--- a/jvmci/jdk.vm.ci.hotspot/src/jdk/vm/ci/hotspot/HotSpotMethodDataAccessor.java	Fri Jul 01 13:31:04 2016 -0700
+++ b/jvmci/jdk.vm.ci.hotspot/src/jdk/vm/ci/hotspot/HotSpotMethodDataAccessor.java	Thu Jun 30 22:07:57 2016 +0200
@@ -1,110 +1,129 @@
-/*
- * Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
 package jdk.vm.ci.hotspot;
 
-import static jdk.vm.ci.hotspot.HotSpotVMConfig.config;
 import jdk.vm.ci.meta.JavaMethodProfile;
 import jdk.vm.ci.meta.JavaTypeProfile;
 import jdk.vm.ci.meta.ProfilingInfo;
 import jdk.vm.ci.meta.TriState;
 
 /**
- * Interface for accessor objects that encapsulate the logic for accessing the different kinds of
- * data in a HotSpot methodDataOop. This interface is similar to the interface {@link ProfilingInfo}
- * , but most methods require a MethodDataObject and the exact position within the methodData.
+ * Base class for accessing the different kinds of data in a HotSpot {@code MethodData}. This is
+ * similar to {@link ProfilingInfo}, but most methods require a {@link HotSpotMethodData} and the
+ * exact position within the method data.
  */
-public interface HotSpotMethodDataAccessor {
+abstract class HotSpotMethodDataAccessor {
 
-    /**
-     * {@code DataLayout} tag values.
-     */
-    enum Tag {
-        No(config().dataLayoutNoTag),
-        BitData(config().dataLayoutBitDataTag),
-        CounterData(config().dataLayoutCounterDataTag),
-        JumpData(config().dataLayoutJumpDataTag),
-        ReceiverTypeData(config().dataLayoutReceiverTypeDataTag),
-        VirtualCallData(config().dataLayoutVirtualCallDataTag),
-        RetData(config().dataLayoutRetDataTag),
-        BranchData(config().dataLayoutBranchDataTag),
-        MultiBranchData(config().dataLayoutMultiBranchDataTag),
-        ArgInfoData(config().dataLayoutArgInfoDataTag),
-        CallTypeData(config().dataLayoutCallTypeDataTag),
-        VirtualCallTypeData(config().dataLayoutVirtualCallTypeDataTag),
-        ParametersTypeData(config().dataLayoutParametersTypeDataTag),
-        SpeculativeTrapData(config().dataLayoutSpeculativeTrapDataTag);
+    final int tag;
+    final int staticSize;
+    final HotSpotVMConfig config;
 
-        private final int value;
-
-        Tag(int value) {
-            this.value = value;
-        }
-
-        public int getValue() {
-            return value;
-        }
-
-        public static Tag getEnum(int value) {
-            Tag result = values()[value];
-            assert value == result.value;
-            return result;
-        }
+    protected HotSpotMethodDataAccessor(HotSpotVMConfig config, int tag, int staticSize) {
+        this.config = config;
+        this.tag = tag;
+        this.staticSize = staticSize;
     }
 
     /**
-     * Returns the {@link Tag} stored in the LayoutData header.
+     * Returns the tag stored in the LayoutData header.
      *
      * @return tag stored in the LayoutData header
      */
-    Tag getTag();
+    int getTag() {
+        return tag;
+    }
+
+    static int readTag(HotSpotVMConfig config, HotSpotMethodData data, int position) {
+        final int tag = data.readUnsignedByte(position, config.dataLayoutTagOffset);
+        assert tag >= config.dataLayoutNoTag && tag <= config.dataLayoutSpeculativeTrapDataTag : "profile data tag out of bounds: " + tag;
+        return tag;
+    }
 
     /**
      * Returns the BCI stored in the LayoutData header.
      *
-     * @return An integer &ge; 0 and &le; Short.MAX_VALUE, or -1 if not supported.
+     * @return an integer between 0 and {@link Short#MAX_VALUE} inclusive, or -1 if not supported
      */
-    int getBCI(HotSpotMethodData data, int position);
+    int getBCI(HotSpotMethodData data, int position) {
+        return data.readUnsignedShort(position, config.dataLayoutBCIOffset);
+    }
 
     /**
      * Computes the size for the specific data at the given position.
      *
-     * @return An integer &gt; 0.
+     * @return a value greater than 0
      */
-    int getSize(HotSpotMethodData data, int position);
+    final int getSize(HotSpotMethodData data, int position) {
+        int size = staticSize + getDynamicSize(data, position);
+        // Sanity check against VM
+        int vmSize = HotSpotJVMCIRuntime.runtime().compilerToVm.methodDataProfileDataSize(data.metaspaceMethodData, position);
+        assert size == vmSize : size + " != " + vmSize;
+        return size;
+    }
+
+    TriState getExceptionSeen(HotSpotMethodData data, int position) {
+        final int exceptionsMask = 1 << config.bitDataExceptionSeenFlag;
+        return TriState.get((getFlags(data, position) & exceptionsMask) != 0);
+    }
 
-    JavaTypeProfile getTypeProfile(HotSpotMethodData data, int position);
+    /**
+     * @param data
+     * @param position
+     */
+    JavaTypeProfile getTypeProfile(HotSpotMethodData data, int position) {
+        return null;
+    }
 
-    JavaMethodProfile getMethodProfile(HotSpotMethodData data, int position);
+    /**
+     * @param data
+     * @param position
+     */
+    JavaMethodProfile getMethodProfile(HotSpotMethodData data, int position) {
+        return null;
+    }
 
-    double getBranchTakenProbability(HotSpotMethodData data, int position);
+    /**
+     * @param data
+     * @param position
+     */
+    double getBranchTakenProbability(HotSpotMethodData data, int position) {
+        return -1;
+    }
 
-    double[] getSwitchProbabilities(HotSpotMethodData data, int position);
+    /**
+     * @param data
+     * @param position
+     */
+    double[] getSwitchProbabilities(HotSpotMethodData data, int position) {
+        return null;
+    }
 
-    TriState getExceptionSeen(HotSpotMethodData data, int position);
+    /**
+     * @param data
+     * @param position
+     */
+    int getExecutionCount(HotSpotMethodData data, int position) {
+        return -1;
+    }
 
-    TriState getNullSeen(HotSpotMethodData data, int position);
+    /**
+     * @param data
+     * @param position
+     */
+    TriState getNullSeen(HotSpotMethodData data, int position) {
+        return TriState.UNKNOWN;
+    }
+
+    protected int getFlags(HotSpotMethodData data, int position) {
+        return data.readUnsignedByte(position, config.dataLayoutFlagsOffset);
+    }
 
-    int getExecutionCount(HotSpotMethodData data, int position);
+    /**
+     * @param data
+     * @param position
+     */
+    protected int getDynamicSize(HotSpotMethodData data, int position) {
+        return 0;
+    }
 
-    StringBuilder appendTo(StringBuilder sb, HotSpotMethodData data, int pos);
+    abstract StringBuilder appendTo(StringBuilder sb, HotSpotMethodData data, int pos);
+
 }