[llvm] [SelectionDAG]: Deduce KnownNeverZero from SMIN and SMAX (PR #85722)

[Jay Foad via llvm-commits]

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@@ -5361,10 +5361,41 @@ bool SelectionDAG::isKnownNeverZero(SDValue Op, unsigned Depth) const {
     return isKnownNeverZero(Op.getOperand(1), Depth + 1) ||
            isKnownNeverZero(Op.getOperand(0), Depth + 1);
 
-    // TODO for smin/smax: If either operand is known negative/positive
+    // For smin/smax: If either operand is known negative/positive
     // respectively we don't need the other to be known at all.
-  case ISD::SMAX:
-  case ISD::SMIN:
+  case ISD::SMAX: {
+    KnownBits Op1 = computeKnownBits(Op.getOperand(1), Depth + 1);
+    if (Op1.isStrictlyPositive())
+      return true;
+
+    KnownBits Op0 = computeKnownBits(Op.getOperand(0), Depth + 1);
+
+    if (Op0.isStrictlyPositive())
+      return true;
+
+    if (Op1.isNonZero() && Op0.isNonZero())
+      return true;
+
+    return isKnownNeverZero(Op.getOperand(1), Depth + 1) &&
+           isKnownNeverZero(Op.getOperand(0), Depth + 1);
+  }
+  case ISD::SMIN: {
+    KnownBits Op1 = computeKnownBits(Op.getOperand(1), Depth + 1);
+    if (Op1.isNegative())
+      return true;
+
+    KnownBits Op0 = computeKnownBits(Op.getOperand(0), Depth + 1);
+
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jayfoad wrote:

And this one?

https://github.com/llvm/llvm-project/pull/85722