Change dfg.inst_results to return a slice.

Now we can access instruction results and arguments as well as EBB
arguments as slices.

Delete the Values iterator which was traversing the linked lists of
values. It is no longer needed.

lib/cretonne/meta/gen_instr.py

@@ -693,14 +693,17 @@ def gen_inst_builder(inst, fmt):
             fmt.line(fcall + '.0')
             return
 
+        fmt.line('let (inst, dfg) = {};'.format(fcall))
+
         if len(inst.value_results) == 1:
-            fmt.line('Value::new_direct({}.0)'.format(fcall))
+            fmt.line('dfg.first_result(inst)')
             return
 
-        fmt.line('let (inst, dfg) = {};'.format(fcall))
-        fmt.line('let mut results = dfg.inst_results(inst);')
-        fmt.line('({})'.format(', '.join(
-            len(inst.value_results) * ['results.next().unwrap()'])))
+        fmt.format(
+            'let results = &dfg.inst_results(inst)[0..{}];',
+            len(inst.value_results))
+        fmt.format('({})', ', '.join(
+            'results[{}]'.format(i) for i in range(len(inst.value_results))))
 
 
 def gen_builder(insts, fmt):