[llvm] [AArch64] - Fold and and cmp into tst (PR #110347)

[David Green via llvm-commits]

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@@ -4299,6 +4299,36 @@ static SDValue LowerPREFETCH(SDValue Op, SelectionDAG &DAG) {
                      Op.getOperand(1));
 }
 
+// Converts SETCC (AND X Y) Z ULT -> SETCC (AND X (Y & ~(Z - 1)) 0 EQ when Y is
+// a power of 2. This is then lowered to ANDS X (Y & ~(Z - 1)) which produces a
+// better opt with EmitComparison.
+static void SimplifySetCCIntoEq(ISD::CondCode &CC, SDValue &LHS, SDValue &RHS,
+                                SelectionDAG &DAG, const SDLoc DL) {
+  switch (CC) {
+  default:
+    break;
+  case ISD::SETULT:
+    if (LHS.getOpcode() == ISD::AND) {
+      ConstantSDNode *LHSAndConst = dyn_cast<ConstantSDNode>(LHS.getOperand(1));
+      ConstantSDNode *RHSConst = dyn_cast<ConstantSDNode>(RHS);
+      if (LHSAndConst && RHSConst && LHSAndConst->hasOneUse() &&
+          RHSConst->hasOneUse()) {
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davemgreen wrote:

Do the const's need to have one use, even if they will be folded into a tst?

https://github.com/llvm/llvm-project/pull/110347