Optimization for miranda

• Optimize cava and edge detection schedules (CPU schedules are multi-core now).
• Add fork-extend pass to make fork dimensions multiple of some number (closes #28 (closed)).
• Make GCM add extra dimensions to per-thread arrays in fork-joins.
• Make GCM allocate extra memory for calls in parallel, make RT backend use different memories per parallel call.
• Make not finding xdot binary crash the compiler.
• Some misc. fixes.
• Add conv-like fork-join test.

hercules_opt/src/fork_transforms.rs

@@ -695,7 +695,8 @@ pub fn fork_coalesce_helper(
 
         editor.edit(|mut edit| {
             let new_tid = edit.add_node(new_tid);
-            let edit = edit.replace_all_uses(tid, new_tid)?;
+            let mut edit = edit.replace_all_uses(tid, new_tid)?;
+            edit.sub_edit(tid, new_tid);
             Ok(edit)
         });
     }
@@ -1598,3 +1599,8 @@ pub fn clean_monoid_reduces(editor: &mut FunctionEditor, typing: &Vec<TypeID>) {
         }
     }
 }
+
+/*
+ * Looks for reads in fork-joins that are linear in the thread IDs for the fork-
+ * join.
+ */