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74 lines
2.9 KiB
ReStructuredText
74 lines
2.9 KiB
ReStructuredText
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***************************
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Incremental Code Generation
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***************************
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By default, Idris 2 is a whole program compiler - that is, it finds all the
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necessary function definitions and compiles them only when you build an
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executable. This gives plenty of optimisation opportunities, but can also
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be slow for rebuilding. However, if the backend supports it, you can build
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modules and executables *incrementally*. To do so, you can either:
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1. Set the ``--inc <backend>`` flag at the command line, for each backend
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you want to use incrementally.
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2. Set the ``IDRIS2_INC_CGS`` environment variable with a comma separated list
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of backends to use incrementally.
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At the moment, only the Chez backend supports incremental builds.
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Building modules incrementally
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==============================
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If either of the above are set, building a module will produce compiled binary
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code for all of the definitions in the module, as well as the usual checked
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TTC file. e.g.:
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::
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$ idris2 --inc chez Foo.idr
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$ IDRIS2_INC_CGS=chez idris2 Foo.idr
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On successful type checking, each of these will produce a Chez Scheme file
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(``Foo.ss``) and compiled code for it (``Foo.so``) as well as the usual
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``Foo.ttc``, in the same build directory as ``Foo.ttc``.
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In incremental mode, you will see a warning for any holes in the module,
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even if those holes will be defined in a different module.
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Building executables incrementally
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==================================
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If either ``--inc`` is used or ``IDRIS2_INC_CGS`` is set, compiling to
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an executable will attempt to link all of the compiled modules together,
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rather than generating code for all of the functions at once. For this
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to work, all the imported modules *must* have been built with incremental
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compilation for the current back end (Idris will revert to whole program
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compilation if any are missing, and you will see a warning.)
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Therefore, all packages used by the executable must also have been built
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incrementally for the current back end. The ``prelude``, ``base``,
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``contrib``, ``network`` and ``test`` packages are all built with
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incremental compilation support for Chez by default.
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When switching between incremental and whole program compilation, it is
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recommended that you remove the ``build`` directory first. This is
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particularly important when switching to incremental compilation, since there
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may be stale object files that Idris does not currently detect!
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Overriding incremental compilation
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==================================
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The ``--whole-program`` flag overrides any incremental compilation settings
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when building an executable.
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Performance note
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================
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Incremental compilation means that executables are generated much quicker,
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especially when only a small proportion of modules have changed. However,
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it means that there are fewer optimisation opportunities, so the resulting
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executable will not perform as well. For deployment, ``--whole-program``
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compilation is recommended.
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