intel/fs: Emit MOV_DISPATCH_TO_FLAGS once for the centroid workaround

There's no reason for us to emit it a pile of times and then have a
whole pass to clean it up.  Just emit it once like we really want.

Reviewed-by: Matt Turner <mattst88@gmail.com>

src/intel/compiler/brw_fs.cpp

@@ -6211,44 +6211,6 @@ fs_visitor::calculate_register_pressure()
    }
 }
 
-/**
- * Look for repeated FS_OPCODE_MOV_DISPATCH_TO_FLAGS and drop the later ones.
- *
- * The needs_unlit_centroid_workaround ends up producing one of these per
- * channel of centroid input, so it's good to clean them up.
- *
- * An assumption here is that nothing ever modifies the dispatched pixels
- * value that FS_OPCODE_MOV_DISPATCH_TO_FLAGS reads from, but the hardware
- * dictates that anyway.
- */
-bool
-fs_visitor::opt_drop_redundant_mov_to_flags()
-{
-   bool flag_mov_found[4] = {false};
-   bool progress = false;
-
-   /* Instructions removed by this pass can only be added if this were true */
-   if (!devinfo->needs_unlit_centroid_workaround)
-      return false;
-
-   foreach_block_and_inst_safe(block, fs_inst, inst, cfg) {
-      if (inst->is_control_flow()) {
-         memset(flag_mov_found, 0, sizeof(flag_mov_found));
-      } else if (inst->opcode == FS_OPCODE_MOV_DISPATCH_TO_FLAGS) {
-         if (!flag_mov_found[inst->flag_subreg]) {
-            flag_mov_found[inst->flag_subreg] = true;
-         } else {
-            inst->remove(block);
-            progress = true;
-         }
-      } else if (inst->flags_written()) {
-         flag_mov_found[inst->flag_subreg] = false;
-      }
-   }
-
-   return progress;
-}
-
 void
 fs_visitor::optimize()
 {
@@ -6306,7 +6268,6 @@ fs_visitor::optimize()
    int iteration = 0;
    int pass_num = 0;
 
-   OPT(opt_drop_redundant_mov_to_flags);
    OPT(remove_extra_rounding_modes);
 
    do {

src/intel/compiler/brw_fs_visitor.cpp

@@ -263,24 +263,29 @@ fs_visitor::emit_interpolation_setup_gen6()
    abld.emit(SHADER_OPCODE_RCP, this->wpos_w, this->pixel_w);
 
    struct brw_wm_prog_data *wm_prog_data = brw_wm_prog_data(prog_data);
-   uint32_t centroid_modes = wm_prog_data->barycentric_interp_modes &
-      (1 << BRW_BARYCENTRIC_PERSPECTIVE_CENTROID |
-       1 << BRW_BARYCENTRIC_NONPERSPECTIVE_CENTROID);
 
    for (int i = 0; i < BRW_BARYCENTRIC_MODE_COUNT; ++i) {
       this->delta_xy[i] = fetch_payload_reg(
          bld, payload.barycentric_coord_reg[i], BRW_REGISTER_TYPE_F, 2);
+   }
 
-      if (devinfo->needs_unlit_centroid_workaround &&
+   uint32_t centroid_modes = wm_prog_data->barycentric_interp_modes &
-          (centroid_modes & (1 << i))) {
+      (1 << BRW_BARYCENTRIC_PERSPECTIVE_CENTROID |
-         const fs_reg &pixel_delta_xy = delta_xy[i - 1];
+       1 << BRW_BARYCENTRIC_NONPERSPECTIVE_CENTROID);
 
+   if (devinfo->needs_unlit_centroid_workaround && centroid_modes) {
       /* Get the pixel/sample mask into f0 so that we know which
        * pixels are lit.  Then, for each channel that is unlit,
        * replace the centroid data with non-centroid data.
        */
       bld.emit(FS_OPCODE_MOV_DISPATCH_TO_FLAGS);
 
+      for (int i = 0; i < BRW_BARYCENTRIC_MODE_COUNT; ++i) {
+         if (!(centroid_modes & (1 << i)))
+            continue;
+
+         const fs_reg &pixel_delta_xy = delta_xy[i - 1];
+
          for (unsigned q = 0; q < dispatch_width / 8; q++) {
             for (unsigned c = 0; c < 2; c++) {
                const unsigned idx = c + (q & 2) + (q & 1) * dispatch_width / 8;