stats: Add a preDumpStats() callback to Stats::Group

Some objects need to know that we are about to dump stats to perform
prepare statistics. This is currently done by registering a callback
with the stat system. Expose this callback as a virtual method
in Stats::Group to make this pattern more convenient.

Change-Id: I5aa475b7d04c288e45f5f413ab7a1907b971dae5
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21139
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>

src/python/m5/stats/__init__.py

@@ -371,6 +371,10 @@ def dump(root=None):
     # Only prepare stats the first time we dump them in the same tick.
     if new_dump:
         _m5.stats.processDumpQueue()
+        # Notify new-style stats group that we are about to dump stats.
+        sim_root = Root.getInstance()
+        if sim_root:
+            sim_root.preDumpStats();
         prepare()
 
     for output in outputList:

src/python/pybind11/stats.cc

@@ -127,6 +127,7 @@ pybind_init_stats(py::module &m_native)
         m, "Group")
         .def("regStats", &Stats::Group::regStats)
         .def("resetStats", &Stats::Group::resetStats)
+        .def("preDumpStats", &Stats::Group::preDumpStats)
         .def("getStats", &Stats::Group::getStats)
         .def("getStatGroups", &Stats::Group::getStatGroups)
         .def("addStatGroup", &Stats::Group::addStatGroup)