RFR: 8264104: Eliminate unnecessary vector mask conversion during VectorUnbox for floating point VectorMask [v5]

[Vladimir Ivanov]

On Thu, 15 Apr 2021 04:02:03 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> The Vector API defines different element types for floating point VectorMask. For example, the bitwise related APIs use "`long/int`", while data related APIs use "`double/float`". This makes some optimizations that based on the type checking cannot work well.
>> 
>> For example, the VectorBox/Unbox elimination like `"VectorUnbox (VectorBox v) ==> v"` requires the types of output and
>> input are equal. Normally this is necessary. However, due to the different element type for floating point VectorMask with the same species, the VectorBox/Unbox pattern is optimized to:
>> 
>>   VectorLoadMask (VectorStoreMask vmask)
>> 
>> Actually the types can be treated as the same one for such cases. And considering the vector mask representation is the same for
>> vectors with the same element size and vector length, it's safe to do the optimization:
>> 
>>   VectorLoadMask (VectorStoreMask vmask) ==> vmask
>> 
>> The same issue exists for GVN which is based on the type of a node. Making the mask node's` hash()/cmp()` methods depends on the element size instead of the element type can fix it.
>
> Xiaohong Gong has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add type restrict in the match rule predicate

Looks good.

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Marked as reviewed by vlivanov (Reviewer).

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