Use tuple statements during CFG->tree lowering

kernel/modelverse_jit/cfg_to_tree.py

@@ -841,10 +841,11 @@ class LoweringState(object):
     def lower_branch(self, branch):
         """Lowers the given (relooped) branch to a tree."""
         instructions = []
-        for param, arg in zip(branch.block.parameters, branch.arguments):
+        if len(branch.arguments) > 0:
             instructions.append(
-                tree_ir.IgnoreInstruction(
-                    self.create_definition_load(param).create_store(self.use_definition(arg))))
+                tree_ir.TupleStoreLocalInstruction(
+                    [(self.create_definition_load(param).name, self.use_definition(arg))
+                     for param, arg in zip(branch.block.parameters, branch.arguments)]))
 
         instructions.append(
             tree_ir.IgnoreInstruction(