llvm dev - Aug 2016 - [RFC] One or many git repositories?

On Sat, Jul 30, 2016 at 2:26 AM, Robinson, Paul via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>
> > Even then, are we seriously ignoring the fact that even if you did
clone
> > the whole repository including everything, that you can still build
just
> > the libc++ and sanitiser runtimes if you wanted to?
>
> Is it that easy to build a subset of a large checked-out tree?  I
haven't
> tried it but my impression is: not so much.  Certainly the advertised
> tactics for configuring/building don't tell you how to do that. 
Somebody
> figuring out what it takes would be very constructive here, instead of
> just asserting it can't possibly be that hard.
>
Right now, no. The build system assumes that if you checked someone out
then you want to build it.

This needs to change.

 I believe David Chisnall up-thread cited a difference in checkout times
> on the order of a handful of seconds versus a couple of minutes.  While
> naively it might seem not a big deal, over time and depending on what you
> are trying to do yes it can be a big burden
>
That's a one time cost, not every time you do an update.
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> > Even then, are we seriously ignoring the fact that even if you did
clone
> > the whole repository including everything, that you can still build
just
> > the libc++ and sanitiser runtimes if you wanted to?
>
> Is it that easy to build a subset of a large checked-out tree?  I
haven't
> tried it but my impression is: not so much.
It's possible to disable subsets of an LLVM build by setting the various
'LLVM_TOOL_*_BUILD' options to 'OFF' in cmake. For example,
'LLVM_TOOL_COMPILER_RT_BUILD=OFF' will prevent the build for
projects/compiler-rt, and 'LLVM_TOOL_CLANG_TOOLS_EXTRA_BUILD=OFF' will
disable the tools/projects/clang/tools/extra (I've just double checked the
latter). IIRC, these are the variables that disable the build for projects that
aren't checked out.

Also, I haven’t tried this myself but we should still be able to do standalone
builds of particular projects by picking the initial CMakeLists.txt like so:
            cmake ../llvm/projects/compiler-rt

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Bruce
Hoult via llvm-dev
Sent: 29 July 2016 15:52
To: Robinson, Paul
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] [RFC] One or many git repositories?



On Sat, Jul 30, 2016 at 2:26 AM, Robinson, Paul via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
> Even then, are we seriously ignoring the fact that even if you did clone
> the whole repository including everything, that you can still build just
> the libc++ and sanitiser runtimes if you wanted to?
Is it that easy to build a subset of a large checked-out tree?  I haven't
tried it but my impression is: not so much.  Certainly the advertised
tactics for configuring/building don't tell you how to do that.  Somebody
figuring out what it takes would be very constructive here, instead of
just asserting it can't possibly be that hard.

Right now, no. The build system assumes that if you checked someone out then you
want to build it.

This needs to change.

 I believe David Chisnall up-thread cited a difference in checkout times
on the order of a handful of seconds versus a couple of minutes.  While
naively it might seem not a big deal, over time and depending on what you
are trying to do yes it can be a big burden

That's a one time cost, not every time you do an update.

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On Fri, Jul 29, 2016 at 8:51 AM, Bruce Hoult via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
>
>
> On Sat, Jul 30, 2016 at 2:26 AM, Robinson, Paul via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>>
>> > Even then, are we seriously ignoring the fact that even if you did
clone
>> > the whole repository including everything, that you can still
build just
>> > the libc++ and sanitiser runtimes if you wanted to?
>>
>> Is it that easy to build a subset of a large checked-out tree?  I
haven't
>> tried it but my impression is: not so much.  Certainly the advertised
>> tactics for configuring/building don't tell you how to do that. 
Somebody
>> figuring out what it takes would be very constructive here, instead of
>> just asserting it can't possibly be that hard.
>>
>
> Right now, no. The build system assumes that if you checked someone out
> then you want to build it.
>
> This needs to change.
>
libc++ and libc++abi already provide make targets that allow you to build
build/install the libraries without
building LLVM/Clang.

>  I believe David Chisnall up-thread cited a difference in checkout times
>
>> on the order of a handful of seconds versus a couple of minutes.  While
>> naively it might seem not a big deal, over time and depending on what
you
>> are trying to do yes it can be a big burden
>>
>
> That's a one time cost, not every time you do an update.
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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