RFR: 8257165: C2: Improve box elimination for vector masks and shuffles

Mon Nov 30 10:39:58 UTC 2020

On Mon, 30 Nov 2020 10:27:42 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> Introduce VectorMask/VectorShuffle-specific transformations to reduce reboxing by eliminating `VectorBox`/`VectorUnbox` pairs. 
>> 
>> It's a trivial transformation when the types on both ends perfectly match, but when type mismatch occurs there are additional steps needed (see `PhaseVector::expand_vunbox_node()` for more details on vector unboxing) .  
>> 
>> Testing:
>> - `jdk/incubator/vector` tests w/ different flag combinations (no flags, `-Xcomp`, `-XX:+DeoptimizeALot`); 
>> - tier1-4
>
> Looks reasonable.

Thanks for the reviews, Vladimir and Tobias.

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PR: https://git.openjdk.java.net/jdk/pull/1457