test/langtools/tools/javac/patterns/NoUnnecessaryCast.java

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/*
 * @test
 * @bug 8237528
 * @summary Verify there are no unnecessary checkcasts and conditions generated
 *          for the pattern matching in instanceof.
 * @modules jdk.jdeps/com.sun.tools.classfile
 * @compile NoUnnecessaryCast.java
 * @run main NoUnnecessaryCast
 */

import java.io.File;
import java.io.IOException;

import com.sun.tools.classfile.Attribute;
import com.sun.tools.classfile.ClassFile;
import com.sun.tools.classfile.Code_attribute;
import com.sun.tools.classfile.Code_attribute.InvalidIndex;
import com.sun.tools.classfile.ConstantPool;
import com.sun.tools.classfile.ConstantPoolException;
import com.sun.tools.classfile.Descriptor.InvalidDescriptor;
import com.sun.tools.classfile.Instruction;
import com.sun.tools.classfile.Method;
import java.util.Arrays;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;

public class NoUnnecessaryCast {
    public static void main(String[] args)
            throws IOException, ConstantPoolException, InvalidDescriptor, InvalidIndex {
        new NoUnnecessaryCast()
                .checkClassFile(new File(System.getProperty("test.classes", "."),
                    NoUnnecessaryCast.class.getName() + ".class"));
    }

    void checkClassFile(File file)
            throws IOException, ConstantPoolException, InvalidDescriptor, InvalidIndex {
        ClassFile classFile = ClassFile.read(file);
        ConstantPool constantPool = classFile.constant_pool;

        Method method = Arrays.stream(classFile.methods)
                              .filter(m -> getName(m, constantPool)
                                               .equals("test"))
                              .findAny()
                              .get();
        String expectedInstructions = """
                                      aload_1
                                      instanceof
                                      ifeq
                                      aload_1
                                      checkcast
                                      astore_2
                                      aload_2
                                      invokevirtual
                                      ifeq
                                      iconst_1
                                      goto
                                      iconst_0
                                      ireturn
                                      """;
        Code_attribute code = (Code_attribute) method.attributes
                .get(Attribute.Code);
        String actualInstructions = printCode(code);
        if (!expectedInstructions.equals(actualInstructions)) {
            throw new AssertionError("Unexpected instructions found:\n" +
                                     actualInstructions);
        }
    }

    String printCode(Code_attribute code) {
        return StreamSupport.stream(code.getInstructions().spliterator(), false)
                            .map(Instruction::getMnemonic)
                            .collect(Collectors.joining("\n", "", "\n"));
    }

    String getName(Method m, ConstantPool constantPool) {
        try {
            return m.getName(constantPool);
        } catch (ConstantPoolException ex) {
            throw new IllegalStateException(ex);
        }
    }

    boolean test(Object o) {
        return o instanceof String s && s.isEmpty();
    }
}