Implement some CFG value->tree lowerings

kernel/modelverse_jit/bytecode_to_cfg.py

@@ -12,6 +12,19 @@ class AnalysisState(object):
         self.loop_instructions = {}
         self.entry_point = cfg_ir.BasicBlock(self.counter)
         self.current_block = self.entry_point
+        self.root_node = None
+        self.__write_prolog()
+
+    def __write_prolog(self):
+        # Write a prolog in CFG IR.
+        # We want to create the following definition:
+        #
+        #     !entry_point():
+        #         $jit_locals = alloc-root-node
+        #
+        # We also want to store '$jit_locals' in an attribute, so we can
+        # use it to shield locals from the GC.
+        self.root_node = self.current_block.append_definition(cfg_ir.AllocateRootNode())
 
     def analyze(self, instruction):
         """Analyzes the given instruction as a basic block."""
@@ -132,6 +145,8 @@ class AnalysisState(object):
             return_value = self.current_block.append_definition(cfg_ir.Literal(None))
         else:
             return_value = self.analyze(instruction.value)
+        # Don't forget to deallocate the root node.
+        self.current_block.append_definition(cfg_ir.DeallocateRootNode(self.root_node))
         self.current_block.flow = cfg_ir.ReturnFlow(return_value)
         self.current_block = cfg_ir.BasicBlock(self.counter)
         return self.current_block.append_definition(cfg_ir.Literal(None))
@@ -155,7 +170,8 @@ class AnalysisState(object):
 
     def analyze_declare(self, instruction):
         """Analyzes a 'declare' instruction."""
-        return self.current_block.append_definition(cfg_ir.DeclareLocal(instruction.variable))
+        return self.current_block.append_definition(
+            cfg_ir.DeclareLocal(instruction.variable, self.root_node))
 
     def analyze_global(self, instruction):
         """Analyzes a 'global' instruction."""