RFR: 8331252: C2: MergeStores: handle negative shift values

[Emanuel Peter]

On Mon, 29 Apr 2024 16:47:03 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Somehow, I have not thought of negative shift constants, and there was no regression test for it.
>> The fuzzer now found a case.
>> 
>> **I convert the assert into a condition.**
>
> Looks good.

Thanks for the reviews @vnkozlov @shipilev !

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PR Comment: https://git.openjdk.org/jdk/pull/19001#issuecomment-2085825255