Bug 1383880: add only-if-dependencies-run optimization for follow-ons; r=ahal

MozReview-Commit-ID: JuhwyQIx3Mh

--HG--
extra : rebase_source : 553eabc3ac408710bd8c0124232985cc4b01e705
extra : source : 4b3fa9587e88431cc28331d129dd7ef4d1a793c2

taskcluster/ci/upload-generated-sources/kind.yml

@@ -31,5 +31,7 @@ job-template:
     command: >
             cd /builds/worker/checkouts/gecko &&
             ./mach python build/upload_generated_sources.py ${ARTIFACT_URL}
+  optimization:
+    only-if-dependencies-run: null
   scopes:
       - secrets:get:project/releng/gecko/build/level-{level}/gecko-generated-sources-upload

taskcluster/ci/upload-symbols/kind.yml

@@ -43,5 +43,7 @@ job-template:
            GECKO_HEAD_REPOSITORY: # see transforms
            GECKO_HEAD_REV: # see transforms
            ARTIFACT_TASKID: {"task-reference": "<build>"}
+   optimization:
+       only-if-dependencies-run: null
    scopes:
        - docker-worker:image:taskclusterprivate/upload_symbols:0.0.4

taskcluster/taskgraph/optimize.py

@@ -77,6 +77,7 @@ def _make_default_strategies():
         'skip-unless-changed': SkipUnlessChanged(),
         'skip-unless-schedules': SkipUnlessSchedules(),
         'skip-unless-schedules-or-seta': Either(SkipUnlessSchedules(), SETA()),
+        'only-if-dependencies-run': OnlyIfDependenciesRun(),
     }
 
 
@@ -281,6 +282,18 @@ class Either(OptimizationStrategy):
             lambda sub, arg: sub.should_replace_task(task, params, arg))
 
 
+class OnlyIfDependenciesRun(OptimizationStrategy):
+    """Run this taks only if its dependencies run."""
+
+    # This takes advantage of the behavior of the second phase of optimization:
+    # a task can only be replaced if it has no un-optimized dependencies. So if
+    # should_replace_task is called, then a task has no un-optimized
+    # dependencies and can be removed (indicated by returning True)
+
+    def should_replace_task(self, task, params, arg):
+        return True
+
+
 class IndexSearch(OptimizationStrategy):
     def should_remove_task(self, task, params, index_paths):
         "If this task has no dependencies, don't run it.."

taskcluster/taskgraph/transforms/task.py

@@ -184,6 +184,9 @@ task_description_schema = Schema({
         {'skip-unless-schedules': list(schedules.ALL_COMPONENTS)},
         # skip if SETA or skip-unless-schedules says to
         {'skip-unless-schedules-or-seta': list(schedules.ALL_COMPONENTS)},
+        # only run this task if its dependencies will run (useful for follow-on tasks that
+        # are unnecessary if the parent tasks are not run)
+        {'only-if-dependencies-run': None}
     ),
 
     # the provisioner-id/worker-type for the task.  The following parameters will