warning X4000: use of potentially uninitialized variable

HLSL compiler emit the error message "warning X4000: use of potentially uninitialized variable" with the following code:

float4 GetPixelColorFromRawImage(
    in ByteAddressBuffer Source,
    in uint2             SourceSize,
    in uint2             XY)
{
    // Check if within range
    if (any(XY >= SourceSize))
        return float4(0.5, 0.0, 0.0, 1.0);  // <<<==== WARNING HERE

    if (BytesPerPixel == 3) {
        // 24 bits RGB color image
        uint4 RGBA = GetPixelRGBAFromRawImage(Source, SourceSize, XY);
        return float4(RGBA.r / 256.0,
                      RGBA.g / 256.0,
                      RGBA.b / 256.0,
                      RGBA.a / 256.0);
    }
    else if (BytesPerPixel == 2) {
        // 16 bit grayscale image
        uint  Gray1 = GetPixel16BitGrayFromRawImage(Source, SourceSize, XY);
        uint  Gray2 = GetByteFromUInt(LUT16.Load(Gray1 & (~3)), Gray1 & 3);
        float Gray3 = (float)Gray2 / 256.0;
        return float4(Gray3, Gray3, Gray3, 1.0);
    }
    else {
        return float4(0.0, 0.0, 0.0, 1.0);
    }
}

I don't understand that warning. There is no variable at all used in the offending line!

Any help appreciated.

The compiler sometimes goes crazy with intermediate return calls, and gives errors where there should be none.

You can try a little workaround.

In the beginning of your method, define and instantiate a variable, then update it in the ifs and the return it.

float4 GetPixelColorFromRawImage(
    in ByteAddressBuffer Source,
    in uint2             SourceSize,
    in uint2             XY)
{
    float4 returnVar = float4(0.0, 0.0, 0.0, 0.0);
    // Check if within range
    if (any(XY >= SourceSize))
        returnVar = float4(0.5, 0.0, 0.0, 1.0);  

    if (BytesPerPixel == 3) {
        // 24 bits RGB color image
        uint4 RGBA = GetPixelRGBAFromRawImage(Source, SourceSize, XY);
        returnVar = float4(RGBA.r / 256.0,
                      RGBA.g / 256.0,
                      RGBA.b / 256.0,
                      RGBA.a / 256.0);
        }
    else if (BytesPerPixel == 2) {
        // 16 bit grayscale image
        uint  Gray1 = GetPixel16BitGrayFromRawImage(Source, SourceSize, XY);
        uint  Gray2 = GetByteFromUInt(LUT16.Load(Gray1 & (~3)), Gray1 & 3);
        float Gray3 = (float)Gray2 / 256.0;
        returnVar = float4(Gray3, Gray3, Gray3, 1.0);
        }
    else {
        returnVar = float4(0.0, 0.0, 0.0, 1.0);
        }
    return returnVar;
}