PrefixSum and PostfixSum not working #28
Description
Even in a very simple compute shader (DX11), the AmdDxExtShaderIntrinsics_WavePrefixSum and AmdDxExtShaderIntrinsics_WavePostfixSum produce wrong results. I tried on different hardware (RX 480, WX7100 and WX9100) all giving completely wrong results. I also tried different driver versions and always check that the AGS_DX11_EXTENSION_INTRINSIC_WAVE_REDUCE extension is supported.
This is a simple shader using the AmdDxExtShaderIntrinsics_WavePrefixSum (which produces bogus values) or optionally (just commenting out the USE_WAVE_PREFIX_SUM define) using AmdDxExtShaderIntrinsics_SwizzleU & AmdDxExtShaderIntrinsics_ReadlaneU to manually creating the prefix sum (which produces the correct values).
#include "ags_shader_intrinsics_dx11.hlsl"
RWBuffer<uint> dst : register(u0);
#define USE_WAVE_PREFIX_SUM
#define MAKE_MASK(XOR, OR, AND) (((XOR) << 10) | ((OR) << 5) | (AND))
[numthreads(8, 8, 1)] void main(uint3 groupId
: SV_GroupID, uint3 dispatchThreadId
: SV_DispatchThreadID, uint3 groupThreadId
: SV_GroupThreadID, uint groupIndex
: SV_GroupIndex) {
uint groupIdx = groupId.x * 8 * 8;
uint v0 = groupIndex;
#ifndef USE_WAVE_PREFIX_SUM
uint sum = v0;
uint value = 0;
value = AmdDxExtShaderIntrinsics_SwizzleU(sum, AmdDxExtShaderIntrinsicsSwizzle_SwapX1);
sum += (groupIndex & 1) == 0 ? 0 : value;
value = AmdDxExtShaderIntrinsics_SwizzleU(sum, MAKE_MASK(0x00, 0x01, 0x1C));
sum += (groupIndex & 2) == 0 ? 0 : value;
value = AmdDxExtShaderIntrinsics_SwizzleU(sum, MAKE_MASK(0x00, 0x03, 0x18));
sum += (groupIndex & 4) == 0 ? 0 : value;
value = AmdDxExtShaderIntrinsics_SwizzleU(sum, MAKE_MASK(0x00, 0x07, 0x10));
sum += (groupIndex & 8) == 0 ? 0 : value;
value = AmdDxExtShaderIntrinsics_SwizzleU(sum, MAKE_MASK(0x00, 0x0F, 0x00));
sum += (groupIndex & 16) == 0 ? 0 : value;
value = AmdDxExtShaderIntrinsics_ReadlaneU(sum, 31);
sum += (groupIndex & 32) == 0 ? 0 : value;
#else
uint sum = AmdDxExtShaderIntrinsics_WavePrefixSum(v0);
#endif
dst[groupIdx + groupIndex] = sum;
}