[PATCH] D101423: [InstCombine] Fold overflow bit of [u|s]mul.with.overflow in a poison-safe way

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune marked an inline comment as done.
aqjune added inline comments.


================
Comment at: llvm/lib/Analysis/ValueTracking.cpp:5023
     if (match(I, m_ExtractValue(m_WithOverflowInst(II))) &&
-        match(ValAssumedPoison, m_ExtractValue(m_Specific(II))))
       return true;
----------------
This update adds an inferences that if `a` is poison, `extract(mul_with_overflow(a, _), _)` is also poison.

This enables transformation
```
select(extract(mul_with_overflow(a, _), _), (a == 0), false)
=>
and(extract(mul_with_overflow(a, _), _), (a == 0))
```.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D101423/new/

https://reviews.llvm.org/D101423