diff --git a/infer/src/IR/BiabductionModels.ml b/infer/src/IR/BiabductionModels.ml
index 1bdd87ea225..fcd5c5ba419 100644
--- a/infer/src/IR/BiabductionModels.ml
+++ b/infer/src/IR/BiabductionModels.ml
@@ -11,15 +11,15 @@ let scan_model_proc_names () =
   let db = Database.get_database AnalysisDatabase in
   Sqlite3.prepare db "SELECT proc_uid FROM model_specs"
   |> SqliteUtils.result_fold_single_column_rows db ~log:"scan model procnames"
-       ~init:String.Set.empty ~f:(fun acc proc_uid_sqlite ->
+       ~init:IString.Set.empty ~f:(fun acc proc_uid_sqlite ->
          let[@warning "-partial-match"] (Sqlite3.Data.TEXT proc_uid) = proc_uid_sqlite in
-         String.Set.add acc proc_uid )
+         IString.Set.add proc_uid acc )
 
 
 let models_index =
-  lazy (if Config.biabduction_models_mode then String.Set.empty else scan_model_proc_names ())
+  lazy (if Config.biabduction_models_mode then IString.Set.empty else scan_model_proc_names ())
 
 
 let mem proc_name =
   let proc_uid = Procname.to_unique_id proc_name in
-  String.Set.mem (Lazy.force models_index) proc_uid
+  IString.Set.mem proc_uid (Lazy.force models_index)
diff --git a/infer/src/IR/inferconfig.ml b/infer/src/IR/inferconfig.ml
index 41458e5c074..91d2e7758a0 100644
--- a/infer/src/IR/inferconfig.ml
+++ b/infer/src/IR/inferconfig.ml
@@ -119,22 +119,20 @@ module FileOrProcMatcher = struct
         List.fold
           ~f:(fun map pattern ->
             let previous =
-              try String.Map.find_exn map pattern.class_name
-              with Not_found_s _ | Stdlib.Not_found -> []
+              IString.Map.find_opt pattern.class_name map |> Option.value ~default:[]
             in
-            String.Map.set ~key:pattern.class_name ~data:(pattern :: previous) map )
-          ~init:String.Map.empty m_patterns
+            IString.Map.add pattern.class_name (pattern :: previous) map )
+          ~init:IString.Map.empty m_patterns
       in
       let do_java pname_java =
         let class_name = Procname.Java.get_class_name pname_java
         and method_name = Procname.Java.get_method pname_java in
-        try
-          let class_patterns = String.Map.find_exn pattern_map class_name in
-          List.exists
-            ~f:(fun p ->
-              match p.method_name with None -> true | Some m -> String.equal m method_name )
-            class_patterns
-        with Not_found_s _ | Stdlib.Not_found -> false
+        IString.Map.find_opt class_name pattern_map
+        |> Option.exists ~f:(fun class_patterns ->
+               List.exists
+                 ~f:(fun p ->
+                   match p.method_name with None -> true | Some m -> String.equal m method_name )
+                 class_patterns )
       in
       fun _ proc_name ->
         match proc_name with Procname.Java pname_java -> do_java pname_java | _ -> false
diff --git a/infer/src/backend/printer.ml b/infer/src/backend/printer.ml
index 74e9c5c73f5..9cd8d29f7ec 100644
--- a/infer/src/backend/printer.ml
+++ b/infer/src/backend/printer.ml
@@ -184,9 +184,9 @@ end = struct
       in
       try
         let set = Hashtbl.find err_per_line err_data.loc.Location.line in
-        Hashtbl.replace err_per_line err_data.loc.Location.line (String.Set.add set err_str)
+        Hashtbl.replace err_per_line err_data.loc.Location.line (IString.Set.add err_str set)
       with Stdlib.Not_found ->
-        Hashtbl.add err_per_line err_data.loc.Location.line (String.Set.singleton err_str)
+        Hashtbl.add err_per_line err_data.loc.Location.line (IString.Set.singleton err_str)
     in
     Errlog.iter add_err err_log ;
     err_per_line
@@ -250,7 +250,7 @@ end = struct
           () ) ;
       ( match Hashtbl.find table_err_per_line line_number with
       | errset ->
-          String.Set.iter errset ~f:(pp_err_message fmt)
+          IString.Set.iter (pp_err_message fmt) errset
       | exception Stdlib.Not_found ->
           () ) ;
       F.fprintf fmt "</td></tr>@\n"
diff --git a/infer/src/base/Config.ml b/infer/src/base/Config.ml
index 6716280629d..193e53c02a8 100644
--- a/infer/src/base/Config.ml
+++ b/infer/src/base/Config.ml
@@ -4720,7 +4720,7 @@ and racerd_always_report_java = !racerd_always_report_java
 
 and racerd_guardedby = !racerd_guardedby
 
-and racerd_ignore_classes = RevList.to_list !racerd_ignore_classes |> String.Set.of_list
+and racerd_ignore_classes = RevList.to_list !racerd_ignore_classes |> IString.Set.of_list
 
 and reactive_mode = !reactive
 
diff --git a/infer/src/base/Config.mli b/infer/src/base/Config.mli
index 54642086f2e..5070344a71f 100644
--- a/infer/src/base/Config.mli
+++ b/infer/src/base/Config.mli
@@ -765,7 +765,7 @@ val racerd_always_report_java : bool
 
 val racerd_guardedby : bool
 
-val racerd_ignore_classes : String.Set.t
+val racerd_ignore_classes : IString.Set.t
 
 val reactive_mode : bool
 
diff --git a/infer/src/base/DBWriter.ml b/infer/src/base/DBWriter.ml
index 47ddb856d04..b0ea71c25d9 100644
--- a/infer/src/base/DBWriter.ml
+++ b/infer/src/base/DBWriter.ml
@@ -429,21 +429,20 @@ module Implementation = struct
     in
     let update_statement =
       let stmts =
-        List.fold PayloadId.database_fields ~init:String.Map.empty ~f:(fun acc payload_id ->
-            String.Map.add_exn ~key:payload_id
-              ~data:
-                (Database.register_statement AnalysisDatabase
-                   {|
+        List.fold PayloadId.database_fields ~init:IString.Map.empty ~f:(fun acc payload_id ->
+            IString.Map.add payload_id
+              (Database.register_statement AnalysisDatabase
+                 {|
                      UPDATE specs SET
                        report_summary = :report_summary,
                        summary_metadata = :summary_metadata,
                        %s = :value
                      WHERE proc_uid = :proc_uid
                    |}
-                   payload_id )
+                 payload_id )
               acc )
       in
-      fun payload_id -> String.Map.find_exn stmts (PayloadId.Variants.to_name payload_id)
+      fun payload_id -> IString.Map.find (PayloadId.Variants.to_name payload_id) stmts
     in
     fun analysis_req ~proc_uid ~proc_name ~merge_pulse_payload ~merge_report_summary
         ~merge_summary_metadata ->
diff --git a/infer/src/base/Scuba.ml b/infer/src/base/Scuba.ml
index e02a510ad3d..fc9a5df0d35 100644
--- a/infer/src/base/Scuba.ml
+++ b/infer/src/base/Scuba.ml
@@ -6,7 +6,7 @@
  *)
 
 open! IStd
-module SMap = Map.Make (String)
+module SMap = IString.Map
 
 type table = InferEvents
 
@@ -27,23 +27,23 @@ let new_sample ~time =
 
 
 let add_int ~name ~value sample =
-  let int_section = SMap.set sample.int_section ~key:name ~data:value in
+  let int_section = SMap.add name value sample.int_section in
   {sample with int_section}
 
 
 let add_normal ~name ~value sample =
-  let normal_section = SMap.set sample.normal_section ~key:name ~data:value in
+  let normal_section = SMap.add name value sample.normal_section in
   {sample with normal_section}
 
 
 let add_tagset ~name ~value sample =
-  let tagset_section = SMap.set sample.tagset_section ~key:name ~data:value in
+  let tagset_section = SMap.add name value sample.tagset_section in
   {sample with tagset_section}
 
 
 let sample_to_json sample =
   let map_to_assoc value_to_json key_value_map =
-    let pairs = SMap.to_alist key_value_map in
+    let pairs = SMap.bindings key_value_map in
     let assocs = List.map pairs ~f:(fun (name, data) -> (name, value_to_json data)) in
     `Assoc assocs
   in
diff --git a/infer/src/base/SourceFile.ml b/infer/src/base/SourceFile.ml
index 4cd5fffb2f2..b8c81055033 100644
--- a/infer/src/base/SourceFile.ml
+++ b/infer/src/base/SourceFile.ml
@@ -235,14 +235,14 @@ let is_under_project_root = function
       false
 
