asahi,hk: optimize no-op FS

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36399>

src/asahi/lib/agx_linker.c

@@ -209,6 +209,7 @@ agx_fast_link(struct agx_linked_shader *linked, struct agx_device *dev,
       if (tag_write_disable) {
          reads_tib = false;
          writes_sample_mask = false;
+         linked->no_op = true;
       }
 
       agx_pack(&linked->fragment_control, FRAGMENT_CONTROL, cfg) {

src/asahi/lib/agx_linker.h

@@ -26,6 +26,9 @@ struct agx_linked_shader {
     */
    bool uses_txf;
 
+   /* Whether the program is a no-op and can be skipped. */
+   bool no_op;
+
    /* Coefficient register bindings */
    struct agx_varyings_fs cf;
 

src/asahi/vulkan/hk_cmd_draw.c

@@ -2374,6 +2374,8 @@ hk_flush_ppp_state(struct hk_cmd_buffer *cmd, struct hk_cs *cs, uint8_t **out)
       .viewport_count = 1, /* irrelevant */
    };
 
+   dirty.fragment_shader &= !linked_fs->b.no_op;
+
    /* Calculate the update size. If it equals the header, there is nothing to
     * update so early-exit.
     */

src/gallium/drivers/asahi/agx_state.c

@@ -3561,7 +3561,8 @@ agx_encode_state(struct agx_batch *batch, uint8_t *out)
       .cull = IS_DIRTY(RS),
       .cull_2 = varyings_dirty,
       .fragment_shader =
-         IS_DIRTY(FS) || varyings_dirty || IS_DIRTY(SAMPLE_MASK),
+         (IS_DIRTY(FS) || varyings_dirty || IS_DIRTY(SAMPLE_MASK)) &&
+         !ctx->linked.fs->no_op,
       .occlusion_query = IS_DIRTY(QUERY),
       .output_size = IS_DIRTY(VS_PROG),
       .viewport_count = 1, /* irrelevant */