[llvm] [SelectionDAG] Use computeForAddSub to prove that ISD::ADD is not 0 (PR #86453)

[Craig Topper via llvm-commits]

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@@ -5405,7 +5405,14 @@ bool SelectionDAG::isKnownNeverZero(SDValue Op, unsigned Depth) const {
       if (isKnownNeverZero(Op.getOperand(1), Depth + 1) ||
           isKnownNeverZero(Op.getOperand(0), Depth + 1))
         return true;
-    // TODO: There are a lot more cases we can prove for add.
+    if (KnownBits::computeForAddSub(
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topperc wrote:

Don't we call `computeKnownBits(Op, Depth).isNonZero();` after the switch in this function? That does the same thing as this in a more general way.

https://github.com/llvm/llvm-project/pull/86453