 
-let exists_cache = String.Table.create ~size:256 ()
+let exists_cache = IString.Hash.create 256
 
 let path_exists abs_path =
-  try String.Table.find_exn exists_cache abs_path
-  with Not_found_s _ | Stdlib.Not_found ->
-    let result = ISys.file_exists abs_path in
-    String.Table.set exists_cache ~key:abs_path ~data:result ;
-    result
+  IString.Hash.find_opt exists_cache abs_path
+  |> Option.value_or_thunk ~default:(fun () ->
+         let result = ISys.file_exists abs_path in
+         IString.Hash.replace exists_cache abs_path result ;
+         result )
 
 
 let of_header ?(warn_on_error = true) header_file =
diff --git a/infer/src/base/ToplLexer.mll b/infer/src/base/ToplLexer.mll
index 1da0b331965..95d015df021 100644
--- a/infer/src/base/ToplLexer.mll
+++ b/infer/src/base/ToplLexer.mll
@@ -22,9 +22,9 @@
   let quoted = Str.regexp "\\\\\\(.\\)"
   let unquote x = Str.global_replace quoted "\\1" x
 
-  (* We open Caml, because ocamllex generates code that uses Array.make,
+  (* We open Stdlib, because ocamllex generates code that uses Array.make,
   which is not available in Core. Ideally, this should go away. *)
-  open! Caml
+  open! Stdlib
 }
 
 let id_tail = ['a'-'z' 'A'-'Z' '0'-'9']*
diff --git a/infer/src/biabduction/BiabductionSummary.ml b/infer/src/biabduction/BiabductionSummary.ml
index 4c3836e7e92..9e8ac51fd66 100644
--- a/infer/src/biabduction/BiabductionSummary.ml
+++ b/infer/src/biabduction/BiabductionSummary.ml
@@ -157,9 +157,9 @@ module Visitedset = struct
   end)
 
   let pp fmt visitedset =
-    let collect_lines (_, ns) acc = List.fold ns ~f:Int.Set.add ~init:acc in
-    let lines = fold collect_lines visitedset Int.Set.empty in
-    Pp.seq F.pp_print_int fmt (Int.Set.elements lines)
+    let collect_lines (_, ns) acc = List.fold ns ~f:(fun acc i -> IInt.Set.add i acc) ~init:acc in
+    let lines = fold collect_lines visitedset IInt.Set.empty in
+    Pp.seq F.pp_print_int fmt (IInt.Set.elements lines)
 end
 
 (** A spec consists of:
diff --git a/infer/src/bufferoverrun/bufferOverrunAnalysis.ml b/infer/src/bufferoverrun/bufferOverrunAnalysis.ml
index 5e1946e16b5..29b96bbea42 100644
--- a/infer/src/bufferoverrun/bufferOverrunAnalysis.ml
+++ b/infer/src/bufferoverrun/bufferOverrunAnalysis.ml
@@ -237,11 +237,10 @@ module TransferFunctions = struct
 
 
   let join_java_static_final =
-    let known_java_static_fields = String.Set.of_list [".EMPTY"] in
+    let known_java_static_fields = IString.Set.of_list [".EMPTY"] in
     let is_known_java_static_field fn =
       let fieldname = Fieldname.to_string fn in
-      String.Set.exists known_java_static_fields ~f:(fun suffix ->
-          String.is_suffix fieldname ~suffix )
+      IString.Set.exists (fun suffix -> String.is_suffix fieldname ~suffix) known_java_static_fields
     in
     let copy_reachable_locs_from loc ~from_mem ~to_mem =
       let copy loc acc =
@@ -279,11 +278,11 @@ module TransferFunctions = struct
 
 
   let modeled_load_of_empty_collection_opt =
-    let known_empty_collections = String.Set.of_list ["EMPTY_LIST"; "EMPTY_SET"; "EMPTY_MAP"] in
+    let known_empty_collections = IString.Set.of_list ["EMPTY_LIST"; "EMPTY_SET"; "EMPTY_MAP"] in
     fun exp model_env ret mem ->
       match exp with
       | Exp.Lfield (_, fieldname, typ)
-        when String.Set.mem known_empty_collections (Fieldname.get_field_name fieldname)
+        when IString.Set.mem (Fieldname.get_field_name fieldname) known_empty_collections
              && String.equal "java.util.Collections" (Typ.to_string typ) ->
           Models.Collection.create_collection model_env ~ret mem ~length:Itv.zero |> Option.some
       | _ ->
diff --git a/infer/src/checkers/LithoDomain.ml b/infer/src/checkers/LithoDomain.ml
index 63c18f9a9c7..709378625bb 100644
--- a/infer/src/checkers/LithoDomain.ml
+++ b/infer/src/checkers/LithoDomain.ml
@@ -30,17 +30,29 @@ end
 
 module LocalAccessPathSet = PrettyPrintable.MakePPSet (LocalAccessPath)
 
-let suffixes = String.Set.of_list ["Attr"; "Dip"; "Px"; "Res"; "Sp"]
+let suffixes = IString.Set.of_list ["Attr"; "Dip"; "Px"; "Res"; "Sp"]
 
 module MethodCallPrefix = struct
   type t =
     {prefix: string; procname: Procname.t [@compare.ignore]; location: Location.t [@compare.ignore]}
   [@@deriving compare]
 
+  exception Found of string
+
   let make_with_prefixes procname location =
     let method_name = Procname.get_method procname in
     let prefix_opt =
-      String.Set.find_map suffixes ~f:(fun suffix -> String.chop_suffix method_name ~suffix)
+      try
+        IString.Set.iter
+          (fun suffix ->
+            match String.chop_suffix method_name ~suffix with
+            | Some res ->
+                raise (Found res)
+            | None ->
+                () )
+          suffixes ;
+        None
+      with Found res -> Some res
     in
     let default = [{prefix= method_name; procname; location}] in
     Option.value_map prefix_opt ~default ~f:(fun prefix ->
@@ -185,9 +197,9 @@ module MethodCalls = struct
 
   let to_string_set method_calls =
     let accum_as_string method_call acc =
-      String.Set.add acc (MethodCallPrefix.procname_to_string method_call)
+      IString.Set.add (MethodCallPrefix.procname_to_string method_call) acc
     in
-    S.fold accum_as_string method_calls String.Set.empty
+    S.fold accum_as_string method_calls IString.Set.empty
 
 
   let get_call_chain method_calls =
diff --git a/infer/src/checkers/LithoDomain.mli b/infer/src/checkers/LithoDomain.mli
index c2607c2f02c..5e158270396 100644
--- a/infer/src/checkers/LithoDomain.mli
+++ b/infer/src/checkers/LithoDomain.mli
@@ -20,7 +20,7 @@ module LocalAccessPath : sig
   val make_from_access_expression : HilExp.AccessExpression.t -> Procname.t -> t
 end
 
-val suffixes : String.Set.t
+val suffixes : IString.Set.t
 
 (** Called procedure & location *)
 module MethodCallPrefix : sig
@@ -76,6 +76,6 @@ val pp_summary : Format.formatter -> summary -> unit
 val get_summary : is_void_func:bool -> t -> summary
 
 val check_required_props :
-     check_on_string_set:(Typ.name -> Location.t -> MethodCallPrefix.t list -> String.Set.t -> unit)
+     check_on_string_set:(Typ.name -> Location.t -> MethodCallPrefix.t list -> IString.Set.t -> unit)
   -> summary
   -> summary
diff --git a/infer/src/checkers/RequiredProps.ml b/infer/src/checkers/RequiredProps.ml
index 0f6c7dff849..bf63c602062 100644
--- a/infer/src/checkers/RequiredProps.ml
+++ b/infer/src/checkers/RequiredProps.ml
@@ -90,13 +90,15 @@ let report_missing_required_prop proc_desc err_log prop parent_typename ~create_
 
