[expensive] Behavior change when the loop has two final instructions

Right now though the compilation time is too high for glpk, I need to
figure out why

1 files changed, 57 insertions, 9 deletions

diff --git a/backend/Duplicateaux.ml b/backend/Duplicateaux.ml
index a9dca583..55414f40 100644
--- a/backend/Duplicateaux.ml
+++ b/backend/Duplicateaux.ml
@@ -619,15 +619,28 @@ type innerLoop = {
   preds: P.t list;
   body: P.t list;
   head: P.t; (* head of the loop *)
-  finals: P.t list (* the final instructions, which loops back to the head *)
+  finals: P.t list; (* the final instructions, which loops back to the head *)
   (* There may be more than one ; for instance if there is an if inside the loop with both
-   * branches leading to a goto backedge *)
+   * branches leading to a goto backedge
+   * Such cases usually happen after a tail-duplication *)
+  sb_final: P.t option; (* if the innerloop wraps a superblock, this is its final instruction *)
 }
 
 let print_pset = LICMaux.pp_pset
 
+let print_option_pint oc o =
+  if !debug_flag then
+    match o with
+    | None -> Printf.fprintf oc "None"
+    | Some n -> Printf.fprintf oc "Some %d" (P.to_int n)
+
 let print_inner_loop iloop =
-  debug "{preds: %a, body: %a}" print_intlist iloop.preds print_intlist iloop.body
+  debug "{preds: %a, body: %a, head: %d, finals: %a, sb_final: %a}\n"
+    print_intlist iloop.preds
+    print_intlist iloop.body
+    (P.to_int iloop.head)
+    print_intlist iloop.finals
+    print_option_pint iloop.sb_final
 
 let rec print_inner_loops = function
 | [] -> ()
@@ -696,6 +709,31 @@ let get_inner_loops f code is_loop_header =
   !iloops
   *)
 
+let rtl_successors_pref = function
+| Itailcall _ | Ireturn _ -> []
+| Icall(_,_,_,_,n) | Ibuiltin(_,_,_,n) | Inop n | Iop (_,_,_,n)
+| Iload (_,_,_,_,_,n) | Istore (_,_,_,_,n) -> [n]
+| Icond (_,_,n1,n2,p) -> (match p with
+  | Some true -> [n1]
+  | Some false -> [n2]
+  | None -> [n1; n2])
+| Ijumptable (_,ln) -> ln
+
+(* Find the last node of a trace (starting at "node"), until a loop is encountered.
+ * If a non-predicted branch is encountered, returns None *)
+let rec find_last_node_before_loop code node trace is_loop_header =
+  let rtl_succ = rtl_successors @@ get_some @@ PTree.get node code in
+  let headers = List.filter (fun n -> 
+    get_some @@ PTree.get n is_loop_header && List.mem n trace) rtl_succ in 
+  match headers with
+  | [] -> (
+      match (rtl_successors_pref @@ get_some @@ PTree.get node code) with
+      | [n] -> find_last_node_before_loop code n trace is_loop_header
+      | _ -> None
+    )
+  | [h] -> Some node
+  | _ -> failwith "Multiple branches leading to a loop"
+
 let get_inner_loops f code is_loop_header =
   let fake_f = { fn_sig = f.fn_sig; fn_params = f.fn_params; 
     fn_stacksize = f.fn_stacksize; fn_code = code; fn_entrypoint = f.fn_entrypoint } in
@@ -722,7 +760,10 @@ let get_inner_loops f code is_loop_header =
           debug "HEADPREDS: %a\n" print_intlist head_preds;
           filtered
         end in
-      { preds = preds; body = (HashedSet.PSet.elements body); head = head; finals = finals }
+      let body = HashedSet.PSet.elements body in
+      let sb_final = find_last_node_before_loop code head body is_loop_header in
+      { preds = preds; body = body; head = head; finals = finals;
+        sb_final = sb_final; }
     ) 
     (* LICMaux.inner_loops also returns non-inner loops, but with a body of 1 instruction
      * We remove those to get just the inner loops *)
@@ -840,16 +881,23 @@ let unroll_inner_loops_single f code revmap =
     (!code', !revmap')
   end
 
+let is_some o = match o with Some _ -> true | None -> false
+
 (* Unrolls the body of the inner loop once - duplicating the exit condition as well 
  * 1) Clones body into body'
- * 2) Links the last instruction of body into the first of body' 
+ * 2) Links the last instruction of body (sb_final) into the first of body' 
  * 3) Links the last instruction of body' into the first of body
  *)
 let unroll_inner_loop_body code revmap iloop =
+  debug_flag := true;
+  debug "iloop = "; print_inner_loop iloop;
   let body = iloop.body in
   let limit = !Clflags.option_funrollbody in
   if count_ignore_nops code body > limit then begin
-    debug "Too many nodes in the loop body (%d > %d)" (List.length body) limit;
+    debug "Too many nodes in the loop body (%d > %d)" (List.length body) limit; debug_flag := false;
+    (code, revmap)
+  end else if not @@ is_some iloop.sb_final then begin
+    debug "The loop body does not form a superblock"; debug_flag := false;
     (code, revmap)
   end else
     let (code2, revmap2, dupbody, fwmap) = clone code revmap body in
@@ -857,14 +905,14 @@ let unroll_inner_loop_body code revmap iloop =
     let head' = apply_map fwmap (iloop.head) in
     let finals' = apply_map_list fwmap (iloop.finals) in
     begin
-      code' := change_pointers !code' iloop.head head' iloop.finals;
+      code' := change_pointers !code' iloop.head head' [get_some @@ iloop.sb_final];
       code' := change_pointers !code' head' iloop.head finals'; 
+      debug_flag := false;
       (!code', revmap2)
     end
 
 let unroll_inner_loops_body f code revmap =
   let is_loop_header = get_loop_headers code (f.fn_entrypoint) in
-  (* debug_flag := true; *)
   let inner_loops = get_inner_loops f code is_loop_header in
   debug "Number of loops found: %d\n" (List.length inner_loops);
   let code' = ref code in
@@ -874,7 +922,7 @@ let unroll_inner_loops_body f code revmap =
     List.iter (fun iloop ->
       let (new_code, new_revmap) = unroll_inner_loop_body !code' !revmap' iloop in
       code' := new_code; revmap' := new_revmap
-    ) inner_loops; (* debug_flag := false; *)
+    ) inner_loops;
     (!code', !revmap')
   end