Make pod support conditional on Serial GC (including Epsilon GC).

Author: peter-hofer

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/graal/jdk/SubstrateObjectCloneSnippets.java

@@ -62,6 +62,7 @@
 import com.oracle.svm.core.graal.snippets.NodeLoweringProvider;
 import com.oracle.svm.core.graal.snippets.SubstrateTemplates;
 import com.oracle.svm.core.heap.InstanceReferenceMapEncoder;
+import com.oracle.svm.core.heap.Pod;
 import com.oracle.svm.core.heap.PodReferenceMapDecoder;
 import com.oracle.svm.core.hub.DynamicHub;
 import com.oracle.svm.core.hub.DynamicHubSupport;
@@ -110,7 +111,7 @@ private static Object doClone(Object original) throws CloneNotSupportedException
                 }
                 return newArray;
 
-            } else if (hub.isPodInstanceClass()) {
+            } else if (Pod.RuntimeSupport.isPresent() && hub.isPodInstanceClass()) {
                 result = PodReferenceMapDecoder.clone(original, hub, layoutEncoding);
 
             } else {

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/Pod.java

@@ -38,6 +38,7 @@
 import java.util.function.Supplier;
 
 import org.graalvm.collections.EconomicMap;
+import org.graalvm.compiler.api.replacements.Fold;
 import org.graalvm.nativeimage.ImageSingletons;
 import org.graalvm.nativeimage.Platform;
 import org.graalvm.nativeimage.Platforms;
@@ -124,11 +125,14 @@ public static <T> Builder<T> createExtending(Class<?> superClass, Class<T> facto
 
         private Builder(Class<?> superClass, Class<?> factoryInterface, Pod<T> superPod) {
             assert superPod == null || (superClass == null && factoryInterface == null);
+            if (!RuntimeSupport.isPresent()) {
+                throw new UnsupportedOperationException("Pods are not available in this native image. Only SerialGC currently supports pods.");
+            }
             if (superPod != null) {
                 this.podInfo = superPod.podInfo;
             } else if (superClass != null && factoryInterface != null) {
                 RuntimeSupport.PodSpec spec = new RuntimeSupport.PodSpec(superClass, factoryInterface);
-                this.podInfo = ImageSingletons.lookup(RuntimeSupport.class).getInfo(spec);
+                this.podInfo = RuntimeSupport.singleton().getInfo(spec);
                 if (this.podInfo == null) {
                     throw new IllegalArgumentException("Pod superclass/factory interface pair was not registered during image build: " + superClass + ", " + factoryInterface);
                 }
@@ -256,6 +260,16 @@ public int compareTo(Field f) {
     }
 
     public static final class RuntimeSupport {
+        @Fold
+        public static boolean isPresent() {
+            return ImageSingletons.contains(RuntimeSupport.class);
+        }
+
+        @Fold
+        public static RuntimeSupport singleton() {
+            return ImageSingletons.lookup(RuntimeSupport.class);
+        }
+
         @Retention(RetentionPolicy.RUNTIME)
         @Target(ElementType.TYPE)
         public @interface PodFactory {

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/hub/InteriorObjRefWalker.java

@@ -36,6 +36,7 @@
 import com.oracle.svm.core.heap.InstanceReferenceMapDecoder;
 import com.oracle.svm.core.heap.ObjectHeader;
 import com.oracle.svm.core.heap.ObjectReferenceVisitor;
+import com.oracle.svm.core.heap.Pod;
 import com.oracle.svm.core.heap.PodReferenceMapDecoder;
 import com.oracle.svm.core.heap.ReferenceAccess;
 
@@ -80,7 +81,7 @@ public static boolean walkObjectInline(final Object obj, final ObjectReferenceVi
                 }
                 pos = pos.add(referenceSize);
             }
-        } else if (objHub.isPodInstanceClass()) {
+        } else if (Pod.RuntimeSupport.isPresent() && objHub.isPodInstanceClass()) {
             if (!PodReferenceMapDecoder.walkOffsetsFromPointer(objPointer, layoutEncoding, visitor, obj)) {
                 return false;
             }

