intel: Avoid no-op calls to anv_image_clear_color

Whenever we execute a fast-clear due to LOAD_OP_CLEAR, we decrease the
number of layers to clear by one. We then enter the slow clear function
and possibly exit without clearing if the layer count is zero.
Unfortunately, we've already compiled the shader for slow clears by the
time we exit. Skip the slow clear function if there are no layers to
clear.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31167>

src/intel/blorp/blorp_clear.c

@@ -608,6 +608,7 @@ blorp_clear(struct blorp_batch *batch,
    if (!compute && !blorp_ensure_sf_program(batch, &params))
       return;
 
+   assert(num_layers > 0);
    while (num_layers > 0) {
       blorp_surface_info_init(batch, &params.dst, surf, level,
                                   start_layer, format, true);
@@ -834,6 +835,7 @@ blorp_clear_depth_stencil(struct blorp_batch *batch,
                           uint8_t stencil_mask, uint8_t stencil_value)
 {
    assert((batch->flags & BLORP_BATCH_USE_COMPUTE) == 0);
+   assert(num_layers > 0);
 
    if (!clear_depth && blorp_clear_stencil_as_rgba(batch, stencil, level,
                                                    start_layer, num_layers,

src/intel/vulkan/anv_blorp.c

@@ -2310,6 +2310,7 @@ anv_image_clear_depth_stencil(struct anv_cmd_buffer *cmd_buffer,
 {
    assert(image->vk.aspects & (VK_IMAGE_ASPECT_DEPTH_BIT |
                                VK_IMAGE_ASPECT_STENCIL_BIT));
+   assert(layer_count > 0);
 
    struct blorp_batch batch;
    anv_blorp_batch_init(cmd_buffer, &batch, 0);

src/intel/vulkan/genX_cmd_buffer.c

@@ -5309,7 +5309,7 @@ void genX(CmdBeginRendering)(
                                      iview->vk.base_array_layer + view, 1,
                                      render_area, clear_color);
             }
-         } else {
+         } else if (clear_rect.layerCount > 0) {
             anv_image_clear_color(cmd_buffer, iview->image,
                                   VK_IMAGE_ASPECT_COLOR_BIT,
                                   aux_usage,

src/intel/vulkan_hasvk/genX_cmd_buffer.c

@@ -5227,7 +5227,7 @@ void genX(CmdBeginRendering)(
                                      iview->vk.base_array_layer + view, 1,
                                      render_area, clear_color);
             }
-         } else {
+         } else if (clear_layer_count > 0) {
             anv_image_clear_color(cmd_buffer, iview->image,
                                   VK_IMAGE_ASPECT_COLOR_BIT,
                                   aux_usage,