[llvm-dev] (Thin)LTO llvm build

[Mehdi Amini via llvm-dev]

> On Sep 16, 2016, at 4:59 PM, Mehdi Amini via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> 
>> On Sep 16, 2016, at 4:46 PM, Carsten Mattner <carstenmattner at gmail.com <mailto:carstenmattner at gmail.com>> wrote:
>> 
>> On Sat, Sep 17, 2016 at 12:48 AM, Teresa Johnson <tejohnson at google.com <mailto:tejohnson at google.com>> wrote:
>>> 
>>> On Fri, Sep 16, 2016 at 2:54 PM, Carsten Mattner via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>>> 
>>>> On Fri, Sep 16, 2016 at 11:28 PM, Mehdi Amini <mehdi.amini at apple.com <mailto:mehdi.amini at apple.com>> wrote:
>>>> 
>>>>> You probably missed -DLLVM_BINUTILS_INCDIR.
>>>>> 
>>>>> See: http://llvm.org/docs/GoldPlugin.html <http://llvm.org/docs/GoldPlugin.html>
>>>> 
>>>> plugin-api.h is in /usr/include, so I'd expect it to be found, but I
>>>> can explicitly set BINUTILS_INCDIR and re-bootstrap with gcc 6.2.1.
>>>> 
>>>> I have ld.gold, but I'm not sure if /usr/bin/ld uses it, though I'd expect
>>>> it to since it's been in for a couple releases now.
>>>> 
>>>> $ ld -v
>>>> GNU ld (GNU Binutils) 2.27
>>>> $ ld.bfd -v
>>>> GNU ld (GNU Binutils) 2.27
>>>> $ ld.gold -v
>>>> GNU gold (GNU Binutils 2.27) 1.12
>>> 
>>> 
>>> Looks like your default ld is GNU ld.bfd not ld.gold. You can either change your
>>> /usr/bin/ld (which probably is a link to /usr/bin/ld.bfd) to point instead to
>>> /usr/bin/ld.gold, or if you prefer, set your PATH before the stage1 compile to a
>>> location that has ld linked to ld.gold.
>> 
>> I can look into and check why Arch Linux has it configured like that.
>> 
>> In the meantime, Mehdi's suggestion to explicitly pass BINUTILS_INCDIR
>> restored the previous configure behavior, and the new llvm build has
>> lib/LLVMgold.so. Thanks to both of you for pointing out the missing cmake
>> flag.
>> 
>> I've checked the configure step and it didn't fail as it did before, but before
>> I try to build in ThinLTO mode: since the configure step checks for the gold
>> plugin, is it safe to assume that I don't have to change the default system
>> ld to gold and ThinLTO will work, or is that a build requirement for
>> bootstrapping llvm in ThinLTO mode?
> 
> Try to build llvm-tblgen, you’ll know quite quickly :)

Also, you should limit the number of parallel link jobs: cmake -DLLVM_PARALLEL_LINK_JOBS=1
And use ninja if you don’t already:  cmake -GNinja

— 
Mehdi

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