[Mesa-dev] [PATCH 4/5] radeonsi: handle ignored LAYER and VIEWPORT_INDEX writes

[Nicolai Hähnle]

From: Nicolai Hähnle <nicolai.haehnle at amd.com>

---
 src/gallium/drivers/radeonsi/si_shader.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/gallium/drivers/radeonsi/si_shader.c b/src/gallium/drivers/radeonsi/si_shader.c
index 669fb3e..5b30ace 100644
--- a/src/gallium/drivers/radeonsi/si_shader.c
+++ b/src/gallium/drivers/radeonsi/si_shader.c
@@ -2679,20 +2679,40 @@ static void si_llvm_emit_ls_epilogue(struct lp_build_tgsi_context *bld_base)
 		unpack_param(ctx, SI_PARAM_VS_STATE_BITS, 24, 8);
 	LLVMValueRef base_dw_addr = LLVMBuildMul(gallivm->builder, vertex_id,
 						 vertex_dw_stride, "");
 
 	/* Write outputs to LDS. The next shader (TCS aka HS) will read
 	 * its inputs from it. */
 	for (i = 0; i < info->num_outputs; i++) {
 		LLVMValueRef *out_ptr = ctx->outputs[i];
 		unsigned name = info->output_semantic_name[i];
 		unsigned index = info->output_semantic_index[i];
+
+		/* The ARB_shader_viewport_layer_array spec contains the
+		 * following issue:
+		 *
+		 *    2) What happens if gl_ViewportIndex or gl_Layer is
+		 *    written in the vertex shader and a geometry shader is
+		 *    present?
+		 *
+		 *    RESOLVED: The value written by the last vertex processing
+		 *    stage is used. If the last vertex processing stage
+		 *    (vertex, tessellation evaluation or geometry) does not
+		 *    statically assign to gl_ViewportIndex or gl_Layer, index
+		 *    or layer zero is assumed.
+		 *
+		 * So writes to those outputs in VS-as-LS are simply ignored.
+		 */
+		if (name == TGSI_SEMANTIC_LAYER ||
+		    name == TGSI_SEMANTIC_VIEWPORT_INDEX)
+			continue;
+
 		int param = si_shader_io_get_unique_index(name, index);
 		LLVMValueRef dw_addr = LLVMBuildAdd(gallivm->builder, base_dw_addr,
 					LLVMConstInt(ctx->i32, param * 4, 0), "");
 
 		for (chan = 0; chan < 4; chan++) {
 			lds_store(bld_base, chan, dw_addr,
 				  LLVMBuildLoad(gallivm->builder, out_ptr[chan], ""));
 		}
 	}
 }
-- 
2.9.3