IRGen: lazy initialize ForeignClassMetadata

lib/IRGen/GenMeta.cpp

@@ -205,18 +205,21 @@ static void emitMetadataCompletionFunction(IRGenModule &IGM,
   IGF.Builder.CreateRet(returnValue);
 }
 
-static bool needsForeignMetadataCompletionFunction(StructDecl *decl) {
+static bool needsForeignMetadataCompletionFunction(IRGenModule &IGM,
+                                                   StructDecl *decl) {
   // Currently, foreign structs never need a completion function.
   return false;
 }
 
-static bool needsForeignMetadataCompletionFunction(EnumDecl *decl) {
+static bool needsForeignMetadataCompletionFunction(IRGenModule &IGM,
+                                                   EnumDecl *decl) {
   // Currently, foreign enums never need a completion function.
   return false;
 }
 
-static bool needsForeignMetadataCompletionFunction(ClassDecl *decl) {
-  return decl->hasSuperclass();
+static bool needsForeignMetadataCompletionFunction(IRGenModule &IGM,
+                                                   ClassDecl *decl) {
+  return IGM.getOptions().LazyInitializeClassMetadata || decl->hasSuperclass();
 }
 
 /*****************************************************************************/
@@ -1171,7 +1174,7 @@ namespace {
     }
 
     bool needsForeignMetadataCompletionFunction() {
-      return ::needsForeignMetadataCompletionFunction(Type);
+      return ::needsForeignMetadataCompletionFunction(IGM, Type);
     }
 
     /// Add an SingletonMetadataInitialization structure to the descriptor.
@@ -3804,7 +3807,7 @@ namespace {
     }
 
     bool needsMetadataCompletionFunction() {
-      return needsForeignMetadataCompletionFunction(Target);
+      return needsForeignMetadataCompletionFunction(IGM, Target);
     }
 
     void createMetadataCompletionFunction() {
@@ -3837,10 +3840,19 @@ namespace {
   public:
     ForeignClassMetadataBuilder(IRGenModule &IGM, ClassDecl *target,
                                 ConstantStructBuilder &B)
-      : ForeignMetadataBuilderBase(IGM, target, B) {}
+        : ForeignMetadataBuilderBase(IGM, target, B) {
+      if (IGM.getOptions().LazyInitializeClassMetadata)
+        CanBeConstant = false;
+    }
 
     void emitInitializeMetadata(IRGenFunction &IGF, llvm::Value *metadata,
                                 MetadataDependencyCollector *collector) {
+      if (!Target->hasSuperclass()) {
+        assert(IGM.getOptions().LazyInitializeClassMetadata &&
+               "should have superclass if not lazy initializing class metadata");
+        return;
+      }
+
       // Emit a reference to the superclass.
       auto superclass = IGF.emitAbstractTypeMetadataRef(
                                    Target->getSuperclass()->getCanonicalType());
@@ -3858,6 +3870,24 @@ namespace {
     // Visitor methods.
 
     void addValueWitnessTable() {
+      // The runtime will fill in the default VWT during allocation for the
+      // foreign class metadata.
+      //
+      // As of Swift 5.1, the runtime will fill in a default VWT during
+      // allocation of foreign class metadata.  We rely on this for correctness
+      // on COFF, where we can't necessarily reference the stanard VWT from the
+      // metadata candidate, but it is a good optimization everywhere.
+      //
+      // The default VWT uses ObjC-compatible reference counting if ObjC interop
+      // is enabled and Swift-compatible reference counting otherwise.  That is
+      // currently always good enough for foreign classes, so we can
+      // unconditionally rely on the default VWT.
+      //
+      // FIXME: take advantage of this on other targets when targeting a
+      // sufficiently recent runtime.
+      if (IGM.getOptions().LazyInitializeClassMetadata)
+        return B.addNullPointer(IGM.WitnessTablePtrTy);
+
       // Without Objective-C interop, foreign classes must still use
       // Swift native reference counting.
       auto type = (IGM.ObjCInterop

