[Mesa-dev] [PATCH 01/21] 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.
---
 src/glsl/link_varyings.cpp | 39 ++++++++++++++++++++++++++++++++++++
 src/glsl/linker.cpp        | 50 ----------------------------------------------
 2 files changed, 39 insertions(+), 50 deletions(-)

diff --git a/src/glsl/link_varyings.cpp b/src/glsl/link_varyings.cpp
index 9f6467b..841f900 100644
--- a/src/glsl/link_varyings.cpp
+++ b/src/glsl/link_varyings.cpp
@@ -309,6 +309,41 @@ 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)
+{
+   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;
+      }
+   }
+
+   /* Eliminate code that is now dead due to unused inputs/outputs being
+    * demoted.
+    */
+   while (do_dead_code(sh->ir, false))
+      ;
+
+}
 
 /**
  * Initialize this object based on a string that was passed to
@@ -1639,10 +1674,14 @@ 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