[llvm] [X86] Fold splat AND on VGF2P8AFFINEQB source (PR #193364)

[Simon Pilgrim via llvm-commits]

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@@ -61882,6 +61882,64 @@ static SDValue combineKSHIFT(SDNode *N, SelectionDAG &DAG,
   return SDValue();
 }
 
+static SDValue combineAndOnGF2P8AFFINEQBOperand(SDNode *N, const SDLoc &DL,
+                                                SelectionDAG &DAG, EVT VT) {
+  using namespace SDPatternMatch;
+
+  SDValue X, Y, SplatOp;
+  APInt Imm, SplatVal, ConstUndef;
+  SmallVector<APInt> ConstEltBits;
+
+  // Removing the same bit within each matrix's row effectively treats the
+  // corresponding source bit like it is set to zero
+  // TODO: Add reverse fold when X is constant
+  if (sd_match(N, m_TernaryOp(X86ISD::GF2P8AFFINEQB, m_Value(AndOp), m_Value(Y),
+                              m_ConstInt(Imm))) &&
+      sd_match(AndOp, m_And(m_Value(X), m_Value(SplatOp))) &&
+      getTargetConstantBitsFromNode(Y, Y.getScalarValueSizeInBits(), ConstUndef,
+                                    ConstEltBits, /*AllowWholeUndefs=*/false)) {
+    bool splatIsConst =
+        X86::isConstantSplat(SplatOp, SplatVal, /*AllowPartialUndefs=*/false);
+
+    // Can still shorten the chain when constant folded with the matrix
+    if (!AndOp->hasOneUse() && !splatIsConst)
+      return SDValue();
+
+    if (!(splatIsConst || DAG.isSplatValue(SplatOp, /*AllowUndefs=*/false)) ||
+        SplatOp.getScalarValueSizeInBits() != 8)
+      return SDValue();
+
+    // ANDs with constants are not folded away this far into lowering
+    SDValue NewMatrix;
+    if (!splatIsConst) {
+      NewMatrix = DAG.getNode(ISD::AND, DL, VT, SplatOp, Y);
+    } else {
+      SmallVector<SDValue> FoldedAnd;
+      for (APInt &Elt : ConstEltBits)
+        FoldedAnd.push_back(DAG.getConstant(SplatVal & Elt, DL, MVT::i8));
+
+      NewMatrix = DAG.getBuildVector(VT, DL, FoldedAnd);
+    }
+
+    return DAG.getNode(X86ISD::GF2P8AFFINEQB, DL, VT, X, NewMatrix,
+                       DAG.getTargetConstant(Imm, DL, MVT::i8));
+  }
+
+  return SDValue();
+}
+
+static SDValue combineGF2P8AFFINEQB(SDNode *N, SelectionDAG &DAG,
+                                    TargetLowering::DAGCombinerInfo &DCI) {
----------------
RKSimon wrote:

Drop unused DCI?

https://github.com/llvm/llvm-project/pull/193364