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Ghost functions have a model supporting their erasure #10

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merged 20 commits into from
Feb 29, 2024
Merged

Ghost functions have a model supporting their erasure #10

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8606ec9
wip, adding an erased heap
nikswamy Feb 27, 2024
def8e24
refine actions, and provide heap extension as an action with pre & po…
nikswamy Feb 28, 2024
1afe5ca
checkpoint; provide heap interface for heap2
nikswamy Feb 28, 2024
7ee821b
cleanup straggling admits
nikswamy Feb 28, 2024
6eecb69
a type of ghost actions
nikswamy Feb 28, 2024
0e3f763
erased non-informative ghost actions can be unerased
nikswamy Feb 28, 2024
a5ad38c
checkpoint; implementing ghost refs
nikswamy Feb 28, 2024
fd13aaa
some genericity with lenses
nikswamy Feb 28, 2024
57c8a1a
ghost interface to heap2
nikswamy Feb 28, 2024
ecc5392
fix up a mis-naming in Heap; add a typeclass for HeapLike
nikswamy Feb 28, 2024
35a4a09
restore PulseCore.Memory, except for alloc_action
nikswamy Feb 28, 2024
814cff0
restore alloc_action
nikswamy Feb 28, 2024
976e47f
add a ghost allocation counter
nikswamy Feb 28, 2024
9774f22
separate ghost actions
nikswamy Feb 28, 2024
d5b2faf
expose more ghost actions in memory
nikswamy Feb 28, 2024
524d3dd
implement ghost_alloc
nikswamy Feb 28, 2024
76c37dc
propagating ghost to PulseCore.Action
nikswamy Feb 29, 2024
70a4e8f
erased ghost actions in PulseCore.Action
nikswamy Feb 29, 2024
8631125
remove axiom about lifting stt_ghost to stt_atomic neutral
nikswamy Feb 29, 2024
4e73180
removing ghost_witness/ghost_recall
nikswamy Feb 29, 2024
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129 changes: 100 additions & 29 deletions lib/pulse/core/PulseCore.Action.fst
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Original file line number Diff line number Diff line change
Expand Up @@ -91,17 +91,29 @@ let stt_of_action2 (#a:Type u#2) #pre #post (m:action a Set.empty pre post)

let iname = iname

let maybe_ghost (r:reifiability { r =!= UsesInvariants}) =
match r with
| Ghost -> true
| _ -> false

let pre_act
(a:Type u#a)
(r:reifiability)
(opens:inames)
(pre:slprop)
(post:a -> slprop)
= match r with
| Reifiable ->
Mem.pst_action_except a opens pre post
| _ ->
| UsesInvariants ->
Mem.action_except a opens pre post
| _ ->
Mem._pst_action_except a (maybe_ghost r) opens pre post

let force
#a (#r:reifiability { r =!= UsesInvariants})
(#opens:inames) (#pre:slprop) (#post:a -> slprop)
(f:pre_act a r opens pre post)
: Mem._pst_action_except a (maybe_ghost r) opens pre post
= f

let mem_action_as_action
(#a:Type u#a)
Expand Down Expand Up @@ -135,8 +147,8 @@ let action_of_pre_act
(f:pre_act a r opens pre post)
: action a opens pre post
= match r with
| Reifiable -> mem_pst_action_as_action f
| _ -> mem_action_as_action f
| UsesInvariants -> mem_action_as_action f
| _ -> mem_pst_action_as_action f

let act
(a:Type u#a)
Expand All @@ -147,14 +159,27 @@ let act
: Type u#(max a 2)
= #ictx:inames_disj opens ->
pre_act a r ictx pre post

let return_pre_act
(#a:Type u#a)
(#except:inames)
(#post:a -> slprop)
(x:a)
: pre_act a Reifiable except (post x) post
= fun frame m0 -> x, m0
: pre_act a Ghost except (post x) post
= Mem.ghost_action_preorder ();
fun frame m0 -> x, m0

let bind_pre_act_ghost
(#a:Type u#a)
(#b:Type u#b)
(#except:inames)
(#pre1 #post1 #post2:_)
(f:pre_act a Ghost except pre1 post1)
(g:(x:a -> pre_act b Ghost except (post1 x) post2))
: pre_act b Ghost except pre1 post2
= Mem.ghost_action_preorder ();
fun frame ->
PST.weaken (PST.bind (f frame) (fun x -> g x frame))

