RFR: 8343629: More MergeStore benchmark

[Shaojin Wen]

On Wed, 6 Nov 2024 07:18:16 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> > ```java
> > "null".getBytes(0, 4, bytes4, off);
> > ```
> > 
> > 
> >     
> >       
> >     
> > 
> >       
> >     
> > 
> >     
> >   
> > Is it possible to do MergeStore in this scenario?
> 
> I don't know. What do the logs say? And what does it currently compile down to, i.e. what assembly instructions?
> 
> Otherwise I think this update seems reasonable.

My thinking is this:


StringBuilder buf = new StringBuilder();
// ...
buf.append("null");


The calling path is as follows:

AbstractStringBuilder::append -> AbstractStringBuilder::putStringAt -> String::getBytes(byte[], int, byte) -> System::arraycopy


In this scenario, if System::arraycopy can be optimized to use putInt or putLong, performance can be improved.

It is similar in the String concatenation scenario

String f(int i) {
	return "abcd" + i;
}


Here `StringConcatHelper::prepend(int, byte, byte[], String, String)` is called, and then `String::getBytes(byte[], int, byte) -> System::arraycopy`


package java.lang;
class StringConcatHelper {
    static int prepend(int index, byte coder, byte[] buf, String value, String prefix) {
        index -= value.length();
        if (coder == String.LATIN1) {
            value.getBytes(buf, index, String.LATIN1);
            index -= prefix.length();
            prefix.getBytes(buf, index, String.LATIN1);
        } else {
            value.getBytes(buf, index, String.UTF16);
            index -= prefix.length();
            prefix.getBytes(buf, index, String.UTF16);
        }
        return index;
    }
}


Here is similar to the above, can we optimize "abcd".getBytes to putInt or putLong?

In summary, can we optimize the System::arraycopy of a stable byte[] with a length of 4 to putInt?

-------------

PR Comment: https://git.openjdk.org/jdk/pull/21659#issuecomment-2461114396