On Wed, 12 Jun 2024 14:16:50 GMT, Shaojin Wen <d...@openjdk.org> wrote:
>> Shaojin Wen has updated the pull request incrementally with one additional
>> commit since the last revision:
>>
>> revert
>
> _putCharStringU will perform MergeStore but with bounds checking. Can the C2
> optimizer perform MergeStore without bounds checking in this case?
>
> StringUTF16.putChar does not have a bounds check, so there should be no
> bounds check after MergeStore?
>
>
> class AbstractStringBuilder {
> private AbstractStringBuilder appendNull() {
> // ...
> StringUTF16.putCharsAt(val, count, 'n', 'u', 'l', 'l');
> // ...
> }
> }
>
> class StringUTF16 {
> public static void putCharsAt(byte[] value, int i, char c1, char c2,
> char c3, char c4) {
> putChar(value, i , c1);
> putChar(value, i + 1, c2);
> putChar(value, i + 2, c3);
> putChar(value, i + 3, c4);
> }
>
> @IntrinsicCandidate
> // intrinsic performs no bounds checks
> static void putChar(byte[] val, int index, int c) {
> assert index >= 0 && index < length(val) : "Trusted caller missed
> bounds check";
> index <<= 1;
> val[index++] = (byte)(c >> HI_BYTE_SHIFT);
> val[index] = (byte)(c >> LO_BYTE_SHIFT);
> }
> }
@wenshao If you look at the tests in https://github.com/openjdk/jdk/pull/16245,
you can see examples like this:
https://github.com/eme64/jdk/blob/93bf2ddc9b7f584724034aec6a4f8b9fe1b2dfda/test/hotspot/jtreg/compiler/c2/TestMergeStores.java#L501-L514
So yes, we can merge them.
-------------
PR Comment: https://git.openjdk.org/jdk/pull/19626#issuecomment-2163150153
