Arrays cast compiler error

HLSL compilers 5.1 and lower compiles this test without any type-cast errors. DXC returns error:
// Internal Compiler error: llvm::cast() argument of incompatible type!

run
dxc -T vs_6_0 test.hlsl

=========== test.hlsl ============

#define MAX_CLIPPINGPLANES_CASCADE_ 8

struct VSOUT
{
	float4 vPos:SV_Position;
	float4 afClipD[MAX_CLIPPINGPLANES_CASCADE_>>2]:SV_ClipDistance;
};

void castFunc(out float4 afClipD[MAX_CLIPPINGPLANES_CASCADE_>>2])
{
	[unroll]
	for (int n=0;n<MAX_CLIPPINGPLANES_CASCADE_;++n)
		((float[MAX_CLIPPINGPLANES_CASCADE_])afClipD)[n]=float(n*n);
}

VSOUT main(float4 pos:POSITION0)
{
	VSOUT ret;
	ret.vPos=1;
	castFunc(ret.afClipD);	
	return ret;
} 

Start by reproducing the issue with dxc -T vs_6_0 test.hlsl using the provided shader. Trace the compiler path handling the array cast and determine why it reaches the internal LLVM cast failure. Done means this input no longer reports an internal compiler error.