[PATCH] D129636: Fix a LSR debug invariance issue

[Chris Jackson via Phabricator via llvm-commits]

chrisjackson added a comment.

I'm looking at the forgetValue() implementation. I think that as long as the SCEV for the value is preserved and accessable in SalvageDVI() then all is well in terms of the salvaging method.

In D129636#3648003 <https://reviews.llvm.org/D129636#3648003>, @jmorse wrote:

> Thanks for hunting this down, caching layers affecting codegen sounds hard to debug.
>
> I'm no SCEV expert, so a couple of possibly obvious questions:
>
> - Is it safe to store the SCEV* for a Value that's then forgotten?
> - Is there a risk that the presence of debug-info will now cause a SCEV to be forgotten that _should_ have been remembered, because of unconditionally forgetting a SCEV if it's used by debug-info?

I think the second point is the crux here. Perhaps there is a way to test if the SCEV already exists, then call forget conditionally.


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https://reviews.llvm.org/D129636