save some work

src/ion/fast_alloc.rs

@@ -1164,27 +1164,32 @@ fn calc_live_bitmaps<'a, F: Function>(
             }
         }
 
-        for inst in insns.rev().iter() {
+        // TODO: evaluate if this generates better code than insns.rev().iter()
-            for pos in &[OperandPos::Late, OperandPos::Early] {
+        let last_idx = insns.last().index();
-                for op in state.func.inst_operands(inst) {
+        let len = last_idx - insns.first().index() + 1;
-                    if op.as_fixed_nonallocatable().is_some() {
+        for inst_rev_idx in 0..len {
-                        continue;
+            let inst = Inst::new(last_idx - inst_rev_idx);
+            // TODO: this differs from the algo in liveranges.rs by not iterating through the positions
+            // as in SSA it should make no difference as there can be no vreg that is both a use and def at
+            // a single instruction
+            for op in state.func.inst_operands(inst) {
+                if op.as_fixed_nonallocatable().is_some() {
+                    continue;
+                }
+                let was_live = live.get(op.vreg().vreg());
+                trace!("op {:?} was_live = {}", op, was_live);
+                match op.kind() {
+                    OperandKind::Use => {
+                        live.set(op.vreg().vreg(), true);
                     }
-                    if op.pos() == *pos {
+                    OperandKind::Def => {
-                        let was_live = live.get(op.vreg().vreg());
+                        live.set(op.vreg().vreg(), false);
-                        trace!("op {:?} was_live = {}", op, was_live);
-                        match op.kind() {
-                            OperandKind::Use => {
-                                live.set(op.vreg().vreg(), true);
-                            }
-                            OperandKind::Def => {
-                                live.set(op.vreg().vreg(), false);
-                            }
-                        }
                     }
                 }
             }
         }
+
+        // TODO: i dont get why blockparams are not live when going in?
         for &blockparam in state.func.block_params(block) {
             live.set(blockparam.vreg(), false);
         }