TAA blend shader redundant barrier

[Katzeee]

I have found in the implementation of TAA that during the blending process, after completing the Prefetch from the Color buffer, there are two calls to the GroupMemoryBarrierWithGroupSync(). However, there is no write to the groupshared memory after the first call, so the second barrier should be redundant, is that correct?

    for (uint i = GI; i < 45; i += 64)
    {
        uint X = (i % ldsHalfPitch) * 2;
        uint Y = (i / ldsHalfPitch) * 2;
        uint TopLeftIdx = X + Y * kLdsPitch;
        int2 TopLeftST = Gid.xy * uint2(8, 8) - 1 + uint2(X / 2, Y);
        float2 UV = RcpBufferDim * (TopLeftST * float2(2, 1) + float2(2, 1));

        float4 Depths = CurDepth.Gather(LinearSampler, UV);
        ldsDepth[TopLeftIdx + 0] = Depths.w;
        ldsDepth[TopLeftIdx + 1] = Depths.z;
        ldsDepth[TopLeftIdx + kLdsPitch] = Depths.x;
        ldsDepth[TopLeftIdx + 1 + kLdsPitch] = Depths.y;

        float4 R4 = InColor.GatherRed(LinearSampler, UV);
        float4 G4 = InColor.GatherGreen(LinearSampler, UV);
        float4 B4 = InColor.GatherBlue(LinearSampler, UV);
        StoreRGB(TopLeftIdx, float3(R4.w, G4.w, B4.w));
        StoreRGB(TopLeftIdx + 1, float3(R4.z, G4.z, B4.z));
        StoreRGB(TopLeftIdx + kLdsPitch, float3(R4.x, G4.x, B4.x));
        StoreRGB(TopLeftIdx + 1 + kLdsPitch, float3(R4.y, G4.y, B4.y));
    }

    GroupMemoryBarrierWithGroupSync();

    uint Idx0 = GTid.x * 2 + GTid.y * kLdsPitch + kLdsPitch + 1;
    uint Idx1 = Idx0 + 1;

    GroupMemoryBarrierWithGroupSync(); // <- redundant?

[stanard]

That does look redundant. It's probably vestigial (left in from an earlier version of the code). However, it is benign because the compiler should remove unnecessary barriers.

[stanard]

PR approved