[sledge] Check is_unsat of stem in Sh.simplify

Reviewed By: jvillard

Differential Revision: D25756579

fbshipit-source-id: c248db51e

sledge/src/sh.ml

@@ -9,6 +9,9 @@
 
 open Fol
 
+(** enable stronger unsat checking during normalization *)
+let strong_unsat = false
+
 [@@@warning "+9"]
 
 type seg = {loc: Term.t; bas: Term.t; len: Term.t; siz: Term.t; cnt: Term.t}
@@ -794,8 +797,12 @@ let rec simplify_ us rev_xss survived ancestor_subst q =
       (* opt: ctx already normalized so just preserve it *)
       {(norm subst {q with djns= emp.djns; ctx= emp.ctx}) with ctx= q.ctx}
     in
+    if strong_unsat && is_unsat stem then false_ stem.us
+    else
       (* recursively simplify subformulas *)
-    let survived = Var.Set.union survived (fv (elim_exists stem.xs stem)) in
+      let survived =
+        Var.Set.union survived (fv (elim_exists stem.xs stem))
+      in
       let q =
         starN
           ( stem
@@ -813,8 +820,8 @@ let rec simplify_ us rev_xss survived ancestor_subst q =
             assert (Var.Set.disjoint removed (Context.fv q.ctx)) ;
             Var.Set.diff removed (fv ~ignore_ctx:() (elim_exists q.xs q)) )
         in
-      (* removed may not contain all variables stem_subst has solutions for,
+        (* removed may not contain all variables stem_subst has solutions
-         so the equations in [∃ removed. stem_subst] that are not
+           for, so the equations in [∃ removed. stem_subst] that are not
            universally valid need to be re-conjoined since they have alredy
            been normalized out *)
         let keep, removed, _ =