Internal error communicating with the shader compiler process...

I get this error when compiling the following shader targeting Android:

Code (CSharp):

1.  
2. Shader "Hidden/Highlighted/Blur"
3. {
4.     Properties
5.     {
6.         [HideInInspector] _MainTex ("", 2D) = "" {}
7.         [HideInInspector] _Intensity ("", Range (0.25,0.5)) = 0.3
8.     }
9.    
10.     SubShader
11.     {
12.         Pass
13.         {
14.             ZTest Always
15.             Cull Off
16.             ZWrite Off
17.             Lighting Off
18.             Fog { Mode Off }
19.            
20.             CGPROGRAM
21.             #pragma vertex vert
22.             #pragma fragment frag
23.             #pragma fragmentoption ARB_precision_hint_fastest
24.            
25.             #include "UnityCG.cginc"
26.            
27.             uniform sampler2D _MainTex;
28.             uniform half4 _MainTex_TexelSize;
29.            
30.             uniform half _HighlightingBlurOffset;
31.             uniform half _Intensity;
32.            
33.             struct v2f
34.             {
35.                 float4 pos : POSITION;
36.                 half2 uv[4] : TEXCOORD0;    // 8 to add straight directions
37.             };
38.            
39.             v2f vert (appdata_img v)
40.             {
41.                 // Shader code optimized for the Unity shader compiler
42.                 v2f o;
43.                 o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
44.                 half2 offs = _HighlightingBlurOffset * _MainTex_TexelSize.xy;
45.                
46.                 // Diagonal directions
47.                 o.uv[0].x = v.texcoord.x - offs.x;
48.                 o.uv[0].y = v.texcoord.y - offs.y;
49.                
50.                 o.uv[1].x = v.texcoord.x + offs.x;
51.                 o.uv[1].y = v.texcoord.y - offs.y;
52.                
53.                 o.uv[2].x = v.texcoord.x + offs.x;
54.                 o.uv[2].y = v.texcoord.y + offs.y;
55.                
56.                 o.uv[3].x = v.texcoord.x - offs.x;
57.                 o.uv[3].y = v.texcoord.y + offs.y;
58.                
59.                 /*
60.                 // Straight directions
61.                 o.uv[4].x = v.texcoord.x - offs.x;
62.                 o.uv[4].y = v.texcoord.y;
63.                
64.                 o.uv[5].x = v.texcoord.x + offs.x;
65.                 o.uv[5].y = v.texcoord.y;
66.                
67.                 o.uv[6].x = v.texcoord.x;
68.                 o.uv[6].y = v.texcoord.y - offs.y;
69.                
70.                 o.uv[7].x = v.texcoord.x;
71.                 o.uv[7].y = v.texcoord.y + offs.y;
72.                 */
73.                
74.                 return o;
75.             }
76.            
77.             half4 frag(v2f i) : COLOR
78.             {
79.                 int start = 0;
80.                 int end = 4;
81.                
82.                 half4 color1 = tex2D(_MainTex, i.uv[start]);
83.                 fixed4 color2;
84.                 for (int n = start + 1; n < end; n++)
85.                 {
86.                     color2 = tex2D(_MainTex, i.uv[n]);
87.                     color1.rgb = max(color1.rgb, color2.rgb);
88.                     color1.a += color2.a;
89.                 }
90.                
91.                 color1.a *= _Intensity;
92.                 return color1;
93.             }
94.             ENDCG
95.         }
96.     }
97.    
98.     Fallback off
99. }
100.  

Debug Error!

Tools64\UnityShaderCompiler.exe

R6010
-abort() has been called


I'm using Unity 5.1.0f3

Is this a bug?

 

Yes, it is.. I've experienced this as well with a compute shader. For some reason, some loops crash it... while almost identical ones don't. I suspect it somehow gets stuck in an infinite loop while parsing the code.
Either way, in your case the loop can be easily unrolled. I don't know why, but the HLSL compiler does not want to unroll this loop by default. So remember to always mark loops that you want to get unrolled explicitly with the [unroll] attribute, which should improve the performance in this case and hopefully get rid of the crash on compile.

 

Thanks I'll use that in the future. I've since updated to version 5.1.1p3 and this problem is fixed in that version.