[llvm-dev] RFC: Updating to CMake 3.15.0

David Blaikie via llvm-dev llvm-dev at lists.llvm.org
Mon Nov 4 09:39:14 PST 2019

On Mon, Nov 4, 2019 at 9:34 AM Chris Bieneman via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I'm not sure what benefit that would provide. For most developers they
> already have configured build directories

While I agree adding a bootstrap script is probably not worth the cost -
an/the important benefit wouldn't be to existing developers, but to making
the barrier of entry lower to encourage new contributors, I think.

> and if their CMake is too old they are going to do a `git pull` and all of
> a sudden their build fails to configure. Then they go fetch a new CMake.
> Not sure a bootstrap script really helps with that. Especially since the
> CMake git repository contains one, and many people might prefer to grab a
> binary distribution rather than build their own.
> -Chris
> On Nov 4, 2019, at 9:29 AM, Stephen Neuendorffer <
> stephen.neuendorffer at gmail.com> wrote:
> Maybe a bootstrap.sh?  I understand that it can get a little tricky, but
> even if it only worked 95% of the time it might be enough to lower the
> barrier to entry.
> Steve
> On Mon, Nov 4, 2019 at 9:16 AM Chris Bieneman <chris.bieneman at me.com>
> wrote:
>> CMake doesn’t have the ability to reliably re-invoke itself in a way that
>> would make that workflow reasonable. To do it would require a meta build
>> system for our meta build system, and that is the road to madness.
>> -Chris
>> On Nov 4, 2019, at 8:59 AM, Stephen Neuendorffer via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>> Since it's 'so easy', I wonder if it would make people's lives easier to
>> add a bootstrap of cmake to the out of the box build flow.
>> Maybe: "You're system Cmake is too old for us.  Downloading and building
>> a cmake 1.15.1 locally for you...."
>> Steve
>> On Mon, Nov 4, 2019 at 7:20 AM James Y Knight via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>> On Sun, Nov 3, 2019 at 7:20 PM Neil Nelson via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>> Glad we are getting some reasonable justifications for CMake 3.15.0.
>>>> There are two points we may be missing.
>>>> Is our plan to just keep updating to the most recent CMake version or
>>>> will our objectives be reached with this version? If we gain what we need
>>>> with this version then after a while we will have the Ubuntu LTS aligned.
>>>> For my current purposes, LLVM can get wild without much worry here. I
>>>> just clone a VM and run what is useful and then delete it. A bit like use
>>>> once and throw away. This is not for production purposes but for getting a
>>>> better view of software structure that LLVM can provide.
>>>> When I was managing IT and the servers for a small company that needed
>>>> to be live 24/7 we used the latest Ubuntu LTS version because we needed
>>>> rock-solid performance as best we could get. The software in the LTS
>>>> version is tested and used by a large user base with necessary updates and
>>>> so we expected to have high reliability.
>>>> Those saying how easy it was to obtain the latest CMake have apparently
>>>> not been faced with the absolute need for solid up-time. Installing
>>>> hack-me-now, buggy, bleeding-edge software was severely discouraged.
>>>> But in the LLVM environment, I can see where that is not a strong necessity.
>>>> But at the same time, does LLVM strive to be the backbone of 24/7
>>>> software? Or is it more of a cool thing with some interesting code analysis
>>>> properties? I suspect its nature is a bit wild, bleeding edge. And that's
>>>> OK.
>>> I'm not really sure what your worry is here -- if you're downloading and
>>> building a development version of LLVM onto this particular production
>>> machine, why is it problematic to also download a newer release version of
>>> CMake to build it with?
>>> Maybe you're worried that you'd have to install the new cmake into
>>> /usr/local/bin? If that's the worry, I'll note that you are not required to
>>> install cmake into /usr/local/bin/ in order to use it to build LLVM, and
>>> I'd recommend not doing so. You can actually invoke the cmake binary
>>> directly from its build/download directory -- no "make install" required at
>>> all. Used that way, it doesn't affect anything else on your system -- if
>>> you like, the new cmake can be used ONLY for building LLVM, and affect
>>> literally nothing else other than a tiny amount of disk-space.
>>> Another important point here is that the version of cmake you use to
>>> build llvm doesn't impact users of the llvm libraries or binaries that were
>>> built with the new cmake. (I'd contrast that with llvm requiring a newer
>>> version of a shared library, which _does_ have runtime impact, and thus is
>>> of potentially larger concern.)
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