[LLVMdev] [cfe-dev] RFC: Upcoming Build System Changes

[Tobias Grosser]

On 11/01/2011 10:24 PM, Óscar Fuentes wrote:
> greened at obbligato.org (David A. Greene) writes:
>
>>>> Oh, it's significant.  When I build the Cray compiler with only non-LLVM
>>>> stuff changed, the actual compiles (the Cray stuff) finish before the
>>>> LLVM figures out nothing has changed.  This is a sginificant
>>>> productivity loss.
>>>
>>> How is that? Your compiler builds in less than 3 seconds? (IIRC, the
>>
>> I have never seen an LLVM up-to-date build take only three seconds.  You
>> must have a much faster machine than I do.
>
> $ ../llvm/configure&&  make -j4
> ...
>
> $ time make -j4
> real    0m5.840s
> user    0m5.232s
> sys     0m1.388s
>
> $ time make -j4
> real    0m1.788s
> user    0m2.304s
> sys     0m0.484s

To support Oscar's claims. On a 1 1/2 year old laptop a cmake build that 
contains LLVM, clang and Polly takes less than 3.5 seconds.

$ time make -j4
real	0m3.459s
user	0m3.990s
sys	0m1.450s

I normally just work on one component e.g. opt or Polly. Their build 
times are:

$ time make -j4 opt
real	0m1.246s
user	0m0.720s
sys	0m0.170s

$ time make -j4 LLVMPolly
real	0m0.550s
user	0m0.290s
sys	0m0.130s

Further increasing performance does not seem to be necessary for me and 
I am against it if involves an increase in build system complexity.

 From my point of view, increased performance is definitely not a valid 
argument for changes in the build system.

Cheers
Tobi