[cost] Fix ignoring function pointer symbols in degree_with_term

Summary:
This diff fixes `degree_with_term` to ignore function pointer symbols. `degree_with_term` does

* calculate the degree
* simplify the polynomial only for printing them to users

thus, there is no problem to ignore the function pointer symbols always, ie which does not affect semantics or summary values.

Reviewed By: ezgicicek

Differential Revision: D24596479

fbshipit-source-id: 1e29d2de0

infer/src/bufferoverrun/polynomials.ml

@@ -527,29 +527,30 @@ module NonNegativeNonTopPolynomial = struct
       degree. When calculating the degree, it ignores symbols of function pointer, so they are
       addressed as if zero cost. *)
   let degree_with_term {poly; autoreleasepool_trace} =
-    let rec degree_with_term_poly ({terms} as poly) =
-      if is_zero_degree_poly poly then (Degree.zero, true, poly)
-      else
+    let rec degree_with_term_poly {const; terms} =
+      let degree_terms =
         M.fold
           (fun t p cur_max ->
-            let degree_term =
-              match (t, degree_with_term_poly p) with
-              | NonNegativeBoundWithDegreeKind b, (d, false, p') ->
-                  ( Degree.succ (NonNegativeBoundWithDegreeKind.degree_kind b) d
-                  , false
-                  , mult_symb_poly p' t )
-              | FuncPtr _, (_, _, p') | _, (_, true, p') ->
-                  (* It ignores function pointers when calculating degree of polynomial, since their
-                     semantics is different to the other symbolic values.  For example, when a
-                     function has a complexity of |fptr| where fptr is a function pointer, it does
-                     not make sense to say the function has a linear complexity. *)
-                  (Degree.zero, true, mult_symb_poly p' t)
-            in
-            if [%compare: Degree.t * bool * poly] degree_term cur_max > 0 then degree_term
-            else cur_max )
-          terms (Degree.zero, false, one_poly)
+            match (t, degree_with_term_poly p) with
+            (* It ignores function pointers when calculating degree of polynomial, since their
+               semantics is different to the other symbolic values.  For example, when a function
+               has a complexity of |fptr| where fptr is a function pointer, it does not make sense
+               to say the function has a linear complexity. *)
+            | FuncPtr _, _ ->
+                cur_max
+            | _, (_, p') when is_zero_poly p' ->
+                cur_max
+            | NonNegativeBoundWithDegreeKind b, (d, p') ->
+                let d' = Degree.succ (NonNegativeBoundWithDegreeKind.degree_kind b) d in
+                if Degree.compare d' (fst cur_max) > 0 then (d', mult_symb_poly p' t) else cur_max
+            )
+          terms (Degree.zero, zero_poly)
+      in
+      if is_zero_poly (snd degree_terms) then
+        if NonNegativeInt.is_zero const then (Degree.zero, zero_poly) else (Degree.zero, one_poly)
+      else degree_terms
     in
-    let d, _, poly = degree_with_term_poly poly in
+    let d, poly = degree_with_term_poly poly in
     (d, {poly; autoreleasepool_trace})