RFR: 8286941: Add mask IR for partial vector operations for ARM SVE [v3]

[Jatin Bhateja]

On Mon, 20 Jun 2022 03:28:05 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

> The mask is generated based on the real vector length, which guarantees only the vector lanes that inside of its valid vector length will do the operations. Higher lanes do nothing. So if a VectorStore has a vector length which equals to `SuperWordMaxVectorSize`, but the MaxVectorSize is larger than the `SuperWordMaxVectorSize`, a mask will be generated based on the real length `SuperWordMaxVectorSize`. And only lanes under the `SuperWordMaxVectorSize` will be stored. So I cannot see the influence on the out of memory issue. Could you please give an example apart of x86 cases? Thanks so much!
> 
Correct, got it 
> BTW, I think flag `SuperWordMaxVectorSize` should be equal to `MaxVectorSize` by default for other platforms instead of 64. If a platform (liken SVE) supports >64 bytes max vector size for auto-vectorization, it can only generate the vectors with 64 bytes vector size. This seems unreasonable. So do you have any plan refactoring this flag, or removing the usages for it in future? Thanks!

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PR: https://git.openjdk.org/jdk/pull/9037