glsl/linker: eliminate unused and set-but-unused built-in varyings

This eliminates built-in varyings such as gl_Color, gl_SecondaryColor,
gl_TexCoord, and gl_FogFragCoord if they are unused by the next stage or
not written at all (e.g. gl_TexCoord elements). The gl_TexCoord array is
broken down into separate vec4s if needed.

v2: - use a switch statement in varying_info_visitor::visit(ir_variable*)
    - use snprintf
    - disable the optimization for GLES2

Reviewed-by: Ian Romanick <[email protected]>

1 files changed, 11 insertions, 2 deletions

diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index 6d7357820c9..ba97ade25e0 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -1887,6 +1887,9 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
             goto done;
       }
 
+      do_dead_builtin_varyings(ctx, sh->ir, NULL,
+                               num_tfeedback_decls, tfeedback_decls);
+
       demote_shader_inputs_and_outputs(sh, ir_var_shader_out);
 
       /* Eliminate code that is now dead due to unused outputs being demoted.
@@ -1895,11 +1898,13 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
          ;
    }
    else if (first == MESA_SHADER_FRAGMENT) {
-      /* If the program only contains a fragment shader, just demote
-       * user-defined varyings.
+      /* If the program only contains a fragment shader...
        */
       gl_shader *const sh = prog->_LinkedShaders[first];
 
+      do_dead_builtin_varyings(ctx, NULL, sh->ir,
+                               num_tfeedback_decls, tfeedback_decls);
+
       demote_shader_inputs_and_outputs(sh, ir_var_shader_in);
 
       while (do_dead_code(sh->ir, false))
@@ -1919,6 +1924,10 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
                 tfeedback_decls))
          goto done;
 
+      do_dead_builtin_varyings(ctx, sh_i->ir, sh_next->ir,
+                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);