python: Add search functions to pystats groups

This change adds three functions, a `children` function which will
iterate through all of the children of group based (optionally) on some
predicate. Then, it implements a `find` function and a `find_re`
function using the `children` function.

The `find` function allows users to match statistics or groups
within a group. For instance, you might want to find all of the groups
within the system which have the name "cpu{i}". This is useful for
aggregate statistic values across multiple components.

Example:
total_instruuctions = sum([cpu.exec_context.thread_0.numInsts.value
                           for cpu in simstat.system.find('cpu')])

The find function matches based on substring. If the name given the find
function is a substring of the stat name or the group name the
stat/group will be returned.

The `find_re` function is the same as find, but matches a regular
expression instead of a simple substring match.

Change-Id: I31c2a029d8a6b1d97225ab4efa34a4d13147ea32
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/41603
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/m5/ext/pystats/group.py

@@ -24,7 +24,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-from typing import Dict, List, Optional, Union
+from typing import Dict, Iterator, List, Optional, Union
 
 from .jsonserializable import JsonSerializable
 from .statistic import Scalar, Statistic
@@ -53,6 +53,26 @@ class Group(JsonSerializable):
         for key,value in kwargs.items():
             setattr(self, key, value)
 
+    def find(self, name: str) -> Iterator[Union["Group", Statistic]]:
+        """ Find all stats that match the name
+        This function searches all of the "children" in this group. It yields
+        the set of attributes (children) that have the `name` as a substring.
+        The order of the objects returned by the generator is arbitrary.
+        ```
+        system.find('cpu') -> [cpu0, cpu1, cpu2, cpu3, other_cpu, ...]
+        ```
+        This is useful for performing aggregates over substats. For instance:
+        ```
+        total_instruuctions = sum([cpu.exec_context.thread_0.numInsts.value
+                                   for cpu in simstat.system.find('cpu')])
+        ```
+        """
+        for attr in self.__dict__:
+            if name in attr:
+                obj = getattr(self, attr)
+                if isinstance(obj, Group) or isinstance(obj, Statistic):
+                    yield obj
+
 class Vector(Group):
     """
     The Vector class is used to store vector information. However, in gem5