clang vs gcc build performance (executable not build time)

Stephan Bergmann sbergman at
Wed Nov 24 09:58:12 UTC 2021

On 23/11/2021 17:11, Luboš Luňák wrote:
> On Tuesday 23 of November 2021, Michael Meeks wrote:
>> On 22/11/2021 16:28, Arnaud Versini wrote:
>>> There is no
>>> significant difference between both clang builds (changing lib C++ from
>>> libstdc++ to libc++) but gcc is slower than clang. Of course all builds
>>> don't use system libraries in this case to compare between lib C++, and
>>> builds are optimised and use LTO.
>> 	Looks interesting.
>> 	Lubos - what are our build defaults currently and do you have thoughts
>> on changing them ? it would be great to poke at Arnaud's blog / work
>> as/when it gets published =)
>   That decision is not really up to me. AFAIK projects like Firefox or Chromium
> build exclusively using Clang. I wouldn't mind using Clang for everything,
> but I don't know how others would see that.

A decision to make Clang the only compiler with which LO can be built, 
or even just a decision to no longer test (via Jenkins and tinderboxes, 
say) with any compiler other than Clang?  I would not be happy with 
that, as I think the heterogeneous set of compilers we target is an 
important factor in keeping our code base healthy and close to 
standards.  And a standards-conforming code base gives us flexibility, 
e.g. when trying out a promising new build toolchain or static or 
dynamic analysis tool.

>   Stephan Bergmann does clang-cl builds on Windows, so it should work, although
> I don't remember how difficult it is to set up.

There's the horribly outdated 
<> that Ilmari 
already mentioned,  But setting up LLVM/Clang (which should only be 
necessary if you want to --enable-compiler-plugins, which is my 
motivation for doing those clang-cl builds; otherwise, the Clang bundled 
with VS probably works fine) and doing a LO build with it has become 
much simpler since when I wrote that.  (If there is demand, I could try 
and update the wiki page, just ping me.)

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