[llvm] [SelectionDAG]: Have isKnownNeverZero treat SRL like division if all else fails (PR #89523)

[Craig Topper via llvm-commits]

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@@ -5443,10 +5443,17 @@ bool SelectionDAG::isKnownNeverZero(SDValue Op, unsigned Depth) const {
     if (ValKnown.isNegative())
       return true;
     // If max shift cnt of known ones is non-zero, result is non-zero.
-    APInt MaxCnt = computeKnownBits(Op.getOperand(1), Depth + 1).getMaxValue();
+    const KnownBits Shift = computeKnownBits(Op.getOperand(1), Depth + 1);
+    APInt MaxCnt = Shift.getMaxValue();
     if (MaxCnt.ult(ValKnown.getBitWidth()) &&
         !ValKnown.One.lshr(MaxCnt).isZero())
       return true;
+    // We try to see if we can turn it into a division
+    const KnownBits One =
+        KnownBits::makeConstant(APInt(ValKnown.getBitWidth(), 1));
+
+    if (KnownBits::uge(ValKnown, KnownBits::lshr(One, Shift)))
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topperc wrote:

Doesn't SRA reach here too? Is this also correct for SRA?

https://github.com/llvm/llvm-project/pull/89523