 let has_prop prop_set prop =
   let check prop =
-    String.Set.mem prop_set prop
+    IString.Set.mem prop prop_set
     || (* @Prop(resType = ...) myProp can also be set via myProp(), myPropAttr(), myPropDip(), myPropPx(), myPropRes() or myPropSp().
           Our annotation parameter parsing is too primitive to identify resType, so just assume
           that all @Prop's can be set any of these 6 ways. *)
-    String.Set.exists prop_set ~f:(fun el ->
+    IString.Set.exists
+      (fun el ->
         String.chop_prefix el ~prefix:prop
-        |> Option.exists ~f:(fun suffix -> String.Set.mem LithoDomain.suffixes suffix) )
+        |> Option.exists ~f:(fun suffix -> IString.Set.mem suffix LithoDomain.suffixes) )
+      prop_set
   in
   match prop with
   | Prop prop ->
diff --git a/infer/src/clang/ClangCommand.ml b/infer/src/clang/ClangCommand.ml
index a1f5fecb269..28e168fc84a 100644
--- a/infer/src/clang/ClangCommand.ml
+++ b/infer/src/clang/ClangCommand.ml
@@ -88,9 +88,9 @@ let filter_and_replace_unsupported_args ?(replace_options_arg = fun _ s -> s) ?(
            arg file, we need to remove its argument now *)
         aux in_argfiles (false, res_rev, true) tl
     | at_argfile :: tl
-      when String.is_prefix at_argfile ~prefix:"@" && not (String.Set.mem in_argfiles at_argfile)
+      when String.is_prefix at_argfile ~prefix:"@" && not (IString.Set.mem at_argfile in_argfiles)
       -> (
-        let in_argfiles' = String.Set.add in_argfiles at_argfile in
+        let in_argfiles' = IString.Set.add at_argfile in_argfiles in
         let argfile = String.slice at_argfile 1 (String.length at_argfile) in
         match In_channel.read_lines argfile with
         | lines ->
@@ -129,7 +129,7 @@ let filter_and_replace_unsupported_args ?(replace_options_arg = fun _ s -> s) ?(
         let arg' = replace_options_arg res_rev arg in
         aux in_argfiles (false, arg' :: res_rev, changed || not (phys_equal arg arg')) tl
   in
-  match aux String.Set.empty (false, [], false) args with
+  match aux IString.Set.empty (false, [], false) args with
   | _, res_rev, _ ->
       (* return non-reversed list *)
       List.append pre_args (List.rev_append res_rev post_args)
diff --git a/infer/src/clang/ClangPointers.ml b/infer/src/clang/ClangPointers.ml
index d50e88149ce..c7aacbf0f8f 100644
--- a/infer/src/clang/ClangPointers.ml
+++ b/infer/src/clang/ClangPointers.ml
@@ -7,15 +7,15 @@
 
 open! IStd
 module L = Logging
-module Map = Map.Make (Int)
+module Map = IInt.Map
 
-let ivar_to_property_table = Int.Table.create ~size:256 ()
+let ivar_to_property_table = IInt.Hash.create 256
 
-let pointer_decl_table = Int.Table.create ~size:256 ()
+let pointer_decl_table = IInt.Hash.create 256
 
-let pointer_stmt_table = Int.Table.create ~size:256 ()
+let pointer_stmt_table = IInt.Hash.create 256
 
-let pointer_type_table = Int.Table.create ~size:256 ()
+let pointer_type_table = IInt.Hash.create 256
 
 let empty_v = Clang_ast_visit.empty_visitor
 
@@ -55,7 +55,7 @@ let get_val_from_node node =
 let add_node_to_cache node cache =
   let key = get_ptr_from_node node in
   let data = get_val_from_node node in
-  Int.Table.set cache ~key ~data
+  IInt.Hash.replace cache key data
 
 
 let process_decl _ decl =
@@ -63,7 +63,7 @@ let process_decl _ decl =
   match decl with
   | Clang_ast_t.ObjCPropertyDecl (_, _, {opdi_ivar_decl= Some decl_ref}) ->
       let ivar_pointer = decl_ref.Clang_ast_t.dr_decl_pointer in
-      Int.Table.set ivar_to_property_table ~key:ivar_pointer ~data:decl
+      IInt.Hash.replace ivar_to_property_table ivar_pointer decl
   | _ ->
       ()
 
@@ -113,10 +113,10 @@ let complete_source_location _ source_loc =
 
 
 let reset_cache () =
-  Int.Table.clear pointer_decl_table ;
-  Int.Table.clear pointer_stmt_table ;
-  Int.Table.clear pointer_type_table ;
-  Int.Table.clear ivar_to_property_table ;
+  IInt.Hash.clear pointer_decl_table ;
+  IInt.Hash.clear pointer_stmt_table ;
+  IInt.Hash.clear pointer_type_table ;
+  IInt.Hash.clear ivar_to_property_table ;
   reset_sloc previous_sloc
 
 
diff --git a/infer/src/clang/ClangPointers.mli b/infer/src/clang/ClangPointers.mli
index eb06640f4ee..4f980eeab2a 100644
--- a/infer/src/clang/ClangPointers.mli
+++ b/infer/src/clang/ClangPointers.mli
@@ -7,15 +7,15 @@
 
 open! IStd
 
-module Map : module type of Map.Make (Int)
+module Map : Stdlib.Map.S with type key = int
 
-val pointer_decl_table : Clang_ast_t.decl Int.Table.t
+val pointer_decl_table : Clang_ast_t.decl IInt.Hash.t
 (** maps decl pointer to its decl record *)
 
-val pointer_stmt_table : Clang_ast_t.stmt Int.Table.t
+val pointer_stmt_table : Clang_ast_t.stmt IInt.Hash.t
 (** maps stmt pointer to its stmt record *)
 
-val pointer_type_table : Clang_ast_t.c_type Int.Table.t
+val pointer_type_table : Clang_ast_t.c_type IInt.Hash.t
 (** map pointer to its type *)
 
 val populate_all_tables : Clang_ast_t.decl -> unit
diff --git a/infer/src/clang/cAst_utils.ml b/infer/src/clang/cAst_utils.ml
index b3315d10eec..774f4fafee5 100644
--- a/infer/src/clang/cAst_utils.ml
+++ b/infer/src/clang/cAst_utils.ml
@@ -146,10 +146,10 @@ let named_decl_info_equal ndi1 ndi2 =
 
 
 let get_decl decl_ptr =
-  let decl = Int.Table.find ClangPointers.pointer_decl_table decl_ptr in
+  let decl = IInt.Hash.find_opt ClangPointers.pointer_decl_table decl_ptr in
   match decl with
   | Some (VarDecl ({di_parent_pointer= Some parent_pointer}, ndi, _, _)) -> (
-    match Int.Table.find ClangPointers.pointer_decl_table parent_pointer with
+    match IInt.Hash.find_opt ClangPointers.pointer_decl_table parent_pointer with
     | Some (CXXRecordDecl (_, _, _, decls, _, _, _, _)) -> (
         let has_same_ndi = function
           | Clang_ast_t.VarDecl (_, ndi', _, _) ->
@@ -169,7 +169,7 @@ let get_decl_opt decl_ptr_opt =
 
 
 let get_stmt stmt_ptr source_range =
-  let stmt = Int.Table.find ClangPointers.pointer_stmt_table stmt_ptr in
+  let stmt = IInt.Hash.find_opt ClangPointers.pointer_stmt_table stmt_ptr in
   if Option.is_none stmt then
     CFrontend_errors.incorrect_assumption __POS__ source_range "stmt with pointer %d not found@\n"
       stmt_ptr ;
@@ -204,28 +204,28 @@ let update_sil_types_map type_ptr sil_type =
 
 let update_enum_map_exn enum_constant_pointer sil_exp =
   let predecessor_pointer_opt, _ =
-    ClangPointers.Map.find_exn !CFrontend_config.enum_map enum_constant_pointer
+    ClangPointers.Map.find enum_constant_pointer !CFrontend_config.enum_map
   in
   let enum_map_value = (predecessor_pointer_opt, Some sil_exp) in
   CFrontend_config.enum_map :=
-    ClangPointers.Map.set !CFrontend_config.enum_map ~key:enum_constant_pointer ~data:enum_map_value
+    ClangPointers.Map.add enum_constant_pointer enum_map_value !CFrontend_config.enum_map
 
 
 let add_enum_constant enum_constant_pointer predecessor_pointer_opt =
   let enum_map_value = (predecessor_pointer_opt, None) in
   CFrontend_config.enum_map :=
-    ClangPointers.Map.set !CFrontend_config.enum_map ~key:enum_constant_pointer ~data:enum_map_value
+    ClangPointers.Map.add enum_constant_pointer enum_map_value !CFrontend_config.enum_map
 
 
 let get_enum_constant_exp_exn enum_constant_pointer =
-  ClangPointers.Map.find_exn !CFrontend_config.enum_map enum_constant_pointer
+  ClangPointers.Map.find enum_constant_pointer !CFrontend_config.enum_map
 
