[Mesa-dev] [PATCH] glsl: remove unused varyings before packing them

[Timothy Arceri]

Previously we would pack varyings before trying to remove them, this
meant the varying would only be removed if all the varyings in the packed
location were unused or if the varying wasn't packed.

This change makes no difference to the public shader-db.
---
 src/glsl/link_varyings.cpp | 43 +++++++++++++++++++++++++++++++++++++++
 src/glsl/linker.cpp        | 50 ----------------------------------------------
 2 files changed, 43 insertions(+), 50 deletions(-)

diff --git a/src/glsl/link_varyings.cpp b/src/glsl/link_varyings.cpp
index 9f6467b..d5c1b20 100644
--- a/src/glsl/link_varyings.cpp
+++ b/src/glsl/link_varyings.cpp
@@ -309,6 +309,45 @@ cross_validate_outputs_to_inputs(struct gl_shader_program *prog,
    }
 }
 
+/**
+ * Demote shader inputs and outputs that are not used in other stages, and
+ * remove them via dead code elimination.
+ */
+void
+remove_unused_shader_inputs_and_outputs(struct gl_shader_program *prog,
+                                        gl_shader *sh,
+                                        enum ir_variable_mode mode)
+{
+   bool var_demoted = false;
+
+   if (prog->SeparateShader)
+      return;
+
+   foreach_in_list(ir_instruction, node, sh->ir) {
+      ir_variable *const var = node->as_variable();
+
+      if ((var == NULL) || (var->data.mode != int(mode)))
+         continue;
+
+      /* A shader 'in' or 'out' variable is only really an input or output if
+       * its value is used by other shader stages. This will cause the
+       * variable to have a location assigned.
+       */
+      if (var->data.is_unmatched_generic_inout) {
+         assert(var->data.mode != ir_var_temporary);
+         var->data.mode = ir_var_auto;
+         var_demoted = true;
+      }
+   }
+
+   /* Eliminate code that is now dead due to unused inputs/outputs being
+    * demoted.
+    */
+   if (var_demoted) {
+      while (do_dead_code(sh->ir, false))
+         ;
+   }
+}
 
 /**
  * Initialize this object based on a string that was passed to
@@ -1639,10 +1678,14 @@ assign_varying_locations(struct gl_context *ctx,
 
    if (!disable_varying_packing) {
       if (producer) {
+         remove_unused_shader_inputs_and_outputs(prog, producer,
+                                                 ir_var_shader_out);
          lower_packed_varyings(mem_ctx, slots_used, ir_var_shader_out,
                                0, producer);
       }
       if (consumer) {
+         remove_unused_shader_inputs_and_outputs(prog, consumer,
+                                                 ir_var_shader_in);
          lower_packed_varyings(mem_ctx, slots_used, ir_var_shader_in,
                                consumer_vertices, consumer);
       }
diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index ff22b3d..17450b8 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -2723,30 +2723,6 @@ match_explicit_outputs_to_inputs(struct gl_shader_program *prog,
 }
 
 /**
- * Demote shader inputs and outputs that are not used in other stages
- */
-void
-demote_shader_inputs_and_outputs(gl_shader *sh, enum ir_variable_mode mode)
-{
-   foreach_in_list(ir_instruction, node, sh->ir) {
-      ir_variable *const var = node->as_variable();
-
-      if ((var == NULL) || (var->data.mode != int(mode)))
-	 continue;
-
-      /* A shader 'in' or 'out' variable is only really an input or output if
-       * its value is used by other shader stages.  This will cause the variable
-       * to have a location assigned.
-       */
-      if (var->data.is_unmatched_generic_inout) {
-         assert(var->data.mode != ir_var_temporary);
-	 var->data.mode = ir_var_auto;
-      }
-   }
-}
-
-
-/**
  * Store the gl_FragDepth layout in the gl_shader_program struct.
  */
 static void
@@ -4442,15 +4418,6 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
 
       do_dead_builtin_varyings(ctx, sh, NULL,
                                num_tfeedback_decls, tfeedback_decls);
-
-      if (!prog->SeparateShader) {
-         demote_shader_inputs_and_outputs(sh, ir_var_shader_out);
-         /* Eliminate code that is now dead due to unused outputs being
-          * demoted.
-          */
-         while (do_dead_code(sh->ir, false))
-            ;
-      }
    }
    else if (first == MESA_SHADER_FRAGMENT) {
       /* If the program only contains a fragment shader...
@@ -4467,13 +4434,6 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
                                        0 /* num_tfeedback_decls */,
                                        NULL /* tfeedback_decls */))
             goto done;
-      } else {
-         demote_shader_inputs_and_outputs(sh, ir_var_shader_in);
-         /* Eliminate code that is now dead due to unused inputs being
-          * demoted.
-          */
-         while (do_dead_code(sh->ir, false))
-            ;
       }
    }
 
@@ -4494,16 +4454,6 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
                 next == MESA_SHADER_FRAGMENT ? num_tfeedback_decls : 0,
                 tfeedback_decls);
 
-      demote_shader_inputs_and_outputs(sh_i, ir_var_shader_out);
-      demote_shader_inputs_and_outputs(sh_next, ir_var_shader_in);
-
-      /* Eliminate code that is now dead due to unused outputs being demoted.
-       */
-      while (do_dead_code(sh_i->ir, false))
-         ;
-      while (do_dead_code(sh_next->ir, false))
-         ;
-
       /* This must be done after all dead varyings are eliminated. */
       if (!check_against_output_limit(ctx, prog, sh_i))
          goto done;
-- 
2.4.3