[flang-dev] Out-of-tree flang builds

Michael Kruse via flang-dev flang-dev at lists.llvm.org
Fri Jul 31 12:29:04 PDT 2020

Should by "incremental build", not "iterative build"


Am Fr., 31. Juli 2020 um 14:01 Uhr schrieb Michael Kruse <llvm at meinersbur.de

> Support for out-of-tree builds, like BUILD_SHARED_LIBS or gn builds, are
> helpful for developers, but not relevant for release builds. Requiring to
> maintain all combinations of build configurations is not feasible before
> every commit, this is why they are only best effort. When you notice a
> out-of-tree build breaking, you are free to fix the problem (and assuming
> the fix is straightforward, low-risk, without review).
> However, I am wondering, why isn't an iterative build sufficient? Assuming
> you are not touching any non-flang files, make/ninja should not try to
> rebuild them.
> Michael
> Am Fr., 31. Juli 2020 um 13:41 Uhr schrieb Peter Steinfeld via flang-dev <
> flang-dev at lists.llvm.org>:
>> Out-of-tree builds are a way to build only the flang code using a
>> pre-existing full build of llvm.  Out-of-tree flang builds are four times
>> faster than full builds.  Thus, for those of us actively developing code
>> and reviewing other people's changes, out-of-tree builds significantly
>> improve our productivity.
>> Unfortunately, out-of-tree builds are not currently supported by the llvm
>> buildbots.  Thus, people changing build files must test this feature
>> themselves.  The process of doing an out-of-tree build is described in the
>> flang overview document --
>> https://github.com/llvm/llvm-project/tree/master/flang.  Alternatively,
>> people changing build files could ask someone familiar with out-of-tree
>> builds to review their changes.
>> A recent update from David Truby broke out-of-tree builds --
>> https://reviews.llvm.org/D84022.  In the conversation in the Phabricator
>> review, David states that he understands that "out-of-tree builds are
>> considered a "best effort" feature that isn't guaranteed to work".  But
>> since out-of-tree builds are critical for my development, I don't consider
>> them optional.
>> I'm writing this note to bring this issue to the broader flang
>> community.  I consider out-of-tree builds to be a critical feature that no
>> change should break.  What do you think?
>> _______________________________________________
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>> flang-dev at lists.llvm.org
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