 
 let get_type type_ptr =
   match type_ptr with
   (* There is chance for success only if type_ptr is in fact clang pointer *)
   | Clang_ast_types.TypePtr.Ptr raw_ptr ->
-      Int.Table.find ClangPointers.pointer_type_table raw_ptr
+      IInt.Hash.find_opt ClangPointers.pointer_type_table raw_ptr
   | _ ->
       (* TODO(T30739447): investigate why this happens *)
       (* otherwise, function fails *)
diff --git a/infer/src/clang/cScope.ml b/infer/src/clang/cScope.ml
index aac1fc94d6b..56a26d1bc47 100644
--- a/infer/src/clang/cScope.ml
+++ b/infer/src/clang/cScope.ml
@@ -269,9 +269,7 @@ module Variables = struct
         L.debug Capture Verbose "~[%d:%a]" stmt_info.Clang_ast_t.si_pointer
           (Pp.seq ~sep:"," CContext.pp_var_to_destroy)
           vars_to_destroy ;
-        let map =
-          ClangPointers.Map.set map ~key:stmt_info.Clang_ast_t.si_pointer ~data:vars_to_destroy
-        in
+        let map = ClangPointers.Map.add stmt_info.Clang_ast_t.si_pointer vars_to_destroy map in
         (scope, map)
     | DeclStmt (_, stmts, decl_list) ->
         let to_destroy =
@@ -323,7 +321,7 @@ module Variables = struct
         L.debug Capture Verbose "~[%d:%a]" pointer
           (Pp.seq ~sep:"," CContext.pp_var_to_destroy)
           vars_to_destroy ;
-        ClangPointers.Map.set map ~key:pointer ~data:vars_to_destroy )
+        ClangPointers.Map.add pointer vars_to_destroy map )
       else (
         L.debug Capture Verbose "~[%d:skip]" pointer ;
         map )
diff --git a/infer/src/clang/cTrans.ml b/infer/src/clang/cTrans.ml
index 5a0783e845c..aa2c9abde62 100644
--- a/infer/src/clang/cTrans.ml
+++ b/infer/src/clang/cTrans.ml
@@ -2100,7 +2100,7 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
     if not (CGeneral_utils.is_cpp_translation context.translation_unit_context) then None
     else
       match
-        CContext.StmtMap.find context.CContext.vars_to_destroy stmt_info.Clang_ast_t.si_pointer
+        CContext.StmtMap.find_opt stmt_info.Clang_ast_t.si_pointer context.CContext.vars_to_destroy
       with
       | None ->
           L.(debug Capture Verbose) "@\nNo variables going out of scope here.@\n" ;
@@ -3084,9 +3084,7 @@ module CTrans_funct (F : CModule_type.CFrontend) : CModule_type.CTranslation = s
 
 
   and init_dynamic_array trans_state array_exp_typ array_stmt_info dynlength_stmt_pointer =
-    let dynlength_stmt =
-      Int.Table.find_exn ClangPointers.pointer_stmt_table dynlength_stmt_pointer
-    in
+    let dynlength_stmt = IInt.Hash.find ClangPointers.pointer_stmt_table dynlength_stmt_pointer in
     let dynlength_stmt_info, _ = Clang_ast_proj.get_stmt_tuple dynlength_stmt in
     let trans_state_pri = PriorityNode.try_claim_priority_node trans_state array_stmt_info in
     let dynlength_trans_result = instruction trans_state_pri dynlength_stmt in
diff --git a/infer/src/concurrency/RacerDModels.ml b/infer/src/concurrency/RacerDModels.ml
index f760305c9a7..1931cb2d633 100644
--- a/infer/src/concurrency/RacerDModels.ml
+++ b/infer/src/concurrency/RacerDModels.ml
@@ -657,7 +657,7 @@ let get_litho_explanation tenv pname =
 
 
 let class_is_ignored_by_racerd class_name =
-  Typ.Name.name class_name |> String.Set.mem Config.racerd_ignore_classes
+  IString.Set.mem (Typ.Name.name class_name) Config.racerd_ignore_classes
 
 
 let proc_is_ignored_by_racerd callee =
diff --git a/infer/src/concurrency/StarvationModels.ml b/infer/src/concurrency/StarvationModels.ml
index cf45040540b..0ea21f62966 100644
--- a/infer/src/concurrency/StarvationModels.ml
+++ b/infer/src/concurrency/StarvationModels.ml
@@ -38,7 +38,7 @@ let android_anr_time_limit = 5.0
 (* get time unit in seconds *)
 let secs_of_timeunit =
   let time_units =
-    String.Map.of_alist_exn
+    Stdlib.List.to_seq
       [ ("NANOSECONDS", 0.000_000_001)
       ; ("MICROSECONDS", 0.000_001)
       ; ("MILLISECONDS", 0.001)
@@ -46,6 +46,7 @@ let secs_of_timeunit =
       ; ("MINUTES", 60.0)
       ; ("HOURS", 3_600.0)
       ; ("DAYS", 86_400.0) ]
+    |> IString.Map.of_seq
   in
   let str_of_access_path = function
     | _, [AccessPath.FieldAccess field]
@@ -61,7 +62,8 @@ let secs_of_timeunit =
     | _ ->
         None
   in
-  fun timeunit_exp -> str_of_exp timeunit_exp |> Option.bind ~f:(String.Map.find time_units)
+  fun timeunit_exp ->
+    str_of_exp timeunit_exp |> Option.bind ~f:(fun t -> IString.Map.find_opt t time_units)
 
 
 let float_of_const_int = function
diff --git a/infer/src/cost/ConfigImpactAnalysis.ml b/infer/src/cost/ConfigImpactAnalysis.ml
index 40bda563c7f..4fbd41e62cb 100644
--- a/infer/src/cost/ConfigImpactAnalysis.ml
+++ b/infer/src/cost/ConfigImpactAnalysis.ml
@@ -1049,7 +1049,7 @@ module TransferFunctions = struct
 
   let is_cheap_system_method =
     let cheap_system_methods =
-      String.Set.of_list
+      IString.Set.of_list
         [ "clearProperty"
         ; "console"
         ; "currentTimeMillis"
@@ -1071,7 +1071,7 @@ module TransferFunctions = struct
         ; "setProperty"
         ; "setSecurityManager" ]
     in
-    fun _ method_name -> String.Set.mem cheap_system_methods method_name
+    fun _ method_name -> IString.Set.mem method_name cheap_system_methods
 
 
   let is_known_cheap_method =
diff --git a/infer/src/integration/Differential.ml b/infer/src/integration/Differential.ml
index 351fc5c810b..de9cc7c44d4 100644
--- a/infer/src/integration/Differential.ml
+++ b/infer/src/integration/Differential.ml
@@ -476,7 +476,7 @@ module ConfigImpactItem = struct
           in
           {config_impact_item; unchecked_callees}
     in
-    let fold_aux ~key:_ ~data ((acc_introduced, acc_fixed) as acc) =
+    let fold_aux _key data ((acc_introduced, acc_fixed) as acc) =
       match data with
       | `Both (current_reports, previous_reports) ->
           (* current/previous reports cannot be empty. *)
@@ -507,14 +507,31 @@ module ConfigImpactItem = struct
           acc
     in
     let map_of_config_impact config_impact =
-      List.fold ~init:String.Map.empty config_impact
+      List.fold ~init:IString.Map.empty config_impact
         ~f:(fun acc ({Jsonconfigimpact_t.hash= key; unchecked_callees} as config_impact_item) ->
           let unchecked_callees = UncheckedCallees.decode unchecked_callees in
-          String.Map.add_multi acc ~key ~data:{config_impact_item; unchecked_callees} )
+          IString.Map.update key
+            (fun v_opt ->
+              Some ({config_impact_item; unchecked_callees} :: Option.value v_opt ~default:[]) )
+            acc )
     in
     let current_map = map_of_config_impact current_config_impact in
     let previous_map = map_of_config_impact previous_config_impact in
-    Map.fold2 ~init:([], []) current_map previous_map ~f:fold_aux
+    let combined_map =
+      IString.Map.merge
+        (fun _key curr_opt prev_opt ->
+          match (curr_opt, prev_opt) with
+          | Some curr, None ->
+              Some (`Left curr)
+          | None, Some prev ->
+              Some (`Right prev)
+          | Some curr, Some prev ->
+              Some (`Both (curr, prev))
+          | None, None ->
+              assert false )
+        current_map previous_map
+    in
+    IString.Map.fold fold_aux combined_map ([], [])
 end
 
 module Report = struct
diff --git a/infer/src/integration/DifferentialFilters.ml b/infer/src/integration/DifferentialFilters.ml
index 01bc6c4bd6b..440497b5281 100644
--- a/infer/src/integration/DifferentialFilters.ml
+++ b/infer/src/integration/DifferentialFilters.ml
@@ -178,14 +178,16 @@ let interesting_paths_filter (interesting_paths : SourceFile.t list option) =
                if (not (SourceFile.is_invalid p)) && SourceFile.is_under_project_root p then
                  Some (SourceFile.to_string p)
                else None )
-        |> String.Set.of_list
+        |> IString.Set.of_list
       in
       fun ~do_log report ->
         let stat = {all= List.length report; filtered_out= 0; filtered_out_header= 0} in
         let filtered_report =
           List.filter
             ~f:(fun issue ->
-              let is_interesting_path = String.Set.mem interesting_paths_set issue.Jsonbug_t.file in
+              let is_interesting_path =
+                IString.Set.mem issue.Jsonbug_t.file interesting_paths_set
+              in
               if do_log then incr_stat is_interesting_path issue.Jsonbug_t.file stat ;
               is_interesting_path )
             report
diff --git a/infer/src/integration/Gradle.ml b/infer/src/integration/Gradle.ml
index 81ce0505ab7..8b8877d70c3 100644
--- a/infer/src/integration/Gradle.ml
+++ b/infer/src/integration/Gradle.ml
@@ -45,11 +45,11 @@ let process_gradle_output_line =
     |> Option.value_map ~default:acc ~f:(fun pos ->
            let content = String.drop_prefix line (pos + String.length arg_start_pattern) in
            L.debug Capture Verbose "Processing: %s@." content ;
-           if String.Set.mem seen content then acc
+           if IString.Set.mem content seen then acc
            else
              let javac_data = parse_gradle_line ~kotlin:Config.kotlin_capture ~line:content in
              let out_dir = Unix.mkdtemp capture_output_template in
-             (String.Set.add seen content, (out_dir, javac_data) :: target_dirs) )
+             (IString.Set.add content seen, (out_dir, javac_data) :: target_dirs) )
 
