RFR: 8318446: C2: optimize stores into primitive arrays by combining values into larger store [v13]

[Emanuel Peter]

On Mon, 4 Mar 2024 15:24:23 GMT, ExE Boss <duke at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - allow only array stores of same type as container
>>  - mismatched access test
>
> Do we also have tests that a compiled method with merged stores like:
> 
> static void storeLongLE(byte[] bytes, int offset, long value) {
> 	bytes[offset + 0] = (byte) (value >>  0);
> 	bytes[offset + 1] = (byte) (value >>  8);
> 	bytes[offset + 2] = (byte) (value >> 16);
> 	bytes[offset + 3] = (byte) (value >> 24);
> 	bytes[offset + 4] = (byte) (value >> 32);
> 	bytes[offset + 5] = (byte) (value >> 40);
> 	bytes[offset + 6] = (byte) (value >> 48);
> 	bytes[offset + 7] = (byte) (value >> 56);
> }
> 
> 
> still produce the correct result even when only a part of the stores fit into the array, e.g.:
> 
> var arr = new byte[4];
> try {
> 	// storeLongLE is already C2 compiled with merged stores:
> 	storeLongLE(arr, 0, -1L);
> 
> 	throw new AssertionError("Expected ArrayIndexOutOfBoundsException");
> } catch (ArrayIndexOutOfBoundsException _) {
> 	// ignore
> }
> 
> assertTrue(
> 	Byte.toUnsignedInt(arr[0]) == 0xFF
> 	&& Byte.toUnsignedInt(arr[1]) == 0xFF
> 	&& Byte.toUnsignedInt(arr[2]) == 0xFF
> 	&& Byte.toUnsignedInt(arr[3]) == 0xFF
> );

@ExE-Boss I have an example, but the IR rules are not yet passing. Need to investigate tomorrow.

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PR Comment: https://git.openjdk.org/jdk/pull/16245#issuecomment-1977206515