Remove more fields from Reg.t (#3838)

Author: xclerc

backend/reg.ml

@@ -40,9 +40,7 @@ type t =
   { mutable raw_name: Raw_name.t;
     stamp: int;
     typ: Cmm.machtype_component;
-    mutable loc: location;
-    mutable spill: bool;
-    mutable spill_cost: int; }
+    mutable loc: location; }
 
 and location =
     Unknown
@@ -58,19 +56,14 @@ and stack_location =
 type reg = t
 
 let dummy =
-  { raw_name = Raw_name.Anon; stamp = 0; typ = Int; loc = Unknown;
-    spill = false; spill_cost = 0;
-  }
+  { raw_name = Raw_name.Anon; stamp = 0; typ = Int; loc = Unknown; }
 
 let currstamp = ref 0
 let reg_list = ref([] : t list)
 let hw_reg_list = ref ([] : t list)
 
 let create ty =
-  let r = { raw_name = Raw_name.Anon; stamp = !currstamp; typ = ty;
-            loc = Unknown;
-            spill = false;
-            spill_cost = 0; } in
+  let r = { raw_name = Raw_name.Anon; stamp = !currstamp; typ = ty; loc = Unknown; } in
   reg_list := r :: !reg_list;
   incr currstamp;
   r
@@ -93,9 +86,7 @@ let clone r =
   nr
 
 let at_location ty loc =
-  let r = { raw_name = Raw_name.R; stamp = !currstamp; typ = ty; loc;
-            spill = false; 
-            spill_cost = 0; } in
+  let r = { raw_name = Raw_name.R; stamp = !currstamp; typ = ty; loc; } in
   hw_reg_list := r :: !hw_reg_list;
   incr currstamp;
   r
@@ -121,11 +112,7 @@ let is_unknown t =
 let name t =
   match Raw_name.to_string t.raw_name with
   | None -> ""
-  | Some raw_name ->
-      if t.spill then
-        "spilled-" ^ raw_name
-      else
-        raw_name
+  | Some raw_name -> raw_name
 
 let first_virtual_reg_stamp = ref (-1)
 
@@ -155,11 +142,7 @@ let all_registers() = !reg_list
 let num_registers() = !currstamp
 
 let reinit_reg r =
-  r.loc <- Unknown;
-  (* Preserve the very high spill costs introduced by the reloading pass *)
-  if r.spill_cost >= 100000
-  then r.spill_cost <- 100000
-  else r.spill_cost <- 0
+  r.loc <- Unknown
 
 let reinit() =
   List.iter reinit_reg !reg_list

backend/reg.mli

@@ -25,9 +25,7 @@ type t =
   { mutable raw_name: Raw_name.t;         (* Name *)
     stamp: int;                           (* Unique stamp *)
     typ: Cmm.machtype_component;          (* Type of contents *)
-    mutable loc: location;                (* Actual location *)
-    mutable spill: bool;                  (* "true" to force stack allocation  *)
-    mutable spill_cost: int; }            (* Estimate of spilling cost *)
+    mutable loc: location; }              (* Actual location *)
 
 and location =
     Unknown

backend/regalloc/regalloc_gi.ml

@@ -134,16 +134,15 @@ let rec main : round:int -> flat:bool -> State.t -> Cfg_with_infos.t -> unit =
     log "main, round #%d" round;
     log_cfg_with_infos cfg_with_infos);
   if debug then log "updating spilling costs";
-  update_spill_cost cfg_with_infos ~flat ();
+  let costs = SpillCosts.compute cfg_with_infos ~flat () in
   State.iter_introduced_temporaries state ~f:(fun (reg : Reg.t) ->
-      reg.Reg.spill_cost <- reg.Reg.spill_cost + 10_000);
+      SpillCosts.add_to_reg costs reg 10_000);
   if debug
   then (
     log "spilling costs";
     indent ();
-    List.iter (Reg.all_registers ()) ~f:(fun (reg : Reg.t) ->
-        reg.Reg.spill <- false;
-        log "%a: %d" Printreg.reg reg reg.spill_cost);
+    SpillCosts.iter costs ~f:(fun (reg : Reg.t) (cost : int) ->
+        log "%a: %d" Printreg.reg reg cost);
     dedent ());
   let hardware_registers, prio_queue =
     make_hardware_registers_and_prio_queue cfg_with_infos
@@ -162,7 +161,7 @@ let rec main : round:int -> flat:bool -> State.t -> Cfg_with_infos.t -> unit =
       indent ();
       log "got register %a (prio=%d)" Printreg.reg reg priority);
     (match
-       Hardware_registers.find_available hardware_registers reg interval
+       Hardware_registers.find_available hardware_registers costs reg interval
      with
     | For_assignment { hardware_reg } ->
       if debug
@@ -211,7 +210,6 @@ let rec main : round:int -> flat:bool -> State.t -> Cfg_with_infos.t -> unit =
     | Split_or_spill ->
       (* CR xclerc for xclerc: we should actually try to split. *)
       if debug then log "spilling %a" Printreg.reg reg;
-      reg.Reg.spill <- true;
       spilling := (reg, interval) :: !spilling);
     if debug then dedent ()
   done;
@@ -280,7 +278,6 @@ let run : Cfg_with_infos.t -> Cfg_with_infos.t =
   (match Reg.Set.elements spilling_because_unused with
   | [] -> ()
   | _ :: _ as spilled_nodes ->
-    List.iter spilled_nodes ~f:(fun reg -> reg.Reg.spill <- true);
     (* note: rewrite will remove the `spilling` registers from the "spilled"
        work list and set the field to unknown. *)
     let (_ : bool) = rewrite state cfg_with_infos ~spilled_nodes in