let bind_pre_act_reifiable
(#a:Type u#a)
Expand Down Expand Up @@ -189,11 +214,21 @@ let bind_pre_act
(g:(x:a -> pre_act b r except (post1 x) post2))
: pre_act b r except pre1 post2
= match r with
| Ghost ->
bind_pre_act_ghost #a #b #except #pre1 #post1 #post2 f g
| Reifiable ->
bind_pre_act_reifiable #a #b #except #pre1 #post1 #post2 f g
| UsesInvariants ->
bind_pre_act_non_reifiable #a #b #except #pre1 #post1 #post2 f g

let frame_pre_act_ghost
(#a:Type u#a)
(#except:inames)
(#pre #post #frame:_)
(f:pre_act a Ghost except pre post)
: pre_act a Ghost except (pre `star` frame) (fun x -> post x `star` frame)
= fun frame' -> f (frame `star` frame')

let frame_pre_act_reifiable
(#a:Type u#a)
(#except:inames)
Expand All @@ -218,9 +253,18 @@ let frame_pre_act
(f:pre_act a r except pre post)
: pre_act a r except (pre `star` frame) (fun x -> post x `star` frame)
= match r with
| Ghost -> frame_pre_act_ghost #a #except #pre #post #frame f
| Reifiable -> frame_pre_act_reifiable #a #except #pre #post #frame f
| _ -> frame_pre_act_non_reifiable #a #except #pre #post #frame f

let lift_pre_act_ghost
(#a:Type u#a)
(#except:inames)
(#pre #post:_)
(f:pre_act a Ghost except pre post)
: pre_act a Reifiable except pre post
= f

let lift_pre_act_reifiablity
(#a:Type u#a)
(#r:_)
Expand All @@ -245,6 +289,7 @@ let return
= fun #ictx ->
let m = return_pre_act #a #ictx #post x in
match r with
| Ghost -> m
| Reifiable -> m
| _ -> lift_pre_act_reifiablity m

Expand All @@ -268,6 +313,15 @@ let frame
: act a r opens (pre `star` frame) (fun x -> post x `star` frame)
= fun #ictx -> frame_pre_act (f #ictx)

let lift_ghost_reifiable
(#a:Type)
(#pre:slprop)
(#post:a -> slprop)
(#opens:inames)
(f:act a Ghost opens pre post)
: act a Reifiable opens pre post
= fun #ictx -> lift_pre_act_ghost (f #ictx)

let lift_reifiability
(#a:Type)
(#r:_)
Expand All @@ -286,22 +340,25 @@ let weaken
(#opens opens':inames)
(f:act a r0 opens pre post)
: act a (r0 ^^ r1) (Set.union opens opens') pre post
= match r0 with
| UsesInvariants -> f
| _ ->
match r1 with
| Reifiable -> f
| _ -> lift_reifiability f
= if r0 = r1 then f
else (
match r0, r1 with
| UsesInvariants, _ -> f
| _, UsesInvariants -> lift_reifiability f
| Reifiable, Ghost -> f
| Ghost, Reifiable -> lift_ghost_reifiable #a #pre #post #opens f
)

let sub_pre_act_reifiable
(#a:Type)
(#r:reifiability { r =!= UsesInvariants})
(#pre:slprop)
(#post:a -> slprop)
(#opens:inames)
(pre':slprop { slprop_equiv pre pre' })
(post':a -> slprop { forall x. slprop_equiv (post x) (post' x) })
(f:pre_act a Reifiable opens pre post)
: pre_act a Reifiable opens pre' post'
(f:pre_act a r opens pre post)
: pre_act a r opens pre' post'
= I.slprop_equiv_elim pre pre';
introduce forall x. post x == post' x
with I.slprop_equiv_elim (post x) (post' x);
Expand Down Expand Up @@ -332,10 +389,10 @@ let sub
(f:act a r opens pre post)
: act a r opens pre' post'
= match r with
| Reifiable ->
fun #ictx -> sub_pre_act_reifiable #a #pre #post #ictx pre' post' (f #ictx)
| _ ->
| UsesInvariants ->
fun #ictx -> sub_pre_act_non_reifiable #a #pre #post #ictx pre' post' (f #ictx)
| _ ->
fun #ictx -> sub_pre_act_reifiable #a #r #pre #post #ictx pre' post' (f #ictx)

