[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())
+    return SDValue();
+
+  SDValue Src;
+  const auto IsSrc = [&](SDValue V) {
+    if (!Src) {
+      Src = V;
+      return true;
+    }
+
+    return Src == V;
+  };
+
+  SmallVector<SDValue> Worklist = {N0};
+  APInt PartsMask(VT.getSizeInBits(), 0);
+  while (!Worklist.empty()) {
+    SDValue V = Worklist.pop_back_val();
+    if (!V.hasOneUse() && Src != V)
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jayfoad wrote:

It feels to me like this should also check `Src != nullptr`. I think perhaps you're getting away without it, because od the order in which nodes are added to the worklist.

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