RFR: 8294194: [AArch64] Create intrinsics compress and expand [v2]

[Stuart Monteith]

On Tue, 1 Nov 2022 09:20:31 GMT, Stuart Monteith <smonteith at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/aarch64.ad line 2299:
>> 
>>> 2297:     case Op_ExpandBits:
>>> 2298:     case Op_CompressBits:
>>> 2299:       if (!(UseSVE > 1 && VM_Version::supports_svebitperm())) {
>> 
>> Do we need to test `UseSVE` here?
>
> We don't want to enable this on detection of the feature - if UseSVE is disable, we'll be missing the SVE infrastructure that we are dependent on in the compiler.

Correction - we don't want to enable this solely on the present of the feature. With -XX:-UseSVE on the command line, this would break, so we need UseSVE and the feature to be present.

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PR: https://git.openjdk.org/jdk/pull/10537