[threadsafety] Limited support for more access path forms

Summary:
The thread safety domain manipulates access paths that are a variable
followed by a sequence of field or index accesses. Some expressions
from C++ code do not fit that form, such as cases where subtraction of
an offset from a pointer is used to obtain another pointer, whose
fields are then accessed. Previously the analyzer would crash on such
expressions. This diff partially treats them by introducing dummy
variables.

Reviewed By: da319

Differential Revision: D5343567

fbshipit-source-id: f73b520

infer/src/IR/HilExp.ml

@@ -85,6 +85,18 @@ let rec of_sil ~f_resolve_id (exp : Exp.t) typ = match exp with
               AccessPath.base_of_pvar pvar typ, of_sil ~f_resolve_id value typ)
           closure.captured_vars in
       Closure (closure.name, environment)
+  | Lfield (root_exp, fld, root_exp_typ) -> (
+      match AccessPath.of_lhs_exp exp typ ~f_resolve_id with
+      | Some access_path ->
+          AccessPath access_path
+      | None ->
+          (* unsupported field expression: represent with a dummy variable *)
+          of_sil ~f_resolve_id
+            (Exp.Lfield
+               (Var (Ident.create_normal (Ident.string_to_name (Exp.to_string root_exp)) 0),
+                fld,
+                root_exp_typ))
+            typ )
   | Lindex (Const (Cstr s), index_exp) ->
       (* indexed string literal (e.g., "foo"[1]). represent this by introducing a dummy variable
          for the string literal. if you actually need to see the value of the string literal in the
@@ -92,12 +104,23 @@ let rec of_sil ~f_resolve_id (exp : Exp.t) typ = match exp with
          literal, e.g. using `const_cast<char*>` *)
       of_sil ~f_resolve_id
         (Exp.Lindex (Var (Ident.create_normal (Ident.string_to_name s) 0), index_exp)) typ
-  | Lvar _ | Lfield _ | Lindex _ ->
+  | Lindex (root_exp, index_exp) -> (
+      match AccessPath.of_lhs_exp exp typ ~f_resolve_id with
+      | Some access_path ->
+          AccessPath access_path
+      | None ->
+          (* unsupported index expression: represent with a dummy variable *)
+          of_sil ~f_resolve_id
+            (Exp.Lindex
+               (Var (Ident.create_normal (Ident.string_to_name (Exp.to_string root_exp)) 0),
+                index_exp))
+            typ )
+  | Lvar _ ->
       match AccessPath.of_lhs_exp exp typ ~f_resolve_id with
       | Some access_path ->
           AccessPath access_path
       | None ->
-          failwithf "Couldn't convert var/field/index expression %a to access path" Exp.pp exp
+          failwithf "Couldn't convert var expression %a to access path" Exp.pp exp
 
 let is_null_literal = function
   | Constant (Cint n) -> IntLit.isnull n