[LLVMdev] [cfe-dev] Meaning of LLVM optimization levels

[Renato Golin]

On 7 June 2013 13:53, Dallman, John <john.dallman at siemens.com> wrote:

>  It needs to be possible to debug code at any optimisation level.
>

Yes, I agree. But after O1, sequential execution is a big impediment for
optimizations, and keeping the debug information valid after so many
transformations might pose a big penalty on the passes (time & memory).
That was the whole idea of metadata being a second-class citizen.


Related to optimisation levels, it's quite helpful to have a way of
> controlling
>
> optimisation on a function-by-function level. This is very useful when
> you're trying
>
> to work out where in a file with many functions an optimiser problem is
> happening;
>
> it isn't foolproof, but it helps a lot.
>

There are already people working on that, and discussions on the list about
this very topic. I agree that it would be extremely helpful for debugging
large programs.

cheers,
--renato
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