Add FuncRef and SigRef entity references.

These refer to external functions and function signatures declared in
the preamble. Since we're already using the type names 'Signature' and
'Function', these entity references don't folow the usual EntityData /
Entity naming convention.

meta/cretonne/entities.py

@@ -18,11 +18,11 @@ stack_slot = EntityRefKind('stack_slot', 'A stack slot.')
 
 #: A reference to a function sugnature declared in the function preamble.
 #: Tbis is used to provide the call signature in an indirect call instruction.
-signature = EntityRefKind('signature', 'A function signature.')
+sig_ref = EntityRefKind('sig_ref', 'A function signature.')
 
 #: A reference to an external function declared in the function preamble.
 #: This is used to provide the callee and signature in a call instruction.
-function = EntityRefKind('function', 'An external function.')
+func_ref = EntityRefKind('func_ref', 'An external function.')
 
 #: A reference to a jump table declared in the function preamble.
 jump_table = EntityRefKind(

meta/cretonne/formats.py

@@ -8,7 +8,7 @@ in this module.
 from __future__ import absolute_import
 from . import InstructionFormat, value, variable_args
 from .immediates import imm64, uimm8, ieee32, ieee64, immvector, intcc, floatcc
-from .entities import ebb, function, jump_table
+from .entities import ebb, func_ref, jump_table
 
 Nullary = InstructionFormat()
 
@@ -46,7 +46,7 @@ Branch = InstructionFormat(value, ebb, variable_args, boxed_storage=True)
 BranchTable = InstructionFormat(value, jump_table)
 
 Call = InstructionFormat(
-        function, variable_args, multiple_results=True, boxed_storage=True)
+        func_ref, variable_args, multiple_results=True, boxed_storage=True)
 Return = InstructionFormat(variable_args, boxed_storage=True)