[NFC] Refactor objcImpl matadata layout logic

Rather than having individual methods return without doing anything, arrange for ClassMetadataVisitor to never call them in the first place. This makes it so ClassMetadataScanner also knows which fields are omitted and it can compute offsets correctly.

The old logic is still present for field offsets to make this change NFC.

Author: beccadax

lib/IRGen/ClassMetadataVisitor.h

@@ -19,6 +19,7 @@
 #define SWIFT_IRGEN_CLASSMETADATAVISITOR_H
 
 #include "swift/AST/ASTContext.h"
+#include "swift/AST/Decl.h"
 #include "swift/AST/SubstitutionMap.h"
 #include "swift/SIL/SILDeclRef.h"
 #include "swift/SIL/SILModule.h"
@@ -67,6 +68,9 @@ template <class Impl> class ClassMetadataVisitor
     : super(IGM), Target(target), VTable(vtable) {}
 
 public:
+  bool isPureObjC() const {
+    return Target->getObjCImplementationDecl();
+  }
 
   // Layout in embedded mode while considering the class type.
   // This is important for adding the right superclass pointer.
@@ -93,6 +97,17 @@ template <class Impl> class ClassMetadataVisitor
       return;
     }
 
+    if (isPureObjC()) {
+      assert(IGM.ObjCInterop);
+      asImpl().noteAddressPoint();
+      asImpl().addMetadataFlags();
+      asImpl().addSuperclass();
+      asImpl().addClassCacheData();
+      asImpl().addClassDataPointer();
+      addClassMembers(Target, Target);
+      return;
+    }
+
     // Pointer to layout string
     asImpl().addLayoutStringPointer();
 
@@ -206,8 +221,10 @@ template <class Impl> class ClassMetadataVisitor
                                  rootClass))
       return;
 
-    // Add vtable entries.
-    asImpl().addVTableEntries(theClass);
+    if (!isPureObjC()) {
+      // Add vtable entries.
+      asImpl().addVTableEntries(theClass);
+    }
   }
 
   /// Add fields associated with the given class and its bases.

lib/IRGen/GenMeta.cpp

@@ -3954,6 +3954,7 @@ namespace {
 
   public:
     const ClassLayout &getFieldLayout() const { return FieldLayout; }
+    using super::isPureObjC;
 
     SILType getLoweredType() {
       return IGM.getLoweredType(Target->getDeclaredTypeInContext());
@@ -3967,9 +3968,7 @@ namespace {
     ClassFlags getClassFlags() { return ::getClassFlags(Target); }
 
     void addClassFlags() {
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
-
+      assert(!isPureObjC());
       B.addInt32((uint32_t)asImpl().getClassFlags());
     }
 
@@ -4005,9 +4004,7 @@ namespace {
     }
 
     void addValueWitnessTable() {
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
-
+      assert(!isPureObjC());
       B.add(asImpl().getValueWitnessTable(false).getValue());
     }
 
@@ -4125,9 +4122,7 @@ namespace {
     }
 
     void addLayoutStringPointer() {
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
-
+      assert(!isPureObjC());
       if (auto *layoutString = getLayoutString()) {
         B.addSignedPointer(layoutString,
                            IGM.getOptions().PointerAuth.TypeLayoutString,
@@ -4152,8 +4147,7 @@ namespace {
         return;
       }
 
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
+      assert(!isPureObjC());
 
       if (auto ptr = getAddrOfDestructorFunction(IGM, Target)) {
         B.addSignedPointer(*ptr,
@@ -4184,8 +4178,7 @@ namespace {
         return;
       }
 
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
+      assert(!isPureObjC());
 
       auto dtorFunc = IGM.getAddrOfIVarInitDestroy(Target,
                                                    /*isDestroyer=*/ true,
@@ -4209,9 +4202,7 @@ namespace {
     }
 
     void addNominalTypeDescriptor() {
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
-
+      assert(!isPureObjC());
       B.addSignedPointer(asImpl().getNominalTypeDescriptor(),
                          IGM.getOptions().PointerAuth.TypeDescriptors,
                          PointerAuthEntity::Special::TypeDescriptor);
@@ -4226,9 +4217,7 @@ namespace {
     }
 
     void addInstanceAddressPoint() {
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
-
+      assert(!isPureObjC());
       // Right now, we never allocate fields before the address point.
       B.addInt32(0);
     }
@@ -4238,9 +4227,7 @@ namespace {
     const ClassLayout &getFieldLayout() { return FieldLayout; }
 
     void addInstanceSize() {
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
-
+      assert(!isPureObjC());
       if (asImpl().hasFixedLayout()) {
         B.addInt32(asImpl().getFieldLayout().getSize().getValue());
       } else {
@@ -4250,9 +4237,7 @@ namespace {
     }
 
     void addInstanceAlignMask() {
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
-
+      assert(!isPureObjC());
       if (asImpl().hasFixedLayout()) {
         B.addInt16(asImpl().getFieldLayout().getAlignMask().getValue());
       } else {
@@ -4262,24 +4247,18 @@ namespace {
     }
 
     void addRuntimeReservedBits() {
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
-
+      assert(!isPureObjC());
       B.addInt16(0);
     }
 
     void addClassSize() {
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
-
+      assert(!isPureObjC());
       auto size = MetadataLayout.getSize();
       B.addInt32(size.FullSize.getValue());
     }
 
     void addClassAddressPoint() {
-      if (asImpl().getFieldLayout().hasObjCImplementation())
-        return;
-
+      assert(!isPureObjC());
       // FIXME: Wrong
       auto size = MetadataLayout.getSize();
       B.addInt32(size.AddressPoint.getValue());
@@ -4516,12 +4495,12 @@ namespace {
       : IGM(IGM), Target(theClass), B(builder), FieldLayout(fieldLayout) {}
 
     llvm::Constant *emitNominalTypeDescriptor() {
-      if (FieldLayout.hasObjCImplementation())
-        return nullptr;
       return ClassContextDescriptorBuilder(IGM, Target, RequireMetadata).emit();
     }
 
     void layout() {
+      assert(!FieldLayout.hasObjCImplementation()
+                && "Resilient class metadata not supported for @objcImpl");
       emitNominalTypeDescriptor();
 
       addRelocationFunction();
@@ -4544,17 +4523,11 @@ namespace {
     }
 
     void addDestructorFunction() {
-      if (FieldLayout.hasObjCImplementation())
-        return;
-
       auto function = getAddrOfDestructorFunction(IGM, Target);
       B.addCompactFunctionReferenceOrNull(function ? *function : nullptr);
     }
 
     void addIVarDestroyer() {
-      if (FieldLayout.hasObjCImplementation())
-        return;
-
       auto function = IGM.getAddrOfIVarInitDestroy(Target,
                                                    /*isDestroyer=*/ true,
                                                    /*isForeign=*/ false,
@@ -4563,9 +4536,6 @@ namespace {
     }
 
     void addClassFlags() {
-      if (FieldLayout.hasObjCImplementation())
-        return;
-
       B.addInt32((uint32_t) getClassFlags(Target));
     }
 
@@ -4628,7 +4598,7 @@ namespace {
       // @_objcImplementation on true (non-ObjC) generic classes doesn't make
       // much sense, and we haven't updated this builder to handle it.
       assert(!FieldLayout.hasObjCImplementation()
-             && "@_objcImplementation class with generic metadata?");
+             && "Generic metadata not supported for @objcImpl");
 
       super::layoutHeader();