JIT: Potential bad codegen with `Avx512BW` intrinsic functions

[jakobbotsch]

// Generated by Fuzzlyn v2.2 on 2024-08-04 15:50:11
// Run on X64 Linux
// Seed: 9513455124659677293-vectort,vector128,vector256,vector512,x86aes,x86avx,x86avx2,x86avx512bw,x86avx512bwvl,x86avx512cd,x86avx512cdvl,x86avx512dq,x86avx512dqvl,x86avx512f,x86avx512fvl,x86avx512fx64,x86avx512vbmi,x86avx512vbmivl,x86bmi1,x86bmi1x64,x86bmi2,x86bmi2x64,x86fma,x86lzcnt,x86lzcntx64,x86pclmulqdq,x86popcnt,x86popcntx64,x86sse,x86ssex64,x86sse2,x86sse2x64,x86sse3,x86sse41,x86sse41x64,x86sse42,x86sse42x64,x86ssse3,x86x86base
// Reduced from 26.0 KiB to 1.1 KiB in 00:00:56
// Debug: Outputs <0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>
// Release: Outputs <0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>
using System;
using System.Runtime.CompilerServices;
using System.Numerics;
using System.Runtime.Intrinsics;
using System.Runtime.Intrinsics.X86;

public class Program
{
    public static byte s_5;
    public static void Main()
    {
        var vr16 = Vector512.CreateScalar(s_5);
        var vr17 = Vector512.Create<byte>(1);
        var vr18 = (byte)0;
        var vr19 = Vector512.CreateScalar(vr18);
        var vr20 = Vector128.Create<byte>(0);
        var vr21 = Avx512BW.BroadcastScalarToVector512(vr20);
        var vr22 = Vector256.Create<byte>(1);
        var vr23 = Avx512F.InsertVector256(vr21, vr22, 0);
        var vr24 = Vector512.Create(249, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0);
        var vr25 = Avx512BW.BlendVariable(vr19, vr23, vr24);
        var vr26 = Avx512BW.Min(vr17, vr25);
        Vector512<byte> vr27 = Avx512BW.UnpackLow(vr16, vr26);
        System.Console.WriteLine(vr27);
    }
}

cc @dotnet/jit-contrib

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[JulieLeeMSFT]

@anthonycanino , PTAL.
cc @dotnet/jit-contrib @tannergooding.

[Ruihan-Yin]

Looking into this issue now.

[Ruihan-Yin]

Here in Release code, JIT tries to fold the BlendVariable node with embedded masking feature, but blend in the repro is supposed to operate on a byte granularity, while if we fold the node into insert64x4, the intrinsic does not support use kmask register at byte granularity.