Internal compiler error on nested switch statement when targeting SM 6.6

[mcbouterse]

Hi, I have encountered an internal compiler error when using nested switch statements. The compiler gives me the following error:

Internal compiler error: access violation. Attempted to read from address 0xFFFFFFFFFFFFFFE8

Here is a minimal shader that reproduces the issue:

static const int kAttribute1 = 0;
static const int kAttribute2 = 1;

struct PackInfo
{
	bool m_fPackAttr1_0;
	bool m_fPackAttr1_1;
	bool m_fPackAttr1_2;
	bool m_fPackAttr2_0;
	bool m_fPackAttr2_1;
	bool m_fPackAttr2_2;
};

bool IsPacked(int attr, int layer, PackInfo pckinf)
{
	switch (attr)
	{
	case kAttribute1:
		switch (layer)
		{
		case 0:
			return pckinf.m_fPackAttr1_0;
		case 1:
			return pckinf.m_fPackAttr1_1;
		case 2:
			return pckinf.m_fPackAttr1_2;
		default:
			return false;
		}

	case kAttribute2:
		switch (layer)
		{
		case 0:
			return pckinf.m_fPackAttr2_0;
		case 1:
			return pckinf.m_fPackAttr2_1;
		case 2:
			return pckinf.m_fPackAttr2_2;
		default:
			return false;
		}

	default:
		return false;
	}
}

int GetChannelCount(int attr)
{
	switch (attr)
	{
	case kAttribute1:	return 2;
	case kAttribute2:	return 1;
	default:
		return 1;
	}
}

float ExtractPackedValue(int attr, int layer, float4 packed, PackInfo pckinf)
{
	int packIndex = 0;

	for (int i = 0; i < attr; i++)
	{
		if (IsPacked(i, layer, pckinf))
			packIndex += GetChannelCount(i);
	}

	return packed[packIndex];
}

RWBuffer<float> out_buf;
StructuredBuffer<PackInfo> pckinf_buf;

[numthreads(8,8,1)]
void main()
{
	PackInfo pckinf = pckinf_buf[0];
	float4 packedA = float4(0,0,0,0);
	out_buf[0] = ExtractPackedValue(kAttribute2, 1, packedA, pckinf);
}

When compiling with /Tcs_6_6. Targeting a lower shader model, I don't get this issue. I hope this is enough information to look into this.

[mcbouterse]

I should probably add that this issue was encountered using the July 2022 release of DXC.

[pow2clk]

Thanks for the report @mcbouterse!

We'll look into this. In the meantime, you can work around this issue by using the -disable-lifetime-markers flag