[llvm] [RISCV] Emit constant on RHS of ADD. NFC (PR #217730)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: Craig Topper (topperc)

<details>
<summary>Changes</summary>

Avoids needing to canonicalize later.

---
Full diff: https://github.com/llvm/llvm-project/pull/217730.diff


1 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+2-2) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 3aceff8a6497d..0208816a8f8a8 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -10630,13 +10630,13 @@ SDValue RISCVTargetLowering::lowerSELECT(SDValue Op, SelectionDAG &DAG) const {
       if ((TrueVal - FalseVal).isPowerOf2() && FalseVal.isSignedIntN(12)) {
         SDValue Log2 = DAG.getConstant((TrueVal - FalseVal).logBase2(), DL, VT);
         SDValue BitDiff = DAG.getNode(ISD::SHL, DL, VT, CondV, Log2);
-        return DAG.getNode(ISD::ADD, DL, VT, FalseV, BitDiff);
+        return DAG.getNode(ISD::ADD, DL, VT, BitDiff, FalseV);
       }
       if ((FalseVal - TrueVal).isPowerOf2() && TrueVal.isSignedIntN(12)) {
         SDValue Log2 = DAG.getConstant((FalseVal - TrueVal).logBase2(), DL, VT);
         CondV = DAG.getLogicalNOT(DL, CondV, CondV->getValueType(0));
         SDValue BitDiff = DAG.getNode(ISD::SHL, DL, VT, CondV, Log2);
-        return DAG.getNode(ISD::ADD, DL, VT, TrueV, BitDiff);
+        return DAG.getNode(ISD::ADD, DL, VT, BitDiff, TrueV);
       }
 
       auto getCost = [&](const APInt &Delta, const APInt &Addend) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/217730