Work-around for prepass-past-side-exits error.

Before, downward scheduling would sometimes give an unverifiable result
because instructions are duplicated before restoration instructions and
aliasing are applied. If for example a loop increment was moved below
multiple side-exits, the restoration code would still mess up the
correct duplication of the instruction because the aliasing logic for
later side exits would overwrite this change.
As a work-around, this commit ensures that the aliasing logic for
side-exits is applied in-order. This may leave aliasing code that is
utterly useless, which should be cleaned up by DCE.

1 files changed, 17 insertions, 11 deletions

diff --git a/scheduling/MyRTLpathScheduleraux.ml b/scheduling/MyRTLpathScheduleraux.ml
index 63e362ad..df5e476f 100644
--- a/scheduling/MyRTLpathScheduleraux.ml
+++ b/scheduling/MyRTLpathScheduleraux.ml
@@ -1251,7 +1251,7 @@ let apply_aliases sb code name_map ~offset =
   let name_map = ref name_map in
   let length = Array.length sb.instructions in
 
-  (* TODO: prepferably there was an early exit condition when there is nothing left to do *)
+  (* TODO: preferably there was an early exit condition when there is nothing left to do *)
   for i = offset to length - 1 do
     let pc = sb.instructions.(i) in
     let inst = get_some @@ PTree.get pc !code in
@@ -1261,10 +1261,13 @@ let apply_aliases sb code name_map ~offset =
       (match RTL.instr_defs inst with
       | None -> !name_map
       | Some r ->
-        if Option.is_some @@ PTree.get r !name_map then
+        if Option.is_some @@ PTree.get r !name_map then (
           (* The restoration code, is no longer incorrectly applicable *)
-          PTree.remove r !name_map
-        else
+          if not !Clflags.option_fpoormansssa then
+            PTree.remove r !name_map
+          else
+            !name_map
+        ) else
           !name_map)
     ;
   done;
@@ -1516,13 +1519,16 @@ let scheduler f =
       PTree.empty
     in
     let (to_insert_restoration, to_rename, next_free_reg) = restoration_instructions' sb code live_renames ~next_free_reg in
-    let code = PTree.fold
-      (fun code side_exit_pc aliases ->
-        let idx = apply_map' pc_to_idx side_exit_pc in
-        let code = apply_aliases sb code aliases ~offset:idx in
-        code)
-      to_rename
-      code
+    let side_exit_pcs = side_exit_pcs sb code in
+    let code = ListLabels.fold_left side_exit_pcs
+      ~init:code
+      ~f:(fun code side_exit_pc ->
+        match PTree.get side_exit_pc to_rename with
+        | None -> code
+        | Some aliases ->
+          let idx = apply_map' pc_to_idx side_exit_pc in
+          let code = apply_aliases sb code aliases ~offset:idx in
+          code)
     in
     let (sb, code, pm, next_free_pc, _fwmap) = insert_code sb code pm to_insert_restoration ~next_free_pc in
     (sb::sbs, code, pm, next_free_pc, next_free_reg) )