Intrinsify RuntimeHelpers.CreateSpan on Mono

[EgorBo]

Context: a lot of benchmarks regressed on Mono after #79461 and #80668

On CoreCLR the following snippet (compiled with the most recent Roslyn):

static int GetInt8(int index)
{
    ReadOnlySpan<byte> RVA = new byte[] { 1, 2, 3, 4 };
    return RVA[index];
}

static int GetInt32(int index)
{
    ReadOnlySpan<int> RVA = new int[] { 1, 2, 3, 4 };
    return RVA[index];
}

produces more or less the same codegen while IL is quite different - in case of ReadOnlySpan<int> a RuntimeHelpers.CreateSpan call is emitted by Roslyn (to handle endianness). CoreCLR has a JIT intrinsics implemented by @davidwrighton in #61079 that helps it to achieve perfect codegen here. As that PR states, Mono doesn't have that intrinsic so CreateSpan ends up calling an icall in vm (ves_icall_System_Runtime_CompilerServices_RuntimeHelpers_GetSpanDataFrom)

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Issue Details

---

Context: a lot of benchmarks regressed on Mono after #79461 and #80668

On CoreCLR the following snippet (compiled with the most recent Roslyn):

static int GetInt8(int index)
{
    ReadOnlySpan<byte> RVA = new byte[] { 1, 2, 3, 4 };
    return RVA[index];
}

static int GetInt32(int index)
{
    ReadOnlySpan<int> RVA = new int[] { 1, 2, 3, 4 };
    return RVA[index];
}

produces more or less the same codegen while IL is quite different - in case of ReadOnlySpan<int> a RuntimeHelpers.CreateSpan call is emitted by Roslyn (to handle endianness). CoreCLR has a JIT intrinsics implemented by @davidwrighton in #61079 that helps it to achieve perfect codegen here. As that PR states, Mono doesn't have that intrinsic so CreateSpan ends up calling an icall in vm (ves_icall_System_Runtime_CompilerServices_RuntimeHelpers_GetSpanDataFrom)

Author:	EgorBo
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[ghost]

Tagging subscribers to this area: @BrzVlad
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Context: a lot of benchmarks regressed on Mono after #79461 and #80668

On CoreCLR the following snippet (compiled with the most recent Roslyn):

static int GetInt8(int index)
{
    ReadOnlySpan<byte> RVA = new byte[] { 1, 2, 3, 4 };
    return RVA[index];
}

static int GetInt32(int index)
{
    ReadOnlySpan<int> RVA = new int[] { 1, 2, 3, 4 };
    return RVA[index];
}

produces more or less the same codegen while IL is quite different - in case of ReadOnlySpan<int> a RuntimeHelpers.CreateSpan call is emitted by Roslyn (to handle endianness). CoreCLR has a JIT intrinsics implemented by @davidwrighton in #61079 that helps it to achieve perfect codegen here. As that PR states, Mono doesn't have that intrinsic so CreateSpan ends up calling an icall in vm (ves_icall_System_Runtime_CompilerServices_RuntimeHelpers_GetSpanDataFrom)

Author:	EgorBo
Assignees:	vargaz, BrzVlad
Labels:	area-Codegen-JIT-mono, area-Codegen-AOT-mono, area-Codegen-Interpreter-mono
Milestone:	8.0.0

[lewing]

cc @SamMonoRT @radekdoulik @marek-safar

[SamMonoRT]

@jandupej has started work on addressing this

[jandupej]

The issue has been addressed in #81695, closing.

[vargaz]

The interpreter support is still missing.

[SamMonoRT]

@BrzVlad will be working on Interpreter support

[jandupej]

Remaining perf issues on Linux AOT x64: #83330