[IRGen] Emit swift_singletonEnum_destructiveInjectEnumTag

Author: drexin

lib/IRGen/GenValueWitness.cpp

@@ -940,7 +940,7 @@ getDestructiveInjectEnumTagFunction(IRGenModule &IGM,
        !isRuntimeInstatiatedLayoutString(IGM, typeLayoutEntry))) {
     return nullptr;
   } else if (typeLayoutEntry->isSingleton()) {
-    return nullptr;
+    return IGM.getSingletonEnumDestructiveInjectEnumTagFn();
   } else if (!typeLayoutEntry->isFixedSize(IGM)) {
     if (typeLayoutEntry->isMultiPayloadEnum()) {
       return IGM.getMultiPayloadEnumGenericDestructiveInjectEnumTagFn();

test/Interpreter/layout_string_witnesses_dynamic.swift

@@ -646,6 +646,22 @@ func testResilientMultiPayloadEnumGenericInjectTag() {
 
 testResilientMultiPayloadEnumGenericInjectTag()
 
+@inline(never)
+func matchResilientSingletonEnumTag(_ x: ResilientSingletonEnum) -> Int {
+    return switch x {
+    case .nonEmpty: 0
+    }
+}
+
+func testResilientSingletonEnumGenericInjectTag() {
+    let x = ResilientSingletonEnum.nonEmpty(SimpleClass(x: 23))
+
+    // CHECK: Enum case: 0
+    print("Enum case: \(matchResilientSingletonEnumTag(x))")
+}
+
+testResilientSingletonEnumGenericInjectTag()
+
 #if os(macOS)
 
 import Foundation