[API Proposal]: VectorNNN.Create with broadcasting

[EgorBo]

Background and motivation

Constant vectors quite often have the same values in 128-bit lanes, it makes them especially verbose with AVX512, consider these: https://github.com/dotnet/runtime/blob/d29d4d04d20252c283b76fa50f04b6ebf5dc9d91/src/libraries/System.Private.CoreLib/src/System/Buffers/Text/Base64Decoder.cs#L665-L681 it'd be nice to have a Create API that can automatically broadcasts lanes to keep code smaller (and data section's size too - but that is irrelevant here)

API Proposal

namespace System.Runtime.Intrinsics
{
    public static partial class Vector128
    {
        public static Vector128<T> Create<T>(Vector64<T> value) where T : struct;
    }

    public static partial class Vector256
    {
        public static Vector256<T> Create<T>(Vector128<T> value) where T : struct;
    }

    public static partial class Vector512
    {
        public static Vector512<T> Create<T>(Vector128<T> value) where T : struct;
        public static Vector512<T> Create<T>(Vector256<T> value) where T : struct;
    }
}

API Usage

Vector512<sbyte> lutShift = Vector512.Create(
    0, 16, 19, 4, -65, -65, -71, -71, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 16, 19, 4, -65, -65, -71, -71, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 16, 19, 4, -65, -65, -71, -71, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 16, 19, 4, -65, -65, -71, -71, 0, 0, 0, 0, 0, 0, 0, 0);

// becomes:

Vector512<sbyte> lutShift = Vector512.Create(
    Vector128.Create(0, 16, 19, 4, -65, -65, -71, -71, 0, 0, 0, 0, 0, 0, 0, 0));

Alternative Designs

No strong opinion on Vector64

Risks

No response

[EgorBo]

cc @tannergooding @dotnet/avx512-contrib

Tagging subscribers to this area: @dotnet/area-system-runtime-intrinsics
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Issue Details

---

Background and motivation

Constant vectors quite often have the same values in 128-bit lanes, it makes them especially verbose with AVX512, consider these: https://github.com/dotnet/runtime/blob/d29d4d04d20252c283b76fa50f04b6ebf5dc9d91/src/libraries/System.Private.CoreLib/src/System/Buffers/Text/Base64Decoder.cs#L665-L681 it'd be nice to have a Create API that can automatically broadcasts lanes to keep code smaller (and data section's size too - but that is irrelevant here)

API Proposal

namespace System.Runtime.Intrinsics
{
    public static partial class Vector256
    {
        public static Vector256<T> Create<T>(Vector128<T> valueToBroadcast) where T : struct;
    }

    public static partial class Vector512
    {
        public static Vector512<T> Create<T>(Vector128<T> valueToBroadcast) where T : struct;
        public static Vector512<T> Create<T>(Vector256<T> valueToBroadcast) where T : struct;
    }
}

API Usage

Vector512<sbyte> lutShift = Vector512.Create(
    0, 16, 19, 4, -65, -65, -71, -71, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 16, 19, 4, -65, -65, -71, -71, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 16, 19, 4, -65, -65, -71, -71, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 16, 19, 4, -65, -65, -71, -71, 0, 0, 0, 0, 0, 0, 0, 0);

// becomes:

Vector512<sbyte> lutShift = Vector512.Create(
    Vector128.Create(0, 16, 19, 4, -65, -65, -71, -71, 0, 0, 0, 0, 0, 0, 0, 0));

Alternative Designs

No strong opinion on Vector64

Risks

No response

Author:	EgorBo
Assignees:	-
Labels:	api-suggestion, area-System.Runtime.Intrinsics, untriaged
Milestone:	-

[tannergooding]

We should include Vector64 for consistency and to ensure it works well on Arm64 where it is supported.

The parameter name should likely just be value for consistency as well. The summary/parameter description helps clarify it is being broadcast as part of the create operation.

[bartonjs]

Video

• We went ahead and squared the circle, adding the Vector64 overloads.

namespace System.Runtime.Intrinsics
{
    public static partial class Vector128
    {
        public static Vector128<T> Create<T>(Vector64<T> value) where T : struct;
    }

    public static partial class Vector256
    {
        public static Vector256<T> Create<T>(Vector64<T> value) where T : struct;
        public static Vector256<T> Create<T>(Vector128<T> value) where T : struct;
    }

    public static partial class Vector512
    {
        public static Vector512<T> Create<T>(Vector64<T> value) where T : struct;
        public static Vector512<T> Create<T>(Vector128<T> value) where T : struct;
        public static Vector512<T> Create<T>(Vector256<T> value) where T : struct;
    }
}