[llvm] [RISCV] Combine two consecutive VSLIDEDOWN_VL nodes into one (PR #225232)

[Pengcheng Wang via llvm-commits]

================
@@ -22299,64 +22299,116 @@ static SDValue performVSlideUpDownCombine(SDNode *N, SelectionDAG &DAG,
   if (N->getOperand(1)->isUndef())
     return N->getOperand(0);
 
-  SDValue SlideDown = N->getOperand(1);
-  SDValue SlideUpOffset = N->getOperand(2);
-  SDValue SlideUpMask = N->getOperand(3);
-  SDValue SlideUpVL = N->getOperand(4);
+  auto isVLMax = [](SDValue VL) {
----------------
wangpc-pp wrote:

There are similar code in combineTruncOfSraSext, make it a static helper?

https://github.com/llvm/llvm-project/pull/225232