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Clang builds a working 2.6.36 KernelClang builds a working 2.6.36 KernelPosted Oct 26, 2010 14:01 UTC (Tue) by juliank (subscriber, #45896)In reply to: Clang builds a working 2.6.36 Kernel by jwakely Parent article: Clang builds a working 2.6.36 Kernel In any case, I simplified it to C and posted it to my blog at http://juliank.wordpress.com/2010/10/26/simple-code-clang-creates-1600x-faster-executable-than-gcc/
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Clang builds a working 2.6.36 Kernel Posted Oct 26, 2010 14:12 UTC (Tue) by rahulsundaram (subscriber, #21946) [Link]
You might want to report this to the GCC developers via mailing list or bugzilla.
Clang builds a working 2.6.36 Kernel Posted Oct 26, 2010 14:35 UTC (Tue) by jwakely (subscriber, #60262) [Link]
Clang builds a working 2.6.36 Kernel Posted Oct 26, 2010 14:32 UTC (Tue) by tzafrir (subscriber, #11501) [Link]
It also becomes way faster in gcc (4.4.5 here) once you remove "__attribute__((noinline))". This looks like a simpler explanation for the simpler code you posted there.
I didn't check it with clang.
And just to provide a working link:
http://juliank.wordpress.com/2010/10/26/simple-code-clang...
Clang builds a working 2.6.36 Kernel Posted Oct 26, 2010 14:37 UTC (Tue) by juliank (subscriber, #45896) [Link]
> It also becomes way faster in gcc (4.4.5 here) once
> you remove "__attribute__((noinline))". This looks > like a simpler explanation for the simpler code you posted there.
Then gcc calculates the result of f() at compile-time and just has a constant integer in the assembler code. Clang does not appear to do this (there's callq f in clang's assembly)
Clang builds a working 2.6.36 Kernel Posted Oct 26, 2010 16:29 UTC (Tue) by gmaxwell (subscriber, #30048) [Link]
"Clang 100x faster than GCC!"
"But.. why did you handicap GCC?"
"Cause if I didn't GCC was much faster!"
(just saying
:) )
Clang builds a working 2.6.36 Kernel Posted Oct 26, 2010 16:31 UTC (Tue) by juliank (subscriber, #45896) [Link]
> "Clang 100x faster than GCC!"
> "But.. why did you handicap GCC?" > "Cause if I didn't GCC was much faster!" > (just saying :) )
GCC 4.5 at -O3 is as fast as clang, although not if you call the function via a pointer. GCC 4.4 has the same slow speed at -O2, -O3, -O4, -O9.
Clang builds a working 2.6.36 Kernel Posted Oct 27, 2010 9:27 UTC (Wed) by jwakely (subscriber, #60262) [Link]
-O4 and -O9 don't exist, no surprise they aren't any better than -O3
GCC 4.5 has apparently already improved. Are you also comparing with a version of Clang from 18 months ago, when GCC 4.4 was released?
Clang builds a working 2.6.36 Kernel Posted Oct 26, 2010 21:47 UTC (Tue) by tzafrir (subscriber, #11501) [Link]
To make this "handicap" more realistic, replace the constant with a command-line parameter.
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