I have a Java method that returns 0 or 1. Can I make it return a boolean without generating a jump instruction?

Question

At the byte code level, the Java logical expression is represented as 0 or 1. I have an expression that results in 0 or 1, but it is evaluated using the int type. A simple example:

public static int isOdd_A(int value) {
    return value & 1;
}

public static boolean isOdd_B(int value) {
    return (value & 1) == 1;
}

The bytecode for the above methods is as follows:

  public static int isOdd_A(int);
    descriptor: (I)I
    Code:
       0: iload_0
       1: iconst_1
       2: iand
       3: ireturn

  public static boolean isOdd_B(int);
    descriptor: (I)Z
    Code:
       0: iload_0
       1: iconst_1
       2: iand
       3: iconst_1
       4: if_icmpne     11
       7: iconst_1
       8: goto          12
      11: iconst_0
      12: ireturn

The method that returns a boolean is much larger and contains a branch, so it is less optimal if the executed machine code is equivalent.

Will the JVM HotSpot know that the Boolean version can be optimized for custom machine code? Is there a way to trick Java into using int-based byte code for a method that returns a boolean (e.g. using ASM)?

EDIT: , , . - jmh int 10%:

@Benchmark
public int countOddA() {
    int odds = 0;
    for (int n : numbers)
        if (Test.isOdd_A(n) == 1)
            odds++;
    return odds;
}
@Benchmark
public int countOddB() {
    int odds = 0;
    for (int n : numbers)
        if(Test.isOdd_B(n))
            odds++;
    return odds;
}

Benchmark                Mode  Cnt      Score    Error  Units
OddBenchmark.countOddA  thrpt  100  18393.818 ± 83.992  ops/s
OddBenchmark.countOddB  thrpt  100  16689.038 ± 90.182  ops/s

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Answer 1

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static boolean isOddAndShort(int i) {
    return (i&1)!=0 && (i>>>16)==0;
}

static boolean isOddAndShort(int);
descriptor: (I)Z
flags: ACC_STATIC
Code:
  stack=2, locals=1, args_size=1
     0: iload_0
     1: iconst_1
     2: iand
     3: ifeq          17
     6: iload_0
     7: bipush        16
     9: iushr
    10: ifne          17
    13: iconst_1
    14: goto          18
    17: iconst_0
    18: ireturn

, and, .

static void evenOrOdd(int i) {
    System.out.println((i&1)!=0? "odd": "even");
}

static void evenOrOdd(int);
descriptor: (I)V
flags: ACC_STATIC
Code:
  stack=3, locals=1, args_size=1
     0: getstatic     #2        // Field java/lang/System.out:Ljava/io/PrintStream;
     3: iload_0
     4: iconst_1
     5: iand
     6: ifeq          14
     9: ldc           #3        // String odd
    11: goto          16
    14: ldc           #4        // String even
    16: invokevirtual #5        // Method java/io/PrintStream.println:(Ljava/lang/String;)V
    19: return

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---

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public class Example {
    private static boolean i2b(int i) {
        return i!=0;
    }
    public static boolean isOdd(int i) {
        return i2b(i&1);
    }
    public static void run() {
        for(int i=0; i<10; i++)
            System.out.println(i+": "+(isOdd(i)? "odd": "even"));
    }
}

public class Int2Bool {
    public static void main(String[] args) throws IOException {
        String clName = Example.class.getName();
        ClassReader cr = new ClassReader(clName);
        ClassWriter cw = new ClassWriter(cr, 0);
        cr.accept(new ClassVisitor(Opcodes.ASM5, cw) {
            @Override
            public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
                if(name.equals("i2b") && desc.equals("(I)Z")) return null;
                return new MethodVisitor(Opcodes.ASM5, super.visitMethod(access, name, desc, signature, exceptions)) {
                    @Override
                    public void visitMethodInsn(int opcode, String owner, String name, String desc, boolean itf) {
                        if(opcode == Opcodes.INVOKESTATIC && name.equals("i2b") &&  desc.equals("(I)Z"))
                            return;
                        super.visitMethodInsn(opcode, owner, name, desc, itf);
                    }
                };
            }
        }, 0);
        byte[] code = cw.toByteArray();
        if(writeBack(clName, code))
            Example.run();
        else
            runDynamically(clName, code);
    }
    private static boolean writeBack(String clName, byte[] code) {
        URL u = Int2Bool.class.getResource("/"+clName.replace('.', '/')+".class");
        if(u==null || !u.getProtocol().equals("file")) return false;
        try {
            Files.write(Paths.get(u.toURI()), code, StandardOpenOption.TRUNCATE_EXISTING);
            return true;
        } catch(IOException|URISyntaxException ex) {
            ex.printStackTrace();
            return false;
        }
    }

    private static void runDynamically(String clName, byte[] code) {
        // example run
        Class<?> rtClass = new ClassLoader() {
            Class<?> get() { return defineClass(clName, code, 0, code.length); }
        }.get();
        try {
            rtClass.getMethod("run").invoke(null);
        } catch (ReflectiveOperationException ex) {
            ex.printStackTrace();
        }
    }
}

public static boolean isOdd(int);
descriptor: (I)Z
flags: ACC_PUBLIC, ACC_STATIC
Code:
  stack=2, locals=1, args_size=1
     0: iload_0
     1: iconst_1
     2: iand
     3: ireturn

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