[llvm-dev] difference with autotools, cmake and ninja building methods

[Justin Bogner via llvm-dev]

David Chisnall via llvm-dev <llvm-dev at lists.llvm.org> writes:
> On 1 Dec 2015, at 10:03, 慕冬亮 via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>> 
>> collect2: fatal error: ld terminated with signal 9 [Killed]
>> compilation terminated.
>> [2706/2983] Linking CXX executable bin/clang-check
>> ninja: build stopped: subcommand failed.
>
> This looks like the linker is running out of memory.  This is a huge
> link job and BFD linker will consume at least one GB of RAM, possibly
> far more depending on your build config.  If you’re on a 32-bit
> platform, then you won’t be able to do this with a debug build.
>
> The big speedup if you’re using BFD ld is to enable shared library
> support.  This is a particularly big win if you’re doing incremental
> builds a lot, because the extra startup time overhead is likely to be
> far less than the 4-5 minutes of extra time spent linking, even on a
> fast machine.
>
> If you do want to do static linking, then your best bet is to do ninja
> -k 10, which should let it skip over the link jobs that fail, but keep
> compiling the sources, then ninja -j1, which will make it do the
> remaining steps one at a time.  In general, the defaults for ninja
> work well for LLVM/Clang if you have at least one GB of RAM per core.

There's a cmake parameter `-DLLVM_PARALLEL_LINK_JOBS=1` that will limit
the number of concurrent link jobs. That makes for a better experience
than running ninja twice :)

> On a modern laptop, you should be able to do a clean build in 5-10
> minutes, but BFD ld can be a bottleneck.  It would be nice if CMake
> had an option to stick -fuse-ld=gold (or -fuse-ld=lld) in all of the
> correct places, but when I’ve tried poking the link flags to add this
> myself I’ve found weird linking errors that I haven’t had time to
> debug.
>
> David
>
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