let action_of_act
(#a:Type)
Expand Down Expand Up @@ -420,7 +477,7 @@ let invariant_name_identifies_invariant
let ref (a:Type u#a) (p:pcm a) = ref a p
let ref_null (#a:Type u#a) (p:pcm a) = core_ref_null
let is_ref_null (#a:Type u#a) (#p:pcm a) (r:ref a p) = core_ref_is_null r
let pts_to = pts_to
let pts_to = Mem.pts_to
let pts_to_not_null #a #p r v #ictx = pts_to_not_null_action ictx r v

let alloc
Expand Down Expand Up @@ -465,7 +522,7 @@ let share
(v0:FStar.Ghost.erased a)
(v1:FStar.Ghost.erased a{composable pcm v0 v1})
: act unit
Reifiable
Ghost
emp_inames
(pts_to r (v0 `op pcm` v1))
(fun _ -> pts_to r v0 `star` pts_to r v1)
Expand All @@ -478,7 +535,7 @@ let gather
(v0:FStar.Ghost.erased a)
(v1:FStar.Ghost.erased a)
: act (squash (composable pcm v0 v1))
Reifiable
Ghost
emp_inames
(pts_to r v0 `star` pts_to r v1)
(fun _ -> pts_to r (op pcm v0 v1))
Expand Down Expand Up @@ -522,11 +579,11 @@ let pure_true ()
coerce_eq () <| slprop_equiv_refl (pure True)

let intro_pure (p:prop) (pf:squash p)
: act unit Reifiable emp_inames emp (fun _ -> pure p)
: act unit Ghost emp_inames emp (fun _ -> pure p)
= fun #ictx -> intro_pure #ictx p pf

let elim_pure (p:prop)
: act (squash p) Reifiable emp_inames (pure p) (fun _ -> emp)
: act (squash p) Ghost emp_inames (pure p) (fun _ -> emp)
= fun #ictx -> elim_pure #ictx p

///////////////////////////////////////////////////////////////////
Expand All @@ -542,23 +599,37 @@ let exists_equiv (#a:_) (#p:a -> slprop)
let thunk (p:slprop) = fun (_:unit) -> p

let intro_exists' (#a:Type u#a) (p:a -> slprop) (x:erased a)
: act unit Reifiable emp_inames (p x) (thunk (op_exists_Star p))
: act unit Ghost emp_inames (p x) (thunk (op_exists_Star p))
= fun #ictx -> intro_exists #ictx (F.on_dom a p) x

let intro_exists'' (#a:Type u#a) (p:a -> slprop) (x:erased a)
: act unit Reifiable emp_inames (p x) (thunk (exists* x. p x))
: act unit Ghost emp_inames (p x) (thunk (exists* x. p x))
= coerce_eq (exists_equiv #a #p) (intro_exists' #a p x)

let intro_exists (#a:Type u#a) (p:a -> slprop) (x:erased a)
: act unit Reifiable emp_inames (p x) (fun _ -> exists* x. p x)
: act unit Ghost emp_inames (p x) (fun _ -> exists* x. p x)
= intro_exists'' p x

let elim_exists' (#a:Type u#a) (p:a -> slprop)
: act (erased a) Reifiable emp_inames (op_exists_Star p) (fun x -> p x)
: act (erased a) Ghost emp_inames (op_exists_Star p) (fun x -> p x)
= fun #ictx -> witness_h_exists #ictx (F.on_dom a p)

let elim_exists (#a:Type u#a) (p:a -> slprop)
: act (erased a) Reifiable emp_inames (exists* x. p x) (fun x -> p x)
: act (erased a) Ghost emp_inames (exists* x. p x) (fun x -> p x)
= coerce_eq (exists_equiv #a #p) (elim_exists' #a p)

let drop p = fun #ictx -> drop #ictx p

let ghost_ref = Mem.ghost_ref
let ghost_pts_to = Mem.ghost_pts_to
let ghost_alloc #a #pcm x = fun #ictx -> ghost_alloc #ictx #a #pcm x
let ghost_read #a #p r x f = fun #ictx -> ghost_read #ictx #a #p r x f
let ghost_write #a #p r x y f = fun #ictx -> ghost_write #ictx #a #p r x y f
let ghost_share #a #pcm r v0 v1 = fun #ictx -> ghost_share #ictx #a #pcm r v0 v1
let ghost_gather #a #pcm r v0 v1 = fun #ictx -> ghost_gather #ictx #a #pcm r v0 v1
let lift_erased #a ni_a #opens #pre #post f =
fun #ictx ->
let f : erased (pre_act a Ghost ictx pre post) =
hide (reveal f #ictx)
in
lift_ghost #a #ictx #pre #post ni_a f
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