Attributes read via `GetAttributeAtVertex` aren't counted as read in the signature

Description

float4 VCMain(
    nointerpolation float4 Color:COLOR0)
    : SV_TARGET0 
{
#ifdef USE_GET_ATTRIBUTE_AT_VERTEX
    return GetAttributeAtVertex(Color,0);
#endif
    return Color;
}

Steps to Reproduce

With above shader the generated assembly shows the input signature. When compiled without extra defines, it reports:

; Input signature:
;
; Name                 Index   Mask Register SysValue  Format   Used
; -------------------- ----- ------ -------- -------- ------- ------
; COLOR                    0   xyzw        0     NONE   float   xyzw

When compiled with -DUSE_GET_ATTRIBUTE_AT_VERTEX it shows:

; Input signature:
;
; Name                 Index   Mask Register SysValue  Format   Used
; -------------------- ----- ------ -------- -------- ------- ------
; COLOR                    0   xyzw        0     NONE   float       

My expectation here is that COLOR would show as used in both cases.

Environment

• dxcompiler.dll: 1.7 - 1.7.2212.40 (e043f4a12); dxil.dll: 1.7(101.7.2212.36)
• Windows 11

Start with the VCMain shader and reproduce the generated input signatures with and without USE_GET_ATTRIBUTE_AT_VERTEX. Trace how GetAttributeAtVertex contributes to signature usage, then verify that COLOR is marked used in both assembly outputs. The payload does not name a source file or test.