Refactored cmm helpers to handle many integer widths

    #Squashed commit of the following:
    #commit c9d7aa6
    #Author: Jacob Van Buren <[email protected]>
    #Date:   Thu Jan 2 14:49:45 2025 -0500
        #cleaned up div/mod
    #commit 4d9f427
    #Author: Jacob Van Buren <[email protected]>
    #Date:   Thu Jan 2 14:45:42 2025 -0500
        #address feedback and simplify division interface
    #unified unboxed field getters/setters. This will be useful once we have unboxed integers of different sizes
    #formatted
    #updated cmm_helpers interface to be more amenable to adding other integer sizes
    #Separate test for vectorizer in the CI (#3414)
    #* Separate test for vectorizer in the CI
    #* Remove vectorizer from "gi" CI job
    #CI: simplify the regalloc jobs (#3389)
    #ASR 64-bit lane not available in sse instruction (#3413)
    #Fix case where parser drops attributes in packed module types. (#3262)
    #* Demonstrate dropped attributes in test.
    #Signed-off-by: Thomas Del Vecchio <[email protected]>
    #* Syntax error on misplaced attribute in packed module types.
    #Signed-off-by: Thomas Del Vecchio <[email protected]>
    #---------
    #Signed-off-by: Thomas Del Vecchio <[email protected]>
    #Add attributes to (unsafely) skip jkind check  (#3385)
    #* Add attributes to (unsafely) skip jkind check
    #Add a pair of attributes, [@@unsafe_allow_any_kind_in_intf] and
    #[@@unsafe_allow_any_kind_in_impl], which if set on both the impl and the intf
    #respectively, skip checking the jkind of the type in a signature against the
    #jkind of the type in a struct entirely. This is a more-selective version of the
    #`--allow-illegal-crossing` flag, and likely eventually subsumes it.
    #Signed-off-by: Aspen Smith <[email protected]>
    #* Emit a warning when unsafe_allow_any_kind is added unnecessarily
    #Note that this is /only/ done if the attribute is set in both signatures but not
    #used - also this is a little over-sensitive (sadly) since this is done during
    #sigature inclusion too. A new test covers the over-sensitivity.
    #Signed-off-by: Aspen Smith <[email protected]>
    #---------
    #Signed-off-by: Aspen Smith <[email protected]>
    #Add `Variant_with_null` and `Null` variant constructors (#2870)
    #* `Variant_with_null`
    #* `Null` tagged constructors
    #* precise value kind
    #* No private re-export
    #---------
    #Co-authored-by: Diana Kalinichenko <[email protected]>
    #Revert "Implement %makearray_dynamic{,_uninit}" (#3408)
    #Revert "Implement %makearray_dynamic{,_uninit} (#3317)"
    #This reverts commit 6da1dde.
    #Upload core files etc upon CI failure (#3405)
    #Fix IRC and Greedy allocators (arm64) (#3388)
    #Convert float32 constants to int32 in first stage compiler (#3371)
    #* convert float32 constants in bytecode output
    #* edit
    #* edit
    #* blocks + test
    #* compare against float64 constants
    #* tests check proper custom ops
    #---------
    #Co-authored-by: Diana Kalinichenko <[email protected]>

Squashed commit of the following:

commit 16f1b23
Author: Jacob Van Buren <[email protected]>
Date:   Wed Jan 22 15:25:23 2025 -0500

    Squashed commit of the following:

    commit 7c5c7f0
    Author: Jacob Van Buren <[email protected]>
    Date:   Wed Jan 22 15:24:10 2025 -0500

        Squashed commit of the following:

        commit a53391d
        Author: Max Slater <[email protected]>
        Date:   Wed Jan 22 13:53:02 2025 -0500

            Rename `atomic_cas`/`Compare_and_swap` (#3491)

        commit 92b327c
        Author: Max Slater <[email protected]>
        Date:   Tue Jan 21 14:18:56 2025 -0500

            Additional operations for int atomics (#3490)

        commit 38e792c
        Author: Luke Maurer <[email protected]>
        Date:   Tue Jan 21 17:09:23 2025 +0000

            Support `-open Foo` where `Foo` is parameterised (#3489)

            The command line

            ```
            ocamlopt -open Foo -parameter P -c bar.ml
            ```

            should be fine, even if `Foo` is itself parameterised by `P`: as usual, we
            compile `bar.ml` as if it began with `open! Foo`, and by the subset rule, `Bar`
            can refer to `Foo` because it takes at least the same parameters. Unfortunately,
            currently we process `-open` before `-parameter`, so when we go to check the
            implicit reference to `Foo`, we think there are no parameters, and we report an
            error. (Confusingly, the error suggests that the user add `-parameter P` to the
            command line.)

