--- /dev/null	2017-01-22 10:16:57.869617664 -0800
+++ new/src/jdk.internal.vm.ci/share/classes/jdk.vm.ci.hotspot/src/jdk/vm/ci/hotspot/HotSpotMethodDataAccessor.java	2017-02-15 16:55:52.045435147 -0800
@@ -0,0 +1,129 @@
+package jdk.vm.ci.hotspot;
+
+import jdk.vm.ci.meta.JavaMethodProfile;
+import jdk.vm.ci.meta.JavaTypeProfile;
+import jdk.vm.ci.meta.ProfilingInfo;
+import jdk.vm.ci.meta.TriState;
+
+/**
+ * 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.
+ */
+abstract class HotSpotMethodDataAccessor {
+
+    final int tag;
+    final int staticSize;
+    final HotSpotVMConfig config;
+
+    protected HotSpotMethodDataAccessor(HotSpotVMConfig config, int tag, int staticSize) {
+        this.config = config;
+        this.tag = tag;
+        this.staticSize = staticSize;
+    }
+
+    /**
+     * Returns the tag stored in the LayoutData header.
+     *
+     * @return tag stored in the LayoutData header
+     */
+    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 between 0 and {@link Short#MAX_VALUE} inclusive, or -1 if not supported
+     */
+    int getBCI(HotSpotMethodData data, int position) {
+        return data.readUnsignedShort(position, config.dataLayoutBCIOffset);
+    }
+
+    /**
+     * Computes the size for the specific data at the given position.
+     *
+     * @return a value greater than 0
+     */
+    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 EXCEPTIONS_MASK = 1 << config.bitDataExceptionSeenFlag;
+        return TriState.get((getFlags(data, position) & EXCEPTIONS_MASK) != 0);
+    }
+
+    /**
+     * @param data
+     * @param position
+     */
+    JavaTypeProfile getTypeProfile(HotSpotMethodData data, int position) {
+        return null;
+    }
+
+    /**
+     * @param data
+     * @param position
+     */
+    JavaMethodProfile getMethodProfile(HotSpotMethodData data, int position) {
+        return null;
+    }
+
+    /**
+     * @param data
+     * @param position
+     */
+    double getBranchTakenProbability(HotSpotMethodData data, int position) {
+        return -1;
+    }
+
+    /**
+     * @param data
+     * @param position
+     */
+    double[] getSwitchProbabilities(HotSpotMethodData data, int position) {
+        return null;
+    }
+
+    /**
+     * @param data
+     * @param position
+     */
+    int getExecutionCount(HotSpotMethodData data, int position) {
+        return -1;
+    }
+
+    /**
+     * @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);
+    }
+
+    /**
+     * @param data
+     * @param position
+     */
+    protected int getDynamicSize(HotSpotMethodData data, int position) {
+        return 0;
+    }
+
+    abstract StringBuilder appendTo(StringBuilder sb, HotSpotMethodData data, int pos);
+
+}
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