+      if (handleTrivialVariable == ExtendTrivialVariable
+          && value->isFromVarDecl()) {
+        break;
+      }
+      return LifetimeCompletion::NoLifetime;
     }
     case OwnershipKind::Owned:
       break;

include/swift/SIL/OwnershipUseVisitor.h

@@ -165,6 +165,8 @@ class OwnershipUseVisitor : OwnershipUseVisitorBase<Impl> {
 protected:
   bool visitConsumes(SILValue ssaDef);
 
+  bool visitExtends(SILValue ssaDef);
+
   bool visitOuterBorrow(SILValue borrowBegin);
 
   bool visitOuterBorrowScopeEnd(Operand *borrowEnd);
@@ -202,8 +204,12 @@ bool OwnershipUseVisitor<Impl>::visitLifetimeEndingUses(SILValue ssaDef) {
   case OwnershipKind::Guaranteed:
     return visitOuterBorrow(ssaDef);
 
-  case OwnershipKind::Any:
   case OwnershipKind::None:
+    if (ssaDef->isFromVarDecl()) {
+      return visitExtends(ssaDef);
+    }
+    LLVM_FALLTHROUGH;
+  case OwnershipKind::Any:
   case OwnershipKind::Unowned:
     llvm_unreachable("requires an owned or guaranteed orignalDef");
   }
@@ -231,6 +237,18 @@ bool OwnershipUseVisitor<Impl>::visitConsumes(SILValue ssaDef) {
   return true;
 }
 
+template <typename Impl>
+bool OwnershipUseVisitor<Impl>::visitExtends(SILValue ssaDef) {
+  for (Operand *use : ssaDef->getUses()) {
+    if (isa<ExtendLifetimeInst>(use->getUser())) {
+      if (!handleUsePoint(use, UseLifetimeConstraint::NonLifetimeEnding))
+        return false;
+      continue;
+    }
+  }
+  return true;
+}
+
 template <typename Impl>
 bool OwnershipUseVisitor<Impl>::visitOuterBorrow(SILValue borrowBegin) {
   BorrowedValue borrow(borrowBegin);

lib/SIL/Utils/OSSALifetimeCompletion.cpp

@@ -80,6 +80,9 @@ static SILInstruction *endOSSALifetime(SILValue value,
   if (auto scopedAddress = ScopedAddressValue(value)) {
     return scopedAddress.createScopeEnd(builder.getInsertionPoint(), loc);
   }
+  if (value->getOwnershipKind() == OwnershipKind::None) {
+    return builder.createExtendLifetime(loc, value);
+  }
   return builder.createEndBorrow(loc, lookThroughBorrowedFromUser(value));
 }
 
@@ -297,9 +300,16 @@ void AvailabilityBoundaryVisitor::computeRegion(
     regionWorklist.push(block);
   };
 
-  for (auto *endBlock : boundary.endBlocks) {
-    if (!consumingBlocks.contains(endBlock)) {
-      collect(endBlock);
+  // Trivial values that correspond to local variables (as opposed to
+  // ScopedAddresses) are available only up to their last extend_lifetime on
+  // non-dead-end paths. They cannot be consumed, but are only "available" up to
+  // the end of their scope.
+  if (value->getOwnershipKind() != OwnershipKind::None
+      || ScopedAddressValue(value)) {
+    for (auto *endBlock : boundary.endBlocks) {
+      if (!consumingBlocks.contains(endBlock)) {
+        collect(endBlock);
+      }
     }
   }
   for (SILBasicBlock *edge : boundary.boundaryEdges) {
@@ -497,12 +507,21 @@ bool OSSALifetimeCompletion::analyzeAndUpdateLifetime(SILValue value,
   if (auto scopedAddress = ScopedAddressValue(value)) {
     return analyzeAndUpdateLifetime(scopedAddress, boundary);
   }
-
   // Called for inner borrows, inner adjacent reborrows, inner reborrows, and
   // scoped addresses.
   auto handleInnerScope = [this, boundary](SILValue innerBorrowedValue) {
     completeOSSALifetime(innerBorrowedValue, boundary);
   };
+  if (value->getOwnershipKind() == OwnershipKind::None) {
+    // Trivial variable lifetimes are only relevant up to the extend_lifetime
+    // instructions emitted by SILGen. Their other uses have no meaning with
+    // respect to lifetime. The only purpose of "completing" their lifetime is
+    // to insert extend_lifetime on dead-end blocks.
+    LinearLiveness liveness(value);
+    liveness.compute();
+    return endLifetimeAtBoundary(value, liveness.getLiveness(), boundary,
+                                 deadEndBlocks);
+  }
   InteriorLiveness liveness(value);
   liveness.compute(domInfo, handleInnerScope);
   // TODO: Rebuild outer adjacent phis on demand (SILGen does not currently

