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-rw-r--r--src/compiler/glsl/lower_variable_index_to_cond_assign.cpp20
1 files changed, 20 insertions, 0 deletions
diff --git a/src/compiler/glsl/lower_variable_index_to_cond_assign.cpp b/src/compiler/glsl/lower_variable_index_to_cond_assign.cpp
index 278d5450bfb..fcb12d1b77d 100644
--- a/src/compiler/glsl/lower_variable_index_to_cond_assign.cpp
+++ b/src/compiler/glsl/lower_variable_index_to_cond_assign.cpp
@@ -385,6 +385,26 @@ public:
case ir_var_const_in:
return this->lower_temps;
+ case ir_var_system_value:
+ /* There are only a few system values that have array types:
+ *
+ * gl_TessLevelInner[]
+ * gl_TessLevelOuter[]
+ * gl_SampleMaskIn[]
+ *
+ * The tessellation factor arrays are lowered to vec4/vec2s
+ * by lower_tess_level() before this pass occurs, so we'll
+ * never see them here.
+ *
+ * The only remaining case is gl_SampleMaskIn[], which has
+ * a length of ceil(ctx->Const.MaxSamples / 32). Most hardware
+ * supports no more than 32 samples, in which case our lowering
+ * produces a single read of gl_SampleMaskIn[0]. Even with 64x
+ * MSAA, the array length is only 2, so the lowering is fairly
+ * efficient. Therefore, lower unconditionally.
+ */
+ return true;
+
case ir_var_shader_in:
/* The input array size is unknown at compiler time for non-patch
* inputs in TCS and TES. The arrays are sized to