TestEliminateAllocation.java

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/*
 * @test
 * @bug 8231412
 * @summary The enhancement eliminates all allocations in the loop body of test() due to an improved field zeroing elimination dominance check.
 * @run main/othervm -XX:-TieredCompilation -XX:CompileCommand=compileonly,compiler.escapeAnalysis.TestEliminateAllocation::test
 *                   compiler.escapeAnalysis.TestEliminateAllocation
 */

package compiler.escapeAnalysis;

public class TestEliminateAllocation {

    public static int a = 20;
    public static int b = 30;
    public static int c = 40;

    public void test() {
        int i = 0;

        /*
         * The resulting IR for the loop body contains 2 allocations, one Wrapper and an int array
         * The array field store in the Wrapper object 'wrapper.arr = arr' cannot be capturued due to an early bail out.
         * Therefore, the initial value of wrapper.arr is null.
         * As a result, the escape analysis marks the array allocation as not scalar replaceable:
         * 'wrapper.arr' which is null is merged with the int array object in the assignment 'wrapper.arr = arr'.
         * Both null and the int array are treated as different objects. As a result the array allocation cannot be eliminated.
         *
         * The new enhancement does not bail out early anymore and therefore escape analysis does not mark it as
         * not scalar replaceable. This results in elimination of all allocations in this method.
         */
        do {
            int[] arr = new int[] { a / b / c };
            Wrapper wrapper = new Wrapper();
            wrapper.setArr(arr);
            i++;
        }
        while (i < 10);
    }

    public static void main(String[] strArr) {
        TestEliminateAllocation _instance = new TestEliminateAllocation();
        for (int i = 0; i < 10_000; i++ ) {
            _instance.test();
        }
    }
}

class Wrapper {
    int[] arr;
    void setArr(int... many) { arr = many; }
}