layers: Don't add VK_SUBPASS_EXTERNAL edges to subpass DAG.

We don't use them, and handling them safely complicates other code that
works with the DAG.

Signed-off-by: Chris Forbes <chrisforbes@google.com>

diff --git a/layers/core_validation.cpp b/layers/core_validation.cpp
index e041b75..9cb0c51 100644 (file)
--- a/layers/core_validation.cpp
+++ b/layers/core_validation.cpp
@@ -9791,23 +9791,27 @@ static bool CreatePassDAG(const layer_data *my_data, VkDevice device, const VkRe
     }
     for (uint32_t i = 0; i < pCreateInfo->dependencyCount; ++i) {
         const VkSubpassDependency &dependency = pCreateInfo->pDependencies[i];
-        if (dependency.srcSubpass > dependency.dstSubpass && dependency.srcSubpass != VK_SUBPASS_EXTERNAL &&
-            dependency.dstSubpass != VK_SUBPASS_EXTERNAL) {
+        if (dependency.srcSubpass == VK_SUBPASS_EXTERNAL || dependency.dstSubpass == VK_SUBPASS_EXTERNAL) {
+            if (dependency.srcSubpass == dependency.dstSubpass) {
+                skip_call |=
+                    log_msg(my_data->report_data, VK_DEBUG_REPORT_ERROR_BIT_EXT, (VkDebugReportObjectTypeEXT)0, 0, __LINE__,
+                            DRAWSTATE_INVALID_RENDERPASS, "DS", "The src and dest subpasses cannot both be external.");
+            }
+
+            // We don't want to add edges to the DAG for dependencies to/from
+            // VK_SUBPASS_EXTERNAL. We don't use them for anything, and their
+            // presence complicates other code.
+            continue;
+        } else if (dependency.srcSubpass > dependency.dstSubpass) {
             skip_call |= log_msg(my_data->report_data, VK_DEBUG_REPORT_ERROR_BIT_EXT, (VkDebugReportObjectTypeEXT)0, 0, __LINE__,
                                  DRAWSTATE_INVALID_RENDERPASS, "DS",
                                  "Depedency graph must be specified such that an earlier pass cannot depend on a later pass.");
-        } else if (dependency.srcSubpass == VK_SUBPASS_EXTERNAL && dependency.dstSubpass == VK_SUBPASS_EXTERNAL) {
-            skip_call |= log_msg(my_data->report_data, VK_DEBUG_REPORT_ERROR_BIT_EXT, (VkDebugReportObjectTypeEXT)0, 0, __LINE__,
-                                 DRAWSTATE_INVALID_RENDERPASS, "DS", "The src and dest subpasses cannot both be external.");
         } else if (dependency.srcSubpass == dependency.dstSubpass) {
             has_self_dependency[dependency.srcSubpass] = true;
         }
-        if (dependency.dstSubpass != VK_SUBPASS_EXTERNAL) {
-            subpass_to_node[dependency.dstSubpass].prev.push_back(dependency.srcSubpass);
-        }
-        if (dependency.srcSubpass != VK_SUBPASS_EXTERNAL) {
-            subpass_to_node[dependency.srcSubpass].next.push_back(dependency.dstSubpass);
-        }
+
+        subpass_to_node[dependency.dstSubpass].prev.push_back(dependency.srcSubpass);
+        subpass_to_node[dependency.srcSubpass].next.push_back(dependency.dstSubpass);
     }
     return skip_call;
 }