anv: Avoid resolves incurred by fast depth clears

Signed-off-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/intel/vulkan/anv_blorp.c

@@ -1265,6 +1265,12 @@ anv_cmd_buffer_clear_subpass(struct anv_cmd_buffer *cmd_buffer)
                                            render_area.offset.y +
                                            render_area.extent.height)) {
                clear_with_hiz = false;
+            } else if (clear_att.clearValue.depthStencil.depth !=
+                       ANV_HZ_FC_VAL) {
+               /* Don't enable fast depth clears for any color not equal to
+                * ANV_HZ_FC_VAL.
+                */
+               clear_with_hiz = false;
             }
          }
 
@@ -1636,8 +1642,7 @@ anv_gen8_hiz_op_resolve(struct anv_cmd_buffer *cmd_buffer,
    };
    surf.aux_usage = ISL_AUX_USAGE_HIZ;
 
-   surf.clear_color.u32[0] = (uint32_t)
-      cmd_state->attachments[ds].clear_value.depthStencil.depth;
+   surf.clear_color.u32[0] = (uint32_t) ANV_HZ_FC_VAL;
 
    blorp_gen6_hiz_op(&batch, &surf, 0, 0, op);
    blorp_batch_finish(&batch);

src/intel/vulkan/anv_private.h

@@ -72,6 +72,21 @@ struct gen_l3_config;
 extern "C" {
 #endif
 
+/* Allowing different clear colors requires us to perform a depth resolve at
+ * the end of certain render passes. This is because while slow clears store
+ * the clear color in the HiZ buffer, fast clears (without a resolve) don't.
+ * See the PRMs for examples describing when additional resolves would be
+ * necessary. To enable fast clears without requiring extra resolves, we set
+ * the clear value to a globally-defined one. We could allow different values
+ * if the user doesn't expect coherent data during or after a render passes
+ * (VK_ATTACHMENT_STORE_OP_DONT_CARE), but such users (aside from the CTS)
+ * don't seem to exist yet. In almost all Vulkan applications tested thus far,
+ * 1.0f seems to be the only value used. The only application that doesn't set
+ * this value does so through the usage of an seemingly uninitialized clear
+ * value.
+ */
+#define ANV_HZ_FC_VAL 1.0f
+
 #define MAX_VBS         32
 #define MAX_SETS         8
 #define MAX_RTS          8

src/intel/vulkan/genX_cmd_buffer.c

@@ -2283,10 +2283,7 @@ cmd_buffer_emit_depth_stencil(struct anv_cmd_buffer *cmd_buffer)
    anv_batch_emit(&cmd_buffer->batch, GENX(3DSTATE_CLEAR_PARAMS), cp) {
       if (has_hiz) {
          cp.DepthClearValueValid = true;
-         const uint32_t ds =
-            cmd_buffer->state.subpass->depth_stencil_attachment;
-         cp.DepthClearValue =
-            cmd_buffer->state.attachments[ds].clear_value.depthStencil.depth;
+         cp.DepthClearValue = ANV_HZ_FC_VAL;
       }
    }
 }