RFR: 8295302: Do not use ArrayList when LambdaForm has a single ClassData [v2]

[Ioi Lam]

On Thu, 13 Oct 2022 22:29:03 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   @iwanowww comments
>
> src/java.base/share/classes/java/lang/invoke/InvokerBytecodeGenerator.java line 321:
> 
>> 319:     private MemberName loadMethod(byte[] classFile) {
>> 320:         Class<?> invokerClass = LOOKUP.makeHiddenClassDefiner(className, classFile, Set.of())
>> 321:                                       .defineClass(true, classDataValues());
> 
> Why not just put it in `classDataValues()` instead?
> 
> 
>     Object classDataValues() {
>         final List<ClassData> cd = classData;
>         return switch(cd.size()) {
>             case 0 -> null; // flatten for zero case
>             case 1 -> cd.get(0).value; // flatten for single value case
>             case 2 -> List.of(cd.get(0).value, cd.get(1).value);
>             ...
> 
> 
> And it also covers zero case for free.

I fixed it as you suggested. I also changed the method to private to make sure no one else is using this method.

> src/java.base/share/classes/java/lang/invoke/InvokerBytecodeGenerator.java line 389:
> 
>> 387:         mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/invoke/MethodHandles",
>> 388:                            "classData", "(Ljava/lang/Class;)Ljava/lang/Object;", false);
>> 389:         if (classData.size() == 1) {
> 
> if (classData.size() < 2) {
> 
> It works for zero case, because `checkcast` always succeeds on nulls.

Actually the zero case is already handled here:


    static void clinit(ClassWriter cw, String className, List<ClassData> classData) {
        if (classData.isEmpty())
            return;


No `<clinit>` method is generated because we have no static field to initialize.

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PR: https://git.openjdk.org/jdk/pull/10706