More precise warnings about function returns

This commit introduces a control-flow static analysis over C abstract syntax (file cparser/Cflow.ml) and uses it to
- warn for non-void functions that can return by falling through the body
- warn more precisely for _Noreturn functions that can return
- introduce the "return 0" in "main" functions less often (cosmetic).

For the control-flow analysis, the following conservative approximations are made:
- any "goto" label is reachable
- all cases of a "switch" statement are reachable as soon as the "switch" is reachable (i.e. the switch expression takes all values needed to reach every case)
- the boolean expressions in "if", "while", "do"-"while" and "for" can take true and false values, unless they are compile-time constants.

1 files changed, 0 insertions, 21 deletions

diff --git a/cparser/Cutil.ml b/cparser/Cutil.ml
index 8a59c147..735dd99b 100644
--- a/cparser/Cutil.ml
+++ b/cparser/Cutil.ml
@@ -1183,24 +1183,3 @@ let rec subst_stmt phi s =
                List.map subst_asm_operand inputs,
                clob)
   }
-
-let contains_return s =
-  let rec aux s =
-    match s.sdesc with
-    | Sskip
-    | Sbreak
-    | Scontinue
-    | Sdo _
-    | Sdecl _
-    | Sasm _
-    | Sgoto _ -> false
-    | Sif(_, s1, s2)
-    | Sseq(s1, s2) -> aux s1 || aux s2
-    | Sswitch (_, s)
-    | Slabeled (_, s)
-    | Swhile (_, s)
-    | Sdowhile(s, _ ) -> aux s
-    | Sfor(s1, _ , s2, s3) ->  aux s1 || aux s2 || aux s3
-    | Sreturn _ -> true
-    | Sblock sl -> List.fold_left (fun acc s -> acc || aux s) false sl in
-  aux s