Limit the number of parameters for an uncurried or untupled function#9620
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xavierleroy merged 3 commits intoocaml:trunkfrom Jun 5, 2020
Merged
Limit the number of parameters for an uncurried or untupled function#9620xavierleroy merged 3 commits intoocaml:trunkfrom
xavierleroy merged 3 commits intoocaml:trunkfrom
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mshinwell
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Jun 1, 2020
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mshinwell
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A couple of comments:
- Flambda can add extra arguments to functions during some of its unboxing passes, but they are limited by the number set in the
Backendmodule (seeoptmain.ml). This should always be (much) lower than the new limit here, since the Flambda transformations don't want to break tail recursion. - Flambda uses the worker-wrapper technique for tupled functions, so I think this code needs modifying, to not do this transformation if the size of the tuple is over the limit. See
tupled_function_call_stubinmiddle_end/flambda/closure_conversion.ml. - Could we please have a backstop in
cmmgen.mlor thereabouts that ensures a fatal error is generated if we do end up generating functions with too many parameters?
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That's part of the other pull request, #9619, file asmcomp/cmm_helpers.ml, line 79. |
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Concerning Flambda, I'm not competent to work on it. Would you @mshinwell, or perhaps @chambart or @lthis, please update Flambda as appropriate? Feel free to push to my branch. |
lthls
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Jun 2, 2020
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@xavierleroy As per the comment I've just resolved, I was mistaken; I don't think we need to do anything with Flambda. This should be good to merge once the CI passes, then. |
mshinwell
approved these changes
Jun 2, 2020
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 proposed in ocaml#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 limited number of parameters.
Addresses review comment. To be squashed with 941c05b
25c85d6 to
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This commit introduces a quantity
Lambda.max_aritythat 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 -> ebecomes a 10-argument function (x1...x10) that returns a 5-argumentfunction (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_arityis set to 126 in native-code, to match the new representation of closures proposed in #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 limited number of parameters.