[PATCH] D140933: [LVI] Look through negations when evaluating conditions

[Nikita Popov via Phabricator via llvm-commits]

nikic requested changes to this revision.
nikic added inline comments.
This revision now requires changes to proceed.


================
Comment at: llvm/lib/Analysis/LazyValueInfo.cpp:1207
+    return inverse(NV->second);
+  }
+
----------------
Hm, I don't think this is correct if N is and and/or, or generally in any case where the returned lattice value does not represent the condition exactly, but is a superset. Inversion would exclude that difference between the exact set and superset. I'd suggest adding a test case for some case where getValueFromCondition() performs an approximation.

Could we instead flip isTrueDest, i.e. do something like this at the top?
```
Value *N;
if (match(Cond, m_Not(m_Value(N)))) {
  isTrueDest = !isTrueDest;
  Cond = N;
}
```


Repository:
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  https://reviews.llvm.org/D140933/new/

https://reviews.llvm.org/D140933