[IRGen+Runtime] Implement getEnumTag for singleton enums in layout strings (#66985)

Author: drexin

include/swift/Runtime/RuntimeFunctions.def

@@ -2326,6 +2326,16 @@ FUNCTION(GenericInitializeBufferWithCopyOfBuffer,
          ATTRS(NoUnwind),
          EFFECT(Refcounting))
 
+// unsigned swift_singletonEnum_getEnumTag(swift::OpaqueValue *address,
+//                                         const Metadata *metadata);
+FUNCTION(SingletonEnumGetEnumTag,
+         swift_singletonEnum_getEnumTag,
+         C_CC, AlwaysAvailable,
+         RETURNS(Int32Ty),
+         ARGS(Int8PtrTy, TypeMetadataPtrTy),
+         ATTRS(NoUnwind),
+         EFFECT(NoEffect))
+
 // unsigned swift_enumSimple_getEnumTag(swift::OpaqueValue *address,
 //                                      const Metadata *metadata);
 FUNCTION(EnumSimpleGetEnumTag,

lib/IRGen/GenValueWitness.cpp

@@ -905,7 +905,7 @@ static llvm::Constant *getEnumTagFunction(IRGenModule &IGM,
   if ((!typeLayoutEntry->layoutString(IGM, genericSig) &&
       !isRuntimeInstatiatedLayoutString(IGM, typeLayoutEntry)) ||
       typeLayoutEntry->isSingleton()) {
-    return nullptr;
+    return IGM.getSingletonEnumGetEnumTagFn();
   } else if (!typeLayoutEntry->isFixedSize(IGM)) {
     if (typeLayoutEntry->isMultiPayloadEnum()) {
       return IGM.getMultiPayloadEnumGenericGetEnumTagFn();

stdlib/public/runtime/BytecodeLayouts.cpp

@@ -652,6 +652,11 @@ swift_generic_assignWithTake(swift::OpaqueValue *dest, swift::OpaqueValue *src,
   return swift_generic_initWithTake(dest, src, metadata);
 }
 
+extern "C" unsigned swift_singletonEnum_getEnumTag(swift::OpaqueValue *address,
+                                                   const Metadata *metadata) {
+  return 0;
+}
+
 extern "C"
 unsigned swift_enumSimple_getEnumTag(swift::OpaqueValue *address,
                                      const Metadata *metadata) {

stdlib/public/runtime/BytecodeLayouts.h

@@ -118,6 +118,9 @@ swift_generic_initializeBufferWithCopyOfBuffer(swift::ValueBuffer *dest,
                                                swift::ValueBuffer *src,
                                                const Metadata *metadata);
 SWIFT_RUNTIME_EXPORT
+unsigned swift_singletonEnum_getEnumTag(swift::OpaqueValue *address,
+                                        const Metadata *metadata);
+SWIFT_RUNTIME_EXPORT
 unsigned swift_enumSimple_getEnumTag(swift::OpaqueValue *address,
                                      const Metadata *metadata);
 SWIFT_RUNTIME_EXPORT

test/Interpreter/Inputs/layout_string_witnesses_types_resilient.swift

@@ -51,6 +51,10 @@ public enum ResilientSinglePayloadEnumSimple {
     case nonEmpty(AnyObject)
 }
 
+public enum ResilientSingletonEnum {
+    case nonEmpty(AnyObject)
+}
+
 public func getResilientSinglePayloadEnumGenericEmpty0<T>(_ t: T.Type) -> ResilientSinglePayloadEnumGeneric<T> {
     return .empty0
 }
@@ -70,3 +74,7 @@ public func getResilientSinglePayloadEnumComplexEmpty0() -> ResilientSinglePaylo
 public func getResilientSinglePayloadEnumSimpleEmpty0() -> ResilientSinglePayloadEnumSimple {
     return .empty0
 }
+
+public func getResilientSingletonEnumNonEmpty(_ x: AnyObject) -> ResilientSingletonEnum {
+    return .nonEmpty(x)
+}

test/Interpreter/layout_string_witnesses_dynamic.swift

@@ -516,6 +516,17 @@ func testGenericSinglePayloadEnumManyXI() {
 
 testGenericSinglePayloadEnumManyXI()
 
+func testResilientSingletonEnumTag() {
+    let x = switch getResilientSingletonEnumNonEmpty(SimpleClass(x: 23)) {
+    case .nonEmpty: 0
+    }
+
+    // CHECK: Enum case: 0
+    print("Enum case: \(x)")
+}
+
+testResilientSingletonEnumTag()
+
 func testResilientSinglePayloadEnumSimpleTag() {
     let x = switch getResilientSinglePayloadEnumSimpleEmpty0() {
     case .nonEmpty: 0