 
 let run_gradle ~prog ~args =
@@ -67,7 +67,7 @@ let run_gradle ~prog ~args =
   L.progress "[GRADLE] running gradle took %a@\n" Mtime.Span.pp (Mtime_clock.count time) ;
   match Utils.read_file gradle_output_file with
   | Ok lines ->
-      List.fold lines ~init:(String.Set.empty, []) ~f:process_gradle_output_line
+      List.fold lines ~init:(IString.Set.empty, []) ~f:process_gradle_output_line
   | Error _ ->
       L.die ExternalError "*** failed to read gradle output: %s@\n" gradle_output_file
 
@@ -133,5 +133,5 @@ let capture ~prog ~args =
   let time = Mtime_clock.counter () in
   run_infer_capture rev_target_data ;
   write_rev_infer_deps rev_target_data ;
-  L.debug Capture Quiet "[GRADLE] infer processed %d lines in %a@\n" (String.Set.length processed)
-    Mtime.Span.pp (Mtime_clock.count time)
+  L.debug Capture Quiet "[GRADLE] infer processed %d lines in %a@\n"
+    (IString.Set.cardinal processed) Mtime.Span.pp (Mtime_clock.count time)
diff --git a/infer/src/integration/JsonReports.ml b/infer/src/integration/JsonReports.ml
index 8d94463822e..7a81982b7ee 100644
--- a/infer/src/integration/JsonReports.ml
+++ b/infer/src/integration/JsonReports.ml
@@ -239,7 +239,7 @@ module JsonIssuePrinter = MakeJsonListPrinter (struct
           match Utils.read_file filename with
           | Error _ ->
               L.user_error "Could not read file %s@\n" filename ;
-              String.Map.empty
+              IString.Map.empty
           | Ok lines ->
               Suppressions.parse_lines ~file:filename lines )
     in
diff --git a/infer/src/integration/StatsDiff.ml b/infer/src/integration/StatsDiff.ml
index 102b4a92926..bf5d3f86598 100644
--- a/infer/src/integration/StatsDiff.ml
+++ b/infer/src/integration/StatsDiff.ml
@@ -29,24 +29,24 @@ module F = Format
   }
     v} *)
 
-(* keep this sorted or else... (the [ok_exn] below will fail) *)
+(* keep this sorted or else... *)
 let stable_stat_events =
-  [| "count.analysis_scheduler_gc_stats.compactions"
-   ; "count.backend_stats.pulse_aliasing_contradictions"
-   ; "count.backend_stats.pulse_captured_vars_length_contradictions"
-   ; "count.backend_stats.pulse_summaries_count_0_percent"
-   ; "count.backend_stats.pulse_summaries_count_1"
-   ; "count.backend_stats.pulse_summaries_unsat_for_caller"
-   ; "count.backend_stats.pulse_summaries_unsat_for_caller_percent"
-   ; "count.backend_stats.pulse_summaries_with_some_unreachable_nodes"
-   ; "count.backend_stats.pulse_summaries_with_some_unreachable_nodes_percent"
-   ; "count.backend_stats.pulse_summaries_with_some_unreachable_returns"
-   ; "count.backend_stats.pulse_summaries_with_some_unreachable_returns_percent"
-   ; "count.backend_stats.timeouts"
-   ; "count.num_analysis_workers"
-   ; "count.source_files_to_analyze"
-   ; "msg.analyzed_file" |]
-  |> String.Set.of_sorted_array |> Or_error.ok_exn
+  IString.Set.of_list
+    [ "count.analysis_scheduler_gc_stats.compactions"
+    ; "count.backend_stats.pulse_aliasing_contradictions"
+    ; "count.backend_stats.pulse_captured_vars_length_contradictions"
+    ; "count.backend_stats.pulse_summaries_count_0_percent"
+    ; "count.backend_stats.pulse_summaries_count_1"
+    ; "count.backend_stats.pulse_summaries_unsat_for_caller"
+    ; "count.backend_stats.pulse_summaries_unsat_for_caller_percent"
+    ; "count.backend_stats.pulse_summaries_with_some_unreachable_nodes"
+    ; "count.backend_stats.pulse_summaries_with_some_unreachable_nodes_percent"
+    ; "count.backend_stats.pulse_summaries_with_some_unreachable_returns"
+    ; "count.backend_stats.pulse_summaries_with_some_unreachable_returns_percent"
+    ; "count.backend_stats.timeouts"
+    ; "count.num_analysis_workers"
+    ; "count.source_files_to_analyze"
+    ; "msg.analyzed_file" ]
 
 
 let error ~expected json =
@@ -269,7 +269,7 @@ let pp_diff fmt diff =
 
 
 let is_changed_entry_significant entry =
-  String.Set.mem stable_stat_events entry.event
+  IString.Set.mem entry.event stable_stat_events
   && Option.exists (delta_of_changed_entry entry) ~f:(fun (_, _, delta) -> Float.(abs delta > 0.5))
 
 
diff --git a/infer/src/integration/Suppressions.ml b/infer/src/integration/Suppressions.ml
index 88486277f95..dd14ea29740 100644
--- a/infer/src/integration/Suppressions.ml
+++ b/infer/src/integration/Suppressions.ml
@@ -23,25 +23,26 @@ module Span = struct
         F.fprintf f "Blocks %a" (Pp.seq ~sep:", " pp_block) b
 end
 
-type t = Span.t String.Map.t
+type t = Span.t IString.Map.t
 
 let pp f suppressions =
-  if Map.is_empty suppressions then F.pp_print_string f "Empty"
-  else Map.iteri suppressions ~f:(fun ~key ~data -> F.fprintf f "%s: %a@\n" key Span.pp data)
+  if IString.Map.is_empty suppressions then F.pp_print_string f "Empty"
+  else IString.Map.iter (fun key data -> F.fprintf f "%s: %a@\n" key Span.pp data) suppressions
 
 
-type fold_state = {current_line: int; block_start: int option; issue_types: String.Set.t; res: t}
+type fold_state = {current_line: int; block_start: int option; issue_types: IString.Set.t; res: t}
 
 let pp_fold_state f {current_line; block_start; issue_types; res} =
   F.fprintf f "current_line: %d@\n" current_line ;
   F.fprintf f "block_start: %a@\n" (Pp.option F.pp_print_int) block_start ;
-  F.fprintf f "issue_types: [%a]@\n" (Pp.seq F.pp_print_string) (Set.to_list issue_types) ;
+  F.fprintf f "issue_types: [%a]@\n" (Pp.seq F.pp_print_string) (IString.Set.elements issue_types) ;
   F.fprintf f "res: %a@\n" pp res
 
 
 let update_suppressions_every issue_types suppressions =
-  Set.fold issue_types ~init:suppressions ~f:(fun m issue_type ->
-      Map.set m ~key:issue_type ~data:Span.Every )
+  IString.Set.fold
+    (fun issue_type m -> IString.Map.add issue_type Span.Every m)
+    issue_types suppressions
 
 
 let update_suppressions block_start current_line issue_types suppressions =
@@ -49,16 +50,19 @@ let update_suppressions block_start current_line issue_types suppressions =
   | None ->
       suppressions
   | Some start ->
-      Set.fold issue_types ~init:suppressions ~f:(fun m issue_type ->
-          match Map.find suppressions issue_type with
+      IString.Set.fold
+        (fun issue_type m ->
+          match IString.Map.find_opt issue_type suppressions with
           | None ->
-              Map.set m ~key:issue_type ~data:(Span.Blocks [{first= start; last= current_line}])
+              IString.Map.add issue_type (Span.Blocks [{first= start; last= current_line}]) m
           | Some (Span.Blocks b) ->
-              Map.set m ~key:issue_type
-                ~data:(Span.Blocks (b @ [{Span.first= start; last= current_line}]))
+              IString.Map.add issue_type
+                (Span.Blocks (b @ [{Span.first= start; last= current_line}]))
+                m
           | Some Span.Every ->
               (* don't override Every with Blocks *)
               m )
+        issue_types suppressions
 
 
 let substring_after_match rx s =
@@ -69,14 +73,14 @@ let substring_after_match rx s =
       Some (String.concat ~sep:"," parts)
 
