I reached the same conclusions as Nicolas by looking at the lambda and
cmm output. I report my findings below, it case it could interest
other members of the list.
Here is the relevant part of the code provided by martin, hereafter 'test1':
let t = create () in
let f = Some 17 in
Obj.set_field (Obj.repr t) 0 (Obj.repr f);
let f1 = t.foo in
let f2 = Obj.obj (Obj.field (Obj.repr t) 0) in
if f1 = f then
print_endline "OK t.foo"
else ...
Here is how you can "fix" it to make the test pass, hereafter 'test2':
let t = create () in
let f = Some 17 in
Obj.set_field (Obj.repr t) 0 (Obj.repr f);
let f1 = (fun t -> t.foo) t in
let f2 = Obj.obj (Obj.field (Obj.repr t) 0) in
if f1 = f then
print_endline "OK t.foo"
else ...
Test1 and test2 -dlambda output both look sane:
(let (t/1036 (apply (field 0 (global Test2!)) 0a) f/1037 [0: 17])
(seq (array.unsafe_set (id t/1036) 0 (id f/1037))
(let
(f1/1038 (field 0 t/1036) <= FIELD ACCESS
f2/1039 (id (array.unsafe_get (id t/1036) 0)))
(seq
(if (caml_equal f1/1038 f/1037) <= COMPARISON HERE
(apply (field 29 (global Pervasives!)) "OK t.foo")
....)))))
(if (== f1/1038 0a)
(apply (field 29 (global Pervasives!))
"ERROR t.foo is None")
(apply (field 29 (global Pervasives!))
"ERROR t.foo is something strange")))
(let (t/1036 (apply (field 0 (global Test!)) 0a) f/1037 [0: 17])
(seq (array.unsafe_set (id t/1036) 0 (id f/1037))
(let
(f1/1038 (apply (function t/1039 (field 0 t/1039)) t/1036)
^= FUNCTION CALL HERE
f2/1040 (id (array.unsafe_get (id t/1036) 0)))
(seq
(if (caml_equal f1/1038 f/1037) <= SAME COMPARISON HERE
(apply (field 29 (global Pervasives!)) "OK t.foo")
...)))))
But the -dcmm change
(let
(t/1036 (app "camlTest2__create_1035" 1a addr)
f/1037 "camlTest2__7")
(if (!= (load unsigned int8 (+a t/1036 -4)) 254)
(extcall "caml_modify" t/1036 f/1037 unit)
(store float64u t/1036 (load float64u f/1037)))
(let
<= NOTHING HERE
f2/1039
(if (!= (load unsigned int8 (+a t/1036 -4)) 254) (load t/1036)
(alloc 2301 (load float64u t/1036)))
(if (!= (extcall "caml_equal" 1a f/1037 addr) 1)
^= 1a "CONSTANT" OPTIMIZED
(app "camlPervasives__print_endline_1274" "camlTest2__6" unit)
...)))
(let
(t/1036 (app "camlTest__create_1035" 1a addr) f/1037 "camlTest__8")
(if (!= (load unsigned int8 (+a t/1036 -4)) 254)
(extcall "caml_modify" t/1036 f/1037 unit)
(store float64u t/1036 (load float64u f/1037)))
(let
(f1/1038 (seq "camlTest__7" [] (load t/1036)) <= FUNCTION CALL HERE
f2/1040
(if (!= (load unsigned int8 (+a t/1036 -4)) 254) (load t/1036)
(alloc 2301 (load float64u t/1036))))
(if (!= (extcall "caml_equal" f1/1038 f/1037 addr) 1) <= COMPARISON
(app "camlPervasives__print_endline_1274" "camlTest__6" unit)
....)))
On Sat, Oct 15, 2011 at 10:10 AM, Martin Jambon
<[email protected]> wrote:
> Dear fellow OCamlers,
>
>
> Hints on how to solve this, using any means necessary, will be greatly
> appreciated.
>
>
> Purpose: deserializing a record efficiently, i.e. creating a record
> whose field values are available one after another in an unpredictable
> order.
>
> Problem: Obj.set_field does the job in most cases but not in the example
> below. How to make it work?
>
> (we don't want to use pure OCaml option refs to store field values
> before putting them into the record because that's too slow)
>
> Requirements:
> - performance is critical
> - code will be machine-generated
> - immutable record fields must be supported
>
>
> The example below shows a record type for which a straight Obj.set_field
> produces a field that cannot be read correctly with the usual dot
> notation (ocamlopt only, tested on Linux/amd64 with OCaml 3.12.1 and
> 3.11.2).
>
>
> $ ocamlopt -o foo.opt foo.ml; ./foo.opt
> ERROR t.foo is None
> OK field0
>
> $ cat foo.ml
> (* ocamlopt -o foo.opt foo.ml; ./foo.opt *)
>
> type t = {
> foo : int option;
> bar : int;
> }
>
> let create () =
> { { foo = None; bar = 42 } with foo = None }
>
> let () =
> assert (create () != create ());
> let t = create () in
> let f = Some 17 in
> Obj.set_field (Obj.repr t) 0 (Obj.repr f);
>
> let f1 = t.foo in
> let f2 = Obj.obj (Obj.field (Obj.repr t) 0) in
>
> if f1 = f then
> print_endline "OK t.foo"
> else if f1 = None then
> print_endline "ERROR t.foo is None"
> else
> print_endline "ERROR t.foo is something strange";
>
> if f2 = f then
> print_endline "OK field0"
> else if f2 = None then
> print_endline "ERROR field0 is None"
> else
> print_endline "ERROR field0 is something strange"
>
> --
> Caml-list mailing list. Subscription management and archives:
> https://sympa-roc.inria.fr/wws/info/caml-list
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>
>
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