stdlib/public/runtime/Metadata.cpp

@@ -3655,6 +3655,17 @@ class ForeignMetadataCacheEntry
         state = PrivateMetadataState::NonTransitiveComplete;
       }
     } else {
+      if (candidate->getValueWitnesses() == nullptr) {
+        assert(isa<ForeignClassMetadata>(candidate) &&
+               "cannot set default value witnesses for non-class foreign types");
+        // Fill in the default VWT if it was not set in the candidate at build
+        // time.
+#if SWIFT_OBJC_INTEROP
+        candidate->setValueWitnesses(&VALUE_WITNESS_SYM(BO));
+#else
+        candidate->setValueWitnesses(&VALUE_WITNESS_SYM(Bo));
+#endif
+      }
       state = inferStateForMetadata(candidate);
     }
 

test/IRGen/cf.sil

@@ -1,6 +1,6 @@
 // RUN: %empty-directory(%t)
 // RUN: %{python} %utils/chex.py < %s > %t/cf.sil
-// RUN: %target-swift-frontend -enable-objc-interop -sdk %S/Inputs %t/cf.sil -emit-ir -import-cf-types | %FileCheck --check-prefix=CHECK --check-prefix=CHECK-%target-ptrsize %t/cf.sil -DINT=i%target-ptrsize
+// RUN: %target-swift-frontend -enable-objc-interop -sdk %S/Inputs %t/cf.sil -emit-ir -import-cf-types | %FileCheck --check-prefix=CHECK --check-prefix=CHECK-%target-ptrsize %t/cf.sil -DINT=i%target-ptrsize -check-prefix CHECK-%target-import-type -check-prefix CHECK-%target-import-type-%target-ptrsize
 
 // REQUIRES: CPU=i386 || CPU=x86_64
 
@@ -9,7 +9,14 @@
 // CHECK: [[MUTABLE_REFRIGERATOR:%TSo24CCMutableRefrigeratorRefa]] = type
 // CHECK: [[OBJC:%objc_object]] = type
 
-// CHECK: @"$sSo17CCRefrigeratorRefaN" = linkonce_odr hidden constant <{ {{.*}} }> <{ i8** @"$sBOWV", [[INT]] 515, {{.*}}"$sSo17CCRefrigeratorRefaMn", [[TYPE]]* null, i8* null }>
+// CHECK: @"$sSo17CCRefrigeratorRefaN" = linkonce_odr hidden
+// CHECK-DIRECT-SAME: constant
+// CHECK-INDIRECT-SAME: global
+// CHECK-SAME: <{ {{.*}} }> <{
+// -- value witness table
+// CHECK-DIRECT-SAME: i8** @"$sBOWV",
+// CHECK-INDIRECT-SAME: i8** null,
+// CHECK-SAME: [[INT]] 515, {{.*}}"$sSo17CCRefrigeratorRefaMn", [[TYPE]]* null, i8* null }>
 
 // CHECK: [[MUTABLE_REFRIGERATOR_NAME:@.*]] = private constant [52 x i8] c"CCMutableRefrigerator\00NCCMutableRefrigeratorRef\00St\00\00"
 
@@ -21,7 +28,10 @@
 // CHECK-64-SAME: @"$sSo24CCMutableRefrigeratorRefaMr"
 
 // CHECK-64: @"$sSo24CCMutableRefrigeratorRefaN" = linkonce_odr hidden global <{ {{.*}} }> <{
-// CHECK-64-SAME: i8** @"$sBOWV", i64 515, {{.*}}"$sSo24CCMutableRefrigeratorRefaMn", %swift.type* null, i8* null }>
+// -- value witness table
+// CHECK-DIRECT-64-SAME: i8** @"$sBOWV",
+// CHECK-INDIRECT-64-SAME: i8** null,
+// CHECK-64-SAME: i64 515, {{.*}}"$sSo24CCMutableRefrigeratorRefaMn", %swift.type* null, i8* null }>
 
 sil_stage canonical