arch, cpu: Factor out the ExecContext into a proper base class

We currently generate and compile one version of the ISA code per CPU
model. This is obviously wasting a lot of resources at compile
time. This changeset factors out the interface into a separate
ExecContext class, which also serves as documentation for the
interface between CPUs and the ISA code. While doing so, this
changeset also fixes up interface inconsistencies between the
different CPU models.

The main argument for using one set of ISA code per CPU model has
always been performance as this avoid indirect branches in the
generated code. However, this argument does not hold water. Booting
Linux on a simulated ARM system running in atomic mode
(opt/10.linux-boot/realview-simple-atomic) is actually 2% faster
(compiled using clang 3.4) after applying this patch. Additionally,
compilation time is decreased by 35%.

1 files changed, 16 insertions, 6 deletions

diff --git a/src/arch/isa_parser.py b/src/arch/isa_parser.py
index 6aa553588..adadbe14d 100755
--- a/src/arch/isa_parser.py
+++ b/src/arch/isa_parser.py
@@ -1178,13 +1178,25 @@ class Stack(list):
 #
 
 class ISAParser(Grammar):
-    def __init__(self, output_dir, cpu_models):
+    class CpuModel(object):
+        def __init__(self, name, filename, includes, strings):
+            self.name = name
+            self.filename = filename
+            self.includes = includes
+            self.strings = strings
+
+    def __init__(self, output_dir):
         super(ISAParser, self).__init__()
         self.output_dir = output_dir
 
         self.filename = None # for output file watermarking/scaremongering
 
-        self.cpuModels = cpu_models
+        self.cpuModels = [
+            ISAParser.CpuModel('ExecContext',
+                               'generic_cpu_exec.cc',
+                               '#include "cpu/exec_context.hh"',
+                               { "CPU_exec_context" : "ExecContext" }),
+            ]
 
         # variable to hold templates
         self.templateMap = {}
@@ -2376,8 +2388,6 @@ StaticInstPtr
             e.exit(self.fileNameStack)
 
 # Called as script: get args from command line.
-# Args are: <path to cpu_models.py> <isa desc file> <output dir> <cpu models>
+# Args are: <isa desc file> <output dir>
 if __name__ == '__main__':
-    execfile(sys.argv[1])  # read in CpuModel definitions
-    cpu_models = [CpuModel.dict[cpu] for cpu in sys.argv[4:]]
-    ISAParser(sys.argv[3], cpu_models).parse_isa_desc(sys.argv[2])
+    ISAParser(sys.argv[2]).parse_isa_desc(sys.argv[1])