 
-let regex_cache = ref String.Map.empty
+let regex_cache = ref IString.Map.empty
 
 let get_regex s =
-  match Map.find !regex_cache s with
+  match IString.Map.find_opt s !regex_cache with
   | None -> (
     try
       let r = Str.regexp s in
-      regex_cache := Map.set !regex_cache ~key:s ~data:r ;
+      regex_cache := IString.Map.add s r !regex_cache ;
       Some r
     with _ ->
       L.user_error "Invalid regex: %s@\n" s ;
@@ -110,7 +114,7 @@ let extract_valid_issue_types s =
          let valid = valid_issue_type s in
          if not valid then L.user_error "%s not a valid issue_type / wildcard@\n" s ;
          valid )
-  |> String.Set.of_list
+  |> IString.Set.of_list
 
 
 (* trailing space intentional *)
@@ -122,14 +126,14 @@ let parse_lines ?file lines =
   let parse_result =
     List.fold lines
       ~init:
-        {current_line= 1; block_start= None; issue_types= String.Set.empty; res= String.Map.empty}
+        {current_line= 1; block_start= None; issue_types= IString.Set.empty; res= IString.Map.empty}
       ~f:(fun {current_line; block_start; issue_types; res} line ->
         let next_line = current_line + 1 in
         match (substring_after_match ignore_all_rx line, substring_after_match ignore_rx line) with
         | None, None ->
             { current_line= next_line
             ; block_start= None
-            ; issue_types= String.Set.empty
+            ; issue_types= IString.Set.empty
             ; res= update_suppressions block_start current_line issue_types res }
         | Some s, other ->
             if Option.is_some other then
@@ -137,12 +141,12 @@ let parse_lines ?file lines =
                 (Option.value ~default:"" file) next_line ;
             { current_line= next_line
             ; block_start= None
-            ; issue_types= String.Set.empty
+            ; issue_types= IString.Set.empty
             ; res= update_suppressions_every (extract_valid_issue_types s) res }
         | _, Some s ->
             { current_line= next_line
             ; block_start= (if Option.is_some block_start then block_start else Some current_line)
-            ; issue_types= Set.union issue_types (extract_valid_issue_types s)
+            ; issue_types= IString.Set.union issue_types (extract_valid_issue_types s)
             ; res } )
   in
   L.debug Report Verbose "Parse state: %a@\n" pp_fold_state parse_result ;
@@ -155,8 +159,8 @@ let parse_lines ?file lines =
 
 
 let first_key_match ~suppressions s =
-  Map.to_sequence suppressions
-  |> Sequence.find ~f:(fun (k, _) ->
+  IString.Map.to_seq suppressions
+  |> Seq.find (fun (k, _) ->
          match get_regex k with Some rx -> Str.string_match rx s 0 | _ -> false )
   |> Option.map ~f:snd
 
@@ -168,7 +172,7 @@ let is_suppressed ~suppressions ~issue_type ~line =
   2. loop trough all keys (treated as regexes) and find first match
 *)
   match
-    match Map.find suppressions issue_type with
+    match IString.Map.find_opt issue_type suppressions with
     | None ->
         first_key_match ~suppressions issue_type
     | v ->
diff --git a/infer/src/integration/Suppressions.mli b/infer/src/integration/Suppressions.mli
index 93fdc3860de..5214a210d25 100644
--- a/infer/src/integration/Suppressions.mli
+++ b/infer/src/integration/Suppressions.mli
@@ -13,7 +13,7 @@ module Span : sig
   type t = Every | Blocks of block list [@@deriving compare, equal]
 end
 
-type t = Span.t String.Map.t
+type t = Span.t IString.Map.t
 
 val parse_lines : ?file:string -> string list -> t
 
diff --git a/infer/src/integration/unit/SuppressionsTest.ml b/infer/src/integration/unit/SuppressionsTest.ml
index 8da92bf8097..0afbade4a08 100644
--- a/infer/src/integration/unit/SuppressionsTest.ml
+++ b/infer/src/integration/unit/SuppressionsTest.ml
@@ -6,7 +6,7 @@
  *)
 
 open! IStd
-module Map = String.Map
+module Map = IString.Map
 
 (** {2 parsing} *)
 
@@ -41,8 +41,8 @@ let%test "parsing matching line multiple issue types" =
     (Suppressions.parse_lines ["1+1 // @infer-ignore BUFFER_OVERRUN_L1,PULSE_UNNECESSARY_COPY"])
     Map.(
       empty
-      |> add_exn ~key:"BUFFER_OVERRUN_L1" ~data:(Suppressions.Span.Blocks [{first= 1; last= 2}])
-      |> add_exn ~key:"PULSE_UNNECESSARY_COPY" ~data:(Suppressions.Span.Blocks [{first= 1; last= 2}]) )
+      |> add "BUFFER_OVERRUN_L1" (Suppressions.Span.Blocks [{first= 1; last= 2}])
+      |> add "PULSE_UNNECESSARY_COPY" (Suppressions.Span.Blocks [{first= 1; last= 2}]) )
 
 
 let%test "parsing matching line multiple noise" =
@@ -51,8 +51,8 @@ let%test "parsing matching line multiple noise" =
        ["1+1 // @infer-ignore BUFFER_OVERRUN_L1,,,, PULSE_UNNECESSARY_COPY,,,,,,,"] )
     Map.(
       empty
-      |> add_exn ~key:"BUFFER_OVERRUN_L1" ~data:(Suppressions.Span.Blocks [{first= 1; last= 2}])
-      |> add_exn ~key:"PULSE_UNNECESSARY_COPY" ~data:(Suppressions.Span.Blocks [{first= 1; last= 2}]) )
+      |> add "BUFFER_OVERRUN_L1" (Suppressions.Span.Blocks [{first= 1; last= 2}])
+      |> add "PULSE_UNNECESSARY_COPY" (Suppressions.Span.Blocks [{first= 1; last= 2}]) )
 
 
 let%test "multi line block" =
@@ -61,8 +61,8 @@ let%test "multi line block" =
        ["// @infer-ignore BUFFER_OVERRUN_L1"; "1+1 // @infer-ignore ,PULSE_UNNECESSARY_COPY"] )
     Map.(
       empty
-      |> add_exn ~key:"BUFFER_OVERRUN_L1" ~data:(Suppressions.Span.Blocks [{first= 1; last= 3}])
-      |> add_exn ~key:"PULSE_UNNECESSARY_COPY" ~data:(Suppressions.Span.Blocks [{first= 1; last= 3}]) )
+      |> add "BUFFER_OVERRUN_L1" (Suppressions.Span.Blocks [{first= 1; last= 3}])
+      |> add "PULSE_UNNECESSARY_COPY" (Suppressions.Span.Blocks [{first= 1; last= 3}]) )
 
 
 let%test "multiple blocks" =
@@ -71,8 +71,8 @@ let%test "multiple blocks" =
        ["// @infer-ignore BUFFER_OVERRUN_L1"; ""; "1+1 // @infer-ignore BUFFER_OVERRUN_L1"] )
     Map.(
       empty
-      |> add_exn ~key:"BUFFER_OVERRUN_L1"
-           ~data:(Suppressions.Span.Blocks [{first= 1; last= 2}; {first= 3; last= 4}]) )
+      |> add "BUFFER_OVERRUN_L1"
+           (Suppressions.Span.Blocks [{first= 1; last= 2}; {first= 3; last= 4}]) )
 
 
 let%test "parsing matching line every" =
diff --git a/infer/src/istd/IList.ml b/infer/src/istd/IList.ml
index a6a5a68391b..6a0cb9e0e81 100644
--- a/infer/src/istd/IList.ml
+++ b/infer/src/istd/IList.ml
@@ -122,21 +122,16 @@ let split_last_rev l = match List.rev l with x :: xs -> Some (x, xs) | [] -> Non
 let append_no_duplicates (type a) ~(cmp : a -> a -> int) =
   (* roughly based on [Core.List.stable_dedup_staged] but also takes care of the append and takes
      into account the invariant that [list1] and [list2] do not contain duplicates individually *)
-  let module Set = Set.Make (struct
+  let module Set = Stdlib.Set.Make (struct
     type t = a
 
     let compare = cmp
-
-    (* we never calls these *)
-    let t_of_sexp _ = assert false
-
-    let sexp_of_t _ = assert false
   end) in
   Staged.stage (fun (list1 : a list) (list2 : a list) ->
       let set1 = Set.of_list list1 in
       let res_rev =
         List.fold_left list2 ~init:(List.rev list1) ~f:(fun res_rev x ->
-            if Set.mem set1 x then res_rev else x :: res_rev )
+            if Set.mem x set1 then res_rev else x :: res_rev )
       in
       List.rev res_rev )
 