            The fix is simple: move the code that processes `-parameter` earlier so that
            the initial environment is constructed with the parameters already available.

        commit 784dc96
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 21 14:07:41 2025 +0000

            Rename [emit.mlp] to [emit.ml] on amd64 (#3488)

        commit f3b720a
        Author: Zesen Qian <[email protected]>
        Date:   Tue Jan 21 10:35:35 2025 +0000

            Module aliases save locks instead of walking them immediately (#3398)

        commit 389a7c3
        Author: Nick Barnes <[email protected]>
        Date:   Mon Jan 20 17:55:51 2025 +0000

            Add OCAMLRUNPARAM d= parameter for max # domains (#3487)

            Allow maximum number of domains to be specified as a OCAMLRUNPARAM parameter.

            (cherry picked from commit f92715f)

            Co-authored-by: KC Sivaramakrishnan <[email protected]>

        commit 63767d7
        Author: Nick Barnes <[email protected]>
        Date:   Mon Jan 20 17:45:30 2025 +0000

            Add caml_runtime_parameters back (#3468)

            Add caml_runtime_parameters back.

        commit 5e9975e
        Author: Greta Yorsh <[email protected]>
        Date:   Mon Jan 20 17:15:15 2025 +0000

            Emit atomic compare and exchange (#3486)

        commit a9821e8
        Author: Basile Clément <[email protected]>
        Date:   Mon Jan 20 15:36:09 2025 +0100

            Make patricia trees big-endian (#3438)

            This patch switches up the implementation of the `Patricia_tree` module
            from little-endian to big-endian, with the main motivation to be able to
            implement in-order traversal.

            The `caml_int_clz_tagged_to_untagged` and `caml_int_tagged_to_tagged` C
            stubs are recognized and replaced with the `clz` instruction when
            compiling with flambda2, so they are only used in the boot compiler.

        commit b8a9789
        Author: Leo White <[email protected]>
        Date:   Fri Jan 17 13:35:19 2025 +0000

            Generate specific instructions for atomics on immediates (#3477)

            * Generate specific instructions for atomics on immediates

            * Fix formatting

        commit 7b93134
        Author: Greta Yorsh <[email protected]>
        Date:   Fri Jan 17 09:30:30 2025 +0000

            Vectorizer: add tests (#3456)

            * Add tests

            * Disable ocamlformat on unboxed tests

            * Increase -vectorize-max-block-size for tests

            * Fix asssertion failure when vectorizing unboxed int32

            * Disable float32 on arm64 (not yet implemented)

            * improve gen_dune.ml for the vectorizer tests

            Co-authored-by: Xavier Clerc <[email protected]>

        commit 6379678
        Author: Mark Shinwell <[email protected]>
        Date:   Thu Jan 16 16:08:29 2025 +0000

            Add "-ocamlrunparam" linker flag (#3483)

        commit f7b2cbe
        Author: Xavier Clerc <[email protected]>
        Date:   Thu Jan 16 15:25:28 2025 +0000

            Bump the version of `actions/upload-artifact` (#3474)

            * Bump the version of actions/upload-artifact.

            * Ensure artifact names are unique.

            * To trigger CI.

            * Try with commit hash.

        commit afb8a55
        Author: Mark Shinwell <[email protected]>
        Date:   Thu Jan 16 14:03:37 2025 +0000

            Move two macOS CI controllers to runtime5 (#3482)

        commit aae5c40
        Author: Mark Shinwell <[email protected]>
        Date:   Thu Jan 16 13:50:34 2025 +0000

            Fix error in caml_get_init_stack_wsize (#3481)

        commit 525868c
        Author: dkalinichenko-js <[email protected]>
        Date:   Wed Jan 15 17:47:30 2025 -0500

            Use null pointers for `or_null`  (#3267)

