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An unexpected perf feature
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I didn't check it with clang.
And just to provide a working link:
Clang builds a working 2.6.36 Kernel
Posted Oct 26, 2010 14:37 UTC (Tue) by juliank (subscriber, #45896)
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)
Posted Oct 26, 2010 16:29 UTC (Tue) by gmaxwell (subscriber, #30048)
"But.. why did you handicap GCC?"
"Cause if I didn't GCC was much faster!"
Posted Oct 26, 2010 16:31 UTC (Tue) by juliank (subscriber, #45896)
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.
Posted Oct 27, 2010 9:27 UTC (Wed) by jwakely (subscriber, #60262)
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?
Posted Oct 26, 2010 21:47 UTC (Tue) by tzafrir (subscriber, #11501)
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