[PATCH] D22753: [docs] Adding target status definition

[Renato Golin via llvm-commits]

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This section of the developer's policy describes the requirements for the targets to become (and remain) as experimental or official back-ends.

I'm avoiding spam, please copy everyone that you feel should see this.

Repository:
  rL LLVM

https://reviews.llvm.org/D22753

Files:
  docs/DeveloperPolicy.rst

Index: docs/DeveloperPolicy.rst
===================================================================
--- docs/DeveloperPolicy.rst
+++ docs/DeveloperPolicy.rst
@@ -553,6 +553,66 @@
   release notes so that it's clear to external users who do not follow the
   project how the C API is changing and evolving.
 
+New Targets
+-----------
+
+LLVM is very receptive to new targets, even experimental ones, but a number of
+problems can appear when adding new large portions of code, and back-ends are
+normally added in bulk. Revisions of large pieces of code is hard, especially
+when the reviewers don't know the full implications of the new back-end with
+details (which is usually the case), makes for a very error prone process.
+
+For these reasons, new targets are *always* added as **experimental** until
+they can be proven stable, and then moved to non-experimental. The difference
+between both classes is that experimental targets are not built by default
+(need to be added to -DLLVM_TARGETS_TO_BUILD at CMake time).
+
+There's also the issue of keeping the targets downstream instead of submitting
+upstream. Secrecy is a reason for companies to keeping them downstream, but
+openness and quality concerns are reasons for the *community* to prefer it
+remains downstream, too.
+
+So, the basic rules for a back-end to be upstreamed in **experimental** mode are:
+
+* There must be an active community behind the target. This community will be
+  the maintainers of the target by providing buildbots, fixing bugs, answering
+  the LLVM community's questions and making sure the new target doesn't break
+  any of the other targets, or generic code.
+* The target must exist in some form (hardware, emulators) and be easily
+  accessible by the community. Either open source, free, cheap or remote access
+  provided by the target maintainers.
+* There must be some documents describing the target: ISA, ABI, etc. Code review
+  will be based on those documents, and their accuracy will dictate the quality
+  of support by the rest of the community.
+* The code must be free of contentious issues, for example, large changes in how
+  the IR behaves or should be formed by the front-ends, unless agreed by the
+  majority of the community via refactoring of the (:doc:`IR standard<LangRef>`)
+  **before** the merge of the new target changes, following the IR backwards
+  compatibility described in this document.
+* The code has a compatible license, patent and copyright statements, or can be
+  converted by the LLVM's :ref:`own model<copyright-license-patents>`.
+
+In addition, the rules for a back-end to be marked as **official** are:
+
+* The target must have been in the tree for at least 6 months, with active
+  contributions including: adding more tests conforming to the documents, fixing
+  bugs reported by unrelated/generic changes, providing support to other members
+  of the community.
+* The target's code must have been adapted to this developers policy as well as
+  the :doc:`coding standards<CodingStandards>`.
+* The test coverage is broad and well written (small tests, documented). Where
+  applicable, both the ``check-all`` and  ``test-suite`` must pass in at least
+  one configuration (publicly demonstrated, ex.  via buildbots).
+
+After targets are made official, they'll need to be maintained with the same
+level of quality as *all* those requirements above. Degradation in support,
+documentation or test coverage will make the target as nuisance to other targets
+and be considered a candidate for deprecation and ultimately removed.
+
+In essences, these rules are necessary for targets to retain their statuses, but
+they're also markers to define bit-rot, and will be used to clean up the tree
+from unmaintained targets.
+
 .. _copyright-license-patents:
 
 Copyright, License, and Patents


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