            * runtime changes

            * runtime4 changes

            * Change `CODE_UNBOXED_INT64` and `CODE_NULL`

            * make `Is_block` an inline function

            * redefine `Is_long`

            * fix

            * Change `CODE_UNBOXED_INT64` back

            * optimize `Is_block`/`Is_long`

            * `null_tag` for `caml_obj_tag`

            * consistent naming

            * slightly more reassuring comment

            * `inline` is unnecessary and might break `#define inline`

            * optimization incorrect in presence of nulls

            * Constructors and pattern-matching

            * Bytecode compilation

            * `or_null` is `Variant_or_null`

            * Accept tests

            * Runtime tests

            * Delete obsolete or_null test

            ---------

            Co-authored-by: Diana Kalinichenko <[email protected]>

        commit 9796b21
        Author: dkalinichenko-js <[email protected]>
        Date:   Wed Jan 15 17:47:13 2025 -0500

            Runtime changes for `or_null` (#3265)

            * runtime changes

            * runtime4 changes

            * Change `CODE_UNBOXED_INT64` and `CODE_NULL`

            * make `Is_block` an inline function

            * redefine `Is_long`

            * fix

            * Change `CODE_UNBOXED_INT64` back

            * optimize `Is_block`/`Is_long`

            * `null_tag` for `caml_obj_tag`

            * consistent naming

            * slightly more reassuring comment

            * `inline` is unnecessary and might break `#define inline`

            * optimization incorrect in presence of nulls

            ---------

            Co-authored-by: Diana Kalinichenko <[email protected]>

        commit df4a6e0
        Author: Chris Casinghino <[email protected]>
        Date:   Wed Jan 15 13:08:53 2025 -0500

            Bump magic numbers for 5.2.0minus-5 (#3478)

        commit d1c8d85
        Author: Mark Shinwell <[email protected]>
        Date:   Wed Jan 15 16:44:39 2025 +0000

            Peek and poke (#3309)

        commit f8caad4
        Author: Greta Yorsh <[email protected]>
        Date:   Wed Jan 15 16:00:39 2025 +0000

            Vectorizer: xmm register can hold ocaml values (#3455)

            * Add [Valx2] to [Cmm.machtype_component]

            * Vectorizer generates [Valx2]

            * Record live offsets of [Valx2] in the frametable

            For runtime4, xmm register are below [gc_regs], use negative offsets.

            * Move [types_are_compatible] from [Reg] to [Proc]

            This information has to be in sync with register classes, stack
            slock classes, and emit for move instructions.

        commit 34a7873
        Author: Zesen Qian <[email protected]>
        Date:   Wed Jan 15 13:13:18 2025 +0000

            Improve coherence of modality zapping (#3462)

        commit 1a6a9d3
        Author: Mark Shinwell <[email protected]>
        Date:   Wed Jan 15 12:06:24 2025 +0000

            Fix caml_obj_with_tag (#3465)

        commit bc5110a
        Author: Nick Barnes <[email protected]>
        Date:   Wed Jan 15 11:52:25 2025 +0000

            Reset the pacing of major collection after any synchronous major GC (#3463)

            Reset the pacing of major collection at the end of any synchronous major collection.

        commit 9faf700
        Author: Mark Shinwell <[email protected]>
        Date:   Wed Jan 15 11:32:59 2025 +0000

            Remove remnants of caml_obj_truncate (#3469)

        commit ff9430b
        Author: Luke Maurer <[email protected]>
        Date:   Wed Jan 15 11:31:22 2025 +0000

            Mangle instance symbol names using `____` rather than `___` (#3472)

            Apparently there are libraries around that have names ending in single
            underscores, leading to ambiguous symbol names if we use triple
            underscores to delimit instances. Other choices are possible but this PR
            opts for newly-developed quadruple-underscore technology.

        commit 9984700
        Author: Vincent Laviron <[email protected]>
        Date:   Wed Jan 15 11:03:43 2025 +0100

            Port upstream PRs 11542 and 12505 to runtime4 (#3431)

            fix #11482: random crash in large closure allocation (#11542)

            Co-authored-by: Damien Doligez <[email protected]>

        commit 058c4db
        Author: Mark Shinwell <[email protected]>
        Date:   Tue Jan 14 22:19:32 2025 +0000

            Enable all makearray_dynamic tests on runtime4 (#3470)

        commit ba15ee5
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 14 20:08:31 2025 +0000

