[RISCV] Continue with early return for shuffle lowering [nfc]

Move two cases where we're not actually going to use any of our computed index vectors or mask values above the computation of the same.

Author: preames

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -4875,6 +4875,19 @@ static SDValue lowerVECTOR_SHUFFLE(SDValue Op, SelectionDAG &DAG,
     return DAG.getNode(ISD::VSELECT, DL, VT, SelectMask, V1, V2);
   }
 
+  // We might be able to express the shuffle as a bitrotate. But even if we
+  // don't have Zvkb and have to expand, the expanded sequence of approx. 2
+  // shifts and a vor will have a higher throughput than a vrgather.
+  if (SDValue V = lowerVECTOR_SHUFFLEAsRotate(SVN, DAG, Subtarget))
+    return V;
+
+  if (VT.getScalarSizeInBits() == 8 && VT.getVectorNumElements() > 256) {
+    // On such a large vector we're unable to use i8 as the index type.
+    // FIXME: We could promote the index to i16 and use vrgatherei16, but that
+    // may involve vector splitting if we're already at LMUL=8, or our
+    // user-supplied maximum fixed-length LMUL.
+    return SDValue();
+  }
 
   // As a backup, shuffles can be lowered via a vrgather instruction, possibly
   // merged with a second vrgather.
@@ -4913,20 +4926,6 @@ static SDValue lowerVECTOR_SHUFFLE(SDValue Op, SelectionDAG &DAG,
   MVT MaskVT = MVT::getVectorVT(MVT::i1, NumElts);
   SDValue SelectMask = DAG.getBuildVector(MaskVT, DL, MaskVals);
 
-  // We might be able to express the shuffle as a bitrotate. But even if we
-  // don't have Zvkb and have to expand, the expanded sequence of approx. 2
-  // shifts and a vor will have a higher throughput than a vrgather.
-  if (SDValue V = lowerVECTOR_SHUFFLEAsRotate(SVN, DAG, Subtarget))
-    return V;
-
-  if (VT.getScalarSizeInBits() == 8 && VT.getVectorNumElements() > 256) {
-    // On such a large vector we're unable to use i8 as the index type.
-    // FIXME: We could promote the index to i16 and use vrgatherei16, but that
-    // may involve vector splitting if we're already at LMUL=8, or our
-    // user-supplied maximum fixed-length LMUL.
-    return SDValue();
-  }
-
   unsigned GatherVXOpc = RISCVISD::VRGATHER_VX_VL;
   unsigned GatherVVOpc = RISCVISD::VRGATHER_VV_VL;
   MVT IndexVT = VT.changeTypeToInteger();