[backend] Perf fix: only load tenv and cfg files once per each file, instead of once per procedure.

Summary:
This fixes a perf issue on large files, where a copy of the type environment and control flow graph were loaded for each procedure analyzed in the file.
If the type environment or the control flow graph are big, and the file contains many procedures, this can cause a big memory overhead.

Reviewed By: jvillard

Differential Revision: D4008655

fbshipit-source-id: 11d07c1

infer/src/backend/exe_env.ml

@@ -33,6 +33,13 @@ let tenv_filename file_base =
   else
     DB.global_tenv_fname
 
+module FilenameHash = Hashtbl.Make(
+  struct
+    type t = DB.filename
+    let equal file1 file2 = DB.filename_compare file1 file2 = 0
+    let hash = Hashtbl.hash
+  end)
+
 (** create a new file_data *)
 let new_file_data source nLOC cg_fname =
   let file_base = DB.chop_extension cg_fname in
@@ -46,11 +53,20 @@ let new_file_data source nLOC cg_fname =
     cfg = None; (* Cfg.load_cfg_from_file cfg_file *)
   }
 
+let create_file_data table source nLOC cg_fname =
+  match FilenameHash.find table cg_fname with
+  | file_data ->
+      file_data
+  | exception Not_found ->
+      let file_data = new_file_data source nLOC cg_fname in
+      FilenameHash.add table cg_fname file_data;
+      file_data
 
 (** execution environment *)
 type t =
   { cg: Cg.t; (** global call graph *)
     proc_map: file_data Procname.Hash.t; (** map from procedure name to file data *)
+    file_map: file_data FilenameHash.t; (** map from cg fname to file data *)
     mutable source_files : DB.SourceFileSet.t; (** Source files in the execution environment *)
   }
 
@@ -64,6 +80,7 @@ let freeze exe_env = exe_env (* TODO: unclear what this function is used for *)
 let create () =
   { cg = Cg.create None;
     proc_map = Procname.Hash.create 17;
+    file_map = FilenameHash.create 1;
     source_files = DB.SourceFileSet.empty;
   }
 
@@ -117,7 +134,7 @@ let get_file_data exe_env pname =
           let nLOC = loc.Location.nLOC in
           let source_dir = DB.source_dir_from_source_file source_file in
           let cg_fname = DB.source_dir_get_internal_file source_dir ".cg" in
-          let file_data = new_file_data source_file nLOC cg_fname in
+          let file_data = create_file_data exe_env.file_map source_file nLOC cg_fname in
           Procname.Hash.replace exe_env.proc_map pname file_data;
           Some file_data
     end