For now linking is just removing unused varyings between stages.
shader-db results BDW:
total instructions in shared programs: 13198288 -> 13191693 (-0.05%)
instructions in affected programs: 48325 -> 41730 (-13.65%)
helped: 473
HURT: 0
total cycles in shared programs: 541184926 -> 541159260 (-0.00%)
cycles in affected programs: 213238 -> 187572 (-12.04%)
helped: 435
HURT: 8
---
src/mesa/drivers/dri/i965/brw_link.cpp | 48 ++++++++++++++++++++++++++++++++++
1 file changed, 48 insertions(+)
diff --git a/src/mesa/drivers/dri/i965/brw_link.cpp
b/src/mesa/drivers/dri/i965/brw_link.cpp
index 9f1634a5459..c4c89a0686e 100644
--- a/src/mesa/drivers/dri/i965/brw_link.cpp
+++ b/src/mesa/drivers/dri/i965/brw_link.cpp
@@ -252,6 +252,54 @@ brw_link_shader(struct gl_context *ctx, struct
gl_shader_program *shProg)
compiler->scalar_stage[stage]);
}
+ /* Determine first and last stage. */
+ unsigned first = MESA_SHADER_STAGES;
+ unsigned last = 0;
+ for (unsigned i = 0; i < MESA_SHADER_STAGES; i++) {
+ if (!shProg->_LinkedShaders[i])
+ continue;
+ if (first == MESA_SHADER_STAGES)
+ first = i;
+ last = i;
+ }
+
+ /* Linking the stages in the opposite order (from fragment to vertex)
+ * ensures that inter-shader outputs written to in an earlier stage
+ * are eliminated if they are (transitively) not used in a later
+ * stage.
+ */
+ if (first != last) {
+ int next = last;
+ for (int i = next - 1; i >= 0; i--) {
+ if (shProg->_LinkedShaders[i] == NULL)
+ continue;
+
+ nir_shader *producer = shProg->_LinkedShaders[i]->Program->nir;
+ nir_shader *consumer = shProg->_LinkedShaders[next]->Program->nir;
+
+
nir_remove_dead_variables(shProg->_LinkedShaders[next]->Program->nir,
+ nir_var_shader_in);
+ nir_remove_dead_variables(shProg->_LinkedShaders[i]->Program->nir,
+ nir_var_shader_out);
+ if (nir_remove_unused_varyings(producer, consumer)) {
+ nir_lower_global_vars_to_local(producer);
+ nir_lower_global_vars_to_local(consumer);
+
+ nir_variable_mode indirect_mask = (nir_variable_mode) 0;
+ if (compiler->glsl_compiler_options[i].EmitNoIndirectTemp)
+ indirect_mask = (nir_variable_mode) nir_var_local;
+
+ nir_lower_indirect_derefs(producer, indirect_mask);
+
+ const bool is_scalar = compiler->scalar_stage[producer->stage];
+ shProg->_LinkedShaders[i]->Program->nir =
+ brw_nir_optimize(producer, compiler, is_scalar);
+ }
+
+ next = i;
+ }
+ }
+
for (stage = 0; stage < ARRAY_SIZE(shProg->_LinkedShaders); stage++) {
struct gl_linked_shader *shader = shProg->_LinkedShaders[stage];
if (!shader)
--
2.13.5
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