[llvm-dev] RFC: Building GlobalISel by default

[Michael Kuperstein via llvm-dev]

As a person not developing on GlobalISel, I can already play with it by
setting the flag. ;-)

The main (and huge) benefit I see is that it will get tested by default.
So, I think it's mainly a question of maturity - if my (non-GlobalISel)
change breaks GlobalISel, how likely is it to be a bug in my code vs. a bug
in GlobalISel?

Michael

On Fri, Jan 13, 2017 at 5:54 PM, Quentin Colombet via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi all,
>
> Now, four backends (if I am counting right: X86, ARM, AArch64, AMDGPU) are
> working on bringing-up GlobalISel, I’d like to switch the default of the
> LLVM_BUILD_GLOBAL_ISEL variable in CMake, such that the framework gets
> built by default.
>
> ** Impact of Flipping the Switch **
>
> * Upsides *
>
> For people developing on GlobalISel, it will:
> - Simplify the CMake command to type :)
> - Build/Test GlobalISel on all the LLVM bots
>
> For people not developing on GlobalISel, it will:
> - Test that GlobalISel still works with your changes (make check will test
> that for you)
> - Allow you to play with it!
>
> Basically flipping the default CMake setting will give access to all the
> ISel schemes that we have in LLVM, instead of just SDISel and FastISel.
>
> * Downsides *
>
> For people developing on GlobalISel, it will:
> - Leave the status as it is now, meaning that mainly only people working
> on GlobalISel look at the failures of GlobalISel specific bots
>
> For people not developing for GlobalISel, it will:
> - Increase the compile time since the GlobalISel framework and the related
> target specific parts will have to be built
> - Increase the size of the binary (depending on what backend you pull)
> - Require the setting of an additional CMake variable to disable it
> (-DLLVM_BUILD_GLOBAL_ISEL=OFF)
>
>
> What do people think?
>
> Thanks,
> -Quentin
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