Add an Index<Value> implementation to Liveness.

Use it to access live ranges that are supposed to be there.

lib/cretonne/src/regalloc/coloring.rs

@@ -474,17 +474,14 @@ impl<'a> Context<'a> {
                     //
                     // It is possible for `dest_arg` to have no affinity, and then it should simply
                     // be ignored.
-                    if self.liveness.get(dest_arg).unwrap().affinity.is_reg() {
+                    if self.liveness[dest_arg].affinity.is_reg() {
                         return true;
                     }
                 }
                 ValueLoc::Reg(dest_reg) => {
                     // We've branched to `dest` before. Make sure we use the correct argument
                     // registers by reassigning `br_arg`.
-                    let br_lr = self.liveness
-                        .get(br_arg)
-                        .expect("Missing live range for branch argument");
-                    if let Affinity::Reg(rci) = br_lr.affinity {
+                    if let Affinity::Reg(rci) = self.liveness[br_arg].affinity {
                         let rc = self.reginfo.rc(rci);
                         let br_reg = self.divert.reg(br_arg, locations);
                         self.solver.reassign_in(br_arg, rc, br_reg, dest_reg);
@@ -518,7 +515,7 @@ impl<'a> Context<'a> {
         for (&dest_arg, &br_arg) in dest_args.iter().zip(br_args) {
             match locations[dest_arg] {
                 ValueLoc::Unassigned => {
-                    if self.liveness.get(dest_arg).unwrap().affinity.is_reg() {
+                    if self.liveness[dest_arg].affinity.is_reg() {
                         let br_reg = self.divert.reg(br_arg, locations);
                         locations[dest_arg] = ValueLoc::Reg(br_reg);
                     }

lib/cretonne/src/regalloc/live_value_tracker.rs

@@ -260,10 +260,7 @@ impl LiveValueTracker {
         // Add the values defined by `inst`.
         let first_def = self.live.values.len();
         for &value in dfg.inst_results(inst) {
-            let lr = match liveness.get(value) {
-                Some(lr) => lr,
-                None => panic!("{} result {} has no live range", dfg[inst].opcode(), value),
-            };
+            let lr = &liveness[value];
             assert_eq!(lr.def(), inst.into());
             match lr.def_local_end().into() {
                 ExpandedProgramPoint::Inst(endpoint) => {

lib/cretonne/src/regalloc/liveness.rs

@@ -183,6 +183,7 @@ use regalloc::affinity::Affinity;
 use regalloc::liverange::LiveRange;
 use sparse_map::SparseMap;
 use std::mem;
+use std::ops::Index;
 
 /// A set of live ranges, indexed by value number.
 type LiveRangeSet = SparseMap<Value, LiveRange>;
@@ -451,3 +452,14 @@ impl Liveness {
         }
     }
 }
+
+impl Index<Value> for Liveness {
+    type Output = LiveRange;
+
+    fn index(&self, index: Value) -> &LiveRange {
+        match self.ranges.get(index) {
+            Some(lr) => lr,
+            None => panic!("{} has no live range", index),
+        }
+    }
+}

lib/cretonne/src/regalloc/reload.rs

@@ -285,8 +285,7 @@ impl<'a> Context<'a> {
 
         for (op, &arg) in constraints.ins.iter().zip(args) {
             if op.kind != ConstraintKind::Stack {
-                let lv = self.liveness.get(arg).expect("Missing live range for arg");
-                if lv.affinity.is_stack() {
+                if self.liveness[arg].affinity.is_stack() {
                     self.candidates
                         .push(ReloadCandidate {
                                   value: arg,