RFR: 8288397: AArch64: Fix register issues in SVE backend match rules

[Xiaohong Gong]

On Wed, 15 Jun 2022 09:40:52 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

> There are register usage issues in the sve backend match rules, which made the two added jtreg tests fail.
> 
> The predicated vector "`not`" rules didn't use the same register for "`src`" and "`dst`", which is necessary to make sure the inactive lanes in "`dst`" save the same elements as "`src`". This patch fixes the rules by using the same register for "`dst`" and "`src`".
> 
> And the input idx register in "`gatherL/scatterL`" rules was overwritten by the first unpack instruction. The same issue also existed in the partial and predicated gatherL/scatterL rules. This patch fixes them by saving the unpack results into a temp register and use it as the index for gather/scatter.

Hi @nick-arm, may I have your review for this PR? Thanks for your time!

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PR: https://git.openjdk.org/jdk19/pull/17