RFR: 8333893: Optimization for StringBuilder append boolean & null [v4]

[Claes Redestad]

On Thu, 20 Jun 2024 14:32:25 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> @cl4es  @wenshao I think we should probably work on `putChar`, or at least figure out what blocks `MergeStore` for `putChar`. Can someone produce a simple stand-alone `.java` file that uses `putChar`, so that I can investigate why `MergeStore` does not work for it?
>> 
>> Otherwise, I agree with @cl4es : the code here may be ok for now, but we would have to revert it again later, should `MergeStore` eventually do the trick.
>
> @eme64 
> 
> simple stand-alone java
> 
> import jdk.internal.misc.Unsafe;
> 
> public class PutCharTest {
>     static final Unsafe UNSAFE = Unsafe.getUnsafe();
> 
>     static void putCharsAt(byte[] val, int index, int c1, int c2, int c3, int c4) {
>         putChar(val, index    , (char)(c1));
>         putChar(val, index + 1, (char)(c2));
>         putChar(val, index + 2, (char)(c3));
>         putChar(val, index + 3, (char)(c4));
>     }
>     
>     static void putChar(byte[] bytes, int index, int c) {
>         UNSAFE.putChar(bytes, Unsafe.ARRAY_BYTE_BASE_OFFSET + (index << 1), (char)(c));
>     }
> 
>     static void putChar0(byte[] bytes, int index, int c) {
>         UNSAFE.putByte(bytes, Unsafe.ARRAY_BYTE_BASE_OFFSET + (index << 1), (byte)(c));
>         UNSAFE.putByte(bytes, Unsafe.ARRAY_BYTE_BASE_OFFSET + (index << 1) + 1, (byte)(c << 8));
>     }
> 
>     static void putNull(byte[] bytes, int index) {
>         putCharsAt(bytes, index, 'n', 'u', 'l', 'l');
>     }
> 
>     public static void main(String[] args) {
>         for (int i = 0; i < 5; i++) {
>             testNull();
>         }
> 
>         System.out.println("done");
>     }
> 
>     private static void testNull() {
>         byte[] bytes = new byte[8192];
> 
>         for (int i = 0; i < 1000; i++) {
>             int index = 0;
>             for (int j = 0; j < 1024; j++) {
>                 putNull(bytes, index);
>                 index += 4;
>             }
>         }
>     }
> }

As long as @wenshao is OK with that I'm happy to let this wait. I'll have limited availability myself in the coming weeks.

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PR Comment: https://git.openjdk.org/jdk/pull/19626#issuecomment-2192459124