ac/nir: only enable used channels when exporting parameters

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@gmail.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>

diff --git a/src/amd/common/ac_nir_to_llvm.c b/src/amd/common/ac_nir_to_llvm.c
index 83d5d19fb8248bcacc5a7eae910692e94ce0e4af..39d92ca0e0a9532e402e1406794bc1c881f1702a 100644 (file)
--- a/src/amd/common/ac_nir_to_llvm.c
+++ b/src/amd/common/ac_nir_to_llvm.c
@@ -5928,11 +5928,11 @@ 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);
 }
@@ -6092,7 +6092,23 @@ 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++;
        }
@@ -6106,7 +6122,7 @@ 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;