[llvm] [SelectionDAG] Fix incorrect fold condition in foldSetCCWithFunnelShift. (PR #137637)

[David Green via llvm-commits]

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@@ -4462,7 +4462,11 @@ static SDValue foldSetCCWithFunnelShift(EVT VT, SDValue N0, SDValue N1,
 
   unsigned BitWidth = N0.getScalarValueSizeInBits();
   auto *ShAmtC = isConstOrConstSplat(N0.getOperand(2));
-  if (!ShAmtC || ShAmtC->getAPIntValue().uge(BitWidth))
+  if (!ShAmtC)
+    return SDValue();
+
+  APInt AmtVal = ShAmtC->getAPIntValue();
+  if (AmtVal.uge(BitWidth) || AmtVal.isZero())
     return SDValue();
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davemgreen wrote:

>From my point of view - just because it should not come up from non-canonical code IIUC, and so fixing the bug is the more important issue and trying to handle other cases that could lead to further bugs for little benefit. But it sounds OK so long as the rest of the code handles it correctly.

https://github.com/llvm/llvm-project/pull/137637