Bug Chaotic UI-Default.shader

The problems listed below are related to Unity 2019, 2020, 2021. I can't believe such a mess can survive for so long time.

Problem 1:
The maskUV variable in vertex shader is calculated but NEVER usued. Do you guys expect to rely on complier optimization?

Problem 2:
The pixelSize variable measures pixel size in clip-space which can be calculated on CPU only once. Why bother doing it thousands of times on GPU?

Problem 3:
The zw components of the output mask variable in vertex shader has nothing to do with the vertex attributes. What's the reason for calculating it in vertex shader instead of passing it in as a uniform?

Code (csharp):

1.            
2. v2f vert(appdata_t v)
3. {
4.     v2f OUT;
5.  
6.     // Part of the source code is omitted here.
7.  
8.     float4 vPosition = UnityObjectToClipPos(v.vertex);
9.     // Problem 2
10.     float2 pixelSize = vPosition.w;
11.     pixelSize /= float2(1, 1) * abs(mul((float2x2)UNITY_MATRIX_P, _ScreenParams.xy));
12.  
13.     float4 clampedRect = clamp(_ClipRect, -2e10, 2e10);
14.  
15.     // Problem 1
16.     float2 maskUV = (v.vertex.xy - clampedRect.xy) / (clampedRect.zw - clampedRect.xy);
17.  
18.     OUT.texcoord = TRANSFORM_TEX(v.texcoord.xy, _MainTex);
19.  
20.     // Problem 3
21.     OUT.mask = half4(v.vertex.xy * 2 - clampedRect.xy - clampedRect.zw, 0.25 / (0.25 * half2(_UIMaskSoftnessX, _UIMaskSoftnessY) + abs(pixelSize.xy)));
22.  
23.     // Part of the source code is omitted here.
24. }
25.