[llvm] [RISCV] Expand multiplication by `(2/4/8 * 3/5/9 + 1) << N` with SHL_ADD (PR #166372)

[Min-Yih Hsu via llvm-commits]

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@@ -16496,32 +16496,39 @@ static SDValue expandMulToAddOrSubOfShl(SDNode *N, SelectionDAG &DAG,
 }
 
 static SDValue getShlAddShlAdd(SDNode *N, SelectionDAG &DAG, unsigned ShX,
-                               unsigned ShY) {
+                               unsigned ShY, bool AddX) {
   SDLoc DL(N);
   EVT VT = N->getValueType(0);
   SDValue X = N->getOperand(0);
   SDValue Mul359 = DAG.getNode(RISCVISD::SHL_ADD, DL, VT, X,
                                DAG.getTargetConstant(ShY, DL, VT), X);
   return DAG.getNode(RISCVISD::SHL_ADD, DL, VT, Mul359,
-                     DAG.getTargetConstant(ShX, DL, VT), Mul359);
+                     DAG.getTargetConstant(ShX, DL, VT), AddX ? X : Mul359);
 }
 
 static SDValue expandMulToShlAddShlAdd(SDNode *N, SelectionDAG &DAG,
                                        uint64_t MulAmt) {
   switch (MulAmt) {
   case 5 * 3:
-    return getShlAddShlAdd(N, DAG, 2, 1);
+    return getShlAddShlAdd(N, DAG, 2, 1, false);
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mshockwave wrote:

could we add `/*AddX=*/false` here?

https://github.com/llvm/llvm-project/pull/166372