[Mesa-dev] [PATCH] st/glsl: refactor st_link_nir()

[Timothy Arceri]

The functional change here is moving the nir_lower_io_to_scalar_early()
calls inside st_nir_link_shaders() and moving the st_nir_opts() call
after the call to nir_lower_io_arrays_to_elements().

This fixes a bug with the following piglit test due to the current code
not cleaning up dead code after we lower arrays. This was causing an
assert in the new duplicate varyings link time opt introduced in
70be9afccb23.

tests/spec/glsl-1.10/execution/vsfs-unused-array-member.shader_test

Moving the nir_lower_io_to_scalar_early() calls also allows us to tidy
up the code a little and merge some loops.
---
 src/mesa/state_tracker/st_glsl_to_nir.cpp | 52 +++++++----------------
 1 file changed, 16 insertions(+), 36 deletions(-)

diff --git a/src/mesa/state_tracker/st_glsl_to_nir.cpp b/src/mesa/state_tracker/st_glsl_to_nir.cpp
index af83a341e9..cbce4661e9 100644
--- a/src/mesa/state_tracker/st_glsl_to_nir.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_nir.cpp
@@ -586,8 +586,16 @@ st_nir_get_mesa_program(struct gl_context *ctx,
 static void
 st_nir_link_shaders(nir_shader **producer, nir_shader **consumer, bool scalar)
 {
+   if (scalar) {
+      NIR_PASS_V(*producer, nir_lower_io_to_scalar_early, nir_var_shader_out);
+      NIR_PASS_V(*consumer, nir_lower_io_to_scalar_early, nir_var_shader_in);
+   }
+
    nir_lower_io_arrays_to_elements(*producer, *consumer);
 
+   st_nir_opts(*producer, scalar);
+   st_nir_opts(*consumer, scalar);
+
    if (nir_link_opt_varyings(*producer, *consumer))
       st_nir_opts(*consumer, scalar);
 
@@ -663,51 +671,23 @@ st_link_nir(struct gl_context *ctx,
    struct pipe_screen *screen = st->pipe->screen;
    bool is_scalar[MESA_SHADER_STAGES];
 
-   /* Determine scalar property of each shader stage */
+   unsigned last_stage = 0;
    for (unsigned i = 0; i < MESA_SHADER_STAGES; i++) {
       struct gl_linked_shader *shader = shader_program->_LinkedShaders[i];
-      enum pipe_shader_type type;
-
       if (shader == NULL)
          continue;
 
-      type = pipe_shader_type_from_mesa(shader->Stage);
-      is_scalar[i] = screen->get_shader_param(screen, type, PIPE_SHADER_CAP_SCALAR_ISA);
-   }
-
-   /* Determine first and last stage. */
-   unsigned first = MESA_SHADER_STAGES;
-   unsigned last = 0;
-   for (unsigned i = 0; i < MESA_SHADER_STAGES; i++) {
-      if (!shader_program->_LinkedShaders[i])
-         continue;
-      if (first == MESA_SHADER_STAGES)
-         first = i;
-      last = i;
-   }
-
-   for (unsigned i = 0; i < MESA_SHADER_STAGES; i++) {
-      struct gl_linked_shader *shader = shader_program->_LinkedShaders[i];
-      if (shader == NULL)
-         continue;
+      /* Determine scalar property of each shader stage */
+      enum pipe_shader_type type = pipe_shader_type_from_mesa(shader->Stage);
+      is_scalar[i] = screen->get_shader_param(screen, type,
+                                              PIPE_SHADER_CAP_SCALAR_ISA);
 
       st_nir_get_mesa_program(ctx, shader_program, shader);
-
-      nir_variable_mode mask = (nir_variable_mode) 0;
-      if (i != first)
-         mask = (nir_variable_mode)(mask | nir_var_shader_in);
-
-      if (i != last)
-         mask = (nir_variable_mode)(mask | nir_var_shader_out);
-
-      nir_shader *nir = shader->Program->nir;
+      last_stage = i;
 
       if (is_scalar[i]) {
-         NIR_PASS_V(nir, nir_lower_io_to_scalar_early, mask);
-         NIR_PASS_V(nir, nir_lower_load_const_to_scalar);
+         NIR_PASS_V(shader->Program->nir, nir_lower_load_const_to_scalar);
       }
-
-      st_nir_opts(nir, is_scalar[i]);
    }
 
    /* Linking the stages in the opposite order (from fragment to vertex)
@@ -715,7 +695,7 @@ st_link_nir(struct gl_context *ctx,
     * are eliminated if they are (transitively) not used in a later
     * stage.
     */
-   int next = last;
+   int next = last_stage;
    for (int i = next - 1; i >= 0; i--) {
       struct gl_linked_shader *shader = shader_program->_LinkedShaders[i];
       if (shader == NULL)
-- 
2.20.1