backend/regalloc/regalloc_gi_utils.ml

@@ -620,11 +620,11 @@ module Hardware_registers = struct
    fun t ~of_reg ~f ~init ->
     Array.fold_left t.(Proc.register_class of_reg) ~f ~init
 
-  let actual_cost (reg : Reg.t) : int =
+  let actual_cost (costs : SpillCosts.t) (reg : Reg.t) : int =
     (* CR xclerc for xclerc: it could make sense to give a lower cost to reg
        already spilled (e.g. by the split preprocessing) since they already have
        a stack slot *)
-    reg.Reg.spill_cost
+    SpillCosts.for_reg costs reg
 
   let overlap (hardware_reg : Hardware_register.t) (interval : Interval.t) :
       bool =
@@ -668,7 +668,8 @@ module Hardware_registers = struct
             else acc)
     |> Option.map fst
 
-  let find_evictable (t : t) (reg : Reg.t) (interval : Interval.t) : available =
+  let find_evictable (t : t) (costs : SpillCosts.t) (reg : Reg.t)
+      (interval : Interval.t) : available =
     let eviction =
       fold_class t ~of_reg:reg ~init:None ~f:(fun acc hardware_reg ->
           if debug
@@ -705,7 +706,8 @@ module Hardware_registers = struct
                      (acc_cost, acc_evictable)
                      { Hardware_register.pseudo_reg; interval = _; evictable }
                    ->
-                  acc_cost + actual_cost pseudo_reg, acc_evictable && evictable)
+                  ( acc_cost + actual_cost costs pseudo_reg,
+                    acc_evictable && evictable ))
             in
             if debug then dedent ();
             if not evictable
@@ -714,7 +716,7 @@ module Hardware_registers = struct
               let evict_cost =
                 match acc with None -> max_int | Some (_, _, c) -> c
               in
-              if cost < evict_cost && cost < actual_cost reg
+              if cost < evict_cost && cost < actual_cost costs reg
               then (
                 if debug
                 then
@@ -729,8 +731,8 @@ module Hardware_registers = struct
       For_eviction { hardware_reg; evicted_regs }
     | None -> Split_or_spill
 
-  let find_available : t -> Reg.t -> Interval.t -> available =
-   fun t reg interval ->
+  let find_available : t -> SpillCosts.t -> Reg.t -> Interval.t -> available =
+   fun t costs reg interval ->
     let with_no_overlap =
       let heuristic =
         match Lazy.force Selection_heuristics.value with
@@ -756,5 +758,5 @@ module Hardware_registers = struct
     | Some hardware_reg -> For_assignment { hardware_reg }
     | None ->
       if debug then log "trying to find an evictable register";
-      find_evictable t reg interval
+      find_evictable t costs reg interval
 end

backend/regalloc/regalloc_gi_utils.mli

@@ -190,5 +190,5 @@ module Hardware_registers : sig
 
   val of_reg : t -> Reg.t -> Hardware_register.t option
 
-  val find_available : t -> Reg.t -> Interval.t -> available
+  val find_available : t -> SpillCosts.t -> Reg.t -> Interval.t -> available
 end

backend/regalloc/regalloc_irc.ml

@@ -256,8 +256,9 @@ let freeze : State.t -> unit =
   State.add_simplify_work_list state reg;
   freeze_moves state reg
 
-let select_spilling_register_using_heuristics : State.t -> Reg.t =
- fun state ->
+let select_spilling_register_using_heuristics : State.t -> SpillCosts.t -> Reg.t
+    =
+ fun state costs ->
   match Lazy.force Spilling_heuristics.value with
   | Set_choose -> (
     (* This is the "heuristics" from the IRC paper: pick any candidate, just try
@@ -280,8 +281,9 @@ let select_spilling_register_using_heuristics : State.t -> Reg.t =
     let weighted_cost (reg : Reg.t) =
       if debug
       then
-        log "register %a has spill cost %d" Printreg.reg reg reg.Reg.spill_cost;
-      (float reg.Reg.spill_cost /. float (State.degree state reg))
+        log "register %a has spill cost %d" Printreg.reg reg
+          (SpillCosts.for_reg costs reg);
+      (float (SpillCosts.for_reg costs reg) /. float (State.degree state reg))
       (* note: while this magic constant is questionable, it is key to not favor
          the introduced temporaries which, by construct, have very few
          occurrences. *)
@@ -300,13 +302,13 @@ let select_spilling_register_using_heuristics : State.t -> Reg.t =
           else acc)
       |> fst)
 
