Color EBB arguments.

When coloring registers for a branch instruction, also make sure that
the values passed as EBB arguments are in the registers expected by the
EBB.

The first time a branch to an EBB is processed, assign the EBB arguments
to the registers where the branch arguments already reside so no
regmoves are needed.

lib/cretonne/src/ir/dfg.rs

@@ -104,6 +104,11 @@ impl DataFlowGraph {
     pub fn ebb_is_valid(&self, ebb: Ebb) -> bool {
         self.ebbs.is_valid(ebb)
     }
+
+    /// Get the total number of values.
+    pub fn num_values(&self) -> usize {
+        self.values.len()
+    }
 }
 
 /// Resolve value aliases.

lib/cretonne/src/ir/valueloc.rs

@@ -8,7 +8,7 @@ use ir::StackSlot;
 use std::fmt;
 
 /// Value location.
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum ValueLoc {
     /// This value has not been assigned to a location yet.
     Unassigned,