scons,sim: Eliminate the generated cxx_config/init.cc file.

This file populated the "cxx_config_directory" map from type names to
directory entry generating types. It used a comprehensive list of
includes of all SimObject headers, and a comprehensive list of the
generating types to fill everything in.

Instead, this change creates a new singleton helper class which, when
instantiated as a static member of a CxxConfigParams subclass, will
install a pointer to a CxxConfigDirectoryEntry to that map during global
object construction time.

Also, this change renames the map to cxxConfigDirectory which is in
compliance with the style guide, and puts it behind an accessor which
returns a static variable which is the actual map. This avoids any
problems that might come from global object construction order.

Change-Id: Iaa913fbe5af1b11d90ca618e29420eeb7cb0faed
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49455
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/SConscript

@@ -133,10 +133,6 @@ class SimObject(PySource):
     '''Add a SimObject python file as a python source object and add
     it to a list of sim object modules'''
 
-    fixed = False
-
-    sim_objects = []
-
     def __init__(self, source, *, sim_objects=None, enums=None,
             tags=None, add_tags=None):
         '''Specify the source file and any tags (automatically in
@@ -150,10 +146,6 @@ class SimObject(PySource):
             enums = []
 
         super().__init__('m5.objects', source, tags, add_tags)
-        if self.fixed:
-            error("Too late to call SimObject now.")
-
-        SimObject.sim_objects.extend(sim_objects)
 
         build_dir = Dir(env['BUILDDIR'])
         module = self.modpath
@@ -587,13 +579,6 @@ def makeTheGPUISA(source, target, env):
 env.Command('config/the_gpu_isa.hh', [],
             MakeAction(makeTheGPUISA, Transform("CFG ISA", 0)))
 
-########################################################################
-#
-# Prevent any SimObjects from being added after this point, they
-# should all have been added in the SConscripts above
-#
-SimObject.fixed = True
-
 
 ########################################################################
 #
@@ -631,25 +616,6 @@ m5_module_source = \
 m5_module_static = list(map(lambda s: s.static(gem5py_env), m5_module_source))
 gem5py_env.Program(gem5py_m5, [ 'python/gem5py.cc' ] + m5_module_static)
 
-########################################################################
-#
-# Create the CXX config init.cc.
-#
-
-all_sim_objects = sorted(SimObject.sim_objects)
-sim_object_args = list(f'"{sim_object}"' for sim_object in all_sim_objects)
-cc_file = File('cxx_config/init.cc')
-gem5py_env.Command([ "${CXXCONFIGINIT_CC}" ],
-        [ "${GEM5PY}", "${CXXCONFIGINITCC_PY}" ],
-        MakeAction('"${GEM5PY}" "${CXXCONFIGINITCC_PY}" "${TARGET}" '
-                '${SIM_OBJECTS}',
-            Transform("CXXCINIT", 0)),
-        CXXCONFIGINITCC_PY=build_tools.File('cxx_config_init_cc.py'),
-        SIM_OBJECTS=' '.join(sim_object_args),
-        CXXCONFIGINIT_CC=cc_file)
-if GetOption('with_cxx_config'):
-    Source(cc_file)
-
 
 # version tags
 tags = \