cross-module-optimiations: Fix an compiler crash and a wrong linkage

In case a property is more visible than its container, an assert was triggering in ValueDecl::isUsableFromInline().

rdar://problem/62403317

Author: eeckstein

lib/SILOptimizer/IPO/CrossModuleSerializationSetup.cpp

@@ -129,7 +129,8 @@ static void makeDeclUsableFromInline(ValueDecl *decl, SILModule &M) {
   if (decl->getEffectiveAccess() >= AccessLevel::Public)
     return;
 
-  if (!decl->isUsableFromInline()) {
+  if (decl->getFormalAccess() < AccessLevel::Public &&
+      !decl->isUsableFromInline()) {
     // Mark the nominal type as "usableFromInline".
     // TODO: find a way to do this without modifying the AST. The AST should be
     // immutable at this point.
@@ -244,15 +245,15 @@ prepareInstructionForSerialization(SILInstruction *inst) {
 void CrossModuleSerializationSetup::handleReferencedFunction(SILFunction *func) {
   if (!func->isDefinition() || func->isAvailableExternally())
     return;
+  if (func->isSerialized() == IsSerialized)
+    return;
+
   if (func->getLinkage() == SILLinkage::Shared) {
     assert(func->isThunk() != IsNotThunk &&
       "only thunks are accepted to have shared linkage");
     assert(canSerialize(func, /*lookIntoThunks*/ false) &&
       "we should already have checked that the thunk is serializable");
 
-    if (func->isSerialized() == IsSerialized)
-      return;
-
     // We cannot make shared functions "usableFromInline", i.e. make them Public
     // because this could result in duplicate-symbol errors. Instead we make
     // them "@alwaysEmitIntoClient"

test/SILOptimizer/Inputs/cross-module.swift

@@ -162,6 +162,25 @@ public class FooClass: PrivateProto {
   }
 }
 
+final class Internalclass {
+  public var publicint: Int = 27
+}
+
+final public class Outercl {
+  var ic: Internalclass = Internalclass()
+}
+
+@inline(never)
+public func classWithPublicProperty<T>(_ t: T) -> Int {
+  return createInternal().ic.publicint
+}
+
+@inline(never)
+func createInternal() -> Outercl {
+  return Outercl()
+}
+
+
 @inline(never)
 @_semantics("optimize.sil.specialize.generic.never")
 fileprivate func callProtocolFoo<T: PrivateProto>(_ t: T) {

test/SILOptimizer/cross-module-optimization.swift

@@ -118,6 +118,9 @@ func testMisc() {
   // CHECK-OUTPUT: 42
   // CHECK-SIL-DAG: sil shared {{.*}} @$s4Test13callUnrelatedyxxlFSi_Tg5
   print(callUnrelated(42))
+
+  // CHECK-OUTPUT: 27
+  print(classWithPublicProperty(33))
 }
 
 testNestedTypes()