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

[Min-Yih Hsu via llvm-commits]

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@@ -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())) &&
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mshockwave wrote:

In addition to InsertElt, what about splat?

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