[llvm] [RISCV] Try to optimize `vp.splice` to `vslide1up`. (PR #144871)

[Craig Topper 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())) &&
+      sd_match(Offset, m_Zero()) && sd_match(EVL1, m_One())) {
+    SDValue Result = DAG.getNode(
+        ContainerVT.isFloatingPoint() ? RISCVISD::VFSLIDE1UP_VL
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topperc wrote:

Please add tests.

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