[inferbo] Do not prune when the pruning target is already bottom

Reviewed By: ezgicicek

Differential Revision: D20067865

fbshipit-source-id: 1067a3482

infer/src/bufferoverrun/bufferOverrunSemantics.ml

@@ -544,8 +544,11 @@ module Prune = struct
   let prune_has_next ~true_branch iterator ({mem} as astate) =
     let accum_prune_common ~prune_f loc acc =
       let length = collection_length_of_iterator iterator mem in
-      let v = prune_f (Mem.find loc mem) length in
-      update_mem_in_prune loc v acc
+      let v = Mem.find loc mem in
+      if Val.is_bot length || Val.is_bot v then acc
+      else
+        let v' = prune_f v length in
+        update_mem_in_prune loc v' acc
     in
     let accum_pruned loc tgt acc =
       match tgt with
@@ -575,15 +578,22 @@ module Prune = struct
           match tgt with
           | AliasTarget.Simple {i} when IntLit.iszero i ->
               let v = Mem.find rhs mem in
+              if Val.is_bot v then acc
+              else
                 let v' = Val.prune_ne_zero v in
                 update_mem_in_prune rhs v' acc
           | AliasTarget.Empty ->
               let v = Mem.find rhs mem in
+              if Val.is_bot v then acc
+              else
                 let v' = Val.prune_length_eq_zero v in
                 update_mem_in_prune rhs v' acc
           | AliasTarget.Fgets ->
               let strlen_loc = Loc.of_c_strlen rhs in
-              let v' = Val.prune_ge_one (Mem.find strlen_loc mem) in
+              let v = Mem.find strlen_loc mem in
+              if Val.is_bot v then acc
+              else
+                let v' = Val.prune_ge_one v in
                 update_mem_in_prune strlen_loc v' acc
           | AliasTarget.IteratorHasNext _ ->
               prune_has_next ~true_branch:true rhs acc
@@ -596,10 +606,14 @@ module Prune = struct
           match tgt with
           | AliasTarget.Simple {i} when IntLit.iszero i ->
               let v = Mem.find rhs mem in
+              if Val.is_bot v then acc
+              else
                 let v' = Val.prune_eq_zero v in
                 update_mem_in_prune rhs v' acc
           | AliasTarget.Empty ->
               let v = Mem.find rhs mem in
+              if Val.is_bot v then acc
+              else
                 let v' = Val.prune_length_ge_one v in
                 update_mem_in_prune rhs v' acc
           | AliasTarget.IteratorHasNext _ ->
@@ -655,7 +669,7 @@ module Prune = struct
             let v' = eval integer_type_widths e mem in
             if IntLit.iszero i then v' else Val.minus_a v' (Val.of_int_lit i)
           in
-          if Val.is_bot rhs then acc
+          if Val.is_bot lhs || Val.is_bot rhs then acc
           else
             let v = val_prune_eq lhs rhs in
             let pruning_exp = make_pruning_exp ~lhs ~rhs in
@@ -676,6 +690,8 @@ module Prune = struct
             |> Val.of_itv |> Val.set_itv_updated_by_addition
           in
           let rhs = eval integer_type_widths e mem in
+          if Val.is_bot lhs || Val.is_bot rhs then astate
+          else
             let prune_target val_prune astate =
               let lhs' = val_prune lhs rhs in
               let array_v' =