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compute the same separability signatures in either "(no) flat float" modes 

In -no-flat-float-array mode, instead of always returning
`best_msig` (the most permissive signature), we first compute the
flat-float-array separability signature -- falling back to `best_msig`
if it fails.

This discipline is conservative: it never rejects -no-flat-float-array
programs. At the same time it guarantees that, for any program that is
also accepted in -flat-float-array mode, the same separability will be
inferred in the two modes. In particular, the same .cmi files and
digests will be produced.

Before we introduced this hack, the production of different .cmi files
would break the build system of the compiler itself, when trying to
build a -no-flat-float-array system from a bootstrap compiler itself
using -flat-float-array. See #9291.
master
Gabriel Scherer 2020-05-22 08:49:46 +02:00
parent 5c9d5db728
commit 8e83130a18
2 changed files with 27 additions and 6 deletions
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@ -139,7 +139,7 @@ OCaml 4.11
For instance, "val f: #F(X).t -> unit" is now allowed.
(Florian Angeletti, review by Gabriel Scherer, suggestion by Leo White)
- #7364, #2188, #9609: improvement of the unboxability check for types
- #7364, #2188, #9592, #9609: improvement of the unboxability check for types
with a single constructor. Mutually-recursive type declarations can
now contain unboxed types. This is based on the paper
https://arxiv.org/abs/1811.02300

31
typing/typedecl_separability.ml
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@ -658,9 +658,10 @@ let msig_of_context : decl_loc:Location.t -> parameters:type_expr list
(** [check_def env def] returns the signature required
for the type definition [def] in the typing environment [env].
The exception [Not_separable] is raised if we discover that
no such signature exists -- the definition will always be invalid. This
only happens when the definition is marked to be unboxed. *)
The exception [Error] is raised if we discover that
no such signature exists -- the definition will always be invalid.
This only happens when the definition is marked to be unboxed. *)
let check_def
: Env.t -> type_definition -> Sep.signature
= fun env def ->
@ -683,9 +684,29 @@ let check_def
~parameters:constructor.result_type_parameter_instances
let compute_decl env decl =
if not Config.flat_float_array then best_msig decl
else check_def env decl
if Config.flat_float_array then check_def env decl
else
(* Hack: in -no-flat-float-array mode, instead of always returning
[best_msig], we first compute the separability signature --
falling back to [best_msig] if it fails.
This discipline is conservative: it never
rejects -no-flat-float-array programs. At the same time it
guarantees that, for any program that is also accepted
in -flat-float-array mode, the same separability will be
inferred in the two modes. In particular, the same .cmi files
and digests will be produced.
Before we introduced this hack, the production of different
.cmi files would break the build system of the compiler itself,
when trying to build a -no-flat-float-array system from
a bootstrap compiler itself using -flat-float-array. See #9291.
*)
try check_def env decl with
| Error _ ->
(* It could be nice to emit a warning here, so that users know
that their definition would be rejected in -flat-float-array mode *)
best_msig decl
(** Separability as a generic property *)
type prop = Types.Separability.signature