[llvm-branch-commits] [llvm] [DAG] Fold (setcc ((x | x >> c0 | ...) & mask)) sequences (PR #146054)

[Jay Foad via llvm-branch-commits]

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@@ -28909,13 +28909,97 @@ SDValue DAGCombiner::SimplifySelectCC(const SDLoc &DL, SDValue N0, SDValue N1,
   return SDValue();
 }
 
+static SDValue matchMergedBFX(SDValue Root, SelectionDAG &DAG,
+                              const TargetLowering &TLI) {
+  // Match a pattern such as:
+  //  (X | (X >> C0) | (X >> C1) | ...) & Mask
+  // This extracts contiguous parts of X and ORs them together before comparing.
+  // We can optimize this so that we directly check (X & SomeMask) instead,
+  // eliminating the shifts.
+
+  EVT VT = Root.getValueType();
+
+  if (Root.getOpcode() != ISD::AND)
+    return SDValue();
+
+  SDValue N0 = Root.getOperand(0);
+  SDValue N1 = Root.getOperand(1);
+
+  if (N0.getOpcode() != ISD::OR || !isa<ConstantSDNode>(N1))
+    return SDValue();
+
+  APInt RootMask = cast<ConstantSDNode>(N1)->getAsAPIntVal();
+  if (!RootMask.isMask())
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jayfoad wrote:

You don't need this check. The optimization still works for any RootMask values.

https://github.com/llvm/llvm-project/pull/146054