[llvm-dev] LLD status update and performance chart

[Andrew Kelley via llvm-dev]

Thank you for this exciting update about LLD.

I will start experimenting with using liblld in Zig (http://ziglang.org/)
instead of starting a child process to invoke the system linker. Once
liblld makes it into the various package managers out there, this will be a
big step toward painless cross-platform compilation.

It should also reduce one of the compilation speed bottlenecks, since I
could transition from writing objects to the file system to passing liblld
LLVM modules directly. Is that correct?

-Andrew

On Sun, Dec 11, 2016 at 10:04 PM, Rui Ueyama via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi,
>
> Now that 2016 is almost over, I wanted to look back and summarize the
> progress we've made to LLD this year, as I guess most people who are not
> looking closely at LLD don't know very well about the current status. I
> think I can say that this year was a fantastic year for LLD. Now I'm pretty
> sure that that is going to be a serious (and better, in my opinion)
> alternative to the existing GNU linkers thanks to all the improvements
> we've made this year.
>
> LLD is now able to link most x86-64 userland programs. The FreeBSD project
> and we are trying to make LLD the system default linker of the operating
> system, and except a few tricky programs such as the kernel or a boot
> loader, the linker works mostly fine. We are still working on implementing
> long-tail features/bugs, but I'd say that's just a matter of time. LLD
> supports x86, x86-64, x32, AArch64, AMDGPU, ARM, PPC64 and MIPS32/64,
> though completeness varies.
>
> Looks like there are already a few systems that are using LLD as system
> linkers, such as CloudABI or Fuchsia. Chromium and Clang/LLVM itself has
> build options to use LLD to build them.
>
> It is hard to argue about the complexity of a program quantitatively, and
> of course I'm biased, but I believe we succeeded to maintain LLD code base
> clean, easy to read, and easy to add new features. It is just 20k lines of
> modern C++ code which is much smaller than GNU linkers.
>
> Even though LLD was fast from day one, LLD got faster this year, despite
> it got a lot of new features. Below is a chart of Clang link time for every
> commit made to the LLD repository this year. At the beginning of this year,
> LLD took about 16 seconds to produce a 1.5 GB clang (debug build)
> executable. Now, it takes about 14.5 seconds on single core and 8.5 seconds
> on 20 cores (*1). ld.gold takes about 25 seconds and 20 seconds,
> respectively, so we've widen the gap. You can see the benchmark results
> here (*2). If you have a problem of too long link time, I'd recommend to
> try LLD.
>
> Last but not least, a lot of people joined to the LLD development this
> year to make LLD better. We are growing as a community, and I'm very happy
> about that!
>
> Thanks,
> Rui
>
> (*1) My machine has Ivy Bridge Xeon 2.8 GHz 20 physical cores (40
> hyper-threading cores). To measure a single-thread performance, I pinned a
> process to (physical and hyper-threading) core 0. To measure a multi-thread
> performance, I pinned to CPU socket 2, so that a process gets 10 physical
> cores (20 hyperthreading cores).
>
> (*2) https://docs.google.com/spreadsheets/d/1VvOqiU5JvqlxU7aof8gsbh-
> yweeNchMgtkamyXrwzrA/edit?usp=sharing. Changes with more than 1% rise or
> drop compared to the average of previous 5 commits are colored in green or
> red, respectively.
>
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>
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