[llvm] Optimized Constant Xor And And Not Operation (PR #161784)

[Matt Arsenault via llvm-commits]

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@@ -1262,6 +1262,41 @@ SDValue DAGCombiner::reassociateOpsCommutative(unsigned Opc, const SDLoc &DL,
     if (N1 == N00 || N1 == N01)
       return N0;
   }
+
+  // Optimize (Constant XOR a) & b & ~c -> (Constant XOR a) & (b & ~c)
+  // This allows the andn operation to be done in parallel with the xor
+  if (Opc == ISD::AND && TLI.hasAndNot(N1)) {
+    // Look for pattern: AND(AND(XOR(Constant, a), b), NOT(c))
+    // Transform to: AND(XOR(Constant, a), AND(b, NOT(c)))
+
+    // Check if N1 is NOT(c) - i.e., XOR(c, -1)
+    if (N1.getOpcode() == ISD::XOR &&
+        DAG.isConstantIntBuildVectorOrConstantInt(N1.getOperand(1)) &&
+        isAllOnesConstant(N1.getOperand(1))) {
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arsenm wrote:

This would probably be cleaner using sd_match. And you can fuse with the above condition into one if? 

https://github.com/llvm/llvm-project/pull/161784