llvm dev - Dec 2021 - '!annotation' type metadata and compiler optimisations

Hi all, 

I was looking for a mechanism for tracking instructions through compiler
optimisations, i.e. annotate before optimisations and check again after
optimisations. 

Am I correct in understanding that '!annotation' type metadata is, by
design,
guaranteed to be left untouched by compiler optimisations if its corresponding
instruction doesn't get optimised away?

Many thanks,
Paul

> On 17 Dec 2021, at 21:31, Paul Heidekrüger via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hi all, 
> 
> I was looking for a mechanism for tracking instructions through compiler
> optimisations, i.e. annotate before optimisations and check again after
> optimisations. 
>  
> Am I correct in understanding that '!annotation' type metadata is,
by design,
> guaranteed to be left untouched by compiler optimisations if its
corresponding
> instruction doesn't get optimised away?
You should be able to use !annotation metadata for this use case.

But preserving !annotation is done one a best effort basis, like for all other
metadata kinds. So depending on your use case you might have to track down and
update passes that remove it unnecessarily.


Cheers Florian 
> Many thanks,
> Paul
> 
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