RFR: 8317515: Unify the code of the parse*() families of methods in j.l.Integer and j.l.Long [v2]

[Raffaello Giulietti]

On Fri, 6 Oct 2023 10:12:53 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> @merykitty For a `String` input that would mean copying the suffix, which could be quite long, or make use of the method that accepts a `CharSequence`, which has different (although more complete) exception messages. Perhaps in a followup PR.
>> 
>> What would be _really_ nice is to be able to write, for example (leaving apart the exception messages issue above)
>> 
>> public static int parseInt(String s, int radix)
>>                 throws NumberFormatException {
>>     return parseInt(s, 0, s.length(), radix);  // delegate to the CharSequence method
>> }
>> 
>> and leave it to the runtime compiler to perform something similar to
>> * make a copy of the `parseInt(CharSequence,int,int,int)` code into `parseInt(String,int)`
>> * adapt the copy to the `String` case by replacing `invokeinterface` for `charAt()` with `invokevirtual`, which can be further optimized to direct invocation because `String` is final, and eventually inlined perfectly.
>> 
>> Currently, that does not seem to happen, but I might be wrong.
>> This would spare us 4 code duplications here, and perhaps in many other places where we have almost identical methods for `String` and `CharSequence`.
>
> @rgiulietti We can do the same thing as the Vector API does, that is to have a private `parseInt(CharSequence, int, int, int)` that is annotated with `@ForceInline`. When called from `parseInt(String, int)`, the compiler, after inlining the former method, can devirtualise all calls to `charAt`, etc. This is like a poor man workaround for monomorphism.
> 
>     @ForceInline
>     private int parseUnsignedInt(CharSequence, int, int, int) {}
> 
>     public int parseUnsignedInt(String s, int radix) {
>         return parseUnsignedInt(s, 0, s.length(), radix); // After inlining, this call behaves as if it is a parseUnsignedInt(String, int, int, int)
>     }
> 
> Thanks.

@merykitty Interesting. I'll prepare a followup PR in the near future.

>> Oops @merykitty, I see right now that `compareUnsigned` is an intrinsic, so I'll give it a try.
>
> It's not really about performance, I just think that it is more readable the other way.

Well, two lines above the usage there's a comment that should help the reader...

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PR Comment: https://git.openjdk.org/jdk/pull/16050#issuecomment-1750348693
PR Review Comment: https://git.openjdk.org/jdk/pull/16050#discussion_r1348523537