[cost] add alloc for NSObject and NSString.init as an example function using alloc

Summary: Implement `alloc` and implement initialisation method that uses the return value of `alloc`, i.e. `NSString.init`.

Reviewed By: ezgicicek

Differential Revision: D22840080

fbshipit-source-id: 47a7523e3

infer/src/bufferoverrun/bufferOverrunModels.ml

@@ -149,18 +149,6 @@ let malloc ~can_be_zero size_exp =
   {exec; check}
 
 
-let objc_malloc exp =
-  let can_be_zero = true in
-  let exec ({tenv} as model) ~ret mem =
-    match exp with
-    | Exp.Sizeof {typ} when PatternMatch.ObjectiveC.implements "NSArray" tenv (Typ.to_string typ) ->
-        (malloc ~can_be_zero Exp.zero).exec model ~ret mem
-    | _ ->
-        (malloc ~can_be_zero exp).exec model ~ret mem
-  in
-  {exec; check= check_alloc_size ~can_be_zero exp}
-
-
 let calloc size_exp stride_exp =
   let byte_size_exp = Exp.BinOp (Binop.Mult (Some Typ.size_t), size_exp, stride_exp) in
   malloc byte_size_exp
@@ -1379,7 +1367,7 @@ end
 module NSString = struct
   let fn = JavaString.fn
 
-  let create_string_from_c_string src_exp =
+  let create_with_c_string src_exp =
     let exec model_env ~ret mem =
       let v = Sem.eval_string_len src_exp mem in
       JavaString.create_with_length model_env ~ret ~begin_idx:Exp.zero ~end_v:v mem
@@ -1422,6 +1410,21 @@ module NSString = struct
     {exec; check= no_check}
 end
 
+let objc_malloc exp =
+  let can_be_zero = true in
+  let exec ({tenv} as model) ~ret mem =
+    match exp with
+    | Exp.Sizeof {typ} when PatternMatch.ObjectiveC.implements "NSArray" tenv (Typ.to_string typ) ->
+        (malloc ~can_be_zero Exp.zero).exec model ~ret mem
+    | Exp.Sizeof {typ} when PatternMatch.ObjectiveC.implements "NSString" tenv (Typ.to_string typ)
+      ->
+        (NSString.create_with_c_string (Exp.Const (Const.Cstr ""))).exec model ~ret mem
+    | _ ->
+        (malloc ~can_be_zero exp).exec model ~ret mem
+  in
+  {exec; check= check_alloc_size ~can_be_zero exp}
+
+
 module Preconditions = struct
   let check_argument exp =
     let exec {integer_type_widths; location} ~ret:_ mem =
@@ -1566,8 +1569,8 @@ module Call = struct
       ; -"CFArrayGetValueAtIndex" <>$ capt_var_exn $+ capt_exp $!--> NSCollection.get_at_index
       ; -"CFDictionaryGetCount" <>$ capt_exp $!--> NSCollection.length
       ; -"MCFArrayGetCount" <>$ capt_exp $!--> NSCollection.length
-      ; +PatternMatch.ObjectiveC.implements "NSArray" &:: "array" <>--> NSCollection.empty_array
       ; +PatternMatch.ObjectiveC.implements "NSArray" &:: "init" <>$ capt_exp $--> id
+      ; +PatternMatch.ObjectiveC.implements "NSArray" &:: "array" <>--> NSCollection.empty_array
       ; +PatternMatch.ObjectiveC.implements "NSArray"
         &:: "count" <>$ capt_exp $!--> NSCollection.length
       ; +PatternMatch.ObjectiveC.implements "NSArray"
@@ -1591,8 +1594,9 @@ module Call = struct
         &:: "allValues" <>$ capt_exp $--> create_copy_array
       ; +PatternMatch.ObjectiveC.implements "NSNumber" &:: "numberWithInt:" <>$ capt_exp $--> id
       ; +PatternMatch.ObjectiveC.implements "NSNumber" &:: "integerValue" <>$ capt_exp $--> id
+      ; +PatternMatch.ObjectiveC.implements "NSString" &:: "init" <>$ capt_exp $--> id
       ; +PatternMatch.ObjectiveC.implements "NSString"
-        &:: "stringWithUTF8String:" <>$ capt_exp $!--> NSString.create_string_from_c_string
+        &:: "stringWithUTF8String:" <>$ capt_exp $!--> NSString.create_with_c_string
       ; +PatternMatch.ObjectiveC.implements "NSString"
         &:: "length" <>$ capt_exp $--> NSString.length
       ; +PatternMatch.ObjectiveC.implements "NSString"

