[Mesa-dev] [PATCH 4/4] ac/nir: only enable used channels when exporting parameters

[Samuel Pitoiset]

This allows us to generate, for example,
"exp param0 v0, off, off, off" if only the first channel is needed.

Not sure if this improves performance but it's worth trying.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
---
 src/amd/common/ac_nir_to_llvm.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/amd/common/ac_nir_to_llvm.c b/src/amd/common/ac_nir_to_llvm.c
index 94648232c8..9fa6773633 100644
--- a/src/amd/common/ac_nir_to_llvm.c
+++ b/src/amd/common/ac_nir_to_llvm.c
@@ -5990,11 +5990,11 @@ si_llvm_init_export_args(struct radv_shader_context *ctx,
 
 static void
 radv_export_param(struct radv_shader_context *ctx, unsigned index,
-		  LLVMValueRef *values)
+		  LLVMValueRef *values, unsigned enabled_channels)
 {
 	struct ac_export_args args;
 
-	si_llvm_init_export_args(ctx, values, 0xf,
+	si_llvm_init_export_args(ctx, values, enabled_channels,
 				 V_008DFC_SQ_EXP_PARAM + index, &args);
 	ac_build_export(&ctx->ac, &args);
 }
@@ -6154,7 +6154,23 @@ handle_vs_outputs_post(struct radv_shader_context *ctx,
 		for (unsigned j = 0; j < 4; j++)
 			values[j] = ac_to_float(&ctx->ac, radv_load_output(ctx, i, j));
 
-		radv_export_param(ctx, param_count, values);
+		unsigned output_usage_mask;
+
+		if (ctx->stage == MESA_SHADER_VERTEX &&
+		    !ctx->is_gs_copy_shader) {
+			output_usage_mask =
+				ctx->shader_info->info.vs.output_usage_mask[i];
+		} else if (ctx->stage == MESA_SHADER_TESS_EVAL) {
+			output_usage_mask =
+				ctx->shader_info->info.tes.output_usage_mask[i];
+		} else {
+			/* Enable all channels for the GS copy shader because
+			 * we don't know the output usage mask currently.
+			 */
+			output_usage_mask = 0xf;
+		}
+
+		radv_export_param(ctx, param_count, values, output_usage_mask);
 
 		outinfo->vs_output_param_offset[i] = param_count++;
 	}
@@ -6168,7 +6184,7 @@ handle_vs_outputs_post(struct radv_shader_context *ctx,
 		for (unsigned j = 1; j < 4; j++)
 			values[j] = ctx->ac.f32_0;
 
-		radv_export_param(ctx, param_count, values);
+		radv_export_param(ctx, param_count, values, 0xf);
 
 		outinfo->vs_output_param_offset[VARYING_SLOT_PRIMITIVE_ID] = param_count++;
 		outinfo->export_prim_id = true;
-- 
2.16.2