AST: Fix ExistentialLayout::isObjC() handling of marker protocols

Fixes rdar://problem/119541554.

Author: slavapestov

include/swift/AST/ExistentialLayout.h

@@ -31,7 +31,8 @@ struct ExistentialLayout {
 
   ExistentialLayout() {
     hasExplicitAnyObject = false;
-    containsNonObjCProtocol = false;
+    containsObjCProtocol = false;
+    containsSwiftProtocol = false;
     containsParameterized = false;
   }
 
@@ -45,8 +46,11 @@ struct ExistentialLayout {
   /// Whether the existential contains an explicit '& AnyObject' constraint.
   bool hasExplicitAnyObject : 1;
 
-  /// Whether any protocol members are non-@objc.
-  bool containsNonObjCProtocol : 1;
+  /// Whether any protocol members are @objc.
+  bool containsObjCProtocol : 1;
+
+  /// Whether any protocol members require a witness table.
+  bool containsSwiftProtocol : 1;
 
   /// Whether any protocol members are parameterized.s
   bool containsParameterized : 1;
@@ -70,8 +74,8 @@ struct ExistentialLayout {
     // FIXME: Does the superclass have to be @objc?
     return ((explicitSuperclass ||
              hasExplicitAnyObject ||
-             !getProtocols().empty()) &&
-            !containsNonObjCProtocol);
+             containsObjCProtocol) &&
+            !containsSwiftProtocol);
   }
 
   /// Whether the existential requires a class, either via an explicit
@@ -105,10 +109,6 @@ struct ExistentialLayout {
   /// Zero or more primary associated type requirements from a
   /// ParameterizedProtocolType
   ArrayRef<Type> sameTypeRequirements;
-
-  /// Existentials allow a relaxed notion of \c ValueDecl::isObjC
-  /// that includes `Sendable` protocol.
-  static bool isObjCProtocol(ProtocolDecl *P);
 };
 
 }

lib/AST/ASTVerifier.cpp

@@ -1659,7 +1659,7 @@ class Verifier : public ASTWalker {
             auto concreteLayout = concreteTy->getCanonicalType()
                                             ->getExistentialLayout();
             canBeClass = concreteLayout.getKind() == ExistentialLayout::Kind::Class
-              && !concreteLayout.containsNonObjCProtocol;
+              && !concreteLayout.containsSwiftProtocol;
           } else {
             canBeClass = false;
           }

lib/AST/Type.cpp

@@ -299,15 +299,18 @@ ExistentialLayout::ExistentialLayout(CanProtocolType type) {
   auto *protoDecl = type->getDecl();
 
   hasExplicitAnyObject = false;
-  containsNonObjCProtocol = !isObjCProtocol(protoDecl);
+  containsObjCProtocol = protoDecl->isObjC();
+  containsSwiftProtocol = (!protoDecl->isObjC() &&
+                           !protoDecl->isMarkerProtocol());
   containsParameterized = false;
 
   protocols.push_back(protoDecl);
 }
 
 ExistentialLayout::ExistentialLayout(CanProtocolCompositionType type) {
   hasExplicitAnyObject = type->hasExplicitAnyObject();
-  containsNonObjCProtocol = false;
+  containsObjCProtocol = false;
+  containsSwiftProtocol = false;
   containsParameterized = false;
 
   auto members = type.getMembers();
@@ -327,7 +330,10 @@ ExistentialLayout::ExistentialLayout(CanProtocolCompositionType type) {
       protoDecl = parameterized->getProtocol();
       containsParameterized = true;
     }
-    containsNonObjCProtocol |= !isObjCProtocol(protoDecl);
+    if (protoDecl->isObjC())
+      containsObjCProtocol = true;
+    else if (!protoDecl->isMarkerProtocol())
+      containsSwiftProtocol = true;
     protocols.push_back(protoDecl);
   }
 }
@@ -338,10 +344,6 @@ ExistentialLayout::ExistentialLayout(CanParameterizedProtocolType type)
   containsParameterized = true;
 }
 
-bool ExistentialLayout::isObjCProtocol(ProtocolDecl *P) {
-  return P->isObjC() || P->isSpecificProtocol(KnownProtocolKind::Sendable);
-}
-
 ExistentialLayout TypeBase::getExistentialLayout() {
   return getCanonicalType().getExistentialLayout();
 }

lib/SIL/IR/SILType.cpp

@@ -255,12 +255,8 @@ static bool isSingleSwiftRefcounted(SILModule &M,
   if (Ty->isAnyExistentialType()) {
     auto layout = Ty->getExistentialLayout();
     // Must be no protocol constraints that aren't @objc or @_marker.
-    if (layout.containsNonObjCProtocol) {
-      for (auto proto : layout.getProtocols()) {
-        if (!proto->isObjC() && !proto->isMarkerProtocol()) {
-          return false;
-        }
-      }
+    if (layout.containsSwiftProtocol) {
+      return false;
     }
 
     // The Error existential has its own special layout.
@@ -592,6 +588,7 @@ SILType::getPreferredExistentialRepresentation(Type containedType) const {
     return ExistentialRepresentation::Class;
 
   // Otherwise, we need to use a fixed-sized buffer.
+  assert(!layout.isObjC());
   return ExistentialRepresentation::Opaque;
 }
 

test/Interpreter/rdar119541554.swift

@@ -0,0 +1,14 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-build-swift %s -o %t/a.out -O -target %target-future-triple
+// RUN: %target-codesign %t/a.out
+// RUN: %target-run %t/a.out
+
+// REQUIRES: executable_test
+// REQUIRES: macos_min_version_13
+
+struct S {
+  var x = 42
+}
+
+_ = [S() as Sendable]