Merge pull request swiftlang#80766 from nate-chandler/rdar149007151

[DCE] Don't delete instructions which consume escaping values.

Author: nate-chandler

include/swift/SIL/OSSALifetimeCompletion.h

@@ -43,34 +43,42 @@ class OSSALifetimeCompletion {
   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.
+  /// 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.
   const DominanceInfo *domInfo = nullptr;
 
   DeadEndBlocks &deadEndBlocks;
 
-  // Cache intructions already handled by the recursive algorithm to avoid
-  // recomputing their lifetimes.
+  /// Cache intructions already handled by the recursive algorithm to avoid
+  /// recomputing their lifetimes.
   ValueSet completedValues;
 
-  // Extend trivial variables for lifetime diagnostics (only in SILGenCleanup).
+  /// Extend trivial variables for lifetime diagnostics (only in SILGenCleanup).
   HandleTrivialVariable_t handleTrivialVariable;
 
+  /// Whether verification of the computed liveness should be run even when the
+  /// global setting is off.
+  /// TODO: Remove this option.
+  bool ForceLivenessVerification;
+
 public:
-  OSSALifetimeCompletion(SILFunction *function, const DominanceInfo *domInfo,
-                         DeadEndBlocks &deadEndBlocks,
-                         HandleTrivialVariable_t handleTrivialVariable = IgnoreTrivialVariable)
+  OSSALifetimeCompletion(
+      SILFunction *function, const DominanceInfo *domInfo,
+      DeadEndBlocks &deadEndBlocks,
+      HandleTrivialVariable_t handleTrivialVariable = IgnoreTrivialVariable,
+      bool forceLivenessVerification = false)
       : domInfo(domInfo), deadEndBlocks(deadEndBlocks),
-        completedValues(function), handleTrivialVariable(handleTrivialVariable) {}
-
-  // The kind of boundary at which to complete the lifetime.
-  //
-  // Liveness: "As early as possible."  Consume the value after the last
-  //           non-consuming uses.
-  // Availability: "As late as possible."  Consume the value in the last blocks
-  //               beyond the non-consuming uses in which the value has been
-  //               consumed on no incoming paths.
+        completedValues(function), handleTrivialVariable(handleTrivialVariable),
+        ForceLivenessVerification(forceLivenessVerification) {}
+
+  /// The kind of boundary at which to complete the lifetime.
+  ///
+  /// Liveness: "As early as possible."  Consume the value after the last
+  ///           non-consuming uses.
+  /// Availability: "As late as possible."  Consume the value in the last blocks
+  ///               beyond the non-consuming uses in which the value has been
+  ///               consumed on no incoming paths.
   struct Boundary {
     enum Value : uint8_t {
       Liveness,

lib/SIL/Utils/OSSALifetimeCompletion.cpp

@@ -501,8 +501,9 @@ bool OSSALifetimeCompletion::analyzeAndUpdateLifetime(
   };
   Walker walker(*this, scopedAddress, boundary, liveness);
   AddressUseKind result = walker.walk(scopedAddress.value);
-  if (VerifyLifetimeCompletion && boundary != Boundary::Availability
-      && result != AddressUseKind::NonEscaping) {
+  if ((VerifyLifetimeCompletion || ForceLivenessVerification) &&
+      boundary != Boundary::Availability &&
+      result != AddressUseKind::NonEscaping) {
     llvm::errs() << "Incomplete liveness for:\n" << scopedAddress.value;
     if (auto *escapingUse = walker.getEscapingUse()) {
       llvm::errs() << "  escapes at:\n";

lib/SILOptimizer/Transforms/DeadCodeElimination.cpp

@@ -77,6 +77,28 @@ static bool seemsUseful(SILInstruction *I) {
     return true;
   }
 
+  // Instructions which end the lifetimes of values which escape can only be
+  // deleted if compensating lifetime ends are added.  Compensating lifetime
+  // ends are added by OSSACompleteLifetime when the def block of the value
+  // is different from the parent block of the instruction.  But
+  // OSSACompleteLifetime requires that liveness be complete--that there are no
+  // pointer escapes.  So we can't delete instructions which end the lifetime
+  // of values which escape to a pointer and whose parent blocks are different.
+  if (llvm::any_of(I->getAllOperands(), [I](Operand &operand) {
+        if (!operand.isLifetimeEnding())
+          return false;
+        auto value = operand.get();
+        if (isa<SILUndef>(value))
+          return false;
+        auto *insertionPoint = value->getDefiningInsertionPoint();
+        ASSERT(insertionPoint);
+        if (insertionPoint->getParent() == I->getParent())
+          return false;
+        return findPointerEscape(value);
+      })) {
+    return true;
+  }
+
   if (auto *BI = dyn_cast<BuiltinInst>(I)) {
     // Although the onFastPath builtin has no side-effects we don't want to
     // remove it.
@@ -813,7 +835,9 @@ bool DCE::removeDead() {
     }
   }
 
-  OSSALifetimeCompletion completion(F, DT, *deadEndBlocks);
+  OSSALifetimeCompletion completion(
+      F, DT, *deadEndBlocks, OSSALifetimeCompletion::IgnoreTrivialVariable,
+      /*forceLivenessVerification=*/true);
   for (auto value : valuesToComplete) {
     if (!value.has_value())
       continue;

test/SILOptimizer/dead_code_elimination_ossa.sil

@@ -15,12 +15,18 @@ class C {}
 
 sil @getC : $@convention(thin) () -> @owned C
 sil @barrier : $@convention(thin) () -> ()
+sil @initC : $@convention(thin) (Builtin.Word) -> (@owned C, Builtin.RawPointer)
+sil [readnone] @finalC : $@convention(thin) (@owned C) -> @owned C
 
 struct CAndBit {
     var c: C
     var bit: Int1
 }
 
+struct Bool {
+  var _value: Builtin.Int1
+}
+
 struct MO: ~Copyable {
   var x: Int
   deinit
@@ -507,3 +513,28 @@ bb0(%0 : @owned $Outer):
   return %6 : $()
 }
 
+// CHECK-LABEL: sil [ossa] @dont_remove_lifetime_end_of_escaping_value
+// CHECK:         [[FINALIZE:%[^,]+]] = function_ref @finalC
+// CHECK:         apply [[FINALIZE]]
+// CHECK-LABEL: } // end sil function 'dont_remove_lifetime_end_of_escaping_value'
+sil [ossa] @dont_remove_lifetime_end_of_escaping_value : $@convention(thin) (Bool) -> () {
+bb0(%0 : $Bool):
+  %1 = integer_literal $Builtin.Word, 1
+  %2 = function_ref @initC : $@convention(thin) (Builtin.Word) -> (@owned C, Builtin.RawPointer)
+  %3 = apply %2(%1) : $@convention(thin) (Builtin.Word) -> (@owned C, Builtin.RawPointer)
+  (%4, %5) = destructure_tuple %3
+  %6 = mark_dependence %5 on %4
+  %7 = pointer_to_address %6 to [strict] $*Bool
+  store %0 to [trivial] %7
+  br bb1
+
+bb1:
+  %13 = function_ref @finalC : $@convention(thin) (@owned C) -> @owned C
+  %14 = apply %13(%4) : $@convention(thin) (@owned C) -> @owned C
+  destroy_value %14
+  br bb2
+
+bb2:
+  %17 = tuple ()
+  return %17
+}