We want to start allowing more information in the payload of
[@tailcall] attributes (currently no payload is supported), for
example we could consider using [@tailcall false] to ask the code
generator to disable a tail call.
A first required step in this direction is to use a custom datatype to
represent the tail-call attribute, instead of a boolean. This is
consistent with the other application-site
attributes (inline_attribute, specialise_attribute, local_attribute),
so it makes the code more regular -- but the change itself is
boilerplate-y.
This commit introduces a quantity Lambda.max_arity that is the maximal
number of parameters that a Lambda function can have.
Uncurrying is throttled so that, for example, assuming the limit is 10,
a 15-argument curried function fun x1 ... x15 -> e
becomes a 10-argument function (x1...x10) that returns a 5-argument
function (x11...x15).
Concerning untupling, a function that takes a N-tuple of arguments,
where N is above the limit, remains a function that takes a single
argument that is a tuple.
Currently, max_arity is set to 126 in native-code, to match the new
representation of closures implemented by #9619. A signed 8-bit field
is used to store the arity. 126 instead of 127 to account for the
extra "environment" argument.
In bytecode the limit is infinity (max_int) because there are no needs
yet for a limit on the number of parameters.
Lambda and Clambda distinguish Const_int from Const_pointer only so
that they can pass the information to Cmm. But now that that
Const_pointer is gone from Cmm (#9578), there's no need for the
distinction in Lambda either.
This PR requires a bootstrap, because the .cmo format changes:
Lambda.structured_constant has one fewer constructor. The bootstrap
is in the following commit.
* Various file moves in the middle end: this is the first stage of improving separation between the middle end and backend.
* Creation of file_formats/ directory (with associated file moves) to hold the definitions of compilation artifact formats.
* Creation of lambda/ directory (with associated file moves) to hold Lambda language definition files, transformation passes and construction passes from Typedtree.
* Disable (hopefully temporarily) dynlink, debugger and ocamldoc for the dune build.
Gabriel Scherer
Xavier Leroy
Stephen Dolan
Mark Shinwell