[llvm] [RISCV] Expand mul X, C where C=2^N*(3, 5, 9)*(3, 5, 9) (PR #108100)

[Yingwei Zheng via llvm-commits]

================
@@ -14131,6 +14131,32 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
     return DAG.getNode(ISD::SUB, DL, VT, Shift1, Shift2);
   }
 
+  if (HasShlAdd) {
+    for (uint64_t Divisor : {3, 5, 9}) {
+      if (MulAmt % Divisor != 0)
+        continue;
+      uint64_t MulAmt2 = MulAmt / Divisor;
+      // 3/5/9 * 3/5/9 * 2^N - In particular, this covers multiples
+      // of 25 which happen to be quite common.
+      for (uint64_t Divisor2 : {3, 5, 9}) {
+        if (MulAmt2 % Divisor2 != 0)
+          continue;
+        uint64_t MulAmt3 = MulAmt2 / Divisor;
----------------
dtcxzyw wrote:

```suggestion
        uint64_t MulAmt3 = MulAmt2 / Divisor2;
```

https://github.com/llvm/llvm-project/pull/108100