Fix issue #21

hercules_opt/src/gcm.rs

@@ -324,6 +324,12 @@ fn basic_blocks(
     // 3: If the node producing the collection is a reduce node, then any read
     //    users that aren't in the reduce's cycle shouldn't anti-depend user any
     //    mutators in the reduce cycle.
+    //
+    // Because we do a liveness analysis based spill of collections, anti-
+    // dependencies can be best effort. Thus, when we encounter a read and
+    // mutator where the read doesn't dominate the mutator, but an anti-depdence
+    // edge is derived for the pair, we just don't draw the edge since it would
+    // break the scheduler.
     let mut antideps = BTreeSet::new();
     for id in reverse_postorder.iter() {
         // Find a terminating read node and the collections it reads.
@@ -385,6 +391,7 @@ fn basic_blocks(
                                 .get(root)
                                 .map(|cycle| cycle.contains(mutator))
                                 .unwrap_or(false))
+                        && dom.does_dom(schedule_early[id.idx()].unwrap(), mutator_early)
                     {
                         antideps.insert((*id, *mutator));
                     }

juno_samples/antideps/src/antideps.jn

@@ -135,3 +135,29 @@ fn array_of_structs(input: i32) -> i32 {
   arr[0].1 = 99;
   return result + sub.1 - arr[0].1;
 }
+
+#[entry]
+fn issue_21<n: usize>() -> i32 {
+  let visited: bool[n];
+  let cost: i32[n];
+
+  for i = 0 to n {
+    if visited[i] {
+      cost[i] = cost[i] + 1;
+    }
+  }
+
+  for i = 0 to n {
+    visited[i] = true;
+  }
+
+  let total : i32;
+  for i = 0 to n {
+    if visited[i] {
+      total += cost[i] + 2;
+    }
+  }
+
+  return total;
+}
+

juno_samples/antideps/src/gpu.sch

@@ -3,7 +3,7 @@ phi-elim(*);
 dce(*);
 
 let out = auto-outline(*);
-gpu(out.simple_antideps, out.loop_antideps, out.complex_antideps1, out.complex_antideps2, out.very_complex_antideps, out.read_chains, out.array_of_structs);
+gpu(out.simple_antideps, out.loop_antideps, out.complex_antideps1, out.complex_antideps2, out.very_complex_antideps, out.read_chains, out.array_of_structs, out.issue_21);
 
 ip-sroa(*);
 sroa(*);

juno_samples/antideps/src/main.rs

@@ -40,6 +40,11 @@ fn main() {
         let output = r.run(2).await;
         println!("{}", output);
         assert_eq!(output, 14);
+
+        let mut r = runner!(issue_21);
+        let output = r.run(42).await;
+        println!("{}", output);
+        assert_eq!(output, 42 * 2);
     });
 }