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/SVMHost.java

@@ -462,7 +462,7 @@ private static HubType computeHubType(AnalysisType type) {
         } else if (type.isInstanceClass()) {
             if (Reference.class.isAssignableFrom(type.getJavaClass())) {
                 return HubType.InstanceReference;
-            } else if (PodSupport.singleton().isPodClass(type.getJavaClass())) {
+            } else if (PodSupport.isPresent() && PodSupport.singleton().isPodClass(type.getJavaClass())) {
                 return HubType.PodInstance;
             }
             assert !Target_java_lang_ref_Reference.class.isAssignableFrom(type.getJavaClass()) : "should not see substitution type here";

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/heap/PodSupport.java

@@ -48,6 +48,7 @@
 import org.graalvm.nativeimage.ImageSingletons;
 import org.graalvm.nativeimage.hosted.Feature;
 
+import com.oracle.svm.core.SubstrateOptions;
 import com.oracle.svm.core.annotate.AutomaticFeature;
 import com.oracle.svm.core.annotate.DeoptTest;
 import com.oracle.svm.core.annotate.Hybrid;
@@ -67,7 +68,14 @@
 
 /** Support for preparing the creation of {@link Pod} objects during the image build. */
 public interface PodSupport {
+    static boolean isPresent() {
+        return ImageSingletons.contains(PodSupport.class);
+    }
+
     static PodSupport singleton() {
+        if (!ImageSingletons.contains(PodSupport.class)) {
+            throw UserError.abort("Pods are not available in this native image build. Only SerialGC currently supports pods.");
+        }
         return ImageSingletons.lookup(PodSupport.class);
     }
 
@@ -107,6 +115,11 @@ final class PodFeature implements PodSupport, Feature {
     private volatile boolean instantiated = false;
     private boolean sealed = false;
 
+    @Override
+    public boolean isInConfiguration(IsInConfigurationAccess access) {
+        return SubstrateOptions.UseSerialGC.getValue();
+    }
+
     @Override
     public void afterRegistration(AfterRegistrationAccess access) {
         ImageSingletons.add(PodSupport.class, this);
@@ -133,11 +146,7 @@ private void registerAsInstantiated(DuringAnalysisAccess access) {
 
     private static void registerPodAsInstantiated(BeforeAnalysisAccess access, PodSpec spec, PodInfo info) {
         access.registerAsInHeap(info.podClass);
-        runtimeSupport().registerPod(spec, info);
-    }
-
-    private static Pod.RuntimeSupport runtimeSupport() {
-        return ImageSingletons.lookup(Pod.RuntimeSupport.class);
+        Pod.RuntimeSupport.singleton().registerPod(spec, info);
     }
 
     @Override

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/meta/UniverseBuilder.java

@@ -401,6 +401,18 @@ private void layoutInstanceFields() {
         layoutInstanceFields(hUniverse.getObjectClass(), ConfigurationValues.getObjectLayout().getFirstFieldOffset(), new HostedField[0]);
     }
 
+    private static boolean mustReserveLengthField(HostedInstanceClass clazz) {
+        if (PodSupport.isPresent() && PodSupport.singleton().mustReserveLengthField(clazz.getJavaClass())) {
+            return true;
+        }
+        if (HybridLayout.isHybrid(clazz)) {
+            // A pod ancestor subclassing Object must have already reserved a length field, unless
+            // the pod subclasses Object itself, in which case we would have returned true earlier.
+            return !PodSupport.isPresent() || !PodSupport.singleton().isPodClass(clazz.getJavaClass());
+        }
+        return false;
+    }
+
     private void layoutInstanceFields(HostedInstanceClass clazz, int superSize, HostedField[] superFields) {
         ArrayList<HostedField> rawFields = new ArrayList<>();
         ArrayList<HostedField> orderedFields = new ArrayList<>();
@@ -414,10 +426,7 @@ private void layoutInstanceFields(HostedInstanceClass clazz, int superSize, Host
             startSize = DeoptimizedFrame.getScratchSpaceOffset() + layout.getDeoptScratchSpace();
         }
 
-        PodSupport pods = PodSupport.singleton();
-        if ((HybridLayout.isHybrid(clazz) && !pods.isPodClass(clazz.getJavaClass())) || pods.mustReserveLengthField(clazz.getJavaClass())) {
-            // Reserve space for the array length field. For pods, the ancestor subclassing Object
-            // must have already reserved this space (unless the pod subclasses Object itself).
+        if (mustReserveLengthField(clazz)) {
             VMError.guarantee(startSize == layout.getArrayLengthOffset());
             int fieldSize = layout.sizeInBytes(JavaKind.Int);
             startSize += fieldSize;