test/hotspot/jtreg/compiler/integerArithmetic/TestIntegerComparison.java

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/*
 * @test TestIntegerComparison
 * @bug 8043284 8042786
 * @summary Tests optimizations of signed and unsigned integer comparison.
 *
 * @run main/othervm -Xcomp
 *      -XX:CompileCommand=compileonly,compiler.integerArithmetic.TestIntegerComparison::testSigned
 *      -XX:CompileCommand=compileonly,compiler.integerArithmetic.TestIntegerComparison::testUnsigned
 *      compiler.integerArithmetic.TestIntegerComparison
 */
package compiler.integerArithmetic;

public class TestIntegerComparison {
    /**
     * Tests optimization of signed integer comparison (see BoolNode::Ideal).
     * The body of the if statement is unreachable and should not be compiled.
     *
     * @param c Character (value in the integer range [0, 65535])
     */
    public static void testSigned(char c) {
        // The following addition may overflow. The result is in one
        // of the two ranges [IntMax] and [IntMin, IntMin + CharMax - 1].
        int result = c + Integer.MAX_VALUE;
        // CmpINode has to consider both result ranges instead of only
        // the general [IntMin, IntMax] range to be able to prove that
        // result is always unequal to CharMax.
        if (result == Character.MAX_VALUE) {
            // Unreachable
            throw new RuntimeException("Should not reach here!");
        }
    }

    /**
     * Tests optimization of unsigned integer comparison (see CmpUNode::Value).
     * The body of the if statement is unreachable and should not be compiled.
     *
     * @param c Character (value in the integer range [0, 65535])
     */
    public static void testUnsigned(char c) {
    /*
     * The following if statement consisting of two CmpIs is replaced
     * by a CmpU during optimization (see 'IfNode::fold_compares').
     *
     * The signed (lo < i) and (i < hi) are replaced by the unsigned
     * (i - (lo+1) < hi - (lo+1)). In this case the unsigned comparison
     * equals (result - 2) < 98 leading to the following CmpUNode:
     *
     * CmpU (AddI result, -2) 98
     *
     * With the value of result this is simplified to:
     *
     * CmpU (AddI c, -(CharMax - IntMin)) 98
     *
     * The subtraction may underflow. The result is in one of the two
     * ranges [IntMin], [IntMax - CharMax + 1]. Both ranges have to be
     * considered instead of only the general [IntMin, IntMax] to prove
     * that due to the overflow the signed comparison result < 98 is
     * always false.
     */
        int result = c - (Character.MAX_VALUE - Integer.MIN_VALUE) + 2;
        if (1 < result && result < 100) {
            // Unreachable
            throw new RuntimeException("Should not reach here!");
        }
    }

    /**
     * Tests optimizations of signed and unsigned integer comparison.
     */
    public static void main(String[] args) {
        // We use characters to get a limited integer range for free
        for (int i = Character.MIN_VALUE; i <= Character.MAX_VALUE; ++i) {
            testSigned((char) i);
            testUnsigned((char) i);
        }
    }
}