[LLVMdev] Tight overlapping loops and performance

[Jonathan Turner]

> Have you tried putting something non-trivial (like asm("nop;");) where
> you'd put the code that runs on the timeout?
>
> -Eli

Using a asm("nop") does fix the llvm output, which makes it sound like a bug.  At least in my expectations, a trivial loop should be faster than a non-trivial one.


> The main issue is incl updates the EFLAGS condition code register. But
> llvm x86 isn't taking advantage of that. This is a known issue,
> hopefully someone will find the time to implement before 2.6.
>
> The second issue is the leal -1 can be turned (back) into a decl.
> Combine that with the optimization previously described, it can
> eliminate the first cmpl.
>
> Feel free to file a bugzilla for this. I'm hopefully this will be
> fixed in the not too far future.
>
> Thanks,
>
> Evan

Will do.  Thanks.


Jonathan

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