RFR: 8361582: AArch64: Some ConH values cannot be replicated with SVE

[Bhavana Kilambi]

On Fri, 1 Aug 2025 14:29:47 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>>> I am still a bit confused what matches `Replicate` with `immH` that does _not_ fit `immH8_shift8` when `Matcher::vector_length_in_bytes(n) > 16`?
>> 
>> Hi, thanks for your review. If the immediate value does not fit `immH8_shift8` for `Matcher::vector_length_in_bytes(n) > 16` , the compiler would generate `loadConH` [1] -> `replicateHF` [2] backend nodes instead. The constant would be loaded from the constant pool instead and then broadcasted/replicated to every lane of an SVE register. 
>> 
>> [1] https://github.com/openjdk/jdk/blob/8ac4a88f3c5ad57824dd192cb3f0af5e71cbceeb/src/hotspot/cpu/aarch64/aarch64.ad#L6963
>> 
>> [2] https://github.com/openjdk/jdk/blob/8ac4a88f3c5ad57824dd192cb3f0af5e71cbceeb/src/hotspot/cpu/aarch64/aarch64_vector.ad#L4806
>
>> If the immediate value does not fit `immH8_shift8` for `Matcher::vector_length_in_bytes(n) > 16` , the compiler would generate `loadConH` [1] -> `replicateHF` [2] backend nodes instead.
> 
> Ah OK, just checking. I ran this patch on the machine where I have originally found the issue, and it seems to work.

Hi @shipilev @theRealAph Can I please ask for another round of review? I have addressed the review comments in the latest patch. Thanks a lot!

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PR Comment: https://git.openjdk.org/jdk/pull/26589#issuecomment-3164177758