[Mesa-dev] [PATCH 4/8] i965: call nir_lower_io_to_scalar() at link time for BDW and above

[Timothy Arceri]

This will allow dead components of varyings to be removed.

BDW shader-db results:

total instructions in shared programs: 13190730 -> 13108459 (-0.62%)
instructions in affected programs: 2110903 -> 2028632 (-3.90%)
helped: 14043
HURT: 486

total cycles in shared programs: 541148990 -> 540544072 (-0.11%)
cycles in affected programs: 290344296 -> 289739378 (-0.21%)
helped: 23418
HURT: 11623

total loops in shared programs: 3923 -> 3920 (-0.08%)
loops in affected programs: 3 -> 0
helped: 3
HURT: 0

total spills in shared programs: 85784 -> 85853 (0.08%)
spills in affected programs: 1374 -> 1443 (5.02%)
helped: 6
HURT: 15

total fills in shared programs: 88717 -> 88801 (0.09%)
fills in affected programs: 1719 -> 1803 (4.89%)
helped: 15
HURT: 9

LOST:   3
GAINED: 0

The fills/spills changes were all in the dolphin uber shaders.

I tested enabling this on IVB but the results went in the other
direction.
---
 src/mesa/drivers/dri/i965/brw_link.cpp | 35 ++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_link.cpp b/src/mesa/drivers/dri/i965/brw_link.cpp
index 7986bdf74c..fe2ad52ad1 100644
--- a/src/mesa/drivers/dri/i965/brw_link.cpp
+++ b/src/mesa/drivers/dri/i965/brw_link.cpp
@@ -221,20 +221,31 @@ extern "C" GLboolean
 brw_link_shader(struct gl_context *ctx, struct gl_shader_program *shProg)
 {
    struct brw_context *brw = brw_context(ctx);
    const struct brw_compiler *compiler = brw->screen->compiler;
    unsigned int stage;
    struct shader_info *infos[MESA_SHADER_STAGES] = { 0, };
 
    if (shProg->data->LinkStatus == linking_skipped)
       return GL_TRUE;
 
+   /* 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;
+   }
+
    for (stage = 0; stage < ARRAY_SIZE(shProg->_LinkedShaders); stage++) {
       struct gl_linked_shader *shader = shProg->_LinkedShaders[stage];
       if (!shader)
          continue;
 
       struct gl_program *prog = shader->Program;
       prog->Parameters = _mesa_new_parameter_list();
 
       process_glsl_ir(brw, shProg, shader);
 
@@ -248,31 +259,35 @@ brw_link_shader(struct gl_context *ctx, struct gl_shader_program *shProg)
 
       if (debug_enabled && shader->ir) {
          fprintf(stderr, "GLSL IR for native %s shader %d:\n",
                  _mesa_shader_stage_to_string(shader->Stage), shProg->Name);
          _mesa_print_ir(stderr, shader->ir, NULL);
          fprintf(stderr, "\n\n");
       }
 
       prog->nir = brw_create_nir(brw, shProg, prog, (gl_shader_stage) stage,
                                  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;
+      if (brw->screen->devinfo.gen >= 8) {
+         nir_variable_mode mask = (nir_variable_mode) 0;
+
+         if (stage != first)
+            mask = (nir_variable_mode)(mask | nir_var_shader_in);
+
+         if (stage != last)
+            mask = (nir_variable_mode)(mask | nir_var_shader_out);
+
+         nir_lower_io_to_scalar_early(prog->nir, mask);
+
+         prog->nir = brw_nir_optimize(prog->nir, compiler,
+                                      compiler->scalar_stage[stage]);
+      }
    }
 
    /* 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.
     *
     * TODO: Look into Shadow of Mordor regressions on HSW and enable this for
     * all platforms. See: https://bugs.freedesktop.org/show_bug.cgi?id=103537
     */
-- 
2.14.3