[llvm] [RISCV] Add ISel patterns for Xqciac QC.MULIADD instruction (PR #147661)

[Sam Elliott via llvm-commits]

================
@@ -15895,6 +15895,13 @@ static SDValue expandMulToNAFSequence(SDNode *N, SelectionDAG &DAG,
 // X * (2^N +/- 2^M) -> (add/sub (shl X, C1), (shl X, C2))
 static SDValue expandMulToAddOrSubOfShl(SDNode *N, SelectionDAG &DAG,
                                         uint64_t MulAmt) {
+  // Don't do this is if the Xqciac extension is enabled and the MulAmt is
+  // simm12.
+  const RISCVSubtarget &Subtarget =
+      DAG.getMachineFunction().getSubtarget<RISCVSubtarget>();
----------------
lenary wrote:

```suggestion
  auto &STI = DAG.getSubtarget<RISCVSubtarget>();
```

https://github.com/llvm/llvm-project/pull/147661