diff --git a/infer/src/istd/IString.ml b/infer/src/istd/IString.ml
new file mode 100644
index 00000000000..17b0fde6f4c
--- /dev/null
+++ b/infer/src/istd/IString.ml
@@ -0,0 +1,16 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+
+open! IStd
+
+module T = struct
+  type t = string [@@deriving compare, hash, equal]
+end
+
+module Map = Stdlib.Map.Make (T)
+module Set = Stdlib.Set.Make (T)
+module Hash = Stdlib.Hashtbl.Make (T)
diff --git a/infer/src/istd/IString.mli b/infer/src/istd/IString.mli
new file mode 100644
index 00000000000..0aeacb41204
--- /dev/null
+++ b/infer/src/istd/IString.mli
@@ -0,0 +1,12 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+
+module Map : Stdlib.Map.S with type key = string
+
+module Set : Stdlib.Set.S with type elt = string
+
+module Hash : Stdlib.Hashtbl.S with type key = string
diff --git a/infer/src/istd/Pp.ml b/infer/src/istd/Pp.ml
index c527b86cc93..1bb588c1eea 100644
--- a/infer/src/istd/Pp.ml
+++ b/infer/src/istd/Pp.ml
@@ -205,8 +205,8 @@ let cli_args_with_verbosity ~verbose fmt args =
                pp_argfile in_argfiles fmt argfile ) ) ;
     if !at_least_one then F.fprintf fmt "@]@\n"
   and pp_argfile in_argfiles fmt fname =
-    if not (String.Set.mem in_argfiles fname) then
-      let in_argfiles' = String.Set.add in_argfiles fname in
+    if not (IString.Set.mem fname in_argfiles) then
+      let in_argfiles' = IString.Set.add fname in_argfiles in
       match In_channel.read_lines fname with
       | args ->
           F.fprintf fmt "++Contents of %s:@\n%a@\n"
@@ -220,7 +220,7 @@ let cli_args_with_verbosity ~verbose fmt args =
             Exn.pp exn
   in
   pp_args fmt args ;
-  if verbose then pp_argfile_args String.Set.empty fmt args
+  if verbose then pp_argfile_args IString.Set.empty fmt args
 
 
 let cli_args fmt args = cli_args_with_verbosity ~verbose:true fmt args
diff --git a/infer/src/java/jClasspath.ml b/infer/src/java/jClasspath.ml
index 32007066da7..48c9332e23b 100644
--- a/infer/src/java/jClasspath.ml
+++ b/infer/src/java/jClasspath.ml
@@ -29,7 +29,7 @@ type file_entry = Singleton of SourceFile.t | Duplicate of (string list * Source
 
 type t =
   { classpath_channel: Javalib.class_path
-  ; sources: file_entry String.Map.t
+  ; sources: file_entry IString.Map.t
   ; classes: JBasics.ClassSet.t }
 
 (* Open the source file and search for the package declaration.
@@ -61,7 +61,7 @@ let add_source_file =
     let basename = Filename.basename path in
     let entry =
       let current_source_file = SourceFile.from_abs_path (convert_to_absolute path) in
-      match String.Map.find map basename with
+      match IString.Map.find_opt basename map with
       | None ->
           (* Most common case: there is no conflict with the base name of the source file *)
           Singleton current_source_file
@@ -80,10 +80,10 @@ let add_source_file =
           let current_package = read_package_declaration current_source_file in
           Duplicate ((current_package, current_source_file) :: previous_source_files)
     in
-    String.Map.set ~key:basename ~data:entry map
+    IString.Map.add basename entry map
 
 
-let add_root_path path roots = String.Set.add roots path
+let add_root_path path roots = IString.Set.add path roots
 
 let read_modules_1 path =
   let temp_dir = Filename.temp_dir "java_modules_lib" "" in
@@ -130,7 +130,7 @@ let load_from_verbose_output =
     match In_channel.input_line file_in with
     | None ->
         let paths = if Config.java_read_modules then read_modules paths else paths in
-        let classpath = classpath_of_paths (String.Set.elements roots @ paths) in
+        let classpath = classpath_of_paths (IString.Set.elements roots @ paths) in
         {classpath_channel= Javalib.class_path classpath; sources; classes}
     | Some line when Str.string_match class_filename_re line 0 -> (
         let path =
@@ -163,7 +163,7 @@ let load_from_verbose_output =
   in
   fun javac_verbose_out ->
     Utils.with_file_in javac_verbose_out
-      ~f:(loop [] String.Set.empty String.Map.empty JBasics.ClassSet.empty)
+      ~f:(loop [] IString.Set.empty IString.Map.empty JBasics.ClassSet.empty)
 
 
 let collect_classnames init jar_filename =
@@ -195,7 +195,7 @@ let search_classes path =
           (add_root_path p paths, collect_classnames classes p)
       | _ ->
           accu )
-    (String.Set.empty, JBasics.ClassSet.empty)
+    (IString.Set.empty, JBasics.ClassSet.empty)
     path
 
 
@@ -207,7 +207,7 @@ let is_valid_source_file path =
 
 let search_sources sources =
   let initial_map =
-    List.fold sources ~init:String.Map.empty ~f:(fun map path ->
+    List.fold sources ~init:IString.Map.empty ~f:(fun map path ->
         if is_valid_source_file path then add_source_file path map
         else (
           L.external_warning "'%s' does not appear to be a valid source file, skipping@\n" path ;
@@ -227,7 +227,7 @@ let load_from_arguments classes_out_path sources =
   let split cp_option = Option.value_map ~f:split_classpath ~default:[] cp_option in
   let classpath =
     (* order follows https://docs.oracle.com/javase/7/docs/technotes/tools/windows/classpath.html *)
-    split Config.bootclasspath @ split Config.classpath @ String.Set.elements roots
+    split Config.bootclasspath @ split Config.classpath @ IString.Set.elements roots
     |> classpath_of_paths
   in
   {classpath_channel= Javalib.class_path classpath; sources= search_sources sources; classes}
@@ -245,13 +245,13 @@ let with_classpath ~f source =
     | FromArguments {path; sources} ->
         load_from_arguments path sources
   in
-  if String.Map.is_empty classpath.sources then
+  if IString.Map.is_empty classpath.sources then
     L.user_warning "No Java source code loaded. Analyzing JAR/WAR files directly" ;
-  if String.Map.is_empty classpath.sources && JBasics.ClassSet.is_empty classpath.classes then
+  if IString.Map.is_empty classpath.sources && JBasics.ClassSet.is_empty classpath.classes then
     L.(die InternalError) "Failed to load any Java source or class files" ;
   L.(debug Capture Quiet)
     "Translating %d source files (%d classes)@."
-    (String.Map.length classpath.sources)
+    (IString.Map.cardinal classpath.sources)
     (JBasics.ClassSet.cardinal classpath.classes) ;
   f classpath ;
   Javalib.close_class_path classpath.classpath_channel
diff --git a/infer/src/java/jClasspath.mli b/infer/src/java/jClasspath.mli
index c347be86ffb..5c0c69d7845 100644
--- a/infer/src/java/jClasspath.mli
+++ b/infer/src/java/jClasspath.mli
@@ -14,7 +14,7 @@ type file_entry = Singleton of SourceFile.t | Duplicate of (string list * Source
 
 type t =
   { classpath_channel: Javalib.class_path
-  ; sources: file_entry String.Map.t
+  ; sources: file_entry IString.Map.t
   ; classes: JBasics.ClassSet.t }
 
