[llvm-dev] RFC: Building GlobalISel by default

[Mehdi Amini via llvm-dev]

Hi,

I tend to view this positively, but I feel you could give a few more data, in particular to help answering the questions you raise below.

> On 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

How long does it take to run `make check` from a clean LLVM build with and without GlobalISel enabled?

> - Increase the size of the binary (depending on what backend you pull)

How large is llc with only X86 and AArch64 configured in, with  and without GlobalISel enabled?

Thanks,

Mehdi