            Vectorize [Ifloatarithmem] (#3452)

            * Add [Isimd_mem] to [Arch.Specific] and emit [addpd] with memory arg

            and similar instructions

            * Vectorize [Ifloatarithmem]

            When the memory alignment is known to be 128-bit (currently, never) emits
            [addpd], otherwise emits a vector load followed by an arithmetic
            instruction.

        commit 9755b39
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 14 18:57:39 2025 +0000

            Fix CI failure (#3473)

        commit 859949c
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 14 17:56:53 2025 +0000

            Vectorize [Specific.Istore_int] (#3450)

            Used for array initialization (amd64)

        commit 50f73cb
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 14 17:38:39 2025 +0000

            Do not allow naked pointers (remove configure option) (#3448)

        commit b7c8ad3
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 14 17:07:39 2025 +0000

            Vectorizer refactor heuristic for select_and_join (#3449)

            * Refactor [Block.find_last_instruction], cache [Computation.last_pos]

            * Improve heuristics in [Computation.select_and_join] using [last_pos]

        commit 22f81d8
        Author: Mark Shinwell <[email protected]>
        Date:   Tue Jan 14 17:00:29 2025 +0000

            Fix mistake in conditional for makearray_dynamic array initialization (#3466)

        commit aaaddfb
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 14 14:57:17 2025 +0000

            Vectorizer: propagate alignment of memory accesses (#3451)

            Currently it's always 8 but having this argument will help us
            consider alignment for new vector sequences.

        commit b15d44e
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 14 14:55:29 2025 +0000

            vectorizer: improve debug printout (#3445)

        commit 6239156
        Author: Stephen Dolan <[email protected]>
        Date:   Tue Jan 14 13:43:21 2025 +0000

            Better hugepage alignment of stacks and heap (#3384)

            Co-authored-by: Mark Shinwell <[email protected]>

        commit 677d79a
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 14 13:23:56 2025 +0000

            Backend dune copy and directive (#3467)

            * Remove unused line directive from [dune]

            * Use [copy_files#] to copy files from ARCH and add a file directive

            * Remove existing file directives

        commit 314b131
        Author: Stephen Dolan <[email protected]>
        Date:   Tue Jan 14 11:58:41 2025 +0000

            Bound stack size in expect tests (#3439)

        commit 02774f8
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 14 10:52:50 2025 +0000

            all_deps is reflexive (#3464)

        commit 117a0a0
        Author: Stephen Dolan <[email protected]>
        Date:   Tue Jan 14 10:44:15 2025 +0000

            Stub implementation of new custom memory API (#3437)

        commit 4f30aac
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Jan 14 10:31:48 2025 +0000

            Vectorizer bug fix: address argument of memory operations (#3446)

            Fix bug: use address arg of the first instruction in a group

            ... not the last!

            Only matters for arrays at the moment, where the address offset
            argument is not always the same register.

        commit cc91e2b
        Author: Vincent Laviron <[email protected]>
        Date:   Tue Jan 14 11:26:59 2025 +0100

            caml_update_dummy: fail on closure blocks (#3429)

        commit 17a01a9
        Author: Mark Shinwell <[email protected]>
        Date:   Tue Jan 14 10:07:39 2025 +0000

            Implement %array_element_size_in_bytes (#3367)

            Co-authored-by: Chris Casinghino <[email protected]>

        commit b487f71
        Author: Greta Yorsh <[email protected]>
        Date:   Mon Jan 13 14:05:25 2025 +0000

            Runtime: make types explicit when reading [gc_regs] (#3453)

            Runtime4: make types explicit when reading [gc_regs].

        commit 67e6eb3
        Author: Max Slater <[email protected]>
        Date:   Fri Jan 10 16:17:32 2025 -0500

            More capsule API updates (#3440)

        commit c7f573f
        Author: Mark Shinwell <[email protected]>
        Date:   Fri Jan 10 18:26:15 2025 +0000

            Reinstate %makearray_dynamic (#3460)

        commit e1e4fb8
        Author: Zesen Qian <[email protected]>
        Date:   Fri Jan 10 16:15:48 2025 +0000

            `portable` lazy allows `nonportable` thunk (#3436)

