From c841bf262a8dae2df672ef4eb413d7aa346bc64e Mon Sep 17 00:00:00 2001
From: Mehdi Bouaziz <mbouaziz@fb.com>
Date: Wed, 30 May 2018 01:08:17 -0700
Subject: [PATCH] Preanal: append_instrs once per node

Summary:
Append can be costly, let's do it once only.

Depends on D8185619

Reviewed By: jeremydubreil

Differential Revision: D8185634

fbshipit-source-id: 67f84a9
---
 infer/src/IR/Procdesc.ml     |  2 +-
 infer/src/backend/preanal.ml | 26 ++++++++++++--------------
 infer/src/istd/IList.ml      |  2 ++
 infer/src/istd/IList.mli     |  3 +++
 4 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/infer/src/IR/Procdesc.ml b/infer/src/IR/Procdesc.ml
index c29609dbf..1fe23ce89 100644
--- a/infer/src/IR/Procdesc.ml
+++ b/infer/src/IR/Procdesc.ml
@@ -121,7 +121,7 @@ module Node = struct
   let get_distance_to_exit node = node.dist_exit
 
   (** Append the instructions to the list of instructions to execute *)
-  let append_instrs node instrs = node.instrs <- node.instrs @ instrs
+  let append_instrs node instrs = if instrs <> [] then node.instrs <- node.instrs @ instrs
 
   (** Add the instructions at the beginning of the list of instructions to execute *)
   let prepend_instrs node instrs = node.instrs <- instrs @ node.instrs
diff --git a/infer/src/backend/preanal.ml b/infer/src/backend/preanal.ml
index f986dc0db..de54a1525 100644
--- a/infer/src/backend/preanal.ml
+++ b/infer/src/backend/preanal.ml
@@ -132,18 +132,12 @@ let add_nullify_instrs pdesc tenv liveness_inv_map =
   in
   (* only nullify pvars that are local; don't nullify those that can escape *)
   let is_local pvar = not (Pvar.is_return pvar || Pvar.is_global pvar) in
-  let node_add_nullify_instructions node pvars =
-    let loc = Procdesc.Node.get_last_loc node in
-    let nullify_instrs =
-      List.rev_filter_map pvars ~f:(fun pvar ->
-          if is_local pvar then Some (Sil.Nullify (pvar, loc)) else None )
-    in
-    if nullify_instrs <> [] then Procdesc.Node.append_instrs node nullify_instrs
+  let node_nullify_instructions loc pvars =
+    List.rev_filter_map pvars ~f:(fun pvar ->
+        if is_local pvar then Some (Sil.Nullify (pvar, loc)) else None )
   in
-  let node_add_removetmps_instructions node ids =
-    if ids <> [] then
-      let loc = Procdesc.Node.get_last_loc node in
-      Procdesc.Node.append_instrs node [Sil.Remove_temps (List.rev ids, loc)]
+  let node_removetmps_instruction loc ids =
+    if ids <> [] then Some (Sil.Remove_temps (List.rev ids, loc)) else None
   in
   List.iter
     ~f:(fun node ->
@@ -163,15 +157,19 @@ let add_nullify_instrs pdesc tenv liveness_inv_map =
                     (pvars_acc, ids_acc) )
               to_nullify ([], [])
           in
-          node_add_removetmps_instructions node ids_to_remove ;
-          node_add_nullify_instructions node pvars_to_nullify
+          let loc = Procdesc.Node.get_last_loc node in
+          node_nullify_instructions loc pvars_to_nullify
+          |> IList.opt_cons (node_removetmps_instruction loc ids_to_remove)
+          |> Procdesc.Node.append_instrs node
       | None ->
           () )
     (ProcCfg.Exceptional.nodes nullify_proc_cfg) ;
   (* nullify all address taken variables *)
   if not (AddressTaken.Domain.is_empty address_taken_vars) then
     let exit_node = ProcCfg.Exceptional.exit_node nullify_proc_cfg in
-    node_add_nullify_instructions exit_node (AddressTaken.Domain.elements address_taken_vars)
+    let exit_loc = Procdesc.Node.get_last_loc exit_node in
+    node_nullify_instructions exit_loc (AddressTaken.Domain.elements address_taken_vars)
+    |> Procdesc.Node.append_instrs exit_node
 
 
 (** perform liveness analysis and insert Nullify/Remove_temps instructions into the IR to make it
diff --git a/infer/src/istd/IList.ml b/infer/src/istd/IList.ml
index 9d3656a18..a68023e4c 100644
--- a/infer/src/istd/IList.ml
+++ b/infer/src/istd/IList.ml
@@ -145,3 +145,5 @@ let rec drop list index =
 
 
 let mem_nth list index = drop list index |> List.is_empty |> not
+
+let opt_cons opt list = match opt with Some x -> x :: list | None -> list
diff --git a/infer/src/istd/IList.mli b/infer/src/istd/IList.mli
index fd340920d..fcd6bb16b 100644
--- a/infer/src/istd/IList.mli
+++ b/infer/src/istd/IList.mli
@@ -41,3 +41,6 @@ val drop : 'a list -> int -> 'a list
 
 val mem_nth : 'a list -> int -> bool
 (** [mem_nth l n] returns whether the list [l] contains a [n]th element. *)
+
+val opt_cons : 'a option -> 'a list -> 'a list
+(** [opt_cons None l] returns [l]. [opt_cons (Some x) l] returns [x :: l]*)