[pypy-issue] Issue #2700: slow warmup running Firefox taskgraph generation (pypy/pypy)

[Chris AtLee]

New issue 2700: slow warmup running Firefox taskgraph generation
https://bitbucket.org/pypy/pypy/issues/2700/slow-warmup-running-firefox-taskgraph

Chris AtLee:

To reproduce:

- clone https://hg.mozilla.org/mozilla-central revision 2e4bef09de27
- download https://queue.taskcluster.net/v1/task/dcvqqnj4RkaJGACao955TA/runs/0/artifacts/public/parameters.yml
- run `time pypy ./mach taskgraph target -p parameters.yml > /dev/null`

this takes about 20s on my system

next, modify taskcluster/mach_commands.py so that we duplicate the call to show_taskgraph:
```
diff --git a/taskcluster/mach_commands.py b/taskcluster/mach_commands.py
--- a/taskcluster/mach_commands.py
+++ b/taskcluster/mach_commands.py
@@ -79,16 +79,17 @@ class MachCommands(MachCommandBase):
     @ShowTaskGraphSubCommand('taskgraph', 'full',
                              description="Show the full taskgraph")
     def taskgraph_full(self, **options):
         return self.show_taskgraph('full_task_graph', options)
 
     @ShowTaskGraphSubCommand('taskgraph', 'target',
                              description="Show the target task set")
     def taskgraph_target(self, **options):
+        self.show_taskgraph('target_task_set', options)
         return self.show_taskgraph('target_task_set', options)
 
     @ShowTaskGraphSubCommand('taskgraph', 'target-graph',
                              description="Show the target taskgraph")
     def taskgraph_target_taskgraph(self, **options):
         return self.show_taskgraph('target_task_graph', options)
 
     @ShowTaskGraphSubCommand('taskgraph', 'optimized',
```

re-run `mach taskgraph`. This time is takes about 34 seconds. I think this means that the second pass only takes 14 seconds to run.