[llvm] [RISCV] Refactor DAG-to-DAG Selection: Port lowering code for `qc.insb/qc.insbi` to RISCVISelLowering.cpp (PR #157618)

[Sam Elliott via llvm-commits]

================
@@ -16214,10 +16213,101 @@ static SDValue combineXorToBitfieldInsert(SDNode *N, SelectionDAG &DAG,
   return DAG.getNode(RISCVISD::QC_INSB, DL, MVT::i32, Ops);
 }
 
+static SDValue combineOrToBitfieldInsert(SDNode *N, SelectionDAG &DAG,
+                                         const RISCVSubtarget &Subtarget) {
+  if (!Subtarget.hasVendorXqcibm())
+    return SDValue();
+
+  using namespace SDPatternMatch;
+
+  SDValue X;
+  APInt MaskImm;
+  if (!sd_match(N, m_Or(m_OneUse(m_Value(X)), m_ConstInt(MaskImm))))
+    return SDValue();
+
+  unsigned ShAmt, Width;
+  if (!MaskImm.isShiftedMask(ShAmt, Width) || MaskImm.isSignedIntN(12))
+    return SDValue();
+
+  if (N->getValueType(0) != MVT::i32)
+    return SDValue();
+
+  // If Zbs is enabled and it is a single bit set we can use BSETI which
+  // can be compressed to C_BSETI when Xqcibm in enabled.
+  if (Width == 1 && Subtarget.hasStdExtZbs())
+    return SDValue();
+
+  // If C1 is a shifted mask (but can't be formed as an ORI),
+  // use a bitfield insert of -1.
+  // Transform (or x, C1)
+  //        -> (qc.insbi x, -1, width, shift)
+  SDLoc DL(N);
+
+  SDValue Ops[] = {X, DAG.getSignedConstant(-1, DL, MVT::i32),
+                   DAG.getConstant(Width, DL, MVT::i32),
+                   DAG.getConstant(ShAmt, DL, MVT::i32)};
+  return DAG.getNode(RISCVISD::QC_INSB, DL, MVT::i32, Ops);
+}
+
+// Generate a QC_INSB/QC_INSBI from 'or (and X, MaskImm), OrImm' iff the value
+// being inserted only sets known zero bits.
+static SDValue combineOrAndToBitfieldInsert(SDNode *N, SelectionDAG &DAG,
+                                            const RISCVSubtarget &Subtarget) {
+  // Supported only in Xqcibm for now.
+  if (!Subtarget.hasVendorXqcibm())
+    return SDValue();
+
+  using namespace SDPatternMatch;
+
+  SDValue And;
----------------
lenary wrote:

This isn't a `AND`, can you give it a name like "Inserted"?

https://github.com/llvm/llvm-project/pull/157618