            * portable lazy allows nonportable thunk

            * add documentation

            * improve documentation

            * add examples

            * improve comments in test

            * say "not stronger"

        commit c30ec74
        Author: Ryan Tjoa <[email protected]>
        Date:   Fri Jan 10 10:41:08 2025 -0500

            Check for type recursion without boxing (#3407)

        commit cb290c5
        Author: Greta Yorsh <[email protected]>
        Date:   Fri Jan 10 11:00:32 2025 +0000

            Vectorizer: rename New (#3454)

            Rename New to New_vec128 to make the type clear

            and distinguish it from the upcoming Valx2

        commit bd39e02
        Author: Greta Yorsh <[email protected]>
        Date:   Fri Jan 10 10:24:48 2025 +0000

            Add function [DLL.for_all_i] (#3442)

            * Add function [DLL.for_all_i]

            * Rename to [for_alli] to match existing [mapi] and [iteri]

            * Remove unused argument of [aux] in [DLL.for_all*]

        commit c048920
        Author: Greta Yorsh <[email protected]>
        Date:   Thu Jan 9 13:16:36 2025 +0000

            Cleanup machtype_component size (#3441)

            Cleanup size_component

        commit 830d5e7
        Author: Greta Yorsh <[email protected]>
        Date:   Thu Jan 9 13:15:59 2025 +0000

            Add "dump-vectorize" to OCAMLPARAM (#3443)

            Add [dump-vectorize] to OCAMLPARAM for debugging

        commit 157c95e
        Author: Greta Yorsh <[email protected]>
        Date:   Thu Jan 9 13:15:33 2025 +0000

            Vectorizer bug fix: 128-bit vectorized constant   (#3447)

            Fix bug: 128-bit vectorized constant high/low correctly ordered

        commit 648155d
        Author: Greta Yorsh <[email protected]>
        Date:   Thu Jan 9 13:09:48 2025 +0000

            Add [Printreg.reglist] for debugging (#3444)

        commit d40254f
        Author: Stephen Dolan <[email protected]>
        Date:   Tue Jan 7 21:25:45 2025 +0000

            Move two misplaced files (#3435)

        commit 4a0bb69
        Author: dkalinichenko-js <[email protected]>
        Date:   Tue Jan 7 15:34:27 2025 -0500

            `Yielding` mode axis (#3283)

            * `Yielding` mode axis

            * Tests

            * fix printing

            ---------

            Co-authored-by: Diana Kalinichenko <[email protected]>

        commit 00275e0
        Author: Max Slater <[email protected]>
        Date:   Mon Jan 6 13:05:58 2025 -0500

            Unbox_float32 should check custom ops name (#3433)

            check sym name

        commit 2e49469
        Author: Max Slater <[email protected]>
        Date:   Mon Jan 6 13:05:03 2025 -0500

            Make Capsule preserve wrapped exception backtraces (#3421)

            * with_password

            * portable

            * don't use polymorphic parameters

            * review

            * protect encapsulated from other capsule

            * raise wrapped exceptions with existing backtrace

            * cr

        commit 2de23a5
        Author: Ryan Tjoa <[email protected]>
        Date:   Mon Jan 6 04:04:29 2025 -0500

            Fix CI by using `setup-ocaml` v3 for ocamlformat workflow (#3426)

            [CI] Use setup-ocaml v3 for ocamlformat workflow

        commit eada0f1
        Author: Ryan Tjoa <[email protected]>
        Date:   Fri Jan 3 21:23:23 2025 -0500

            Move unboxed records to stable (#3419)

        commit a273a33
        Author: Jacob Van Buren <[email protected]>
        Date:   Fri Jan 3 11:17:18 2025 -0500

            Changed make fmt to run in parallel (#3422)

            changed make fmt to run in parallel

        commit 4de5a72
        Author: Max Slater <[email protected]>
        Date:   Thu Jan 2 20:10:08 2025 -0500

            Add `Capsule.with_password` (#3420)

        commit b084ff3
        Author: Greta Yorsh <[email protected]>
        Date:   Wed Jan 1 15:34:11 2025 +0000

            vectorizer: new test (#3418)

            Add test for register compatiblity

        commit 5549015
        Author: Greta Yorsh <[email protected]>
        Date:   Tue Dec 31 17:20:56 2024 +0000

            Vectorizer: check register compatibility (#3412)

