[PATCH] D149414: [ValueTracking] Add logic for `isKnownNonZero(sadd.sat X, Y)`

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: llvm/lib/Analysis/ValueTracking.cpp:2940
+                            II->getArgOperand(0), II->getArgOperand(1),
+                            /*NSW*/ false);
       case Intrinsic::uadd_sat:
----------------
goldstein.w.n wrote:
> nikic wrote:
> > I think you can set NSW=true here, based on the following reasoning: If the addition were to overflow, then the result would be either SignedMin or SignedMax, neither of which is zero. As such, we can ignore overflow cases.
> I don't think we have `NSW` I tried:
> https://alive2.llvm.org/ce/z/ZBJP5e to see if `sadd.sat` was a superset and think we might run into some edge cases.
> https://alive2.llvm.org/ce/z/9Hz7sn OTOH verifies.
Here's a variant of your proof that works: https://alive2.llvm.org/ce/z/qFwKbT You need to use logical or in this case.

Alternatively, this one also works: https://alive2.llvm.org/ce/z/6px6Ss

We have to exclude undef due to use count increases, but that's just an artifact of the proof.


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https://reviews.llvm.org/D149414