lib/SIL/Utils/OwnershipLiveness.cpp

@@ -79,10 +79,21 @@ struct LinearLivenessVisitor :
 LinearLiveness::LinearLiveness(SILValue def,
                                IncludeExtensions_t includeExtensions)
     : OSSALiveness(def), includeExtensions(includeExtensions) {
-  if (def->getOwnershipKind() != OwnershipKind::Owned) {
+  switch (def->getOwnershipKind()) {
+  case OwnershipKind::Owned:
+    break;
+  case OwnershipKind::Guaranteed: {
     BorrowedValue borrowedValue(def);
     assert(borrowedValue && borrowedValue.isLocalScope());
     (void)borrowedValue;
+    break;
+  }
+  case OwnershipKind::None:
+    assert(def->isFromVarDecl());
+    break;
+  case OwnershipKind::Unowned:
+  case OwnershipKind::Any:
+    llvm_unreachable("bad ownership for LinearLiveness");
   }
 }
 

lib/SILOptimizer/Mandatory/SILGenCleanup.cpp

@@ -267,7 +267,9 @@ bool SILGenCleanup::completeOSSALifetimes(SILFunction *function) {
   }
 
   bool changed = false;
-  OSSALifetimeCompletion completion(function, /*DomInfo*/ nullptr, *deba);
+  OSSALifetimeCompletion completion(
+    function, /*DomInfo*/ nullptr, *deba,
+    OSSALifetimeCompletion::ExtendTrivialVariable);
   BasicBlockSet completed(function);
   for (auto *root : roots) {
     if (root == function->getEntryBlock()) {

test/SILOptimizer/lifetime_dependence/semantics.swift

@@ -228,6 +228,19 @@ func testTrivialScope<T>(a: Array<T>) -> Span<T> {
   // expected-note  @-3{{this use causes the lifetime-dependent value to escape}}
 }
 
+extension Span {
+  public func withThrowingClosure<E: Error>(_ body: () throws(E) -> ()) throws(E) -> () {
+    try body()
+  }
+}
+
+// Test dependence on an local variable that needs to be extended into the dead-end block of a never-throwing apply.
+public func test(p: UnsafePointer<Int>) {
+  let pointer = p
+  let span = Span(base: pointer, count: 1)
+  span.withThrowingClosure {}
+}
+
 // =============================================================================
 // Scoped dependence on property access
 // =============================================================================

test/SILOptimizer/silgen_cleanup_complete_ossa.sil

@@ -6,6 +6,8 @@ sil_stage raw
 
 typealias AnyObject = Builtin.AnyObject
 
+protocol Error {}
+
 class Klass {
   var property: Builtin.Int64
 }
@@ -28,6 +30,12 @@ struct UInt8 {
 
 protocol P : AnyObject {}
 
+struct Err: Error {
+  var i: Int
+}
+
+sil @throwing : $@convention(thin) (UInt8) -> @error_indirect Err
+
 // =============================================================================
 // Test complete OSSA lifetimes
 // =============================================================================
@@ -367,3 +375,33 @@ left:
 right:
   unreachable
 }
+
+// CHECK-LABEL: sil [ossa] @testExtendTrivialToDeadEnd : $@convention(thin) (UInt8) -> () {
+// CHECK: bb0(%0 : $UInt8):
+// CHECK:   [[MV:%.*]] = move_value [var_decl] %0 : $UInt8
+// CHECK:   try_apply %{{.*}}(%{{.*}}, [[MV]]) : $@convention(thin) (UInt8) -> @error_indirect Err, normal bb1, error bb2
+// CHECK: bb1(
+// CHECK:   extend_lifetime [[MV]] : $UInt8
+// CHECK:   return
+// CHECK: bb2:
+// CHECK:   dealloc_stack
+// CHECK:   extend_lifetime [[MV]] : $UInt8
+// CHECK:   unreachable
+// CHECK-LABEL: } // end sil function 'testExtendTrivialToDeadEnd'
+sil [ossa] @testExtendTrivialToDeadEnd : $@convention(thin) (UInt8) -> () {
+bb0(%0 : $UInt8):
+  %mv = move_value [var_decl] %0
+  %e = alloc_stack $Err
+  %f = function_ref @throwing : $@convention(thin) (UInt8) -> @error_indirect Err
+  try_apply %f(%e, %mv) : $@convention(thin) (UInt8) -> @error_indirect Err, normal bb1, error bb2
+
+bb1(%ret : $()):
+  extend_lifetime %mv
+  dealloc_stack %e : $*Err
+  %99 = tuple ()
+  return %99
+
+bb2:
+  dealloc_stack %e : $*Err
+  unreachable
+}