            Check that registers are compatible when joining computations

Author: jvanburen

backend/arm64/cfg_selection.ml

@@ -171,7 +171,7 @@ class selector =
     method! insert_move_extcall_arg env ty_arg src dst =
       let ty_arg_is_int32 =
         match ty_arg with
-        | XInt32 -> true
+        | XInt8 | XInt16 | XInt32 -> true
         | XInt | XInt64 | XFloat32 | XFloat | XVec128 -> false
       in
       if macosx && ty_arg_is_int32 && is_stack_slot dst

backend/arm64/proc.ml

@@ -297,7 +297,7 @@ let external_calling_conventions
     begin match ty_arg with
     | XInt | XInt64 ->
         loc.(i) <- [| loc_int last_int make_stack int ofs |]
-    | XInt32 ->
+    | XInt32 | XInt16 | XInt8 ->
         loc.(i) <- [| loc_int32 last_int make_stack int ofs |]
     | XFloat ->
         loc.(i) <- [| loc_float last_float make_stack float ofs |]

backend/arm64/selection.ml

@@ -157,7 +157,12 @@ class selector =
       | _ -> super#select_operation op args dbg
 
     method! insert_move_extcall_arg env ty_arg src dst =
-      if macosx && ty_arg = XInt32 && is_stack_slot dst
+      let ty_arg_is_int32 =
+        match ty_arg with
+        | XInt8 | XInt16 | XInt32 -> true
+        | XInt | XInt64 | XFloat32 | XFloat | XVec128 -> false
+      in
+      if macosx && ty_arg_is_int32 && is_stack_slot dst
       then self#insert env (Iop (Ispecific Imove32)) src dst
       else self#insert_moves env src dst
   end

backend/cmm.ml

@@ -1,3 +1,4 @@
+# 1 "backend/cmm.ml"
 (**************************************************************************)
 (*                                                                        *)
 (*                                 OCaml                                  *)
@@ -107,6 +108,8 @@ let ge_component comp1 comp2 =
 
 type exttype =
   | XInt
+  | XInt8
+  | XInt16
   | XInt32
   | XInt64
   | XFloat32
@@ -115,6 +118,8 @@ type exttype =
 
 let machtype_of_exttype = function
   | XInt -> typ_int
+  | XInt8 -> typ_int
+  | XInt16 -> typ_int
   | XInt32 -> typ_int
   | XInt64 -> typ_int
   | XFloat -> typ_float
@@ -590,21 +595,19 @@ let equal_machtype_component (left : machtype_component) (right : machtype_compo
   | Float32, (Val | Addr | Int | Float | Vec128 | Valx2) ->
     false
 
-let equal_exttype left right =
-  match left, right with
-  | XInt, XInt -> true
-  | XInt32, XInt32 -> true
-  | XInt64, XInt64 -> true
-  | XFloat32, XFloat32 -> true
-  | XFloat, XFloat -> true
-  | XVec128, XVec128 -> true
-  | XInt, (XInt32 | XInt64 | XFloat | XFloat32 | XVec128)
-  | XInt32, (XInt | XInt64 | XFloat | XFloat32 | XVec128)
-  | XInt64, (XInt | XInt32 | XFloat | XFloat32 | XVec128)
-  | XFloat, (XInt | XInt32 | XFloat32 | XInt64 | XVec128)
-  | XVec128, (XInt | XInt32 | XInt64 | XFloat | XFloat32)
-  | XFloat32, (XInt | XInt32 | XInt64 | XFloat | XVec128) ->
-    false
+let equal_exttype
+      ((XInt
+       | XInt8
+       | XInt16
+       | XInt32
+       | XInt64
+       | XFloat32
+       | XFloat
+       | XVec128) as left)
+      right
+  =
+  (* we can use polymorphic compare as long as exttype is all constant constructors *)
+  left = right
 
 let equal_vec128_type v1 v2 =
   match v1, v2 with

backend/cmm.mli

@@ -75,6 +75,8 @@ val ge_component
 
 type exttype =
   | XInt                                (**r OCaml value, word-sized integer *)
+  | XInt8                               (**r 8-bit integer *)
+  | XInt16                              (**r 16-bit integer  *)
   | XInt32                              (**r 32-bit integer *)
   | XInt64                              (**r 64-bit integer  *)
   | XFloat32                            (**r single-precision FP number *)