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mcimadamore · Dec 19, 2024 · 0b8117d · 0b8117d
1 parent 8efc558
commit 0b8117d
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diff --git a/src/java.base/share/classes/jdk/internal/foreign/LayoutPath.java b/src/java.base/share/classes/jdk/internal/foreign/LayoutPath.java
@@ -235,6 +235,18 @@ public VarHandle dereferenceHandle(boolean adapt) {
         return handle;
     }
 
+    public VarHandle arrayElementHandle() {
+        Utils.checkElementAlignment(layout, "Element layout size is not multiple of alignment");
+        long[] arrayStrides = new long[strides.length + 1];
+        long[] arrayBounds = new long[strides.length + 1];
+        System.arraycopy(strides, 0, arrayStrides, 1, strides.length);
+        System.arraycopy(bounds, 0, arrayBounds, 1, bounds.length);
+        arrayStrides[0] = layout.byteSize();
+        arrayBounds[0] = (Long.MAX_VALUE - 1) / layout.byteSize(); // avoid overflows
+        LayoutPath arrayPath = nestedPath(layout, offset, arrayStrides, arrayBounds, derefAdapters, enclosing);
+        return arrayPath.dereferenceHandle();
+    }
+
     @ForceInline
     private static long addScaledOffset(long base, long index, long stride, long bound) {
         Objects.checkIndex(index, bound);

diff --git a/src/java.base/share/classes/jdk/internal/foreign/layout/AbstractLayout.java b/src/java.base/share/classes/jdk/internal/foreign/layout/AbstractLayout.java
@@ -192,7 +192,8 @@ public VarHandle varHandleInternal(PathElement... elements) {
     }
 
     public VarHandle arrayElementVarHandle(PathElement... elements) {
-        return MethodHandles.collectCoordinates(varHandle(elements), 1, scaleHandle());
+        return computePathOp(LayoutPath.rootPath((MemoryLayout) this), LayoutPath::arrayElementHandle,
+                Set.of(), elements);
     }
 
     public MethodHandle sliceHandle(PathElement... elements) {

diff --git a/test/micro/org/openjdk/bench/java/lang/foreign/Alignment.java b/test/micro/org/openjdk/bench/java/lang/foreign/Alignment.java
@@ -0,0 +1,107 @@
+package org.openjdk.bench.java.lang.foreign;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+
+import java.lang.foreign.Arena;
+import java.lang.foreign.MemorySegment;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+import java.util.concurrent.TimeUnit;
+
+import static java.lang.foreign.MemoryLayout.sequenceLayout;
+import static java.lang.foreign.ValueLayout.JAVA_LONG;
+import static java.lang.foreign.ValueLayout.JAVA_LONG_UNALIGNED;
+
+@BenchmarkMode(Mode.AverageTime)
+@Warmup(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
+@Measurement(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
+@State(org.openjdk.jmh.annotations.Scope.Thread)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+@Fork(value = 3)
+public class Alignment {
+    // base offset = 0
+    static final VarHandle ALIGNED = MethodHandles.insertCoordinates(JAVA_LONG.arrayElementVarHandle(), 1, 0).withInvokeExactBehavior();
+    static final VarHandle UNALIGNED = MethodHandles.insertCoordinates(JAVA_LONG_UNALIGNED.arrayElementVarHandle(), 1, 0).withInvokeExactBehavior();
+    // base offset = 8
+    static final VarHandle NEXT_ALIGNED = MethodHandles.insertCoordinates(JAVA_LONG.arrayElementVarHandle(), 1, JAVA_LONG.byteSize()).withInvokeExactBehavior();
+    static final VarHandle NEXT_UNALIGNED = MethodHandles.insertCoordinates(JAVA_LONG_UNALIGNED.arrayElementVarHandle(), 1, JAVA_LONG.byteSize()).withInvokeExactBehavior();
+
+    static final long HAYSTACK = 30_000_000L;
+    static final long NEEDLE_INDEX = 934L;
+    static final long NEEDLE = 456L;
+
+    final MemorySegment segment = Arena.global().allocate(sequenceLayout(HAYSTACK, JAVA_LONG));
+
+    {
+        ALIGNED.set(segment, NEEDLE_INDEX, NEEDLE);
+    }
+
+    // 6 different ways to loop over segment[1, size):
+
+    @Benchmark
+    public void findUnaligned() {
+        long size = segment.byteSize() / JAVA_LONG.byteSize();
+        int numFound = 0;
+        for (long i = 1; i < size; ++i) {
+            if ((long) UNALIGNED.get(segment, i) == NEEDLE) ++numFound;
+        }
+        if (numFound != 1) throw new IllegalStateException();
+    }
+
+    @Benchmark
+    public void findAligned() {
+        long size = segment.byteSize() / JAVA_LONG.byteSize();
+        int numFound = 0;
+        for (long i = 1; i < size; ++i) {
+            if ((long) ALIGNED.get(segment, i) == NEEDLE) ++numFound;
+        }
+        if (numFound != 1) throw new IllegalStateException();
+    }
+
+    @Benchmark
+    public void findUnalignedPlusOne() {
+        long size = segment.byteSize() / JAVA_LONG.byteSize();
+        int numFound = 0;
+        for (long i = 0; i < size - 1; ++i) {
+            if ((long) UNALIGNED.get(segment, i + 1) == NEEDLE) ++numFound;
+        }
+        if (numFound != 1) throw new IllegalStateException();
+    }
+
+    @Benchmark
+    public void findAlignedPlusOne() {
+        long size = segment.byteSize() / JAVA_LONG.byteSize();
+        int numFound = 0;
+        for (long i = 0; i < size - 1; ++i) {
+            if ((long) ALIGNED.get(segment, i + 1) == NEEDLE) ++numFound;
+        }
+        if (numFound != 1) throw new IllegalStateException();
+    }
+
+    @Benchmark
+    public void findUnalignedNext() {
+        long size = segment.byteSize() / JAVA_LONG.byteSize();
+        int numFound = 0;
+        for (long i = 0; i < size - 1; ++i) {
+            if ((long) NEXT_UNALIGNED.get(segment, i) == NEEDLE) ++numFound;
+        }
+        if (numFound != 1) throw new IllegalStateException();
+    }
+
+    @Benchmark
+    public void findAlignedNext() {
+        long size = segment.byteSize() / JAVA_LONG.byteSize();
+        int numFound = 0;
+        for (long i = 0; i < size - 1; ++i) {
+            if ((long) NEXT_ALIGNED.get(segment, i) == NEEDLE) ++numFound;
+        }
+        if (numFound != 1) throw new IllegalStateException();
+    }
+}