IRGen: Refactor ClassLayoutBuilder a bit to help distinguish resilient-metadata from resilient-storage

We want @_fixed_layout classes to have non-resilient storage, but still have
resilient metadata.

Author: slavapestov

lib/IRGen/ClassMetadataVisitor.h

@@ -118,8 +118,8 @@ template <class Impl> class ClassMetadataVisitor
     // This must always be the first item in the immediate members.
     asImpl().addGenericFields(theClass, theClass);
 
-    // If the class is resilient, we cannot make any assumptions about its
-    // member layout at all, so skip the rest of this method.
+    // If the class has resilient storage, we cannot make any assumptions about
+    // its storage layout, so skip the rest of this method.
     if (IGM.isResilient(theClass, ResilienceExpansion::Maximal))
       return;
 

lib/IRGen/GenClass.cpp

@@ -200,8 +200,8 @@ namespace {
     bool ClassHasGenericLayout = false;
 
     // Is this class or any of its superclasses resilient from the viewpoint
-    // of the current module? This means that their metadata can change size
-    // and field offsets, generic arguments and virtual methods must be
+    // of the current module? This means that their metadata can change size,
+    // hence field offsets, generic arguments and virtual methods must be
     // accessed relative to a metadata base global variable.
     bool ClassHasResilientAncestry = false;
 
@@ -261,14 +261,11 @@ namespace {
       return Elements;
     }
 
-    /// Does the class metadata have a completely known, static layout that
-    /// does not require initialization at runtime beyond registeration of
-    /// the class with the Objective-C runtime?
+    /// Do instances of the class have a completely known, static layout?
     bool isFixedSize() const {
       return !(ClassHasMissingMembers ||
                ClassHasResilientMembers ||
                ClassHasGenericLayout ||
-               ClassHasResilientAncestry ||
                ClassHasObjCAncestry);
     }
 
@@ -336,6 +333,7 @@ namespace {
           // If the class is resilient, don't walk over its fields; we have to
           // calculate the layout at runtime.
           ClassHasResilientAncestry = true;
+          ClassHasResilientMembers = true;
 
           // Furthermore, if the superclass is generic, we have to assume
           // that its layout depends on its generic parameters. But this only
@@ -358,6 +356,7 @@ namespace {
 
       if (IGM.isResilient(theClass, ResilienceExpansion::Maximal)) {
         ClassHasResilientAncestry = true;
+        ClassHasResilientMembers = true;
         return;
       }
 

lib/IRGen/Linking.cpp

@@ -484,7 +484,7 @@ SILLinkage LinkEntity::getLinkage(ForDefinition_t forDefinition) const {
 
     auto linkage = getDeclLinkage(varDecl);
 
-    // Resilient classes don't expose field offset symbols.
+    // Classes with resilient storage don't expose field offset symbols.
     if (cast<ClassDecl>(varDecl->getDeclContext())->isResilient()) {
       assert(linkage != FormalLinkage::PublicNonUnique &&
             "Cannot have a resilient class with non-unique linkage");