|| ||Vladimir Makarov <vmakarov-AT-redhat.com> |
|| ||Development discussions related to Fedora <devel-AT-lists.fedoraproject.org> |
|| ||Re: Apple will use LLVM |
|| ||Thu, 16 Feb 2012 10:25:19 -0500|
|| ||Article, Thread
On 02/16/2012 10:02 AM, Adam Jackson wrote:
> On Thu, 2012-02-16 at 10:22 +0530, Rahul Sundaram wrote:
>> On 02/16/2012 10:08 AM, Genes MailLists wrote:
>>> Not to mention that the kernel devs use gcc to compile the kernel -
>>> and it most certainly puts a lot of pressure on the compiler. I suspect
>>> unless linus drops gcc as well, we'll at a minimum need to keep it to
>>> build the kernel itself.
>> Not quite. LLVM can be used to build the kernel and what Linus does
>> doesn't matter as much (kernel is important but only one component) as
>> showing that Fedora on the whole will actually benefit from moving to
>> LLVM. For that, LLVM has to so much better than GCC and someone has to
>> do the work within Fedora to show that it is the case.
> Since I was a bit (intentionally) curt and dismissive in my other
> response in this thread, I'll add some anecdata here. I have actually
> tried building xserver with clang and running the standard set of
> microbenchmarks. I found one relevant path where the clang build was
> ~15% faster . Something like 60% of the rest were within ±3%. For
> everything else clang was uniformly worse by usually about 5%.
The another usual mistake when people compare speed of GCC and LLVM is
to use -O2 for the both compilers. But the true is that -O1 of GCC is
-O2 of LLVM with the point of code generation quality. The compiler
speed of GCC with -O1 is the same as for LLVM with -O2. You can find
the latest comparison of LLVM and GCC on
http://vmakarov.fedorapeople.org/spec/ (see 2011 comparison at the
bottom of the left frame).
GCC has a big community of very dedicated people. LLVM has no such
community. So IMHO GCC will be more high quality compiler than LLVM
until LLVM gets such community.
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