GetAttributeAtVertex() doesn't work on function parameters

Description

When using an array member of a VS interpolant structure, GetAttributeAtVertex fails to compile.

Steps to Reproduce

// dxc.exe repro.hlsl /Tps_6_1 /EMainPS

cbuffer Globals : register (b0)
{
    int GIndex;
};

struct Interpolants
{
	float3 BaryWeights : SV_Barycentrics;
	nointerpolation float4 PackedTexCoords[1] : COLOR0;
	nointerpolation uint PrimitiveId : PRIMITIVE_ID;
};

float4 GetUV(Interpolants vs, int index)
{
	float4 a1 = GetAttributeAtVertex(vs.PackedTexCoords[index], 0);
	float4 a2 = GetAttributeAtVertex(vs.PackedTexCoords[index], 1);
	float4 a3 = GetAttributeAtVertex(vs.PackedTexCoords[index], 2);

	return a1 * vs.BaryWeights.x + a2 * vs.BaryWeights.y + a3 * vs.BaryWeights.z;
}

[RootSignature("CBV(b0)")]
float4 MainPS(Interpolants vs) : SV_Target0
{
    float4 x = GetUV(vs, 0); // FAIL
    return x;
}

Actual Behavior

gaav-repro.hlsl:19:14: error: attribute evaluation can only be done on values taken directly from inputs.
        float4 a3 = GetAttributeAtVertex(vs.PackedTexCoords[index], 2);
                    ^
gaav-repro.hlsl:18:14: error: attribute evaluation can only be done on values taken directly from inputs.
        float4 a2 = GetAttributeAtVertex(vs.PackedTexCoords[index], 1);
                    ^
gaav-repro.hlsl:17:14: error: attribute evaluation can only be done on values taken directly from inputs.
        float4 a1 = GetAttributeAtVertex(vs.PackedTexCoords[index], 0);
                    ^

Note that moving the GetAttributeAtVertex calls to be inside MainPS can compile successfully.

Environment

• DXC version dxcompiler.dll: 1.7 - 1.7.2308.7 (69e54e290); dxil.dll: 1.7(101.7.2308.12)
• Host Operating System Windows 11

Start by compiling the provided repro.hlsl with dxc.exe using /Tps_6_1 and /EMainPS, comparing GetUV(Interpolants vs, int index) with the working calls inside MainPS. Trace the compiler handling of GetAttributeAtVertex when its input is a function parameter and verify that the repro compiles successfully without the attribute-evaluation errors.