[PATCH] D58248: [EarlyCSE & MSSA] Cap the clobbering calls in EarlyCSE.

George Burgess IV via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Fri Feb 15 13:57:58 PST 2019

george.burgess.iv added a reviewer: davide.
george.burgess.iv added inline comments.

Comment at: lib/Transforms/Scalar/EarlyCSE.cpp:1206
   // Reset the current generation.
   CurrentGeneration = LiveOutGeneration;
asbirlea wrote:
> george.burgess.iv wrote:
> > Should we be resetting `ClobberCounter` here, as well?
> AFAICT `run()` is only invoked once for an EarlyCSE instance and it's not recursive.
> I'm also missing the purpose of `CurrentGeneration = LiveOutGeneration;` and
> the above
> ```
>   // Save the current generation.
>   unsigned LiveOutGeneration = CurrentGeneration;
> ```
> Could you please clarify?
> AFAICT run() is only invoked once for an EarlyCSE instance and it's not recursive.

That's what I thought, too, but I saw this, so I assumed I was missing something.

Looks like that was added circa 2012; I assume this pass has changed quite a lot since then. I'm hoping davide (or one of the subscribers) may have context on EarlyCSE's usage patterns?

If no one is sure, I vote that we replace it with an early `assert(!CurrentGeneration && "Create a new EarlyCSE instance to run it again")` (which can optionally be removed if no one complains within a reasonable amount of time). 




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