[PATCH] D128374: [docs][NewPM] Add more info on why accessing mutable outer analyses is disallowed

[Reid Kleckner via Phabricator via llvm-commits]

rnk accepted this revision.
rnk added a comment.
This revision is now accepted and ready to land.

lgtm

Thanks for expanding our docs!



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Comment at: llvm/docs/NewPassManager.rst:329-330
+as the key for cached analyses. Take care in the pass to either clear the
+results for that function, not create new functions which may reuse the same
+address as the deleted function, or not use analyses at all.
+
----------------
I would skip the second alternative. Leaving pointers to freed data as cache keys is unsafe at any speed. The only two solutions that work are to not use the inner analysis, or to clear the results for a function before it is deleted.

Personally, I like to call this problem "the ABA problem", but [[ https://en.wikipedia.org/wiki/ABA_problem | Wikipedia says ]] that has to do with concurrency, not cache keys.


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https://reviews.llvm.org/D128374