vkd3d: Add a macro to mark unreachable code.

This should silence warnings about some branches non returning any value
without requiring additional "return 0" statement or similar.

Also, in theory this might enable to compiler to optimize the program
a little bit more, though that's unlikely to have any measurable effect.

libs/vkd3d-shader/hlsl_sm4.c

@@ -279,8 +279,7 @@ static D3D_SHADER_VARIABLE_CLASS sm4_class(const struct hlsl_type *type)
             return D3D_SVC_VECTOR;
         default:
             ERR("Invalid class %#x.\n", type->type);
-            assert(0);
-            return 0;
+            vkd3d_unreachable();
     }
 }
 
@@ -313,7 +312,7 @@ static D3D_SHADER_VARIABLE_TYPE sm4_base_type(const struct hlsl_type *type)
                 case HLSL_SAMPLER_DIM_GENERIC:
                     return D3D_SVT_SAMPLER;
                 default:
-                    assert(0);
+                    vkd3d_unreachable();
             }
             break;
         case HLSL_TYPE_STRING:
@@ -332,7 +331,7 @@ static D3D_SHADER_VARIABLE_TYPE sm4_base_type(const struct hlsl_type *type)
                 case HLSL_SAMPLER_DIM_GENERIC:
                     return D3D_SVT_TEXTURE;
                 default:
-                    assert(0);
+                    vkd3d_unreachable();
             }
             break;
         case HLSL_TYPE_UINT:
@@ -342,10 +341,8 @@ static D3D_SHADER_VARIABLE_TYPE sm4_base_type(const struct hlsl_type *type)
         case HLSL_TYPE_VOID:
             return D3D_SVT_VOID;
         default:
-            assert(0);
+            vkd3d_unreachable();
     }
-    assert(0);
-    return 0;
 }
 
 static void write_sm4_type(struct hlsl_ctx *ctx, struct vkd3d_bytecode_buffer *buffer, struct hlsl_type *type)
@@ -414,8 +411,7 @@ static D3D_SHADER_INPUT_TYPE sm4_resource_type(const struct hlsl_type *type)
         case HLSL_TYPE_TEXTURE:
             return D3D_SIT_TEXTURE;
         default:
-            assert(0);
-            return 0;
+            vkd3d_unreachable();
     }
 }
 
@@ -439,8 +435,7 @@ static D3D_RESOURCE_RETURN_TYPE sm4_resource_format(const struct hlsl_type *type
             return D3D_RETURN_TYPE_UINT;
 
         default:
-            assert(0);
-            return 0;
+            vkd3d_unreachable();
     }
 }
 
@@ -467,8 +462,7 @@ static D3D_SRV_DIMENSION sm4_rdef_resource_dimension(const struct hlsl_type *typ
         case HLSL_SAMPLER_DIM_CUBEARRAY:
             return D3D_SRV_DIMENSION_TEXTURECUBEARRAY;
         default:
-            assert(0);
-            return D3D_SRV_DIMENSION_UNKNOWN;
+            vkd3d_unreachable();
     }
 }
 
@@ -764,8 +758,7 @@ static enum vkd3d_sm4_resource_type sm4_resource_dimension(const struct hlsl_typ
         case HLSL_SAMPLER_DIM_CUBEARRAY:
             return VKD3D_SM4_RESOURCE_TEXTURE_CUBEARRAY;
         default:
-            assert(0);
-            return 0;
+            vkd3d_unreachable();
     }
 }
 
@@ -800,8 +793,7 @@ static uint32_t sm4_encode_instruction_modifier(const struct sm4_instruction_mod
             break;
 
         default:
-            assert(0);
-            break;
+            vkd3d_unreachable();
     }
 
     return word;
@@ -1528,7 +1520,7 @@ static void write_sm4_cast(struct hlsl_ctx *ctx,
                     break;
 
                 default:
-                    assert(0);
+                    vkd3d_unreachable();
             }
             break;
 
@@ -1554,7 +1546,7 @@ static void write_sm4_cast(struct hlsl_ctx *ctx,
                     break;
 
                 default:
-                    assert(0);
+                    vkd3d_unreachable();
             }
             break;
 
@@ -1580,7 +1572,7 @@ static void write_sm4_cast(struct hlsl_ctx *ctx,
                     break;
 
                 default:
-                    assert(0);
+                    vkd3d_unreachable();
             }
             break;
 
@@ -1594,11 +1586,8 @@ static void write_sm4_cast(struct hlsl_ctx *ctx,
 
         case HLSL_TYPE_BOOL:
             /* Casts to bool should have already been lowered. */
-            assert(0);
-            break;
-
         default:
-            assert(0);
+            vkd3d_unreachable();
     }
 }
 
@@ -1754,11 +1743,8 @@ static void write_sm4_expr(struct hlsl_ctx *ctx,
                             break;
 
                         case 1:
-                            assert(0);
-                            break;
-
                         default:
-                            assert(0);
+                            vkd3d_unreachable();
                     }
                     break;