TestNaNVector.java

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/**
 * @test
 * @bug 8160425
 * @summary Test vectorization with a signalling NaN.
 * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:-OptimizeFill
 *      compiler.vectorization.TestNaNVector
 * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:-OptimizeFill
 *      -XX:MaxVectorSize=4 compiler.vectorization.TestNaNVector
 */

package compiler.vectorization;

public class TestNaNVector {
    private char[] array;
    private static final int LEN = 1024;

    public static void main(String args[]) {
        TestNaNVector test = new TestNaNVector();
        // Check double precision NaN
        for (int i = 0; i < 10_000; ++i) {
          test.vectorizeNaNDP();
        }
        System.out.println("Checking double precision Nan");
        test.checkResult(0xfff7);

        // Check single precision NaN
        for (int i = 0; i < 10_000; ++i) {
          test.vectorizeNaNSP();
        }
        System.out.println("Checking single precision Nan");
        test.checkResult(0xff80);
    }

    public TestNaNVector() {
        array = new char[LEN];
    }

    public void vectorizeNaNDP() {
        // This loop will be vectorized and the array store will be replaced by
        // a 64-bit vector store to four subsequent array elements. The vector
        // should look like this '0xfff7fff7fff7fff7' and is read from the constant
        // table. However, in floating point arithmetic this is a signalling NaN
        // which may be converted to a quiet NaN when processed by the x87 FPU.
        // If the signalling bit is set, the vector ends up in the constant table
        // as '0xfffffff7fff7fff7' which leads to an incorrect result.
        for (int i = 0; i < LEN; ++i) {
            array[i] = 0xfff7;
        }
    }

    public void vectorizeNaNSP() {
        // Same as above but with single precision
        for (int i = 0; i < LEN; ++i) {
            array[i] = 0xff80;
        }
    }

    public void checkResult(int expected) {
        for (int i = 0; i < LEN; ++i) {
            if (array[i] != expected) {
                throw new RuntimeException("Invalid result: array[" + i + "] = " + (int)array[i] + " != " + expected);
            }
        }
    }
}