[cfe-dev] [LLVMdev] TargetParser - Always build all table-gen files?

[Mehdi Amini]

> On Mar 10, 2015, at 10:07 AM, Renato Golin <renato.golin at linaro.org> wrote:
> 
> On 10 March 2015 at 16:20, Mehdi Amini <mehdi.amini at apple.com> wrote:
>> I’d like to avoid as much as possible adding compilation time to the process unless it is necessary (I’m not saying it does not worth it here).
> 
> As I said in the review, it may end up being faster, because of the
> amount of crap we'll remove from all tools and LLVM.

Only if you build all those tools ;)
But yes that’s a good point overall.


>> It is not clear to me why do you need to generate *all* the table-gen files and not only the one related to target features?
> 
> I don't know which of them yet, but I'll certainly need CPU/FPU/ARCH
> names, register names, feature names and anything to populate a target
> description object.
> 
> I moved them all into the include file because I didn't want to have
> to choose now and get it wrong. I realise that this might not have
> been the best course of action.
> 
> Having said that, we can always go back. So, I'm open to suggestions.
> I could start with only a few per arch, and then add as we see fit. My
> guess is that only ARMGenRegisterInfo.inc and ARMGenSubtargetInfo.inc
> would be a good start, with possibly ARMGenCallingConv.inc and
> ARMGenInstrInfo.inc being the next ones to add for Clang's benefit.
> 
> That would mean separating the calls to tablegen() between
> CMakeLists.txt and CMakeTblgen.txt, but that's ok.

I just re-timed and the recent improvements Owen and Chris made to table-gen turn the full generation of table-gen files for my out-of-tree backend from ~8min down to ~35s in debug builds, pretty nice.
At this point I’m no longer afraid about the potential compile time impact of this change.

Thanks for working on this.

— 
Mehdi