[zorg] r297359 - Do not use parallel link jobs with ThinLTO on Green Dragon

[Mehdi Amini via llvm-commits]

> On Mar 15, 2017, at 9:59 AM, Tobias Edler von Koch <tobias at codeaurora.org> wrote:
> 
> On 03/13/2017 12:05 PM, Mehdi Amini via llvm-commits wrote:
>> I also plan to add a CMake warning in LLVM when ThinLTO is enabled but LLVM_PARALLEL_LINK_JOBS isn’t set. This is unlikely that it is intended by the end user.
> 
> Wouldn't it make most sense to default to LLVM_PARALLEL_LINK_JOBS=1 when ThinLTO is enabled and LLVM_PARALLEL_LINK_JOBS isn't set? Otherwise you're basically requiring everyone to set an additional option when enabling ThinLTO.

LGTM.


> 
> Actually, you could warn if LLVM_PARALLEL_LINK_JOBS is explicitly set to != 1 with ThinLTO, because that's likely unintended.

Well I’ve been using 2 as a value for quite some time: the linker process is not fully parallel and some overlap while one linker process is working on a serial phase and the other can “fill the gap” could still be beneficial. Also the default parallelism is the number of physical cores, so there is a bit of room with HT. YMMV.

— 
Mehdi