[llvm-dev] RFC: Building GlobalISel by default

[Tom Stellard via llvm-dev]

On Fri, Jan 13, 2017 at 05:54:15PM -0800, Quentin Colombet via llvm-dev 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?
> 

I would like to see this built by default it makes it easier for users
using PPAs or other bleeding edge package repositories to test
GlobalISel.

-Tom

> Thanks,
> -Quentin
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