-let select_spill : State.t -> unit =
- fun state ->
+let select_spill : State.t -> SpillCosts.t -> unit =
+ fun state costs ->
   if debug
   then (
     log "select_spill";
     indent ());
-  let reg = select_spilling_register_using_heuristics state in
+  let reg = select_spilling_register_using_heuristics state costs in
   if debug
   then
     log "chose %a using heuristics %S" Printreg.reg reg
@@ -461,7 +463,7 @@ let rec main : round:int -> State.t -> Cfg_with_infos.t -> unit =
   make_work_list state;
   State.invariant state;
   if debug then log_work_list_desc "before loop";
-  let spill_cost_is_up_to_date = ref false in
+  let spill_costs = ref (None : SpillCosts.t option) in
   let continue = ref true in
   while !continue do
     if not (State.is_empty_simplify_work_list state)
@@ -471,16 +473,24 @@ let rec main : round:int -> State.t -> Cfg_with_infos.t -> unit =
     else if not (State.is_empty_freeze_work_list state)
     then freeze state
     else if not (State.is_empty_spill_work_list state)
-    then (
-      if not !spill_cost_is_up_to_date
-      then (
-        (match Lazy.force Spilling_heuristics.value with
-        | Set_choose ->
-          (* note: `spill_cost` will not be used by the heuristics *) ()
-        | Flat_uses -> update_spill_cost cfg_with_infos ~flat:true ()
-        | Hierarchical_uses -> update_spill_cost cfg_with_infos ~flat:false ());
-        spill_cost_is_up_to_date := true);
-      select_spill state)
+    then
+      let costs =
+        match !spill_costs with
+        | Some costs -> costs
+        | None ->
+          let costs =
+            match Lazy.force Spilling_heuristics.value with
+            | Set_choose ->
+              (* note: `spill_cost` will not be used by the heuristics *)
+              SpillCosts.empty ()
+            | Flat_uses -> SpillCosts.compute cfg_with_infos ~flat:true ()
+            | Hierarchical_uses ->
+              SpillCosts.compute cfg_with_infos ~flat:false ()
+          in
+          spill_costs := Some costs;
+          costs
+      in
+      select_spill state costs
     else continue := false;
     if debug then log_work_list_desc "end of loop";
     State.invariant state

backend/regalloc/regalloc_ls.ml

@@ -110,7 +110,6 @@ let allocate_stack_slot : Reg.t -> spilling_reg =
  fun reg ->
   indent ();
   log "spilling register %a" Printreg.reg reg;
-  reg.spill <- true;
   dedent ();
   Spilling reg
 
@@ -119,9 +118,8 @@ exception No_free_register
 let allocate_free_register : State.t -> Interval.t -> spilling_reg =
  fun state interval ->
   let reg = interval.reg in
-  match reg.loc, reg.spill with
-  | Unknown, true -> allocate_stack_slot reg
-  | Unknown, _ -> (
+  match reg.loc with
+  | Unknown -> (
     let reg_class = Proc.register_class reg in
     let intervals = State.active state ~reg_class in
     let first_available = Proc.first_available_register.(reg_class) in
@@ -161,7 +159,6 @@ let allocate_free_register : State.t -> Interval.t -> spilling_reg =
         else if available.(idx)
         then (
           reg.loc <- Reg (first_available + idx);
-          reg.spill <- false;
           Interval.DLL.insert_sorted intervals.active_dll interval;
           if debug
           then (
@@ -172,7 +169,7 @@ let allocate_free_register : State.t -> Interval.t -> spilling_reg =
         else assign (succ idx)
       in
       assign 0)
-  | (Reg _ | Stack _), _ -> Not_spilling
+  | Reg _ | Stack _ -> Not_spilling
 
 let allocate_blocked_register : State.t -> Interval.t -> spilling_reg =
  fun state interval ->
@@ -282,7 +279,6 @@ let run : Cfg_with_infos.t -> Cfg_with_infos.t =
   (match Reg.Set.elements spilling_because_unused with
   | [] -> ()
   | _ :: _ as spilled_nodes ->
-    List.iter spilled_nodes ~f:(fun reg -> reg.Reg.spill <- true);
     rewrite state cfg_with_infos ~spilled_nodes ~block_temporaries:false;
     Cfg_with_infos.invalidate_liveness cfg_with_infos);
   main ~round:1 state cfg_with_infos;