[llvm] [DAG] visitORCommutative - fold build_pair(not(x),not(y)) -> not(build_pair(x,y)) style patterns (PR #90050)

[Craig Topper via llvm-commits]

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@@ -7689,6 +7690,26 @@ static SDValue visitORCommutative(SelectionDAG &DAG, SDValue N0, SDValue N1,
       peekThroughZext(N0.getOperand(2)) == peekThroughZext(N1.getOperand(1)))
     return N0;
 
+  // Attempt to match a legalized build_pair-esque pattern:
+  // or(shl(aext(X),BW/2),zext(Y))
+  SDValue Lo, Hi;
+  if (sd_match(N0,
+               m_OneUse(m_Shl(m_AnyExt(m_Value(Hi)), m_SpecificInt(BW / 2)))) &&
+      sd_match(N1, m_ZExt(m_Value(Lo))) &&
+      Lo.getScalarValueSizeInBits() == (BW / 2) &&
+      Lo.getValueType() == Hi.getValueType()) {
+    // Fold build_pair(not(Lo),not(Hi)) -> not(build_pair(Lo,Hi)).
+    SDValue NotLo, NotHi;
+    if (sd_match(Lo, m_OneUse(m_Not(m_Value(NotLo)))) &&
+        sd_match(Hi, m_OneUse(m_Not(m_Value(NotHi))))) {
+      Lo = DAG.getZExtOrTrunc(NotLo, DL, VT);
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topperc wrote:

Is the OrTrunc just because it's shorter than `getNode(ISD::ZERO_EXTEND`?

https://github.com/llvm/llvm-project/pull/90050