test/hotspot/jtreg/compiler/loopopts/TestOverunrolling.java

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/*
 * @test
 * @bug 8159016
 * @summary Tests correct dominator information after over-unrolling a loop.
 * @requires vm.gc == "Parallel" | vm.gc == "null"
 *
 * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -Xcomp -XX:-TieredCompilation
 *                   -XX:-UseG1GC -XX:+UseParallelGC
 *                   compiler.loopopts.TestOverunrolling
 */

package compiler.loopopts;

public class TestOverunrolling {

    public static Object test(int arg) {
        Object arr[] = new Object[3];
        int lim = (arg & 3);
        // The pre loop is executed for one iteration, initializing p[0].
        // The main loop is unrolled twice, initializing p[1], p[2], p[3] and p[4].
        // The p[3] and p[4] stores are always out of bounds and removed. However,
        // C2 is unable to remove the "over-unrolled", dead main loop. As a result,
        // there is a control path from the main loop to the post loop without a
        // memory path (because the last store was replaced by TOP). We crash
        // because we use a memory edge from a non-dominating region.
        for (int i = 0; i < lim; ++i) {
            arr[i] = new Object();
        }
        // Avoid EA
        return arr;
    }

    public static void main(String args[]) {
        for (int i = 0; i < 42; ++i) {
            test(i);
        }
    }
}