Do not unroll loops with a nesting higher than 3

src/util/loopUnrolling.ml

@@ -402,16 +402,19 @@ let copy_and_patch_labels break_target current_continue_target stmts =
   let patchLabelsVisitor = new patchLabelsGotosVisitor(StatementHashTable.find_opt gotos) in
   List.map (visitCilStmt patchLabelsVisitor) stmts'
 
-class loopUnrollingVisitor(func, totalLoops) = object
+class loopUnrollingVisitor (func, totalLoops) = object
   (* Labels are simply handled by giving them a fresh name. Jumps coming from outside will still always go to the original label! *)
   inherit nopCilVisitor
 
-  method! vstmt s =
-    let duplicate_and_rem_labels s =
-      match s.skind with
-      | Loop (b,loc, loc2, break , continue) ->
-        let factor = loop_unrolling_factor s func totalLoops in
-        if(factor > 0) then (
+  val mutable nests = 0
+
+  method! vstmt stmt =
+    let duplicate_and_rem_labels stmt =
+      match stmt.skind with
+      | Loop (b, loc, loc2, break, continue) ->
+        nests <- nests - 1; Logs.debug "nests: %i" nests;
+        let factor = loop_unrolling_factor stmt func totalLoops in
+        if factor > 0 then (
           Logs.info "unrolling loop at %a with factor %d" CilType.Location.pretty loc factor;
           annotateArrays b;
           (* top-level breaks should immediately go to the end of the loop, and not just break out of the current iteration *)
@@ -423,11 +426,14 @@ class loopUnrollingVisitor(func, totalLoops) = object
               one_copy_stmts @ [current_continue_target]
             )
           in
-          mkStmt (Block (mkBlock (List.flatten copies @ [s; break_target])))
-        ) else s (*no change*)
-      | _ -> s
+          mkStmt (Block (mkBlock (List.flatten copies @ [stmt; break_target])))
+        ) else stmt (*no change*)
+      | _ -> stmt
     in
-    ChangeDoChildrenPost(s, duplicate_and_rem_labels)
+    match stmt.skind with
+    | Loop _ when nests + 1 < 4 -> nests <- nests + 1; ChangeDoChildrenPost(stmt, duplicate_and_rem_labels)
+    | Loop _ -> SkipChildren
+    | _ -> ChangeDoChildrenPost(stmt, duplicate_and_rem_labels)
 end
 
 let unroll_loops fd totalLoops =