[LLVMdev] Why code doesn't speed up much with optimization level increase?
yuri at rawbw.com
Fri Jun 25 15:06:23 PDT 2010
I run large piece of code in JIT and it runs only marginallty faster
with optimization levels 1,2,3. I think differences are within the
margin or error.
level user time
Level is set with builder->setOptLevel(olev);
Compilation time is excluded by taking the only top-level function
address before the run with getPointerToFunction. So I measure time
Why optimization almost doesn't speed it up? What are the other than
setOptLevel ways to control optimization?
My mindset is defined by experience with gcc, when increasing inlining
levels speeds the code up significantly. Does JIT inline at all?
It's hard to believe that even only local (no inlining) optimization
wouldn't bring timing down by at least 10%.
i386 on i7
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