 type source =
diff --git a/infer/src/java/jFrontend.ml b/infer/src/java/jFrontend.ml
index c20df83599f..4c99cb7e053 100644
--- a/infer/src/java/jFrontend.ml
+++ b/infer/src/java/jFrontend.ml
@@ -27,7 +27,7 @@ let add_edges (context : JContext.t) start_node exn_node exit_nodes method_body_
     | JTrans.Skip when is_last pc && not (JContext.is_goto_jump context pc) ->
         exit_nodes
     | JTrans.Skip ->
-        direct_successors pc (Int.Set.add visited pc)
+        direct_successors pc (IInt.Set.add pc visited)
     | JTrans.Instr node ->
         [node]
     | JTrans.Prune (node_true, node_false) ->
@@ -40,20 +40,20 @@ let add_edges (context : JContext.t) start_node exn_node exit_nodes method_body_
       match JContext.get_goto_jump context pc with
       | JContext.Next ->
           let next_pc = pc + 1 in
-          if Int.Set.mem visited next_pc || is_a_throw pc then []
+          if IInt.Set.mem next_pc visited || is_a_throw pc then []
           else get_body_nodes_ next_pc visited
-      | JContext.Jump goto_pc when Int.Set.mem visited goto_pc ->
+      | JContext.Jump goto_pc when IInt.Set.mem goto_pc visited ->
           [] (* loop in goto *)
       | JContext.Jump goto_pc ->
           get_body_nodes_ goto_pc visited
       | JContext.Exit ->
           exit_nodes
   in
-  let get_body_nodes pc = get_body_nodes_ pc Int.Set.empty in
+  let get_body_nodes pc = get_body_nodes_ pc IInt.Set.empty in
   let get_succ_nodes node pc =
     match JContext.get_if_jump context node with
     | None ->
-        direct_successors pc Int.Set.empty
+        direct_successors pc IInt.Set.empty
     | Some jump_pc ->
         get_body_nodes jump_pc
   in
@@ -81,7 +81,7 @@ let add_edges (context : JContext.t) start_node exn_node exit_nodes method_body_
   in
   let first_nodes =
     (* deals with the case of an empty array *)
-    direct_successors (-1) Int.Set.empty
+    direct_successors (-1) IInt.Set.empty
   in
   (* the exceptions edges here are going directly to the exit node *)
   Procdesc.node_set_succs context.procdesc start_node ~normal:first_nodes ~exn:exit_nodes ;
diff --git a/infer/src/java/jMain.ml b/infer/src/java/jMain.ml
index 88532ca3d72..c454599b2a5 100644
--- a/infer/src/java/jMain.ml
+++ b/infer/src/java/jMain.ml
@@ -101,7 +101,7 @@ let do_all_files classpath program =
   let translate_source_file basename package_opt source_file =
     if not (skip source_file) then do_source_file program tenv basename package_opt source_file
   in
-  if String.Map.is_empty sources then (
+  if IString.Map.is_empty sources then (
     L.(debug Capture Medium) "no source files found, capturing class files directly@." ;
     JBasics.ClassSet.iter
       (fun cn ->
@@ -113,8 +113,8 @@ let do_all_files classpath program =
             Option.iter ~f:(do_class tenv program cn) node )
       classes )
   else
-    String.Map.iteri
-      ~f:(fun ~key:basename ~data:file_entry ->
+    IString.Map.iter
+      (fun basename file_entry ->
         match file_entry with
         | JClasspath.Singleton source_file ->
             translate_source_file basename None source_file
diff --git a/infer/src/java/jTrans.ml b/infer/src/java/jTrans.ml
index bad3feb9a21..6bfab97cc5e 100644
--- a/infer/src/java/jTrans.ml
+++ b/infer/src/java/jTrans.ml
@@ -912,11 +912,11 @@ let get_array_length context pc expr_list content_type =
 let detect_loop entry_pc impl =
   let code = JBir.code impl in
   let pc_bound = Array.length code in
-  let empty = Int.Set.empty in
+  let empty = IInt.Set.empty in
   let rec loop visited pc =
-    if Int.Set.mem visited pc || pc >= pc_bound then (false, visited)
+    if IInt.Set.mem pc visited || pc >= pc_bound then (false, visited)
     else
-      let visited_updated = Int.Set.add visited pc in
+      let visited_updated = IInt.Set.add pc visited in
       match code.(pc) with
       | JBir.Goto goto_pc when Int.equal goto_pc entry_pc ->
           (true, empty)
diff --git a/infer/src/pulse/Pulse.ml b/infer/src/pulse/Pulse.ml
index a74c8483769..13006d293e2 100644
--- a/infer/src/pulse/Pulse.ml
+++ b/infer/src/pulse/Pulse.ml
@@ -1646,11 +1646,11 @@ let log_summary_count proc_name summary =
   let counts =
     let summary_kinds = List.map ~f:ExecutionDomain.to_name summary in
     let map =
-      let incr_or_one val_opt = match val_opt with Some v -> v + 1 | None -> 1 in
-      let update acc s = String.Map.update acc s ~f:incr_or_one in
-      List.fold summary_kinds ~init:String.Map.empty ~f:update
+      let incr_or_one val_opt = Some (match val_opt with Some v -> v + 1 | None -> 1) in
+      let update acc s = IString.Map.update s incr_or_one acc in
+      List.fold summary_kinds ~init:IString.Map.empty ~f:update
     in
-    let alist = List.map ~f:(fun (s, i) -> (s, `Int i)) (String.Map.to_alist map) in
+    let alist = List.map ~f:(fun (s, i) -> (s, `Int i)) (IString.Map.bindings map) in
     let alist =
       match PulseModelsErlang.Custom.exists_db_model proc_name with
       | true ->
diff --git a/infer/src/pulse/PulseModelsHack.ml b/infer/src/pulse/PulseModelsHack.ml
index 40cdccd34e1..2c367239e77 100644
--- a/infer/src/pulse/PulseModelsHack.ml
+++ b/infer/src/pulse/PulseModelsHack.ml
@@ -1465,7 +1465,7 @@ let check_against_type_struct v tdict : DSL.aval DSL.model_monad =
                   let rootname = replace_backslash_with_colon rootname in
                   L.d_printfln "got root_name = %s, type_prop_name = %s" rootname type_prop_name ;
                   let concatenated_name = Printf.sprintf "%s$$%s" rootname type_prop_name in
-                  if String.Set.mem visited_set concatenated_name then (
+                  if IString.Set.mem concatenated_name visited_set then (
                     L.d_printfln "Cyclic type constant detected!" ;
                     ret None )
                   else
@@ -1479,12 +1479,12 @@ let check_against_type_struct v tdict : DSL.aval DSL.model_monad =
                     L.d_printfln "type structure for projection=%a" AbstractValue.pp
                       (fst type_constant_ts) ;
                     find_name type_constant_ts nullable
-                      (String.Set.add visited_set concatenated_name)
+                      (IString.Set.add concatenated_name visited_set)
               | _, _ ->
                   ret None )
             else ret None )
   in
-  let* name_opt = find_name tdict false String.Set.empty in
+  let* name_opt = find_name tdict false IString.Set.empty in
   match name_opt with
   | Some (name, nullable) ->
       L.d_printfln "type structure test against type name %a" Typ.Name.pp name ;
diff --git a/infer/src/textual/TextualBasicVerification.ml b/infer/src/textual/TextualBasicVerification.ml
index c3e739452c3..a023d62db80 100644
--- a/infer/src/textual/TextualBasicVerification.ml
+++ b/infer/src/textual/TextualBasicVerification.ml
@@ -81,7 +81,7 @@ let count_generics_args args generics =
 
 let verify_decl ~env errors (decl : Module.decl) =
   let verify_label errors declared_labels pname label =
-    if String.Set.mem declared_labels label.NodeName.value then errors
+    if IString.Set.mem label.NodeName.value declared_labels then errors
     else UnknownLabel {label; pname} :: errors
   in
   let verify_field errors field =
@@ -221,8 +221,8 @@ let verify_decl ~env errors (decl : Module.decl) =
                   idents ) )
     in
     let declared_labels =
-      List.fold procdesc.nodes ~init:String.Set.empty ~f:(fun set node ->
-          String.Set.add set node.Node.label.value )
+      List.fold procdesc.nodes ~init:IString.Set.empty ~f:(fun set node ->
+          IString.Set.add node.Node.label.value set )
     in
     let verify_label errors =
       verify_label errors declared_labels procdesc.procdecl.qualified_name
diff --git a/infer/src/textual/TextualTransform.ml b/infer/src/textual/TextualTransform.ml
index 2091f201334..2168fa41916 100644
--- a/infer/src/textual/TextualTransform.ml
+++ b/infer/src/textual/TextualTransform.ml
@@ -56,11 +56,11 @@ module FixClosureAppExpr = struct
     let open ProcDesc in
     let globals_and_locals =
       List.fold pdesc.locals ~init:globals ~f:(fun set (varname, _) ->
-          String.Set.add set varname.VarName.value )
+          IString.Set.add varname.VarName.value set )
     in
     let is_varname ({enclosing_class; name} : QualifiedProcName.t) =
       match enclosing_class with
-      | TopLevel when String.Set.mem globals_and_locals name.value ->
+      | TopLevel when IString.Set.mem name.value globals_and_locals ->
           let varname : VarName.t = {value= name.value; loc= name.loc} in
           Some (Exp.Load {exp= Lvar varname; typ= None})
       | TopLevel when is_ident name.value ->
@@ -142,10 +142,10 @@ module FixClosureAppExpr = struct
   let transform (module_ : Module.t) =
     let open Module in
     let globals =
-      List.fold module_.decls ~init:String.Set.empty ~f:(fun set decl ->
+      List.fold module_.decls ~init:IString.Set.empty ~f:(fun set decl ->
           match decl with
           | Global {name} ->
-              String.Set.add set name.VarName.value
+              IString.Set.add name.VarName.value set
           | Proc _ | Struct _ | Procdecl _ ->
               set )
     in