[llvm] [RISCV] Combine (vp.splice (insert_elt poison, scalar, 0), vec, 0, mask, 1, vl) to vslide1up. (PR #144871)

[Craig Topper via llvm-commits]

================
@@ -13281,6 +13283,19 @@ RISCVTargetLowering::lowerVPSpliceExperimental(SDValue Op,
                       SplatZeroOp2, DAG.getUNDEF(ContainerVT), EVL2);
   }
 
+  SDValue FirstEle;
+  if (!IsMaskVector &&
+      sd_match(Op1, m_InsertElt(m_Poison(), m_Value(FirstEle), m_Zero())) &&
+      sd_match(Offset, m_Zero()) && sd_match(EVL1, m_One())) {
----------------
topperc wrote:

Use isNullConstant(Offset) or isOneConstant(EVL1).

https://github.com/llvm/llvm-project/pull/144871