RFR: 8264104: Eliminate unnecessary vector mask conversion during VectorUnbox for floating point VectorMask [v4]

[Jatin Bhateja]

On Tue, 13 Apr 2021 11:16:33 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> src/hotspot/share/opto/vectornode.hpp line 1240:
>> 
>>> 1238: };
>>> 1239: 
>>> 1240: class VectorMaskCastNode : public VectorNode {
>> 
>> VectorMaskReinterpret seems better choice, since its a re-interpretation and not a casting (up/down).
>
> Considering masks have platform-specific representation, full-blown casts between different element types look more appropriate here.
> 
> In this particular case, the focus is on the cheapest possible case when representations share the same bit pattern and the cast degenerates into a no-op. But in the longer term, it makes perfect sense to support the full matrix of conversions and don't rely on `VectorLoadMask <=> VectorStoreMask` and intermediate canonical vector representation.

Got it.

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PR: https://git.openjdk.java.net/jdk/pull/3238