Use value lists for call arguments.

Add a new kind of instruction format that keeps all of its value
arguments in a value list. These value lists are all allocated out of
the dfg.value_lists memory pool.

Instruction formats with the value_list property set store *all* of
their value arguments in a single value list. There is no distinction
between fixed arguments and variable arguments.

Change the Call instruction format to use the value list representation
for its arguments.

This change is only the beginning. The intent is to eliminate the
boxed_storage instruction formats completely. Value lists use less
memory, and when the transition is complete, InstructionData will have a
trivial Drop implementation.

lib/cretonne/meta/cdsl/formats.py

@@ -34,6 +34,8 @@ class InstructionFormat(object):
         enums.
     :param multiple_results: Set to `True` if this instruction format allows
         more than one result to be produced.
+    :param value_list: Set to `True` if this instruction format uses a
+        `ValueList` member to store its value operands.
     :param boxed_storage: Set to `True` is this instruction format requires a
         `data: Box<...>` pointer to additional storage in its `InstructionData`
         variant.
@@ -52,6 +54,7 @@ class InstructionFormat(object):
         # type: (*Union[OperandKind, Tuple[str, OperandKind]], **Any) -> None # noqa
         self.name = kwargs.get('name', None)  # type: str
         self.multiple_results = kwargs.get('multiple_results', False)
+        self.has_value_list = kwargs.get('value_list', False)
         self.boxed_storage = kwargs.get('boxed_storage', False)
         self.members = list()  # type: List[str]
         self.kinds = tuple(self._process_member_names(kinds))