[llvm] [RISCV] Expand constant multiplication for targets without M extension (PR #137195)

[Iris Shi via llvm-commits]

================
@@ -15436,6 +15439,134 @@ static SDValue performXORCombine(SDNode *N, SelectionDAG &DAG,
   return combineSelectAndUseCommutative(N, DAG, /*AllOnes*/ false, Subtarget);
 }
 
+static SDValue expandMulToNAFSequence(SDNode *N, SelectionDAG &DAG,
+                                      const SDLoc &DL, uint64_t MulAmt) {
+  EVT VT = N->getValueType(0);
+  const uint64_t BitWidth = VT.getFixedSizeInBits();
+
+  // Find the Non-adjacent form of the multiplier.
+  llvm::SmallVector<std::pair<bool, uint64_t>> Sequence; // {isAdd, shamt}
+  for (auto E = MulAmt, I = 0; E && I < BitWidth; ++I, E >>= 1) {
----------------
el-ev wrote:

```suggestion
  for (uint64_t E = MulAmt, I = 0; E && I < BitWidth; ++I, E >>= 1) {
```

https://github.com/llvm/llvm-project/pull/137195