Eliminate more ABI vestigates of marker protocols

Author: DougGregor

include/swift/AST/ASTMangler.h

@@ -68,6 +68,14 @@ class ASTMangler : public Mangler {
   std::function<bool (SymbolicReferent)> CanSymbolicReference;
 
   bool canSymbolicReference(SymbolicReferent referent) {
+    // Marker protocols cannot ever be symbolically referenced.
+    if (auto nominal = referent.dyn_cast<const NominalTypeDecl *>()) {
+      if (auto proto = dyn_cast<ProtocolDecl>(nominal)) {
+        if (proto->isMarkerProtocol())
+          return false;
+      }
+    }
+
     return AllowSymbolicReferences
       && (!CanSymbolicReference || CanSymbolicReference(referent));
   }

lib/IRGen/GenMeta.cpp

@@ -5243,6 +5243,11 @@ GenericRequirementsMetadata irgen::addGenericRequirements(
     case RequirementKind::Conformance: {
       auto protocol = requirement.getSecondType()->castTo<ProtocolType>()
         ->getDecl();
+
+      // Marker protocols do not record generic requirements at all.
+      if (protocol->isMarkerProtocol())
+        break;
+
       bool needsWitnessTable =
         Lowering::TypeConverter::protocolRequiresWitnessTable(protocol);
       auto flags = GenericRequirementFlags(GenericRequirementKind::Protocol,

lib/TBDGen/TBDGen.cpp

@@ -1037,7 +1037,7 @@ static bool isValidProtocolMemberForTBDGen(const Decl *D) {
 #endif
 
 void TBDGenVisitor::visitProtocolDecl(ProtocolDecl *PD) {
-  if (!PD->isObjC()) {
+  if (!PD->isObjC() && !PD->isMarkerProtocol()) {
     addSymbol(LinkEntity::forProtocolDescriptor(PD));
 
     struct WitnessVisitor : public SILWitnessVisitor<WitnessVisitor> {

test/IRGen/marker_protocol.swift

@@ -5,7 +5,6 @@
 
 // CHECK-NOT: $s15marker_protocol1PP
 // CHECK-NOT: $s15marker_protocol1PMp
-// CHECK-NOT: "\01l_protocols"
 
 @_marker public protocol P { }
 
@@ -20,3 +19,5 @@ public func testGeneric(i: Int, array: [Int]) {
   generic(i)
   generic(array)
 }
+
+public protocol Q: P { }