iris: Stall on the CPU and resolve predication during fast clears.

Only if the clear color/depth is changing. In those cases, it's hard to
keep track of the current clear color, and aux state of some layers,
when predication is enabled. So simplify everything by stalling on the
few cases where we would have a fast clear color change with
predication.

v2:
 - fix comment (Ken)
 - explicitly check for predicate state after resolving it (Ken)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/gallium/drivers/iris/iris_clear.c

@@ -201,6 +201,25 @@ fast_clear_color(struct iris_context *ice,
 
    color = convert_fast_clear_color(ice, res, color, swizzle);
 
+   if (memcmp(&res->aux.clear_color, &color, sizeof(color)) != 0) {
+      /* We decided that we are going to fast clear, and the color is
+       * changing. But if we have a predicate bit set, the predication
+       * affects whether we should clear or not, and if we shouldn't, we
+       * also shouldn't update the clear color.
+       *
+       * However, we can't simply predicate-update the clear color (the
+       * commands don't support that). And we would lose track of the
+       * color, preventing us from doing some optimizations later.
+       *
+       * Since changing the clear color when the predication bit is enabled
+       * is not something that should happen often, we stall on the CPU here
+       * to resolve the predication, and then proceed.
+       */
+      iris_resolve_conditional_render(ice);
+      if (ice->state.predicate == IRIS_PREDICATE_STATE_DONT_RENDER)
+         return;
+   }
+
    iris_resource_set_clear_color(ice, res, color);
 
    /* If the buffer is already in ISL_AUX_STATE_CLEAR, the clear
@@ -355,6 +374,27 @@ fast_clear_depth(struct iris_context *ice,
     * flags out of the HiZ buffer into the real depth buffer.
     */
    if (res->aux.clear_color.f32[0] != depth) {
+      /* We decided that we are going to fast clear, and the color is
+       * changing. But if we have a predicate bit set, the predication
+       * affects whether we should clear or not, and if we shouldn't, we
+       * also shouldn't update the clear color.
+       *
+       * However, we can't simply predicate-update the clear color (the
+       * commands don't support that). And we would lose track of the
+       * color, preventing us from doing some optimizations later.
+       *
+       * For depth clears, things are even more complicated, because here we
+       * resolve the other levels/layers if they have a different color than
+       * the current one. That resolve can be predicated, but we also set those
+       * layers as ISL_AUX_STATE_RESOLVED, and this can't be predicated.
+       * Keeping track of the aux state when predication is involved is just
+       * even more complex, so the easiest thing to do when the fast clear
+       * depth is changing is to stall on the CPU and resolve the predication.
+       */
+      iris_resolve_conditional_render(ice);
+      if (ice->state.predicate == IRIS_PREDICATE_STATE_DONT_RENDER)
+         return;
+
       for (unsigned res_level = 0; res_level < res->surf.levels; res_level++) {
          if (!(res->aux.has_hiz & (1 << res_level)))
             continue;