RFR: 8278171: [vectorapi] Mask incorrectly computed for zero extending cast

[Paul Sandoz]

On Wed, 1 Dec 2021 12:03:15 GMT, Mai Đặng Quân Anh <duke at openjdk.java.net> wrote:

> When doing an unsigned upcast, we perform a signed cast followed by a bitwise and operation to clip the extended signed bit. The sign clip mask is currently calculated incorrectly, the correct mask should have the number of least significant bit set equal to the size of the source elements. This patch fixes this trivial issue and adds several tests for zero extension casts.
> 
> Thank you very much.

Looks good. Running tests. 

Something we should consider later: split this test out into smaller files and support the max vector. On supported platforms we could consider using the IR test framework to verify the correct IR node is generated.

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PR: https://git.openjdk.java.net/jdk/pull/6634