[vectorIntrinsics] RFR: Improve mask reduction operations on AVX [v3]

[Sandhya Viswanathan]

On Wed, 17 Nov 2021 18:37:20 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> The latest change reverts the change in the mid-end and lets the x86 back-end perform the elision when matching. Some minor changes in the C2_MacroAssembler were made to improve the code emitted by first true operations, as well as to reduce the width of instructions that operate on index calculations from 64 bits to 32 bits.
>> Thank you very much.
>
> @merykitty Please send this PR directly versus the openjdk/jdk mainline. This is a good optimization to have in JDK 18.

> @sviswa7 I have addressed your reviews and created a pull request in mainline. May you create an issue for the PR, please. Thank you very much.

The PR is:
https://bugs.openjdk.java.net/browse/JDK-8277426

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PR: https://git.openjdk.java.net/panama-vector/pull/158