Why isn't Unity Burst's inspector showing some variables?

Question

While looking at the native code generated by Unity Burst to see whether it's leveraging SIMD, I have a hard time reading it as it is incompletely shown in the inspector.

For instance, there are variables that simply aren't shown, h1, h2, h3 and hv.

I've modified the attributes so as to avoid any kind of optimization but still the same:

[BurstCompile(OptimizeFor = OptimizeFor.FastCompilation)]
[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.NoOptimization)]

The Burst inspector:

The actual code:

[BurstCompile(OptimizeFor = OptimizeFor.FastCompilation)]
[MethodImpl(MethodImplOptions.NoInlining | MethodImplOptions.NoOptimization)]
[MonoPInvokeCallback(typeof(FilterMethod))]
public static unsafe void VectorFullBandInner(
    in float* source, in float* target, in int length, in int stride, in int offset, ref Filter filter)
{
    ValidateArguments(source, target, length, stride, offset, ref filter);

    var h = filter.H;
    var z = filter.Z;
    var n = filter.HLength;
    var v = filter.VLength;

    for (var sample = 0; sample < length; sample += v)
    {
        var pos = Filter.UpdateZ(ref filter, source, sample);

        var sum = 0.0f;

        var tap = 0;

        int end;

        for (end = n - 4; tap < end; tap += 4)
        {
            var h0 = h[tap + 0];
            var h1 = h[tap + 1];
            var h2 = h[tap + 2];
            var h3 = h[tap + 3];

            var zP = pos - tap;

            var z0 = z[zP - 0];
            var z1 = z[zP - 1];
            var z2 = z[zP - 2];
            var z3 = z[zP - 3];

            var hv = new float4(h0, h1, h2, h3);
            var zh = new float4(z0, z1, z2, z3);

            sum += math.dot(hv, zh);
        }

        for (end = n - 1; tap < end; tap += 2)
        {
            var h0 = h[tap + 0];
            var h1 = h[tap + 1];

            var zP = pos - tap;

            var z0 = z[zP - 0];
            var z1 = z[zP - 1];

            var hv = new float2(h0, h1);
            var zv = new float2(z0, z1);

            sum += math.dot(hv, zv);
        }

        for (end = n - 0; tap < end; tap += 1)
        {
            var h0 = h[tap];

            var zP = pos - tap;

            var z0 = z[zP - 0];

            sum += math.dot(h0, z0);
        }

        target[sample] = sum;
    }
}

These variables are used and can't be optimized out but they're not shown.

Tried different options in UI, even for full debug information it's the same.

Am I missing something or is this expected?

Answer 1

var h0 = h[tap + 0];
var h1 = h[tap + 1];
var h2 = h[tap + 2];
var h3 = h[tap + 3];

movsxd    rcx, ecx 

Burst compiler optimizes struct operations by packing and vectorizing them. h0-h3 existing next to each other in memory can be reinterpreted as a single wider "struct" read/move operation. So h1,h2,h3 declarations haven't disappeared but been collapsed to a single instruction in places of h0.