diffing_with_keys.ml: heterogeneous typing#2
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gasche wants to merge 2 commits intoOctachron:semdiff_type_declfrom
Closed
diffing_with_keys.ml: heterogeneous typing#2gasche wants to merge 2 commits intoOctachron:semdiff_type_declfrom
gasche wants to merge 2 commits intoOctachron:semdiff_type_declfrom
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gasche
commented
Jun 7, 2021
| (x : l with_pos) | ||
| (y : r with_pos) | ||
| : Swap.key | ||
| * (l with_pos * r with_pos, l with_pos * r with_pos, state) partial_edge |
Author
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Note: I am not sure whether the type of swaps should be (l * r, l * r) partial_edge or rather (l * r, r * l) partial_erge.
| if kx <= ky then | ||
| (kx,ky), Left (pos x, state, (x,y)) | ||
| else | ||
| (ky,kx), Right(pos x,state, (x,y)) |
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If we used (l * r, r * l), we would need to swap (x, y) into (y, x) in the Right case here.
| | None | Some (Left _ | Right _)-> None | ||
| | Some Both (state, (ll,lr),(rl,rr)) -> | ||
| match test state ll rr, test state lr rl with | ||
| match test state ll rr, test state rl lr with |
Author
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There is a change here, that is mandated by the typing from the choice of using (l * r, l * r) partial_edge for swaps.
I believe that the change is not observable, due to the fact that the typeful information inside the result case is ignored (and likely to be uninteresting in the Ok case anyway, which is the one we care about here).
gasche
commented
Jun 7, 2021
| | Some reason -> | ||
| Error (Diffing_with_keys.Type {pos; got=cd1; expected=cd2; reason}) | ||
| | None -> Ok (Ident.name cd1.cd_id) | ||
| | None -> Ok () |
Author
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I suspect that this was a leftover from a previous implementation approach, that was accepted for no good reason due to lax typing.
Owner
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Why not? I am not completely convinced that this is simpler. (or that there is non-symmetric use cases) but this seems fine. |
Author
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I have two arguments in favor of the change:
|
Owner
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Superseded by #4 |
Octachron
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Jul 26, 2024
…l#13294) The toplevel printer detects cycles by keeping a hashtable of values that it has already traversed. However, some OCaml runtime types (at least bigarrays) may be partially uninitialized, and hashing them at arbitrary program points may read uninitialized memory. In particular, the OCaml testsuite fails when running with a memory-sanitizer enabled, as bigarray printing results in reads to uninitialized memory: ``` ==133712==WARNING: MemorySanitizer: use-of-uninitialized-value #0 0x4e6d11 in caml_ba_hash /var/home/edwin/git/ocaml/runtime/bigarray.c:486:45 #1 0x52474a in caml_hash /var/home/edwin/git/ocaml/runtime/hash.c:251:35 #2 0x599ebf in caml_interprete /var/home/edwin/git/ocaml/runtime/interp.c:1065:14 #3 0x5a909a in caml_main /var/home/edwin/git/ocaml/runtime/startup_byt.c:575:9 #4 0x540ccb in main /var/home/edwin/git/ocaml/runtime/main.c:37:3 #5 0x7f0910abb087 in __libc_start_call_main (/lib64/libc.so.6+0x2a087) (BuildId: 8f53abaad945a669f2bdcd25f471d80e077568ef) #6 0x7f0910abb14a in __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x2a14a) (BuildId: 8f53abaad945a669f2bdcd25f471d80e077568ef) #7 0x441804 in _start (/var/home/edwin/git/ocaml/runtime/ocamlrun+0x441804) (BuildId: 7a60eef57e1c2baf770bc38d10d6c227e60ead37) Uninitialized value was created by a heap allocation #0 0x47d306 in malloc (/var/home/edwin/git/ocaml/runtime/ocamlrun+0x47d306) (BuildId: 7a60eef57e1c2baf770bc38d10d6c227e60ead37) #1 0x4e7960 in caml_ba_alloc /var/home/edwin/git/ocaml/runtime/bigarray.c:246:12 #2 0x4e801f in caml_ba_create /var/home/edwin/git/ocaml/runtime/bigarray.c:673:10 #3 0x59b8fc in caml_interprete /var/home/edwin/git/ocaml/runtime/interp.c:1058:14 #4 0x5a909a in caml_main /var/home/edwin/git/ocaml/runtime/startup_byt.c:575:9 #5 0x540ccb in main /var/home/edwin/git/ocaml/runtime/main.c:37:3 #6 0x7f0910abb087 in __libc_start_call_main (/lib64/libc.so.6+0x2a087) (BuildId: 8f53abaad945a669f2bdcd25f471d80e077568ef) #7 0x7f0910abb14a in __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x2a14a) (BuildId: 8f53abaad945a669f2bdcd25f471d80e077568ef) #8 0x441804 in _start (/var/home/edwin/git/ocaml/runtime/ocamlrun+0x441804) (BuildId: 7a60eef57e1c2baf770bc38d10d6c227e60ead37) SUMMARY: MemorySanitizer: use-of-uninitialized-value /var/home/edwin/git/ocaml/runtime/bigarray.c:486:45 in caml_ba_hash ``` The only use of hashing in genprintval is to avoid cycles, that is, it is only useful for OCaml values that contain other OCaml values (including possibly themselves). Bigarrays cannot introduce cycles, and they are always printed as "<abstr>" anyway. The present commit proposes to be more conservative in which values are hashed by the cycle detector to avoid this issue: we skip hashing any value with tag above No_scan_tag -- which may not contain any OCaml values. Suggested-by: Gabriel Scherer <gabriel.scherer@gmail.com> Signed-off-by: Edwin Török <edwin.torok@cloud.com> Co-authored-by: Edwin Török <edwin.torok@cloud.com>
Octachron
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Feb 6, 2025
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