teresajohnson wrote:

> > @teresajohnson Do you have any concern or comment on this direction?
> 
> Just a quick reply to say that I am taking a look today (unfamiliar with this 
> approach so need to read through the RFC etc) and will get back later today

Sorry I was obviously over optimistic on when I could do this! A couple of high 
level comments / questions:

- Looking at the NFC, this seems like it has very similar issues to Propeller, 
which wants to redo just the codegen with a new injected profile and BB 
ordering. It would be good to see if we can converge to similar approaches. I 
asked @rlavaee to take a look and he is reading through the background on this 
work. @rlavaee do you think Propeller could use a similar approach to this 
where it saves the pre-codegen bitcode and re-loads it instead of redoing opt? 
This isn't necessarily an action item for this PR, but I wanted Rahman to take 
a look since he is more familiar with codegen.

- I think this should be doable to implement with distributed ThinLTO if we 
want in the future, from what I can tell. But we'll need a way to save the 
bitcode before codegen from a non-in-process backend (e.g. the thinBackend 
invoked from clang). Not asking you to do anything for this PR on that, but 
just thinking through it. Seems doable...

- My biggest concern about this patch as written is whether it will break down 
under LTO's caching mechanism - have you tested it with caching? It seems like 
it might just skip the backend completely since you aren't adding anything to 
the cache key.



https://github.com/llvm/llvm-project/pull/90933
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