[Arm64] Add Short Vector ABI support for HW Intrinsics

[sdmaclea]

The types Vector64<T> and Vector128<T> are intended to map to ABI Short Vector fundamental types. These should be passed in vector registers.

Current code will pass these in integer registers.

IsShortVector can be crudely implemented as follows:

bool Compiler::IsShortVector(CORINFO_CLASS_HANDLE hClass)
{
    return isIntrinsicType(hClass) && (getBaseTypeOfSIMDType(hClass) != TYP_UNKNOWN);
}

Compiler::getPrimitiveTypeForStruct() can be trivially updated to return TYP_SIMD8 or TYP_SIMD16 when IsShortVector() == true

I made an initial naive attempt to implement and failed, but I really need a design discussion.

@CarolEidt @tannergooding @dotnet/arm64-contrib @dotnet/jit-contrib

category:reach
theme:intrinsics
skill-level:expert
cost:medium

[sdmaclea]

#9578

[sdmaclea]

I an issue with Vector64 return again.

Rather than hacking it. I am thinking about fixing this.

[BruceForstall]

@sdmaclea Is this fixed already? dotnet/coreclr#16310 is merged.

If not, @CarolEidt, maybe this is related to your ABI work https://github.com/dotnet/coreclr/issues/14371

[sdmaclea]

@BruceForstall dotnet/coreclr#16310 was abandoned (not merged). It never passed all tests and it diverged with the master branch enough that I didn't have time to fix it.

I think @CarolEidt is working on it. Probably the #9079 is part of it.

[CarolEidt]

I am working on #9079, and also dotnet/coreclr#16022, though progress is slow.

[CarolEidt]

Fixed with dotnet/coreclr#23675