Make casts of pointers to _Bool semantically well defined (again).

In compCert 2.5 the semantics of pointer comparisons against the NULL pointer was made more accurate by making it undefined if the pointer is invalid (outside bounds).  Technical difficulties prevented this change from being propagated to the semantics of casts from pointer types to the _Bool type, which involves an implicit pointer comparison against NULL.  Hence, this kind of casts was temporarily given undefined semantics.

This commit makes pointer-to-_Bool casts semantically defined (again), provided the pointer is valid.  This reinstates the equivalence between casts to _Bool and comparisons != 0.  The technical difficulties mentioned above came from the translation of assignments in a value context in the SimplExpr pass.  The pass was lightly modified to work around the issue.

1 files changed, 8 insertions, 8 deletions

diff --git a/cfrontend/SimplExpr.v b/cfrontend/SimplExpr.v
index a5a6ad66..a3af8114 100644
--- a/cfrontend/SimplExpr.v
+++ b/cfrontend/SimplExpr.v
@@ -114,7 +114,7 @@ Fixpoint eval_simpl_expr (a: expr) : option val :=
   | Ecast b ty =>
       match eval_simpl_expr b with
       | None => None
-      | Some v => sem_cast v (typeof b) ty
+      | Some v => sem_cast v (typeof b) ty Mem.empty
       end
   | _ => None
   end.
@@ -327,10 +327,10 @@ Fixpoint transl_expr (dst: destination) (a: Csyntax.expr) : mon (list statement
       let ty2 := Csyntax.typeof r2 in
       match dst with
       | For_val | For_set _ =>
-          do t <- gensym ty2;
+          do t <- gensym ty1;
           ret (finish dst
-                 (sl1 ++ sl2 ++ Sset t a2 :: make_assign a1 (Etempvar t ty2) :: nil)
-                 (Ecast (Etempvar t ty2) ty1))
+                 (sl1 ++ sl2 ++ Sset t (Ecast a2 ty1) :: make_assign a1 (Etempvar t ty1) :: nil)
+                 (Etempvar t ty1))
       | For_effects =>
           ret (sl1 ++ sl2 ++ make_assign a1 a2 :: nil,
                dummy_expr)
@@ -342,12 +342,12 @@ Fixpoint transl_expr (dst: destination) (a: Csyntax.expr) : mon (list statement
       do (sl3, a3) <- transl_valof ty1 a1;
       match dst with
       | For_val | For_set _ =>
-          do t <- gensym tyres;
+          do t <- gensym ty1;
           ret (finish dst
                  (sl1 ++ sl2 ++ sl3 ++
-                  Sset t (Ebinop op a3 a2 tyres) ::
-                  make_assign a1 (Etempvar t tyres) :: nil)
-                 (Ecast (Etempvar t tyres) ty1))
+                  Sset t (Ecast (Ebinop op a3 a2 tyres) ty1) ::
+                  make_assign a1 (Etempvar t ty1) :: nil)
+                 (Etempvar t ty1))
       | For_effects =>
           ret (sl1 ++ sl2 ++ sl3 ++ make_assign a1 (Ebinop op a3 a2 tyres) :: nil,
                dummy_expr)