[release/10.0] Fix codegen for SVE Scatter*With*Offsets* and GatherVector*With*Offsets*

[SwapnilGaikwad]

Backport of #119712 and #119853 to release/10.0

/cc @EgorBo @SwapnilGaikwad

Customer Impact

• Customer reported
• Found internally

These changes fix the incorrect codegen for some of the SVE Scatter and Gather APIs. These APIs take byte offsets are one of the arguments but the current codegen treats them as indices. It leads to incorrect behaviour and is a bug.
The current patch fixes this bug. The SVE APIs are introduced in .Net9, thus, the fix needs to be backported to .Net10.

Regression

• Yes
• No

Testing

Fix is verified by updating the corresponding tests to ensure the desired behaviour is exhibited by the program. Furthermore, it's also verified manually by inspecting generated assembly instructions before and after the fix.

Risk

Low. This is a low risk change as the SVE feature remains experimental in .Net9 and .Net10.

[SwapnilGaikwad]

@dotnet/arm64-contrib @a74nh @tannergooding @EgorBo

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[tannergooding]

The backport template needs to be filled out still. I've updated the original post to have that, but someone with all the relevant details would be better to fill it in.

[SwapnilGaikwad]

The backport template needs to be filled out still. I've updated the original post to have that, but someone with all the relevant details would be better to fill it in.

I have filled in most of the details. Could you or someone verify if the target branch is correct? Not sure whether this work would fall against servicing category and needs target branch as release-10.0-staging.

[JulieLeeMSFT]

Needs code review and please check test failures.

[SwapnilGaikwad]

Needs code review and please check test failures.

The test failures seems unrelated to the changes. Also, they are on x64 machines and the change is SVE only so should be unrelated to the failures.