Add a ControlFlowGraph argument to legalize_function.

Legalizing some instructions may require modifications to the control
flow graph, and some operations need to use the CFG analysis.

The CFG reference is threaded through all the legalization functions to
reach the generated expansion functions as well as the legalizer::split
module where it will be used first.

lib/cretonne/meta/gen_legalizer.py

@@ -140,7 +140,7 @@ def emit_dst_inst(node, fmt):
         # special functions in the `legalizer::split` module. These functions
         # will eliminate concat-split patterns.
         fmt.line(
-                'let {} = split::{}(dfg, pos, {});'
+                'let {} = split::{}(dfg, cfg, pos, {});'
                 .format(
                     wrap_tup(node.defs),
                     node.expr.inst.snake_name(),
@@ -220,9 +220,10 @@ def gen_xform_group(xgrp, fmt):
     fmt.doc_comment("Legalize the instruction pointed to by `pos`.")
     fmt.line('#[allow(unused_variables,unused_assignments)]')
     with fmt.indented(
-            'fn ' + xgrp.name +
-            '(pos: &mut Cursor, dfg: &mut DataFlowGraph) -> bool {',
-            '}'):
+            'fn {}(dfg: &mut DataFlowGraph, '
+            'cfg: &mut ControlFlowGraph, pos: &mut Cursor) -> '
+            'bool {{'.format(xgrp.name), '}'):
+
         # Gen the instruction to be legalized. The cursor we're passed must be
         # pointing at an instruction.
         fmt.line('let inst = pos.current_inst().expect("need instruction");')