RFR: 8365911: AArch64: Fix encoding error in sve_cpy for negative floats [v3]

[erifan]

On Fri, 5 Sep 2025 06:30:16 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> Is the issue at all observable from Java? With the wrong encoding, could there be a wrong result that we could test in a jtreg test?

No this is not observable from java because the JVM currently doesn't use `sve_cpy` to copy negative floating-point numbers, only positive floating-point numbers.

I discovered this issue while trying to use this instruction to optimize `VectorMask.toVector()` , which needs to do `sve_cpy(-1.0)`.

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PR Comment: https://git.openjdk.org/jdk/pull/26951#issuecomment-3257238951