[cost] fix iterator for constant array

Summary:
Fix the FP when iterating through constant collection.

facebook
This fix is a hack for now.

Reviewed By: ezgicicek, skcho

Differential Revision: D23241338

fbshipit-source-id: e2e0c05f8

infer/src/bufferoverrun/absLoc.ml

@@ -231,6 +231,13 @@ module Loc = struct
         false
 
 
+  let is_objc_iterator_offset = function
+    | BoField.Field {fn} ->
+        Fieldname.equal fn BoField.objc_iterator_offset
+    | _ ->
+        false
+
+
   let is_frontend_tmp = function
     | BoField.Prim (Var x) ->
         not (Var.appears_in_source_code x)
@@ -354,7 +361,8 @@ module Loc = struct
         false
     | BoField.Prim (Allocsite allocsite) ->
         Allocsite.represents_multiple_values allocsite
-    | BoField.Field _ as x when is_c_strlen x || is_java_collection_internal_array x ->
+    | BoField.Field _ as x
+      when is_c_strlen x || is_java_collection_internal_array x || is_objc_iterator_offset x ->
         false
     | BoField.Field {prefix= l} ->
         represents_multiple_values l

infer/tests/codetoanalyze/objc/performance/NSArray.m

@@ -168,7 +168,7 @@ void nsarray_next_object_linear(NSArray* array) {
   }
 }
 
-void nsarray_next_object_constant_FP() {
+void nsarray_next_object_constant() {
   NSArray* array = @[ @1, @2 ];
   for (id item in array) {
   }

infer/tests/codetoanalyze/objc/performance/cost-issues.exp

@@ -19,7 +19,7 @@ codetoanalyze/objc/performance/NSArray.m, nsarray_init_with_objects_constant, 39
 codetoanalyze/objc/performance/NSArray.m, nsarray_is_equal_to_array_linear, 4 + array1->elements.length.ub,  OnUIThread:false, [{array1->elements.length.ub},Modeled call to NSArray.isEqualToArray:]
 codetoanalyze/objc/performance/NSArray.m, nsarray_iterate_linear, 6 + 4 ⋅ array->elements.length.ub + 4 ⋅ (array->elements.length.ub + 1),  OnUIThread:false, [{array->elements.length.ub + 1},Loop,{array->elements.length.ub},Loop]
 codetoanalyze/objc/performance/NSArray.m, nsarray_last_object_constant, 4,  OnUIThread:false, []
-codetoanalyze/objc/performance/NSArray.m, nsarray_next_object_constant_FP, ⊤,  OnUIThread:false, [Unbounded loop,Loop]
+codetoanalyze/objc/performance/NSArray.m, nsarray_next_object_constant, 25,  OnUIThread:false, []
 codetoanalyze/objc/performance/NSArray.m, nsarray_next_object_linear, 5 + array->elements.length.ub + 4 ⋅ (array->elements.length.ub + 1),  OnUIThread:false, [{array->elements.length.ub + 1},Loop,{array->elements.length.ub},Loop]
 codetoanalyze/objc/performance/NSArray.m, nsarray_object_at_indexed_constant, 34,  OnUIThread:false, []
 codetoanalyze/objc/performance/NSArray.m, nsarray_sort_using_descriptors_constant, 34,  OnUIThread:false, []

infer/tests/codetoanalyze/objc/performance/issues.exp

@@ -1,7 +1,6 @@
 codetoanalyze/objc/performance/NSArray.m, nsarray_empty_array_constant, 3, CONDITION_ALWAYS_FALSE, no_bucket, WARNING, [Here]
 codetoanalyze/objc/performance/NSArray.m, nsarray_enumerator_linear_FP, 0, INFINITE_EXECUTION_TIME, no_bucket, ERROR, [Unbounded loop,Loop]
 codetoanalyze/objc/performance/NSArray.m, nsarray_init_constant, 3, CONDITION_ALWAYS_FALSE, no_bucket, WARNING, [Here]
-codetoanalyze/objc/performance/NSArray.m, nsarray_next_object_constant_FP, 0, INFINITE_EXECUTION_TIME, no_bucket, ERROR, [Unbounded loop,Loop]
 codetoanalyze/objc/performance/NSDictionary.m, nsdictionary_init_with_dictionary_linear_FP, 0, INFINITE_EXECUTION_TIME, no_bucket, ERROR, [Unbounded loop,Loop]
 codetoanalyze/objc/performance/NSDictionary.m, nsdictionary_init_with_dictionary_linear_FP, 2, INTEGER_OVERFLOW_U5, no_bucket, ERROR, [<LHS trace>,Unknown value from: NSDictionary.initWithDictionary:,Binary operation: ([0, +oo] + 1):signed32]
 codetoanalyze/objc/performance/NSMutableArray.m, nsmarray_add_in_loop_constant_FP, 0, INFINITE_EXECUTION_TIME, no_bucket, ERROR, [Unbounded loop,Loop]