Implement a conversion from ValueDef into ProgramPoint.

A ValueDef is really no more than a program point plus an
argument/result number.

lib/cretonne/src/ir/progpoint.rs

@@ -1,7 +1,7 @@
 //! Program points.
 
 use entity_map::EntityRef;
-use ir::{Ebb, Inst};
+use ir::{Ebb, Inst, ValueDef};
 use std::fmt;
 use std::u32;
 use std::cmp;
@@ -32,6 +32,15 @@ impl From<Ebb> for ProgramPoint {
     }
 }
 
+impl From<ValueDef> for ProgramPoint {
+    fn from(def: ValueDef) -> ProgramPoint {
+        match def {
+            ValueDef::Res(inst, _) => inst.into(),
+            ValueDef::Arg(ebb, _) => ebb.into(),
+        }
+    }
+}
+
 /// An expanded program point directly exposes the variants, but takes twice the space to
 /// represent.
 #[derive(PartialEq, Eq, Clone, Copy)]