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

@@ -63,6 +63,12 @@ void init_with_bytes_linear_FP(const void* bytes,
   }
 }
 
+void init_string_constant() {
+  NSString* str = [[NSString alloc] init];
+  for (int i = 0; i < str.length; i++) {
+  }
+}
+
 void init_with_string_constant_FP() {
   NSString* s = @"abcd";
   NSString* str = [[NSString alloc] initWithString:s];

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

@@ -56,6 +56,7 @@ codetoanalyze/objc/performance/NSString.m, call_init_with_string_constant_FP,
 codetoanalyze/objc/performance/NSString.m, component_seperated_by_char_linear, 6 + m.length.ub + 3 ⋅ (-1+max(2, m.length.ub)) + 3 ⋅ (max(2, m.length.ub)),  OnUIThread:false, [{max(2, m.length.ub)},Loop,{-1+max(2, m.length.ub)},Loop,{m.length.ub},Modeled call to NSString.componentsSeparatedByString:]
 codetoanalyze/objc/performance/NSString.m, component_seperated_by_string_linear, 6 + sep.length.ub × m.length.ub + 3 ⋅ (-1+max(2, m.length.ub)) + 3 ⋅ (max(2, m.length.ub)),  OnUIThread:false, [{max(2, m.length.ub)},Loop,{-1+max(2, m.length.ub)},Loop,{m.length.ub},Modeled call to NSString.componentsSeparatedByString:,{sep.length.ub},Modeled call to NSString.componentsSeparatedByString:]
 codetoanalyze/objc/performance/NSString.m, has_prefix_constant, 13,  OnUIThread:false, []
+codetoanalyze/objc/performance/NSString.m, init_string_constant, 9,  OnUIThread:false, []
 codetoanalyze/objc/performance/NSString.m, init_with_bytes_linear_FP, ⊤,  OnUIThread:false, [Unbounded loop,Loop]
 codetoanalyze/objc/performance/NSString.m, init_with_string_constant_FP, ⊤,  OnUIThread:false, [Unbounded loop,Loop]
 codetoanalyze/objc/performance/NSString.m, init_with_string_linear_FP, ⊤,  OnUIThread:false, [Unbounded loop,Loop]

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

@@ -19,6 +19,7 @@ codetoanalyze/objc/performance/NSMutableArray.m, nsmarray_remove_in_loop_constan
 codetoanalyze/objc/performance/NSMutableArray.m, nsmarray_set_in_loop_constant, 6, CONDITION_ALWAYS_FALSE, no_bucket, WARNING, [Here]
 codetoanalyze/objc/performance/NSMutableArray.m, nsmarray_set_linear, 2, INTEGER_OVERFLOW_U5, no_bucket, ERROR, [<LHS trace>,Unknown value from: NSNumber.intValue,Binary operation: ([-oo, +oo] + 1):signed32]
 codetoanalyze/objc/performance/NSString.m, call_init_with_string_constant_FP, 0, INFINITE_EXECUTION_TIME, no_bucket, ERROR, [Call to init_with_string_linear_FP,Unbounded loop,Loop]
+codetoanalyze/objc/performance/NSString.m, init_string_constant, 2, CONDITION_ALWAYS_FALSE, no_bucket, WARNING, [Here]
 codetoanalyze/objc/performance/NSString.m, init_with_bytes_linear_FP, 0, INFINITE_EXECUTION_TIME, no_bucket, ERROR, [Unbounded loop,Loop]
 codetoanalyze/objc/performance/NSString.m, init_with_bytes_linear_FP, 6, INTEGER_OVERFLOW_U5, no_bucket, ERROR, [<LHS trace>,Unknown value from: NSString.initWithBytes:length:encoding:,Binary operation: ([0, +oo] + 1):signed32]
 codetoanalyze/objc/performance/NSString.m, init_with_string_constant_FP, 0, INFINITE_EXECUTION_TIME, no_bucket, ERROR, [Unbounded loop,Loop]