On Wed, 12 Jun 2024 14:24:00 GMT, Emanuel Peter <epe...@openjdk.org> wrote:
>> _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.
@eme64 It seems like MergeStore didn't happen, is there something I did wrong?
class StringUTF16 {
public static void putCharsAt(byte[] value, int i, char c1, char c2, char
c3, char c4) {
int address = Unsafe.ARRAY_BYTE_BASE_OFFSET + (i << 1);
UNSAFE.putChar(value, address , c1);
UNSAFE.putChar(value, address + 2, c2);
UNSAFE.putChar(value, address + 4, c3);
UNSAFE.putChar(value, address + 6, c4);
}
}
-------------
PR Comment: https://git.openjdk.org/jdk/pull/19626#issuecomment-2163242785
